CN117776710A - Three-layer-structure pressure-sensitive ceramic only comprising single double Schottky grain boundary barriers, and sol-gel preparation method and application thereof - Google Patents
Three-layer-structure pressure-sensitive ceramic only comprising single double Schottky grain boundary barriers, and sol-gel preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier, a sol-gel preparation method and application thereof, and belongs to the technical field of pressure-sensitive materials; the three-layer structure pressure sensitive ceramic with a simple structure and only comprising a single double Schottky grain boundary barrier is obtained after sintering, and the three-layer structure pressure sensitive ceramic comprises two ZnO ceramic layers and a middle bismuth-rich layer, and based on the structure, the research on the structure, the performance and the conduction mechanism of the single double Schottky grain boundary barrier in the ZnO pressure sensitive ceramic has remarkable advantages, and the three-layer structure pressure sensitive ceramic can simulate the single ZnO grain-grain boundary-ZnO grain structure formed in the complex structure of the conventional ZnO pressure sensitive ceramic, so that powerful evidence is provided for exploring the internal characteristics of polycrystal.
Description
Technical Field
The invention belongs to the technical field of pressure sensitive materials, and particularly relates to a three-layer structure pressure sensitive ceramic only comprising a single double Schottky grain boundary barrier, and a sol-gel preparation method and application thereof.
Background
The ZnO varistor has a characteristic that the current changes abruptly with the voltage after the voltage reaches a certain value, i.e., an excellent nonlinear characteristic. Because of the characteristics, the ZnO pressure-sensitive ceramic material is the oxide pressure-sensitive ceramic material which is most widely used and studied in the most deep way. In zinc oxide pressure sensitive ceramic systems, the device has a non-linear character because of the incorporation therein of metal oxides having a relatively large ionic radius. The phase of transition metal oxide segregated at grain boundaries and the zinc oxide main crystal phases on both sides form Schottky barriers (Schottky barriers), respectively, which are called Double Schottky Barriers (DSBs). Due to the existence of the potential barrier, when the voltage at two ends of the device suddenly increases, the corresponding current also increases rapidly, so that the function of protecting the load circuit is achieved.
However, in the previous researches, the ZnO varistor produced by the conventional solid-phase sintering is a polycrystalline ceramic material, the grain boundary types inside the polycrystalline ceramic material are extremely complex, and most of the ZnO varistor are distributed among grains in an extremely complex manner, and the theoretical research method of voltage nonlinearity of the ZnO varistor is performed on the basis of the conventional semiconductor physics, however, the polycrystalline oxide nonlinear material such as the ZnO varistor must be researched by using a structural parameter which is most basic and difficult to determine, namely, the structural dimension of the grain boundary barrier inside the material, and for the polycrystalline oxide, the exact shape and the area of the effective grain boundary inside the researched material cannot be accurately obtained by any method, so that the characteristics of a single grain boundary cannot be accurately obtained by testing the electrical property of the whole resistor. Researchers have prepared a three-layer structure (ZnO layer-Bi) using ZnO targets and bismuth oxide targets 2 O 3 layer-ZnO layer). However, the power is too small, the grain size is small and uneven, potential barriers are not formed, the power is too large, more defects are caused, the performance of the film is reduced, and meanwhile, the preparation method and the conditions of the zinc oxide pressure-sensitive ceramic are greatly different from those of the traditional zinc oxide pressure-sensitive ceramic. Therefore, the solid phase sintering method is adoptedThe three-layer structure pressure-sensitive ceramic with single double Schottky grain boundary barriers has strong significance for researching ZnO pressure-sensitive ceramic, and meanwhile, the problem that if oxides are directly dissolved in polyvinyl alcohol (PVA) aqueous solution to prepare a Bi-rich layer, the probability of success rate of the three-layer structure unstable experiment is reduced due to larger molecular radius and increased gaps is considered, and if the three-layer structure unstable experiment is wrapped and sintered, the subsequent experiment process is complex.
Aiming at the technical problems that the conventional ZnO voltage-sensitive ceramic cannot be used for constructing ZnO voltage-sensitive ceramic only comprising a single double Schottky barrier through polycrystalline ZnO ceramic and the experiment success rate is reduced because the gap between a Bi-rich layer and a ZnO layer is larger and the Bi-rich layer cannot be tightly adhered, the ZnO ceramic-Bi-rich layer-ceramic single grain boundary ZnO voltage-sensitive ceramic is urgently needed to be constructed according to a double Schottky barrier model so as to simulate the single double Schottky barrier, and macroscopic electrical performance parameters of the type of ceramic are tested so as to characterize the electrical performance characteristics of the single grain boundary barrier inside the ZnO voltage-sensitive ceramic material and further prepare for exploring the internal characteristics of polycrystalline.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a three-layer structure pressure-sensitive ceramic only comprising a single double-Schottky-grain-boundary barrier, and a sol-gel preparation method and application thereof, so as to solve the problems that the conventional ZnO pressure-sensitive ceramic cannot be used for constructing the ZnO pressure-sensitive ceramic only comprising the single double-Schottky-grain-boundary barrier through polycrystalline ZnO ceramic, and experimental success rate is reduced due to larger gap between Bi-rich and ZnO layers and incapability of tight adhesion.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
the invention discloses a sol-gel preparation method of a three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier, which comprises the following steps:
1) Uniformly mixing ZnO, doped oxide, polyvinyl alcohol aqueous solution, tributyl phosphate and deionized water, drying, ball-milling to obtain powder, and sieving, granulating and press-forming to obtain an oxide doped ZnO green body;
2) Mixing Bi salt, precursor solution and solvent, heating in water bath, and stirring uniformly to obtain a sol-gel solution rich in Bi element; mixing the Bi salt with the mixture of other metal salts, the precursor solution and the solvent, heating in water bath, and stirring uniformly to obtain a sol-gel solution rich in Bi element and other metal elements;
3) Uniformly coating the surface of the oxide doped ZnO green body obtained in the step 1) with the sol-gel solution rich in Bi elements or the sol-gel solution rich in Bi elements and other metal elements prepared in the step 2); coating a polyvinyl alcohol aqueous solution on the surface of the oxide doped ZnO green body obtained in the step 1), and placing the surface of the oxide doped ZnO green body coated with the sol-gel solution rich in Bi elements and other metal elements; applying pressure to bond the ZnO green body and the Bi-rich layer to obtain a ZnO green body three-layer structure green body;
4) And 3) discharging glue from the ZnO green body-Bi-rich layer-ZnO green body three-layer structure green body prepared in the step 3), and sintering to obtain the three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier.
Preferably, in step 1), znO: the mole percentage of the doped metal oxide is (96.00-100.00): (0.00-4.00);
the addition amount of the polyvinyl alcohol aqueous solution is 10% -20% of the total mass of ZnO and doped metal oxide;
the adding amount of tributyl phosphate is 1% -5% of the total mass of ZnO and doped metal oxide;
the addition amount of deionized water is 80% -180% of the total mass of ZnO and doped metal oxide.
Preferably, in the step 1), the mass percentage of the polyvinyl alcohol aqueous solution is 1% -5%; doped metal oxide as Co 2 O 3 ，MnO 2 ，SiO 2 The method comprises the steps of carrying out a first treatment on the surface of the When the powder is pressed and formed, 0.1-0.15g of powder is pressed into a green body with the diameter of 8.0mm and the thickness of 0.6-0.8 mm.
Preferably, in step 2), the Bi salt: precursor solution: the mass ratio of the solvent is (0.5% -2.0%): (0.0% -49.75%): (49.0% -99.5%); mixture of Bi salts with other metal salts: precursor solution: the mass ratio of the solvent is (0.5% -2.0%): (0.0% -49.75%): (49.0% -99.5%);bi salt is Bi (NO) 3 ) 3 ·5H 2 O; other metal salts are MnSO 4 ·H 2 O or Mn (NO) 3 ) 2 ·4H 2 O; the precursor solution is absolute ethyl alcohol; the solvent is glycerol or deionized water; bi salt: the mass ratio of other metal salts is (1-3): (1-3).
Preferably, in the step 2), the temperature of water bath heating is 40-80 ℃, and the stirring time of water bath heating is 1-4h.
Preferably, in step 3), the mass percentage of the aqueous solution of polyvinyl alcohol is 1% -5% and the applied pressure is 0.1-0.5MPa.
Preferably, in the step 4), the glue discharging temperature is 500-600 ℃, and the glue discharging time is 100-300min.
Preferably, in step 4), the sintering temperature is 600-1000 ℃ and the sintering time is 2-3h.
The invention also discloses the three-layer structure pressure-sensitive ceramic which only comprises a single double-Schottky-grain boundary barrier and is prepared by the preparation method, the three-layer structure pressure-sensitive ceramic which only comprises the single double-Schottky-grain-boundary barrier is a three-layer structure green body of ZnO layer-Bi-rich layer-ZnO layer, the nonlinear coefficient is 2.02-18.73, the breakdown voltage is 12.38-1072.40V, and the leakage current density is 0.03-2.13mA/cm 2 The thickness of the Bi-rich layer is less than or equal to 10.23 mu m.
The invention also discloses application of the three-layer-structure pressure-sensitive ceramic containing only a single double Schottky grain boundary barrier in power systems and electronic circuits.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a sol-gel preparation method of three-layer-structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier, which adopts a solid phase sintering method, takes ZnO as a raw material, and presses doped oxide to obtain a doped oxide ZnO green body; the oxide doped ZnO green body can improve the conductivity and the density, and the requirements on the ball milling uniformity degree of ZnO and doped oxide additives are reduced, so that the operation is simple and easy to implement; coating the sol-gel solution rich in Bi element and other metal elements on the surface of the oxide doped ZnO green body, and then coating the surface of the suspensionPlacing a ZnO green body with the surface coated with a polyvinyl alcohol aqueous solution, and applying a certain pressure under the condition of being not destroyed to enable the ZnO green body to be fully adhered to obtain a ZnO green body-Bi-rich layer-ZnO green body three-layer structure green body; the pressure sensitive ceramic with a three-layer structure can be obtained after sintering; the experimental process is improved on the basis of the traditional solid-phase sintering method by improving the conventional ZnO pressure-sensitive ceramic preparation process, and the ZnO ceramic is brushed with a doped layer to prepare the brand-new pressure-sensitive ceramic with a three-layer structure, which only comprises a single double Schottky barrier, so that the analysis of the single double Schottky barrier is facilitated. The three-layer structure of the three-layer structure pressure-sensitive ceramic only comprising the single double Schottky grain boundary barrier comprises two ZnO ceramic outer layers and a middle bismuth-rich layer, and based on the structure, the performance and the conduction mechanism research of the single double Schottky grain boundary barrier in the ZnO pressure-sensitive ceramic have remarkable advantages, and the structure of single ZnO crystal grains-grain boundaries-ZnO crystal grains formed in the complex structure of the conventional ZnO pressure-sensitive ceramic can be simulated. The preparation method disclosed by the invention directly adopts Bi 2 O 3 Compared with the method for preparing the Bi-rich layer by dissolving metal oxide in PVA solution, the sol-gel method adopts the raw materials which are basically alcohols or inorganic salts and are easy to purify, so that the prepared material has high purity, meanwhile, the chemical reaction of the solution is utilized, so that the raw materials can be mixed at the molecular level (or atomic level), the thickness of the Bi-rich layer is smaller, the uniformity is better, and the micro doping is easy, thus the method is also a main reason for greatly improving the success rate of the ZnO pressure-sensitive ceramic with the three-layer structure by adopting the sol-gel method. The reaction process is easy to control, the density, specific surface area and the like of the gel can be adjusted, and the process is simple.
The invention also discloses the three-layer structure pressure-sensitive ceramic which only comprises a single double-Schottky-grain boundary barrier and is prepared by the sol-gel preparation method, the three-layer structure pressure-sensitive ceramic which only comprises the single double-Schottky-grain boundary barrier is of a polycrystalline structure, the density is high, the uniformity degree is controllable, the electrical property of the ceramic can be improved by doping metal oxide, the preparation method of the doped layer is simple and easy, the content of metal salt in a sol-gel solution is controllable, and the oxide doped ZnO ceramic and the oxide doped Bi-rich layer are in good contact. Its nonlinear coefficient is2.02-18.73, breakdown voltage of 12.38-1072.40V, leakage current density of 0.03-2.13mA/cm 2 The average thickness of the Bi-rich layer is less than or equal to 10.23 mu m. The Bi-rich layer has smaller thickness, which is consistent with the grain boundary structure size proportion of the crystal grains in the conventional ZnO voltage-sensitive ceramic, and meanwhile, the breakdown voltage range is larger, so that the ZnO voltage-sensitive ceramic can be applied to different circuits according to the voltage required by the circuits.
The invention also discloses application of the three-layer structure pressure-sensitive ceramic containing only a single double Schottky grain boundary barrier in a power system and an electronic circuit. Meanwhile, the trend of electronic devices is now to miniaturize, so smaller-sized materials are required, which leads to a reduction in the number of grain boundaries, and thus, improvement of the characteristics of individual grain boundaries is required. The single crystal boundary ZnO voltage-sensitive ceramic is prepared by the sol-gel method for the first time, and can be used as miniaturized electronic equipment in an electric power system according to the breakdown voltage and the nonlinearity of the single crystal boundary ZnO voltage-sensitive ceramic.
Drawings
Fig. 1 is an SEM image of a three-layer structure pressure-sensitive ceramic sample Mn1 containing only a single double schottky grain boundary barrier, which was prepared in example 1 of the present invention;
FIG. 2 is an E-J characteristic curve of a part of samples in the three-layer structure pressure-sensitive ceramics comprising only a single double Schottky barrier obtained in inventive examples 1 to 5;
fig. 3 is an SEM image of a three-layer structure pressure-sensitive ceramic sample Mn4 containing only a single double schottky grain boundary barrier, which was prepared in example 4 of the present invention;
FIG. 4 is an E-J characteristic curve of a part of samples in the three-layer structure pressure-sensitive ceramics comprising only a single double Schottky barrier obtained in inventive examples 6 to 10;
fig. 5 is an SEM image of a three-layer structure pressure-sensitive ceramic sample Si4 containing only a single double schottky grain boundary barrier, which was prepared in example 9 of the present invention;
FIG. 6 is an E-J characteristic curve of a part of samples in the three-layer structure pressure-sensitive ceramics comprising only a single double Schottky barrier obtained in inventive examples 11 to 13;
fig. 7 is an SEM image of a three-layer structure pressure-sensitive ceramic sample Co3 containing only a single double schottky grain boundary barrier, which was prepared in example 13 of the present invention;
fig. 8 is an E-J characteristic curve of a part of samples in the three-layer structure pressure-sensitive ceramics containing only a single double schottky grain boundary barrier manufactured in inventive examples 14 and 15;
fig. 9 is an SEM image of a three-layer structure pressure-sensitive ceramic sample Zn2 containing only a single double schottky grain boundary barrier, which was prepared in example 15 of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the attached drawing figures:
the invention provides a sol-gel preparation method of a three-layer-structure pressure-sensitive ceramic with a ZnO crystal grain-grain boundary-ZnO crystal grain structure similar to that of the pressure-sensitive ceramic, which only comprises a single double Schottky grain boundary barrier, and is favorable for carrying out deep research on the grain boundary characteristics of the pressure-sensitive ceramic.
A sol-gel method for preparing a three-layer structured pressure sensitive ceramic comprising only a single double schottky grain boundary barrier, comprising the steps of:
1) Uniformly mixing ZnO, doped oxide, polyvinyl alcohol aqueous solution, tributyl phosphate and deionized water, drying, ball-milling to obtain powder, and sieving, granulating and press-forming to obtain an oxide doped ZnO green body;
2) Mixing Bi salt, precursor solution and solvent, heating in water bath, and stirring uniformly to obtain a sol-gel solution rich in Bi element; mixing the Bi salt with the mixture of other metal salts, the precursor solution and the solvent, heating in water bath, and stirring uniformly to obtain a sol-gel solution rich in Bi element and other metal elements;
3) Uniformly coating the surface of the oxide doped ZnO green body obtained in the step 1) with the sol-gel solution rich in Bi elements or the sol-gel solution rich in Bi elements and other metal elements prepared in the step 2); coating a polyvinyl alcohol aqueous solution on the surface of the oxide doped ZnO green body obtained in the step 1), and placing the surface of the oxide doped ZnO green body coated with the sol-gel solution rich in Bi elements and other metal elements; applying pressure to bond the ZnO green body and the Bi-rich layer to obtain a ZnO green body three-layer structure green body;
4) And 3) discharging glue from the ZnO green body-Bi-rich layer-ZnO green body three-layer structure green body prepared in the step 3), and sintering to obtain the three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier.
In step 1), the mole percentage of ZnO and doped metal oxide is (96.00-100.00): (0.00-4.00);
the addition amount of the polyvinyl alcohol aqueous solution is 10% -20% of the total mass of ZnO and doped metal oxide;
the adding amount of tributyl phosphate is 1% -5% of the total mass of ZnO and doped metal oxide;
the adding amount of deionized water is 80% -180% of the total mass of ZnO and doped metal oxide;
doped oxide of Co 2 O 3 ，MnO 2 ，SiO 2 。
Pressing 0.1-0.15g of powder into green body with diameter of 8.0mm and thickness of 0.6-0.8 mm.
In step 2), bi salt, mixture of Bi salt and other metal salt: precursor solution: the mass ratio of the solvent is (0.5% -2.0%): (0.0% -49.75%): (49.0% -99.5%);
bi salt: the mass ratio of other metal salts is (1-3): (1-3);
bi salt is Bi (NO) 3 ) 3 ·5H 2 O; other metal salts are MnSO 4 ·H 2 O or Mn (NO) 3 ) 2 ·4H 2 O; the precursor solution is absolute ethyl alcohol; the solvent is glycerol or deionized water.
In the step 3), the mass percentage of the polyvinyl alcohol aqueous solution is 1% -5%;
the applied pressure is 0.1-0.5Mpa;
the heating temperature in water bath is 40-80 deg.C, and stirring time is 1-4h.
In the step 4), the glue discharging temperature is 500-600 ℃, and the glue discharging time is 100-300min.
In the step 4), the sintering temperature is 600-1000 ℃ and the sintering time is 2-3h.
Example 1
By doping with 0.01mol% MnO 2 Is a ZnO ceramic green body of (2)
The preparation method of the three-layer structure pressure-sensitive ceramic based on the sol-gel method comprises the following steps:
1) 9.9988g ZnO and 0.0012g MnO were first mixed 2 Mixing with 18g of deionized water and 2g of polyvinyl alcohol (PVA) aqueous solution, ball-milling 0.1g of tributyl phosphate for 5 hours at a rotating speed of 500r/min by using a planetary ball mill, and drying the obtained slurry at 90 ℃ for 12 hours to obtain mixed powder;
2) Grinding and sieving the mixed powder obtained in the step 1), selecting uniform powder between 40 meshes and 120 meshes, weighing 0.1g of powder, and uniaxially pressing to obtain a green body with the diameter of 8.0mm and the thickness of 0.6 mm;
3) The following sol-gel solutions were prepared: a. 0.1g Bi (NO) 3 ) 3 ·5H 2 Placing O in 19.9g of glycerol, and stirring for 1h in a water bath heating process at 40 ℃ to form colorless transparent gel solution with the mass percent of 0.5%;
4) Placing 2.5g of polyvinyl alcohol into 47.5g of deionized water, and stirring for 3 hours in the water bath heating process at 40 ℃ to form a polyvinyl alcohol aqueous solution with the mass percent of 5%;
5) Uniformly coating the sol-gel solution obtained in the step 3) on the surface of the oxide doped ZnO green body obtained in the step 2), then placing a piece of oxide doped ZnO green body coated with the polyvinyl alcohol solution obtained in the step 4) on the surface of the coating suspension, and applying a pressure of 0.1MPa under the condition of being not damaged to enable the ZnO green body to be fully bonded to obtain a ZnO green body-Bi-rich layer-ZnO green body three-layer structure green body with a sandwich structure;
6) And 5) heating the ZnO green body-Bi-rich layer-ZnO green body three-layer structure green body prepared in the step 5) to 600 ℃ at a heating rate of 3 ℃/min for 5h for discharging glue, heating to 1000 ℃ at a heating rate of 3 ℃/min for 2h for heat preservation and sintering, cooling to 500 ℃ at 3 ℃/min, and naturally cooling to room temperature to obtain the three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier.
Example 2
Unlike example 1, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: b. 0.1g Bi (NO) 3 ) 3 ·5H 2 O and 0.1g MnSO 4 ·H 2 O is placed in a mixed solution of 9.8g of deionized water and 9.8g of absolute ethyl alcohol, and is stirred for 2 hours in the water bath heating process at 50 ℃ to form a uniform milky gel solution with the mass percent of 1.0%.
Example 3
Unlike example 1, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: c. 0.05g Bi (NO) 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.95g of deionized water and 9.95g of absolute ethyl alcohol, and is stirred for 3 hours in the water bath heating process at 60 ℃ to form a uniform milky gel solution with the mass percent of 0.5%; in step 6), the sintering temperature was 900 ℃.
Example 4
Unlike example 1, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: d. 0.1g Bi (NO) was taken separately 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.9g of deionized water and 9.9g of absolute ethyl alcohol, and is stirred for 3 hours in the water bath heating process at 70 ℃ to form a uniform milky gel solution with the mass percent of 1.0%; in step 6), the sintering temperature was 900 ℃.
Example 5
Unlike example 1, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: e. respectively taking 0.2g Bi (NO) 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.8g of deionized water and 9.8g of absolute ethyl alcohol, and is stirred for 4 hours in the water bath heating process at 80 ℃ to form a uniform milky gel solution with the mass percent of 2.0%; in step 6), the sintering temperature was 900 ℃.
Finally, the three-layer structure pressure-sensitive ceramic prepared in the examples 1-5 and only comprising a single double Schottky grain boundary barrier is subjected to polishing, silver coating, drying and other steps, and then the silver-impregnated electrode is burned, so that silver oxide is reduced to elemental silver and is tightly attached to the surface of a sample as an electrode, and the electrical property of the electrode is conveniently tested. Table 1 below shows the electrical properties of the samples of the parts produced.
TABLE 1 electrical properties of three-layer pressure-sensitive ceramic samples each comprising only a single double Schottky grain boundary barrier prepared in examples 1-5
Referring to FIG. 1, there is shown an SEM image of Mn1 prepared in example 1 of the present invention; from the figure, the Bi-rich layer and the ZnO layer are in close contact in the three-layer structure pressure-sensitive ceramic sample prepared by the sol-gel method and only comprising a single double Schottky grain boundary barrier, and the sample surface has good uniformity and flatness.
Referring to fig. 2, the E-J characteristic curves of a part of samples in the three-layer structure pressure-sensitive ceramics comprising only a single double schottky grain boundary barrier prepared in inventive examples 1 to 5 are shown; as can be seen from the graph, the Mn doped ZnO voltage-sensitive ceramic has obvious nonlinear influence on the ceramic, the nonlinear coefficient can reach 18.73 at the highest, meanwhile, the breakdown voltage is larger, the change trend of the leakage current density is opposite to the change trend of the nonlinear coefficient, and the characteristics of the Mn doped ZnO voltage-sensitive ceramic are the same as those of the polycrystalline ZnO voltage-sensitive ceramic.
Referring to fig. 3, there is an SEM image of a three-layer structure pressure-sensitive ceramic sample Mn4 containing only a single double schottky grain boundary barrier, which was prepared in example 4 of the present invention; as can be seen from the graph, the ZnO ceramic has high density, the close contact gap between the doped layer and the ceramic is small, meanwhile, the thickness of the Bi-rich layer calculated by analysis is 8.75-10.37 mu m, and the average thickness is 9.45 mu m.
Example 6
By doping 0.01mol% SiO 2 Is a ZnO ceramic green body of (2)
A method for producing a three-layer pressure-sensitive ceramic comprising only a single double Schottky barrier grain boundary, differing from example 1 in that in step 1), 9.9993g of ZnO and 0.0.0007g of SiO are first mixed 2 Mixing with 15g deionized water and 1.5g polyvinyl alcohol (PVA) aqueous solution, and 0.3g tributyl phosphate, ball-milling for 5 hours at 550r/min by using a planetary ball mill, and drying the obtained slurry at 90 ℃ for 12 hours to obtain mixed powder;
in the step 2), 0.12g of powder is weighed and uniaxially pressed to obtain a green body with the diameter of 8.0mm and the thickness of 0.7 mm;
in the step 5), a pressure of 0.3MPa is applied to fully bond the materials;
in the step 6), the temperature is raised to 550 ℃ at 3 ℃/min, and the glue is discharged after the heat preservation is carried out for 100 min; the sintering time is 2.5h.
Example 7
Unlike example 6, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: b. 0.1g Bi (NO) 3 ) 3 ·5H 2 O and 0.1g MnSO 4 ·H 2 O is placed in a mixed solution of 9.8g of deionized water and 9.8g of absolute ethyl alcohol, and is stirred for 2 hours in the water bath heating process at 50 ℃ to form a uniform milky gel solution with the mass percent of 1.0%.
Example 8
Unlike example 6, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: c. 0.05g Bi (NO) 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.95g of deionized water and 9.95g of absolute ethyl alcohol, and is stirred for 3 hours in the water bath heating process at 60 ℃ to form a uniform milky gel solution with the mass percent of 0.5%; in step 6), the sintering temperature was 900 ℃.
Example 9
Unlike example 6, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: d. 0.1g Bi (NO) was taken separately 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.9g of deionized water and 9.9g of absolute ethyl alcohol, and is stirred for 3 hours in the water bath heating process at 70 ℃ to form a uniform milky gel solution with the mass percent of 1.0%; in step 6), the sintering temperature was 900 ℃.
Example 10
Unlike example 6, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: e. respectively taking 0.2g Bi (NO) 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.8g of deionized water and 9.8g of absolute ethyl alcohol, and is stirred for 4 hours in the water bath heating process at 80 ℃ to form a uniform milky gel solution with the mass percent of 2%; in step 6), the sintering temperature was 900 ℃.
The three-layer structure pressure sensitive ceramics prepared in examples 6 to 10 only comprising a single double schottky grain boundary barrier were subjected to polishing, silver coating, baking and the like, and then the silver-impregnated electrode was fired, so that silver oxide was reduced to elemental silver and was tightly adhered to the surface of the sample as an electrode to facilitate the measurement of the electrical properties thereof, and the electrical properties of the prepared partial samples were shown in table 2 below.
TABLE 2 electrical Properties of three-layer pressure-sensitive ceramic samples each comprising only a single double Schottky grain boundary barrier prepared in examples 6-10
Referring to fig. 4, the E-J characteristic curves of a part of samples in the three-layer structure pressure-sensitive ceramics comprising only a single double schottky grain boundary barrier prepared in inventive examples 6 to 10 are shown; as can be seen from the graph, the nonlinear effect of the Si-doped ZnO voltage-sensitive ceramic is small, the nonlinear coefficient is 12.15 at most, but the breakdown voltage is reduced by doping Si, the change trend of the leakage current density is opposite to the change trend of the nonlinear coefficient, and the characteristics of the Si-doped ZnO voltage-sensitive ceramic are the same as those of the polycrystalline ZnO voltage-sensitive ceramic.
Referring to fig. 5, there is an SEM image of a three-layer structure pressure-sensitive ceramic sample Si4 containing only a single double schottky grain boundary barrier, which was prepared in example 9 of the present invention; as can be seen from the graph, the ZnO ceramic has higher density, the close contact gap between the doped layer and the ceramic is small, and meanwhile, the thickness of the Bi-rich layer calculated by analysis is 3.92-6.91 mu m, and the average thickness is 6.16 mu m.
Example 11
By doping with 4.00mol% Co 2 O 3 Is a ZnO ceramic green body of (2)
A method for producing a three-layer pressure-sensitive ceramic comprising only a single double Schottky barrier grain boundary, differing from example 1 in that in step 1), 9.3100g of ZnO and 0.7900g of Co are first added 2 O 3 Mixing with 10g deionized water, 1g polyvinyl alcohol (PVA) aqueous solution and 0.4g tributyl phosphate, ball-milling for 5 hours at 600r/min by using a planetary ball mill, and drying the obtained slurry at 90 ℃ for 12 hours to obtain mixed powder;
in the step 2), 0.15g of powder is weighed and uniaxially pressed to obtain a green body with the diameter of 8.0mm and the thickness of 0.8 mm;
in the step 5), 0.5MPa pressure is applied to fully bond the materials;
in the step 6), the temperature is raised to 600 ℃ at 3 ℃/min, and the glue is discharged after the heat preservation is carried out for 250 min; the sintering time is 3h.
Example 12
Unlike example 11, in step 3), the sol-gel preparation method of the three-layer structure pressure-sensitive ceramic containing only a single double schottky grain boundary barrier is as follows: d. 0.1g Bi (NO) was taken separately 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.9g of deionized water and 9.9g of absolute ethyl alcohol, and is stirred for 3 hours in the water bath heating process at 70 ℃ to form a uniform milky gel solution with the mass percent of 1.0%; in step 6), the sintering temperature was 900 ℃.
Example 13
A sol-gel method for preparing a three-layer pressure-sensitive ceramic comprising only a single double schottky grain boundary barrier, unlike example 12, in step 6), the sintering temperature is 900 ℃.
The three-layer structured pressure sensitive ceramics prepared in examples 11 to 13 containing only a single double schottky grain boundary barrier were subjected to polishing, silver coating, baking, and the like, followed by firing of the silver impregnated electrode, thereby reducing silver oxide to elemental silver and tightly adhering the elemental silver as an electrode to the surface of the sample for testing the electrical properties thereof, and table 3 below shows the electrical properties of the prepared part of the sample.
TABLE 3 electrical Properties of three-layer pressure-sensitive ceramic samples each comprising only a single double Schottky grain boundary barrier prepared in examples 11-13
Referring to fig. 6, the E-J characteristic curves of a part of samples in the three-layer structure pressure-sensitive ceramics comprising only a single double schottky grain boundary barrier prepared in inventive examples 11 to 13 are shown; from the graph, the Co doped ZnO voltage-sensitive ceramic has small nonlinear influence and the nonlinear coefficient is 6.70 at most, but the Co doping has large contribution to the increase of breakdown voltage, the change trend of leakage current density is opposite to the change trend of the nonlinear coefficient, and the Co doped ZnO voltage-sensitive ceramic has the same characteristics as the polycrystalline ZnO voltage-sensitive ceramic.
Referring to fig. 7, an SEM image of a three-layer structure pressure-sensitive ceramic sample Co3 containing only a single double schottky grain boundary barrier, which was prepared in example 13 of the present invention; as can be seen from the graph, the ZnO ceramic has higher density, the doped layer is in close contact with the ceramic, and meanwhile, the thickness of the Bi-rich layer calculated by analysis is 6.51-10.23 mu m, and the average thickness is 8.72 mu m.
Example 14
Using pure ZnO ceramic green bodies
In the preparation method of the three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier, unlike in the example 1, in the step 1), 10.0g of ZnO is firstly mixed with 8g of deionized water and 2g of polyvinyl alcohol (PVA) aqueous solution, 0.5g of tributyl phosphate is ball-milled for 5 hours at 600r/min by using a ball-milling machine, and the obtained slurry is dried for 12 hours at 90 ℃ to obtain mixed powder;
in step 6), the sintering temperature was 600 ℃.
Example 15
Comprising only a single oneUnlike example 14, in step 3), the sol-gel preparation method of the pressure-sensitive ceramic with a three-layer structure of the double schottky grain boundary barrier is as follows: d. 0.1g Bi (NO) was taken separately 3 ) 3 ·5H 2 O is equal to Mn (NO) 3 ) 2 ·4H 2 O is placed in a mixed solution of 9.9g of deionized water and 9.9g of absolute ethyl alcohol, and is stirred for 3 hours in the water bath heating process at 70 ℃ to form a uniform milky gel solution with the mass percent of 1.0%; in step 6), the sintering temperature was 1000 ℃.
The three-layer structure pressure-sensitive ceramics comprising only a single double schottky grain boundary barrier prepared in examples 14 and 15 were subjected to polishing, silver coating, baking, and the like, followed by firing of the silver-impregnated electrode, thereby reducing silver oxide to elemental silver and tightly adhering the elemental silver as an electrode to the surface of the sample for testing the electrical properties thereof, and table 4 below shows the electrical properties of the prepared partial samples.
TABLE 4 electrical properties of three-layer pressure-sensitive ceramic samples each comprising only a single double Schottky grain boundary barrier prepared in example 14 and example 15
Referring to fig. 8, the E-J characteristic curves of a part of samples in the three-layer structure pressure-sensitive ceramics including only a single double schottky grain boundary barrier prepared in inventive examples 14 and 15 are shown; the graph shows that the three-layer pressure-sensitive ceramic prepared from the pure ZnO ceramic green body has smaller breakdown voltage, and meanwhile, the Bi-rich layer prepared from different sol-gel solutions has smaller nonlinear contribution to the pressure-sensitive ceramic.
Referring to fig. 9, there is an SEM image of a three-layer structure pressure-sensitive ceramic sample Zn2 containing only a single double schottky grain boundary barrier, which was prepared in example 15 of the present invention; as can be seen from the graph, the ZnO ceramic has higher density, but the edge is easy to break and the flatness is lower because the pure ZnO has stronger brittleness, but the close contact gap between the internal doped layer and the ceramic is small, and meanwhile, the thickness of the Bi-rich layer calculated by analysis is 8.67-12.19 mu m, and the average thickness is 10.23 mu m.
For the three-layer structure pressure sensitive ceramics which are obtained based on the sol-gel method and only contain a single double Schottky grain boundary barrier in the embodiment, the nonlinear coefficient alpha and the pressure sensitive voltage U are respectively tested 1mA Leakage current density J L . The nonlinear coefficient alpha is 18.73 at maximum and the voltage-sensitive voltage U is measured in examples 1-5 in Table 1 1mA At 975.84V and leakage current density J L 0.03mA/cm 2 The average thickness of the Bi-rich layer calculated by the simultaneous analysis was 9.45 μm; the nonlinear coefficient alpha is maximally 12.15 and the voltage-sensitive voltage U is measured in examples 6-10 in Table 2 1mA At 766.44V and leakage current density J L 0.06mA/cm 2 The average thickness of the Bi-rich layer calculated by the simultaneous analysis was 6.16 μm; the nonlinear coefficient alpha is 6.70 at maximum and the voltage-sensitive voltage U is measured in examples 11-13 in Table 3 1mA At 948.41V and leakage current density J L 0.39mA/cm 2 The average thickness of the Bi-rich layer calculated by the simultaneous analysis was 8.72 μm; examples 14 and 15 in Table 4 measured a nonlinear coefficient of at most 4.17 and a voltage-dependent voltage U 1mA At 366.77V and leakage current density J L Is 0.58mA/cm 2 The average thickness of the Bi-rich layer calculated by the simultaneous analysis was 10.23. Mu.m. As a result, it was found that when the Bi-rich layer was prepared using the same sol-gel solution, mnO was prepared in examples 1 to 5 2 The doped ZnO ceramic has obvious effect on improving the nonlinear coefficient, the voltage-sensitive voltage is up to 975.84V, the leakage current is smaller, and the SiO prepared in examples 6-10 2 ZnO-doped ceramic, co produced in examples 11-13 2 O 3 The doped ZnO ceramic has small contribution to the improvement of the nonlinear coefficient of the ZnO ceramic, but SiO 2 The doped ZnO ceramics significantly reduced their breakdown voltage, and the pure ZnO ceramics prepared in examples 14 and 15 contributed minimal improvement in their nonlinear coefficients. When the same ceramic green body is used, bi (NO 3 ) 3 ·5H 2 O and Mn (NO) 3 ) 2 ·4H 2 The effect of preparing the Bi-rich layer by the sol-gel solution of O is remarkable, and the Bi-rich layer is most remarkable when 0.1g is weighed.
As can be seen from SEM images of the embodiment, in the ZnO ceramic-Bi-rich layer-ZnO ceramic three-layer structure pressure-sensitive ceramic prepared by a sol-gel method, the gap between the Bi-rich layer and the ZnO ceramic is smaller, and the contact is tight, which also proves that the method is used for preparing the ZnO ceramic-Bi-rich layer-ZnO ceramic three-layer structure pressure-sensitive ceramicCan effectively improve the stability and uniformity of the sample. The thickness of the Bi-rich layer is basically controlled within 10 mu m, which is similar to the size proportion of the structure of the conventional single ZnO crystal grain-crystal boundary-ZnO crystal grain, so the invention has important significance for researching the structure, the performance and the conduction mechanism of the single double Schottky crystal boundary barrier in the ZnO pressure-sensitive ceramic. As is evident from examples 1 to 15, mnO 2 The doped ZnO ceramic has obvious effect on improving the nonlinear coefficient, and can be considered as MnO 2 Doping can effectively increase the double schottky barrier height and thus the nonlinear coefficient.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A sol-gel method for preparing a three-layer pressure sensitive ceramic comprising only a single double schottky grain boundary barrier, comprising:
1) Uniformly mixing ZnO, doped oxide, polyvinyl alcohol aqueous solution, tributyl phosphate and deionized water, drying, ball-milling to obtain powder, and sieving, granulating and press-forming to obtain an oxide doped ZnO green body;
2) Mixing Bi salt, precursor solution and solvent, heating in water bath, and stirring uniformly to obtain a sol-gel solution rich in Bi element; mixing the Bi salt with the mixture of other metal salts, the precursor solution and the solvent, heating in water bath, and stirring uniformly to obtain a sol-gel solution rich in Bi element and other metal elements;
3) Uniformly coating the surface of the oxide doped ZnO green body obtained in the step 1) with the sol-gel solution rich in Bi elements or the sol-gel solution rich in Bi elements and other metal elements prepared in the step 2); coating a polyvinyl alcohol aqueous solution on the surface of the oxide doped ZnO green body obtained in the step 1), and placing the surface of the oxide doped ZnO green body coated with the sol-gel solution rich in Bi elements and other metal elements; applying pressure to bond the ZnO green body and the Bi-rich layer to obtain a ZnO green body three-layer structure green body;
4) And 3) discharging glue from the ZnO green body-Bi-rich layer-ZnO green body three-layer structure green body prepared in the step 3), and sintering to obtain the three-layer structure pressure-sensitive ceramic only comprising a single double Schottky grain boundary barrier.
2. The sol-gel process for preparing a three-layer structured pressure sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 1), the ZnO: the mole percentage of the doped metal oxide is (96.00-100.00): (0.00-4.00);
the addition amount of the polyvinyl alcohol aqueous solution is 10% -20% of the total mass of ZnO and doped metal oxide;
the adding amount of tributyl phosphate is 1% -5% of the total mass of ZnO and doped metal oxide;
the addition amount of the deionized water is 80% -180% of the total mass of ZnO and doped metal oxide.
3. The sol-gel process for preparing a three-layer structured pressure sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 1), the mass percentage of the aqueous polyvinyl alcohol solution is 1% -5%; the doped metal oxide is Co 2 O 3 ，MnO 2 ，SiO 2 The method comprises the steps of carrying out a first treatment on the surface of the When the powder is pressed and formed, 0.1-0.15g of powder is pressed into a green body with the diameter of 8.0mm and the thickness of 0.6-0.8 mm.
4. The sol-gel process for preparing a three-layer structured pressure sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 2), the Bi salt: precursor solution: the mass ratio of the solvent is (0.5% -2.0%): (0.0% -49.75%): (49.0% -99.5%); mixtures of the Bi salts with other metal salts: precursor solution: the mass ratio of the solvent is (0.5% -2.0%): (0.0% -49.75%): (49.0% -99.5%); the Bi salt is Bi (NO) 3 ) 3 ·5H 2 O; said otherThe metal salt is MnSO 4 ·H 2 O or Mn (NO) 3 ) 2 ·4H 2 O; the precursor solution is absolute ethyl alcohol; the solvent is glycerol or deionized water; the Bi salt: the mass ratio of other metal salts is (1-3): (1-3).
5. The method for preparing a three-layer-structured pressure-sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 2), the water bath heating temperature is 40-80 ℃ and the stirring time of the water bath heating is 1-4h.
6. The method for preparing a three-layer-structured pressure-sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 3), the mass percentage of the aqueous polyvinyl alcohol solution is 1% -5%, and the applied pressure is 0.1-0.5MPa.
7. The method for preparing a three-layer-structured pressure-sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 4), the paste ejection temperature is 500-600 ℃ and the paste ejection time is 100-300min.
8. The method for preparing a three-layer-structured pressure-sensitive ceramic containing only a single double schottky grain boundary barrier according to claim 1, wherein in step 4), the sintering temperature is 600 to 1000 ℃ and the sintering time is 2 to 3 hours.
9. The three-layer structure pressure-sensitive ceramic comprising only a single double schottky barrier layer produced by the production method according to any one of claims 1 to 8, characterized in that the three-layer structure pressure-sensitive ceramic comprising only a single double schottky barrier layer is a three-layer structure green body of ZnO layer-Bi-rich layer-ZnO layer having a nonlinear coefficient of 2.02 to 18.73, a breakdown voltage of 12.38 to 1072.40V, and a leakage current density of 0.03 to 2.13mA/cm 2 The thickness of the Bi-rich layer is less than or equal to 10.23 mu m.
10. Use of the three-layer structured pressure sensitive ceramic comprising only a single dual schottky grain boundary barrier according to claim 9 in electrical power systems and electronic circuits.
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