CN112521166B - Low dielectric loss CaCu 3 Ti 4 O 12 Negative pressure sintering method of ceramic - Google Patents
Low dielectric loss CaCu 3 Ti 4 O 12 Negative pressure sintering method of ceramic Download PDFInfo
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Abstract
The invention discloses a method for preparing calcium copper titanate CaCu with low dielectric loss and high dielectric constant 3 Ti 4 O 12 A negative pressure sintering method of (CCTO) ceramics aims at solving the technical problem that the CCTO ceramics prepared by the existing sintering technology have higher dielectric loss. The technical scheme of the invention is as follows: the CCTO ceramic body is subjected to a heating stage 1 under the atmosphere of normal pressure air, a heat preservation stage 1 under the atmosphere of normal pressure air, a heating stage 2 under the atmosphere of negative pressure air, a heat preservation stage 2 under the atmosphere of negative pressure air, a cooling stage 1 under the atmosphere of oxygen and nitrogen with high oxygen content, a heat preservation stage 3 under the atmosphere of oxygen and nitrogen with high oxygen content and a cooling stage 2 under the atmosphere of normal pressure air and cooled along with the furnace in an atmosphere furnace to obtain the CCTO ceramic. The CCTO ceramic obtained by the technical scheme of the invention not only has improved dielectric constant, but also has obviously reduced dielectric loss, and the dielectric loss value is as low as 0.02.
Description
Technical Field
The invention relates to the field of functional ceramic sintering process, in particular to CaCu with low dielectric loss 3 Ti 4 O 12 A method for sintering ceramics.
Background
High dielectric constant dielectric materials have been one of the key materials in the research and development of microelectronics. In recent years, caCu of perovskite structure 3 Ti 4 O 12 (CCTO) ceramic materials with a ceramic composition of up to 10 4 ～10 5 The dielectric constant of the stage has received a great deal of attention from both academia and industry. CCTO ceramic materials not only have an ultra-high dielectric constant, but also a high dielectric constant exhibits good temperature stability over a fairly wide temperature range around room temperature. These characteristics make CCTO ceramic materials promising for future miniaturized applications of new electronic devices. However, the CCTO ceramic also has relatively high dielectric loss, and generates a large amount of heat to affect the stability of the device in practical device applications, which is one of the important technical bottlenecks that currently limit the commercial application of the CCTO ceramic. The existing research literature indicates that the dielectric loss of the CCTO ceramics can be reduced by a method for doping and modifying a proper element, but on the other hand, the dielectric constant is generally reduced by the doping method, or the dielectric constant can be kept at the original level, but the dielectric loss is not obviously reduced, and the dielectric loss value is still 0.05Above, the comprehensive dielectric properties of CCTO ceramic materials are difficult to meet the application requirements in practical electronic devices. In addition, for the modified CCTO material without doping, the dielectric loss of the CCTO ceramic obtained by conventional sintering only in an air atmosphere is usually above 0.1 at a frequency of 1kHz, and the dielectric loss value is relatively high, which limits the wide application of the CCTO ceramic in practical devices.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a method for sintering CCTO ceramics by combining negative pressure atmosphere, which realizes the cooperative regulation and control of CCTO ceramic crystal grains and grain boundary resistance by introducing the process steps of negative pressure atmosphere sintering, oxygen-enriched atmosphere cooling and heat preservation in the CCTO ceramics sintering process, thereby achieving the beneficial effects of reducing the dielectric loss of the CCTO ceramics and improving the electrical constant.
The technical scheme adopted by the invention is as follows: and putting the formed CCTO ceramic blank into an atmosphere furnace, and then performing a heating stage 1 under the atmosphere of normal pressure air, a heat preservation stage 1 under the atmosphere of normal pressure air, a heating stage 2 under the atmosphere of negative pressure air, a heat preservation stage 2 under the atmosphere of negative pressure air, a cooling stage 1 under the atmosphere of mixed gas with high oxygen, a heat preservation stage 3 under the atmosphere of mixed gas with high oxygen and a cooling stage 2 of natural cooling along with the furnace under the atmosphere of normal pressure air to obtain the fired CCTO dielectric ceramic.
In order to overcome the defects in the prior art, the invention provides a method for sintering CCTO ceramic blank with low dielectric loss under negative pressure. When the CCTO ceramic body is placed in an atmosphere furnace, the following process steps are sequentially carried out:
s1, temperature rise stage 1: raising the temperature in the atmosphere furnace from room temperature to 650 ℃, wherein the temperature raising rate of the atmosphere furnace is 8-10 ℃/min in the temperature raising process, and meanwhile, the inside of the atmosphere furnace is communicated with the external atmosphere, so that the inside of the atmosphere furnace is in the atmospheric air atmosphere;
s2, heat preservation stage 1: when the temperature of the atmosphere furnace is raised to 650 ℃, preserving the heat for 40-60 min in the atmosphere of normal pressure air;
s3, a heating stage 2: after the heat preservation stage 1 is finished, isolating the inside of the atmosphere furnace from the outside air, generating negative pressure with the relative vacuum degree of-40 kPa to-20 kPa in the atmosphere furnace by a vacuumizing method, and simultaneously heating the temperature in the atmosphere furnace to 1070 to 1110 ℃ at the heating rate of 6 to 8 ℃/min;
s4, a heat preservation stage 2: when the temperature in the atmosphere furnace rises to 1070-1110 ℃, adjusting the internal air pressure of the atmosphere furnace to keep the internal air pressure in the negative pressure atmosphere with the relative vacuum degree of-20 kPa to-15 kPa, and preserving the heat for 6-8 hours;
s5, cooling stage 1: after the heat preservation stage 2 is finished, reducing the temperature in the atmosphere furnace to 780 ℃ at a cooling rate of 30-45 ℃/min, and continuously introducing mixed gas of oxygen and nitrogen with the volume content of 40-45% into the atmosphere furnace in the process of the cooling stage 1;
s6, heat preservation stage 3: when the temperature in the atmosphere furnace is reduced to 780 ℃, introducing mixed gas of oxygen and nitrogen with the oxygen volume content of 50-60% into the atmosphere furnace, and preserving the heat for 2-3 hours at 780 ℃;
s7, a cooling stage 2: and after the heat preservation stage 3 is finished, naturally cooling to room temperature along with the furnace temperature in the atmosphere of normal pressure air to obtain the sintered body of the CCTO ceramic.
The technical scheme of the invention has the following beneficial effects: the technical scheme of the invention not only can improve the dielectric constant of the CCTO ceramic, but also can simultaneously reduce the dielectric loss of the CCTO ceramic. The dielectric property of the CCTO ceramic obtained by the sintering method in the technical scheme of the invention is obviously improved, and the dielectric constant of the obtained CCTO ceramic is up to 4 multiplied by 10 under the frequency of 1kHz 4 Meanwhile, the dielectric loss is lower than 0.02, thus solving the technical defects in the background technology. In addition, the temperature control and the atmosphere control related to the ceramic sintering process in the technical scheme of the invention can be realized through the control program of the atmosphere furnace, the program setting can be completed in one step, and the operation is simple.
The technical scheme of the invention has the following beneficial effects: the CCTO ceramic obtained by the technical scheme of the invention is heated and sintered in a heat preservation way under the negative pressure air atmosphere as a result of the heating stage 2 in the step S3 and the heat preservation stage 2 in the step S4, so that the oxygen vacancy concentration of crystal grains in the CCTO ceramic is obviously improved compared with the heating and sintering under the normal pressure air atmosphere, and the conductive capability of the CCTO ceramic crystal grains is obviously improved. Meanwhile, in the cooling process 1 in the step S5, because the oxygen-nitrogen mixed gas with high oxygen content is introduced into the atmosphere furnace, the crystal boundary of the outer surface of the CCTO ceramic crystal grain is firstly in the oxygen-rich atmosphere, so that the oxygen vacancy of the crystal boundary is firstly compensated at high temperature, and the insulativity of the crystal boundary is obviously improved; meanwhile, the temperature is reduced at a relatively fast cooling rate of 30-45 ℃/min in the S5 temperature reduction stage, so that oxygen vacancies in the crystal grains are not compensated, namely oxygen atoms positioned at the crystal boundary stop diffusing or cannot effectively diffuse into the crystal grains due to the temperature reduction until the oxygen atoms enter the crystal grains, and the high conductivity of the CCTO ceramic crystal grains formed in the S4 temperature preservation stage 2 is maintained. In addition, in the S6 heat preservation stage 3, the heat preservation is carried out at a relatively low temperature of 780 ℃, the diffusion rate of oxygen atoms at the grain boundary to the interior of the crystal grains is very slow, so that the oxygen atoms at the grain boundary are difficult to diffuse into the interior of the crystal grains, and for the grain boundary at the surface of the crystal grains, because the grain boundary is in an oxygen-rich atmosphere, oxygen vacancies at the grain boundary are continuously compensated, so that the insulation property of the grain boundary is continuously increased, and the oxygen vacancies in the crystal grains are not obviously influenced. Therefore, in the technical scheme provided by the invention, the crystal grain conductivity of the CCTO ceramic is improved by adopting the processes of negative pressure air atmosphere heating and negative pressure air atmosphere heat preservation, and meanwhile, the insulativity of a crystal boundary is obviously improved due to rapid cooling and heat preservation in an oxygen-rich atmosphere, so that the dielectric response of the CCTO ceramic is enhanced and the dielectric constant is improved; more importantly, the dielectric loss of the CCTO ceramic is greatly reduced by remarkably improving the resistance of grain boundaries.
Drawings
The invention is further described below with reference to the drawings and examples;
FIG. 1 is a flow chart of the process steps of a low dielectric loss CCTO ceramic negative pressure sintering method provided by the invention;
FIG. 2 is a comparison result of dielectric constants of CCTO ceramics obtained in example 1 using the technical solution of the present invention and comparative example 1 using a conventional sintering method in a frequency range of 20Hz to 1 MHz;
FIG. 3 is a comparison result of dielectric loss in the frequency range of 20Hz to 1MHz of CCTO ceramics obtained in example 1 using the technical solution of the present invention and comparative example 1 using the conventional sintering method.
Detailed Description
The invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic drawings and illustrate only the basic aspects of the invention in a schematic way, and examples, and which therefore show only the aspects relevant to the invention.
FIG. 1 is a flow chart of the process steps of the negative pressure sintering method of the CCTO ceramic with low dielectric loss provided by the invention. Referring to the attached figure 1, the technical scheme of the invention is as follows: and putting the formed CCTO ceramic blank into an atmosphere furnace, and then carrying out a heating stage 1 under the S1 normal pressure air atmosphere, a heat preservation stage 1 under the S2 normal pressure air atmosphere, a heating stage 2 under the S3 negative pressure air atmosphere, a heat preservation stage 2 under the S4 negative pressure air atmosphere, a cooling stage 1 under the S5 oxygen-nitrogen mixed atmosphere, a heat preservation stage 3 under the S6 oxygen-nitrogen mixed atmosphere and a cooling stage 2 under the S7 normal pressure air atmosphere along with furnace cooling to finally obtain the fired CCTO dielectric ceramic.
Specifically, in a preferred embodiment 1 of the present invention, a tube-type atmosphere furnace is used for sintering the CCTO ceramic, wherein the inner diameter of the furnace tube of the tube-type atmosphere furnace is 20cm. In the implementation process of the embodiment, the formed CCTO ceramic blank with the diameter of 10mm and the thickness of about 2mm is placed on a corundum base plate and then is placed into an atmosphere furnace, and the following steps are sequentially implemented with reference to the attached drawing 1:
s1, temperature rise stage 1: and (3) heating the temperature in the atmosphere furnace from room temperature to 650 ℃, wherein the heating rate in the heating process is 8-10 ℃/min, and simultaneously opening a gas circuit switch for communicating the inside of the atmosphere furnace with the external atmosphere, so that the inside of the furnace tube of the atmosphere furnace is in the atmosphere of normal pressure air.
S2, heat preservation stage 1: when the temperature of the atmosphere furnace is raised to 650 ℃, the heat is preserved in the air atmosphere for 40-60 min; preferably, the incubation time used in example 1 is 50min.
S3, a heating stage 2: after the heat preservation stage 1 of S2 is finished, closing a gas path communicated with the external atmosphere in the atmosphere furnace, simultaneously enabling negative pressure with the relative vacuum degree of-40 kPa to-20 kPa to be generated in the atmosphere furnace by a vacuumizing method, and enabling the temperature in the atmosphere furnace to rise to 1070-1110 ℃, wherein the temperature rise rate is 6-8 ℃/min; preferably, in the temperature raising process in step S3 of example 1, the atmospheric pressure in the atmosphere furnace is maintained at a negative pressure state with a relative vacuum degree of-30. + -. 5kPa, and the furnace temperature of the atmosphere furnace is raised to 1100. + -. 5 ℃ at a temperature raising rate of 6 to 8 ℃/min.
S4, a heat preservation stage 2: when the temperature in the atmosphere furnace rises to 1100 +/-5 ℃, adjusting the air pressure in the atmosphere furnace through a vacuumizing device, and keeping the temperature in the furnace tube of the atmosphere furnace in a negative pressure atmosphere with the relative vacuum degree of-20 kPa to-15 kPa for 6 to 8 hours; preferably, the incubation time in this example 1 is 8 hours.
S5, cooling stage 1: after the heat preservation stage 2 of S4 is finished, closing a vacuumizing pipeline of the atmosphere furnace, simultaneously opening a gas path switch communicated with the external atmosphere in the atmosphere furnace, and introducing mixed gas of oxygen and nitrogen into the atmosphere furnace through another pipeline of the atmosphere furnace; in the S5 temperature reduction stage 1 process, the temperature in the atmosphere furnace is controlled to be reduced to 780 ℃ at the temperature reduction rate of 30-45 ℃/min; in example 1, the oxygen volume content of the oxygen-nitrogen mixture gas introduced into the atmospheric furnace was about 40 to 45%, and the gas flow rate when the oxygen-nitrogen mixture gas was introduced was 3.0 ± 0.5L/min.
S6, heat preservation stage 3: when the temperature in the atmosphere furnace is reduced to 780 ℃, closing the pipeline for introducing the oxygen-nitrogen mixed gas in the step S5, simultaneously introducing the oxygen-nitrogen mixed gas with the oxygen volume content of 50-60% into the atmosphere furnace through another pipeline of the atmosphere furnace, and preserving the heat for 2-3 hours at 780 ℃; preferably, in example 1, the flow rate of the oxygen-nitrogen mixture gas introduced into the atmospheric furnace is about 0.3 to 0.4L/min, and the temperature is maintained at 780 ℃ for 2.5 hours.
S7, a cooling stage 2: and after the heat preservation stage 3 of S6 is finished, closing the pipeline for introducing the oxygen-nitrogen mixed gas in the S6, simultaneously closing a heating power supply of the atmosphere furnace, and opening the pipeline communicated with the external atmosphere in the atmosphere furnace to naturally cool the atmosphere furnace to the room temperature along with the furnace temperature in the normal-pressure air atmosphere.
After the steps of S1-S7, the CCTO ceramic sintered body obtained in the embodiment 1 of the technical scheme is obtained.
In order to further show the beneficial effect of the negative pressure sintering method of the CCTO ceramic with low dielectric loss provided by the invention, the CCTO ceramic is prepared by adopting the conventional sintering method only under the air atmosphere, and the method is taken as comparative example 1. In comparative example 1, the same atmosphere furnace and CCTO ceramic body as in example 1 were used, wherein in comparative example 1, the following process steps were sequentially performed after the CCTO ceramic body was placed in the atmosphere furnace:
(1) Temperature rise stage 1: and (3) heating the temperature in the atmosphere furnace from room temperature to 650 ℃, wherein the heating rate in the heating process is 8-10 ℃/min, and simultaneously opening a gas circuit switch for communicating the atmosphere furnace with the external atmosphere to ensure that the atmosphere in the atmosphere furnace is the atmospheric air atmosphere.
(2) A heat preservation stage 1: and when the temperature of the atmosphere furnace is raised to 650 ℃, preserving the heat for 50min in the atmosphere of normal-pressure air.
(3) A temperature rise stage 2: after the heat preservation stage 1 is finished, the temperature in the atmosphere furnace is raised to 1100 +/-5 ℃ at the temperature rise rate of 6-8 ℃/min under the atmosphere of normal pressure air.
(4) And (3) a heat preservation stage 2: when the temperature in the atmosphere furnace rises to 1100 +/-5 ℃, the temperature is kept for 8 hours in the atmosphere of normal pressure air.
(5) Cooling stage 1: and after the heat preservation stage 2 is finished, closing a heating power supply of the atmosphere furnace, and naturally cooling the temperature of the atmosphere furnace to room temperature along with the temperature of the furnace in the atmosphere of normal-pressure air.
Through the above process steps, the CCTO ceramic sintered body in comparative example 1 was obtained.
After the CCTO ceramic sintered bodies obtained in example 1 according to the embodiment of the present invention and comparative example 1 according to the conventional art were respectively subjected to electrode fabrication, dielectric constants and dielectric losses were measured, wherein the results of comparing the dielectric constants are shown in fig. 2, and the results of comparing the dielectric losses are shown in fig. 3.
As is apparent from fig. 2, the CCTO ceramic obtained in example 1 according to the present invention has a dielectric constant significantly higher than that of the CCTO ceramic obtained in comparative example 1 according to the conventional art over the entire test frequency range of 20Hz to 1 MHz. In particular, at a frequency of 1kHz, the dielectric constant of the ceramic obtained in example 1 is as high as 44672, whereas the dielectric constant of the ceramic obtained in comparative example 1 is only 16895.
As is apparent from fig. 3, the CCTO ceramic obtained in example 1 according to the present invention has a dielectric loss lower than that of the CCTO ceramic obtained in comparative example 1 according to the conventional art over the entire test frequency range of 20Hz to 1 MHz. In particular, at a frequency of 1kHz, the dielectric loss of the ceramic obtained in example 1 is as low as 0.0194, while the dielectric loss of the ceramic obtained in comparative example 1 is as high as 0.154.
The comparison result between the attached drawings 2 and 3 can clearly show the beneficial effects generated by the technical scheme of the invention: compared with the prior art, the CCTO ceramic obtained by adopting the technical scheme of the invention not only has obviously reduced dielectric loss, but also has improved dielectric constant, thereby overcoming the technical defects existing in the prior art in the background art.
The technical scheme of the invention has the following beneficial effects: prior literature studies have shown that CCTO ceramics are composed of semiconducting grains with insulating grain boundaries, i.e., the grains of CCTO ceramics have relatively high electrical conductivity, while the grain boundaries at the grain boundaries are highly insulating. According to the internal barrier capacitor principle, a large amount of charges are accumulated at grain boundaries due to a large difference in conductivity between the grain boundaries and the grains under the action of an external electric field, thereby forming a large amount of barrier capacitors inside the ceramic, exhibiting a high dielectric constant. Therefore, the conductivity of the CCTO ceramic crystal grains is improved, and the insulativity of the crystal boundary is enhanced, thereby being beneficial to enhancing the dielectric response of the CCTO ceramic and improving the dielectric constant. For dielectric loss, the improvement of the grain boundary insulativity can greatly reduce the leakage current between crystal grains in the CCTO ceramics, thereby reducing the dielectric loss. Based on the principle, the CCTO ceramic obtained by adopting the technical scheme of the invention is heated and sintered in a negative pressure air atmosphere through the heating stage 2 in the step S3 and the heat preservation stage 2 in the step S4, so that the oxygen vacancy concentration of crystal grains in the CCTO ceramic is obviously improved compared with that in the heating and sintering process in a normal pressure air atmosphere, and the conductive capability of the crystal grains of the CCTO ceramic is obviously improved; meanwhile, in the cooling process 1 of the step S5, since the oxygen-nitrogen mixed gas with high oxygen content is introduced into the atmosphere furnace, the crystal boundary of the outer surface of the CCTO ceramic crystal grain is firstly in the oxygen-rich atmosphere. Compared with the atmosphere of normal pressure air, under the atmosphere rich in oxygen, the oxygen vacancy in the grain boundary at high temperature is compensated more easily, and further the insulating property of the grain boundary is improved obviously. Meanwhile, the temperature is reduced at a relatively fast cooling rate of 30-45 ℃/min in the S5 temperature reduction stage, so that oxygen vacancies in the crystal grains are not compensated, namely oxygen atoms positioned at the crystal boundary stop diffusing or cannot effectively diffuse into the crystal grains due to the temperature reduction until the oxygen atoms enter the crystal grains, and the high conductivity of the CCTO ceramic crystal grains formed in the S4 temperature preservation stage 2 is maintained. In addition, in the S6 heat preservation stage 3, the heat preservation is carried out at a relatively low temperature of 780 ℃, the diffusion rate of oxygen atoms at the grain boundary to the interior of the crystal grains is very slow, so that the oxygen atoms at the grain boundary are difficult to diffuse into the interior of the crystal grains, and for the grain boundary at the surface of the crystal grains, because the grain boundary is in an oxygen-rich atmosphere, oxygen vacancies at the grain boundary are continuously compensated, so that the insulation property of the grain boundary is continuously increased, and the oxygen vacancies in the crystal grains are not obviously influenced. Therefore, in the technical scheme provided by the invention, the crystal grain conductivity of the CCTO ceramic is improved by adopting the processes of negative pressure atmosphere heating and negative pressure atmosphere heat preservation, and meanwhile, the insulativity of a crystal boundary is further improved by rapid cooling and heat preservation in an oxygen-rich atmosphere, so that the dielectric response of the CCTO ceramic is enhanced, and the dielectric constant is improved; more importantly, the dielectric loss of the CCTO ceramic is greatly reduced due to the obvious improvement of the grain boundary resistance.
In order to further demonstrate the beneficial effects of the technical solution of the present invention, and in particular to more clearly illustrate the effect of using the negative pressure air atmosphere in steps S3 and S4 to enhance the electrical conductivity of the crystal grains and the effect of using the oxygen-rich atmosphere in steps S5 and S6 to improve the insulation of the grain boundaries in the technical solution of the present invention, the following description will be made in conjunction with example 2 and comparative example 2, comparative example 3, and comparative example 4 using the technical solution of the present invention.
In another preferred embodiment 2 of the present invention, the sintering of the CCTO ceramic is performed using a tube-type atmosphere furnace having an inner diameter of a furnace tube of 20cm. In the implementation process of the embodiment, the formed CCTO ceramic blank with the diameter of 10mm and the thickness of about 2mm is placed on a corundum base plate and then is placed into an atmosphere furnace, and the following steps are sequentially implemented with reference to the attached drawing 1:
s1, temperature rise stage 1: and (3) raising the temperature in the atmosphere furnace from room temperature to 650 ℃, wherein the raising rate in the raising process is 8-10 ℃/min, and simultaneously opening a gas circuit switch for communicating the atmosphere furnace with the external atmosphere, so that the atmosphere in the furnace tube of the atmosphere furnace is the normal-pressure air atmosphere.
S2, heat preservation stage 1: and when the temperature of the atmosphere furnace is raised to 650 ℃, preserving the heat in the air atmosphere for 40min.
S3, a heating stage 2: and after the heat preservation stage 1 of S2 is finished, closing a gas path switch communicated with the atmosphere furnace and the external atmosphere, simultaneously generating negative pressure in the atmosphere furnace by a vacuumizing method, and raising the temperature to 1090 +/-5 ℃ under the condition that the air pressure in the atmosphere furnace is maintained at the negative pressure condition of-35 +/-5 kPa, wherein the temperature raising rate is 6-8 ℃/min.
S4, a heat preservation stage 2: when the temperature in the atmosphere furnace rises to 1090 +/-5 ℃, the air pressure in the atmosphere furnace is adjusted through a vacuumizing device, so that the temperature in the atmosphere furnace is kept under the negative pressure atmosphere with the relative vacuum degree of-20 kPa to-15 kPa, and the heat preservation time is 6 hours.
S5, cooling stage 1: after the heat preservation stage 2 of S4 is finished, closing a vacuumizing pipeline of the atmosphere furnace, simultaneously opening a gas path switch communicated with the external atmosphere in the atmosphere furnace, and introducing mixed gas of oxygen and nitrogen into the atmosphere furnace through another pipeline of the atmosphere furnace; in the S5 temperature reduction stage 1 process, controlling the temperature in the atmosphere furnace to be reduced to 780 ℃ at the temperature reduction rate of 30-45 ℃/min; in example 2, the oxygen volume content of the oxygen-nitrogen mixture gas was about 40 to 45% and the gas flow rate when the oxygen-nitrogen mixture gas was introduced was 2.5 ± 0.5L/min.
S6, heat preservation stage 3: when the temperature in the atmosphere furnace is reduced to 780 ℃, closing the pipeline for introducing the oxygen-nitrogen mixed gas in the step S5, and simultaneously introducing the oxygen-nitrogen mixed gas with the oxygen volume content of 50-60% into the atmosphere furnace through another pipeline of the atmosphere furnace, wherein the gas flow rate of the introduced oxygen-nitrogen mixed gas is about 0.3-0.4L/min; in example 2, the incubation time at 780 ℃ was 2 hours.
S7, a cooling stage 2: and after the heat preservation stage 3 of S6 is finished, closing a pipeline for introducing the oxygen-nitrogen mixed gas into the S6, and simultaneously closing a heating power supply of the atmosphere furnace to naturally cool the temperature of the atmosphere furnace to room temperature along with the furnace temperature under the atmosphere of normal-pressure air.
After the above process steps, the CCTO ceramic sintered body in embodiment 2 of the present invention is obtained.
In the sintering process of the CCTO ceramic in the comparative example 2, the same atmosphere furnace and CCTO ceramic green body as those in the example 2 were used to prepare a sample, and the sintering process used was: referring to the sintering process step of example 2, the process step of comparative example 2 is identical to example 2 except that the process conditions in steps S3 and S4 are different from example 2, and the other process steps and corresponding process conditions are identical to example 2. In comparative example 2, the process conditions for steps s3 and s4 were:
s3 temperature rise stage 2: after the heat preservation stage 1 of S2 is finished, the temperature in the atmosphere furnace is increased to 1090 +/-5 ℃ at the temperature increase rate of 6-8 ℃/min under the atmosphere of normal pressure air.
s4 incubation stage 2: when the temperature in the atmosphere furnace rises to 1090 +/-5 ℃, the heat preservation time is 6 hours under the atmosphere of normal pressure air.
It should be noted that comparative example 2 and example 2 are intended to show that: in the technical scheme of the invention, when the steps S3 and S4 are carried out, the conductive capability of the CCTO ceramic crystal grains is improved by the negative-pressure air atmosphere in the atmosphere furnace.
In the sintering process of the CCTO ceramic in the comparative example 3, the same atmosphere furnace and CCTO ceramic green body as those in the example 2 were used to prepare a sample, and the sintering process used was: referring to the sintering process step of example 2, the process step of comparative example 3 is identical to example 2 except that the process conditions of step S5 are different from those of example 2. In comparative example 3, the process conditions of the cooling stage 1 of step s5 are: after the heat preservation stage 2 of S4 is finished, closing a vacuumizing pipeline of the atmosphere furnace, simultaneously opening a gas path switch communicated with the external atmosphere in the atmosphere furnace, and introducing air into the atmosphere furnace through another pipeline of the atmosphere furnace, wherein the gas flow when the air is introduced is 2.5 +/-0.5L/min; in the s5 temperature reduction stage 1 process, the temperature in the atmosphere furnace is controlled to be reduced to 780 ℃ at the temperature reduction rate of 30-45 ℃/min.
It should be noted that comparative example 3 and example 2 are intended to show: in the technical scheme of the invention, when the step S5 is carried out, the mixed gas rich in oxygen is introduced into the atmosphere furnace to improve the insulativity of the CCTO ceramic grain boundary.
In the sintering process of the CCTO ceramic in the comparative example 4, the same atmosphere furnace and CCTO ceramic green body as those in the example 2 were used to prepare a sample, and the sintering process used was: referring to the sintering process step of example 2, the process step of comparative example 4 is identical to example 2 except that the process conditions of step S6 are different from example 2, and other process steps and corresponding process conditions are identical to example 2. In comparative example 4, the process conditions for incubation stage 3 of step s6 were: when the temperature in the atmosphere furnace is reduced to 780 ℃, introducing air into the atmosphere furnace, wherein the flow rate of the introduced air is 0.3-0.4L/min, and preserving the heat for 2 hours at 780 ℃.
It should be noted that comparative example 4 and example 2 are intended to show: in the technical scheme of the invention, when the step S6 is carried out, the mixed gas rich in oxygen is introduced into the atmosphere furnace, so that the CCTO ceramic grain boundary insulativity and the dielectric loss are further optimized.
The CCTO ceramic sintered bodies obtained in example 2 and comparative examples 2, 3 and 4 were subjected to electrode fabrication, then dielectric properties and impedance spectrum tests were measured, and grain resistance and grain boundary resistance of each ceramic sample were calculated by impedance spectrum derivation, with the results shown in table 1.
Table 1 shows key process information and performance test results during the sintering process of the CCTO ceramics obtained in example 2 and comparative examples 2, 3, and 4. As can be seen from the results of example 2 and comparative example 2, in comparative example 2, after the furnace atmosphere was changed to the atmospheric air atmosphere when steps s3 and s4 were performed, the grain resistance of the obtained CCTO ceramic was 52.2 Ω, which is significantly higher than that of example 2 according to the present invention. It is shown that the implementation of steps S3 and S4 in the negative pressure air atmosphere in the technical scheme of the invention is beneficial to improving the conductivity of the CCTO ceramic crystal grains, and is further beneficial to improving the dielectric constant of the CCTO ceramic.
As is clear from example 2 and comparative example 3 in Table 1, in comparative example 3, the grain boundary resistance of the ceramic obtained by rapid temperature reduction in an atmospheric pressure air atmosphere at the time of carrying out step s5 was 6.87X 10 7 Ω, significantly lower than the grain boundary resistance of 9.62X 10 in example 2 8 Ω, while the dielectric loss of comparative example 3 was as high as 0.3235. The above results show that the rapid cooling in the oxygen-rich atmosphere in step S5 in the technical solution of the present invention plays an important role in reducing the dielectric loss of the CCTO ceramic.
In addition, as can be seen from example 2 and comparative example 4 in table 1, the grain boundary resistance of the CCTO ceramic obtained in comparative example 4 by performing heat preservation in an atmospheric pressure air atmosphere at the time of performing step s6 is also lower than that of example 2, and the corresponding dielectric loss is also higher than that of example 2. Therefore, it can be proved that the dielectric loss of the CCTO ceramic can be further reduced by adopting the method of preserving heat in the oxygen-rich atmosphere in step S6 in the technical scheme of the present invention.
TABLE 1 CCTO ceramics obtained in example 2 and comparative examples 2, 3 and 4
In light of the foregoing description of the preferred embodiment of the present invention, it is to be understood that various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (2)
1. Calcium copper titanate CaCu 3 Ti 4 O 12 The negative pressure sintering method of the ceramic is characterized in that: the CaCu 3 Ti 4 O 12 The CaCu is obtained by heating a ceramic blank in an atmosphere furnace in the atmosphere of atmospheric air 1, maintaining the temperature in the atmosphere of atmospheric air 1, heating in the atmosphere of negative pressure air 2, maintaining the temperature in the atmosphere of negative pressure air 2, cooling in the atmosphere of a high-oxygen mixed gas 1, maintaining the temperature in the atmosphere of a high-oxygen mixed gas 3, and naturally cooling in the atmosphere of atmospheric air 2 3 Ti 4 O 12 A dielectric ceramic; wherein the content of the first and second substances,
the temperature rise stage 1: raising the temperature in the atmosphere furnace from room temperature to 650 ℃ in an air atmosphere;
the heat preservation stage 1: when the temperature is raised to 650 ℃, the temperature is preserved in the atmosphere of normal pressure air;
the temperature rise stage 2: heating the temperature in the atmosphere furnace to 1070-1110 ℃ at a heating rate of 6-8 ℃/min, wherein in the heating process, the air pressure in the atmosphere furnace is negative pressure of-40 kPa to-20 kPa;
and the heat preservation stage 2: after the temperature in the atmosphere furnace rises to 1070 to 1110 ℃, preserving the heat for 6 to 8 hours, and simultaneously, in the heat preservation stage, the air pressure in the atmosphere furnace is negative pressure of-20 kPa to-15 kPa;
the cooling stage 1: after the heat preservation stage 2 is finished, reducing the temperature in the atmosphere furnace to 780 ℃ at a cooling rate of 30-45 ℃/min, and simultaneously introducing mixed gas of oxygen and nitrogen with the volume content of 40-45% into the atmosphere furnace in the process of the cooling stage 1;
and a heat preservation stage 3: introducing mixed gas of oxygen and nitrogen with the oxygen volume content of 50-60% into the atmosphere furnace, and preserving the heat for 2-3 hours at 780 ℃.
2. The copper calcium titanate CaCu according to claim 1 3 Ti 4 O 12 The negative pressure sintering method of ceramics is characterized in that calcium copper titanate CaCu 3 Ti 4 O 12 After the ceramic blank is placed in an atmosphere furnace, the following process steps are sequentially carried out:
s1, temperature rise stage 1: raising the temperature in the atmosphere furnace from room temperature to 650 ℃, wherein the temperature raising rate of the atmosphere furnace is 8-10 ℃/min in the temperature raising process, and meanwhile, the inside of the atmosphere furnace is communicated with the external atmosphere so that the inside of the atmosphere furnace is in the atmospheric air atmosphere;
s2, heat preservation stage 1: when the temperature of the atmosphere furnace is raised to 650 ℃, preserving the heat for 40-60 min in the atmosphere of normal pressure air;
s3, a heating stage 2: after the heat preservation stage 1 is finished, isolating the interior of the atmosphere furnace from the outside air, generating negative pressure with the relative vacuum degree of-40 kPa to-20 kPa in the atmosphere furnace by a vacuumizing method, and simultaneously heating the temperature in the atmosphere furnace to 1070 to 1110 ℃ at the heating rate of 6 to 8 ℃/min;
s4, a heat preservation stage 2: when the temperature in the atmosphere furnace rises to 1070-1110 ℃, adjusting the internal air pressure of the atmosphere furnace to keep the internal air pressure in the negative pressure atmosphere with the relative vacuum degree of-20 kPa to-15 kPa, and preserving the heat for 6-8 hours;
s5, cooling stage 1: after the heat preservation stage 2 is finished, reducing the temperature in the atmosphere furnace to 780 ℃ at the cooling rate of 30-45 ℃/min, and simultaneously introducing mixed gas of oxygen and nitrogen with the volume content of 40-45% into the atmosphere furnace in the process of the cooling stage 1;
s6, heat preservation stage 3: when the temperature in the atmosphere furnace is reduced to 780 ℃, introducing mixed gas of oxygen and nitrogen with the oxygen volume content of 50-60% into the atmosphere furnace, and preserving the heat for 2-3 hours at 780 ℃;
s7, a cooling stage 2: after finishing the heat preservation stage 3, naturally cooling to room temperature along with the furnace temperature in the atmosphere of normal pressure air to obtain the calcium copper titanate CaCu 3 Ti 4 O 12 A sintered body of ceramics.
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