CN112457026A - Copper calcium titanate ceramic reduction-oxidation atmosphere co-sintering method - Google Patents
Copper calcium titanate ceramic reduction-oxidation atmosphere co-sintering method Download PDFInfo
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Abstract
The invention discloses a method for preparing low dielectric loss and high dielectric constant calcium copper titanate CaCu based on reduction-oxidation atmosphere co-sintering3Ti4O12A method for sintering (CCTO) ceramics. The invention belongs to the field of ceramic sintering, and adopts the technical scheme that a CCTO ceramic blank is firstly placed into an atmosphere sintering furnace, and then the ceramic blank is subjected to a heating stage I under the air atmosphere, a heat preservation stage I under the air atmosphere, a heating stage II under the air atmosphere, a heat preservation stage II under the atmosphere of introduced reducing mixed gas, a cooling stage I under the condition of introduced non-reducing gas without oxygen, a rapid cooling stage II under the condition of introduced mixed gas rich in oxygen and a furnace cooling stage III in the atmosphere sintering furnace to obtain a CCTO ceramic sintered body. The CCTO ceramic obtained by the sintering method of the technical scheme of the invention has obviously improved dielectric property and high dielectric constant at the frequency of 1 kHzUp to 5X 104While the dielectric loss is below 0.02.
Description
Technical Field
The invention relates to the field of dielectric materials, in particular to a sintering method of high-dielectric-constant low-dielectric-loss copper calcium titanate ceramic.
Background
In recent years, the application demand of high dielectric constant materials in the field of microelectronics is increased year by year, and the perovskite structure of copper calcium titanate CaCu3Ti4O12(CCTO) ceramic materials have gained widespread attention in both academia and industry. The dielectric ceramic material has an ultra-high dielectric constant (10)4～105) And a high dielectric constant is rather broad around room temperatureWithin the temperature range, the material has good thermal stability; CCTO materials, on the other hand, also exhibit strong I-V nonlinearity. These superior characteristics make CCTO ceramic material have application prospect in the aspect of future novel electronic devices. However, CCTO ceramics also have relatively high dielectric loss, which can generate excessive heat to affect device performance in practical device applications. Numerous studies at present have shown that the method of element doping modification is one of the effective methods for reducing dielectric loss of CCTO ceramic materials. The results of the existing research show that: the dielectric loss of the CCTO ceramic can be reduced by proper doping elements and doping processes, but the dielectric constant is reduced to a certain extent; or the dielectric constant can be basically kept at the original level, but the dielectric loss is not obviously reduced, the dielectric loss value under 1k Hz is still above 0.05, the comprehensive dielectric property of the CCTO ceramic material is difficult to improve, and the application requirement in the practical electronic device is still difficult to meet. Meanwhile, the conventional process method for sintering the CCTO ceramic is mostly carried out in the air atmosphere, the CCTO ceramic is generally sintered through stages of temperature rise, heat preservation, temperature rise, heat preservation and temperature reduction, the dielectric loss value of the CCTO ceramic obtained by the conventional method is relatively high, the dielectric loss under 1 kHz is usually more than 0.1, and the requirements of practical device application are difficult to achieve.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a method for cooperatively sintering Calcium Copper Titanate (CCTO) ceramic based on a reducing-oxidizing atmosphere, which realizes the cooperative regulation and control of CCTO ceramic crystal grains and grain boundary resistance by mainly utilizing a high-temperature sintering mode under the reducing atmosphere and a rapid reduction mode under the oxidizing atmosphere in the CCTO ceramic sintering process, thereby achieving the purposes of reducing the dielectric loss of the CCTO ceramic and improving the dielectric constant.
The technical scheme adopted by the invention is as follows: firstly, placing a formed CCTO ceramic blank into an atmosphere furnace, then cooling the CCTO ceramic blank to room temperature in the atmosphere furnace through a heating stage I under the air atmosphere, a heat preservation stage I under the air atmosphere, a heating stage II under the air atmosphere, a heat preservation stage II under the atmosphere of introducing reductive mixed gas, a cooling stage I under the condition of introducing non-reductive gas without oxygen, a rapid cooling stage II under the condition of introducing mixed gas rich in oxygen and a furnace cooling stage III.
Specifically, in order to overcome the defects in the prior art, the method for co-sintering the CCTO ceramic based on the reducing-oxidizing atmosphere provided by the invention sequentially implements the following process steps in the implementation process:
s1, the formed CCTO ceramic blank is put into an atmosphere furnace.
S2 implementing a temperature rise stage i: and raising the temperature in the atmosphere furnace from room temperature to 600 ℃ in an air atmosphere, wherein the temperature raising rate in the temperature raising process is 5-8 ℃/min.
S3 implementation of incubation stage i: and (3) keeping the temperature of the atmosphere furnace at 600 ℃ for 30-50 min in the air atmosphere.
S4 implementing a temperature raising stage ii: the temperature in the atmosphere furnace is increased from 600 ℃ to 1080-1120 ℃ in the air atmosphere, and the temperature increase rate in the temperature increase process is 8-10 ℃/min.
S5, implementing a heat preservation sintering stage II: and (4) after the step S4 is finished, introducing the reducing mixed gas into the atmosphere furnace, and preserving the heat for 8-10 h at the heat preservation temperature of 1080-1120 ℃.
S6 implementation of cooling stage i: and after the step S5 is finished, introducing non-reducing gas without oxygen into the atmosphere furnace, and reducing the temperature in the atmosphere furnace from the heat preservation temperature to 1020-1040 ℃ at a temperature reduction rate of 15-20 ℃/min.
S7 implementing a rapid cool down stage ii: and after the step S6 is finished, introducing mixed gas rich in oxygen into the atmosphere furnace, and rapidly cooling the temperature in the atmosphere furnace from 1020-1040 ℃ to 720-750 ℃ by adopting a rapid cooling mode.
S8 implementation of cooling stage iii: and after the step S7 is finished, naturally cooling the furnace temperature of the atmosphere furnace from 720-750 ℃ at the air atmosphere.
In a preferred embodiment of the present invention, during the step S5 of performing the insulation sintering stage II, the reducing mixed gasIs formed by a reducing gas H2At least one gas of CO and N2A mixed gas composed of at least one of Ar and He; the volume content of the reducing gas in the reducing mixed gas is 10-20%.
In a preferred embodiment of the present invention, during the cooling stage I performed in step S6, the non-reducing gas containing no oxygen is N2Ar, or N2And Ar, mixed gas.
In a preferred embodiment of the present invention, in the process of performing the rapid cooling stage ii in step S7, the oxygen-rich gas mixture is oxygen and N2And at least one of Ar and He, wherein the volume content of oxygen in the mixed gas is 40-70%;
in a preferred embodiment of the present invention, in the process of performing the rapid cooling stage ii in step S7, the cooling rate of the rapid cooling manner is 40 to 60 ℃/min.
After the steps S1-S8, the CCTO ceramic sintered body prepared by the technical scheme of the invention is obtained.
The invention solves the defects in the background technology and has the following beneficial effects: 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 is as high as 5 multiplied by 10 under the frequency of 1 kHz4Meanwhile, the dielectric loss is lower than 0.02, and compared with the conventional technology, the CCTO ceramic dielectric constant and dielectric loss are synchronously optimized. In addition, in the technical scheme of the invention, the temperature control and the atmosphere control related to each step in the CCTO ceramic sintering process can be completed by one-step setting of the control program of the atmosphere furnace, the operation is simple, and the method is suitable for industrial production.
Drawings
FIG. 1 is a flow chart of the process steps of a method for co-sintering CCTO ceramics based on a reducing-oxidizing atmosphere according to the invention.
Fig. 2 is a comparison result of dielectric constants at different frequencies of CCTO ceramics obtained in example 1 using the technical solution of the present invention and comparative example 1 using the conventional sintering method.
Fig. 3 is a comparison result of dielectric losses at different frequencies of CCTO ceramics obtained in example 1 using the technical solution of the present invention and comparative example 1 using the conventional sintering method.
Fig. 4 is a test result of grain resistance, grain boundary resistance, and dielectric constant and dielectric loss at a frequency of 1 kHz of CCTO ceramics obtained in example 2 and comparative examples 2, 3, and 4 using the technical solution of the present invention.
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 CCTO ceramic reduction-oxidation atmosphere co-sintering method provided by the technical scheme of the invention. Referring to the attached figure 1, the technical scheme of the invention is as follows:
firstly, putting a CCTO ceramic blank to be sintered into an atmosphere furnace, then, carrying out a heating stage I under the air atmosphere, a heat preservation stage I under the air atmosphere, a heating stage II under the air atmosphere, a heat preservation stage II under the atmosphere of introducing reductive mixed gas, a cooling stage I under the condition of introducing non-reductive gas without oxygen, a rapid cooling stage II under the condition of introducing mixed gas rich in oxygen, and a cooling stage III cooled along with the furnace in the atmosphere furnace, and then, cooling to room temperature to obtain the CCTO ceramic sintered body.
Referring to fig. 1, the following steps are performed in a preferred embodiment 1 of the present invention:
s1, the formed CCTO ceramic blank is put into an atmosphere furnace. In this embodiment 1, a tubular atmosphere furnace with an inner diameter of 20cm is used as the atmosphere furnace, and a circular CCTO green body pressed into a disc shape is selected for sintering, wherein the diameter of the circular ceramic green body is 10mm, and the thickness of the circular ceramic green body is about 2 mm; in the implementation process of the step, the CCTO ceramic body is placed on a corundum base plate, and then placed in an atmosphere furnace.
S2 performs a temperature raising stage i. In the implementation process of the step, a gas circuit switch communicated with the atmosphere furnace and the outside atmosphere is opened, so that the temperature of the atmosphere furnace is raised from room temperature to 600 ℃ in the air atmosphere, and the temperature raising rate of the atmosphere furnace is 5-8 ℃/min in the temperature raising process.
S3, carrying out an incubation stage I. During the implementation of the step, the inside of the atmosphere furnace is kept communicated with the outside atmosphere, and the heat preservation is carried out for 30 min at the heat preservation temperature of 600 ℃.
S4 carries out a temperature raising stage ii. In the process of implementing the step, the inside of the atmosphere furnace is kept communicated with the outside atmosphere, and the temperature in the atmosphere furnace is increased from 600 ℃ to 1080-1100 ℃ at the temperature increasing rate of 8-10 ℃/min.
S5, carrying out a heat preservation sintering stage II. After step S4 is completed, introducing the reducing mixed gas into the atmosphere furnace, and discharging the introduced reducing mixed gas from a gas path pipeline communicated with the external atmosphere in the furnace tube after the introduced reducing mixed gas passes through the interior of the furnace tube; the reducing mixed gas may be a reducing gas H2At least one gas of CO and N2And at least one of Ar and He, wherein the volume content of the non-reducing gas is about 10-20%. In the process of implementing the step S5, the holding temperature of the atmosphere furnace is set to 1100 ℃, and the holding time is 10 h. Preferably, in this embodiment, the reducing mixed gas is selected from H2And N2As a reducing mixed gas, wherein H2The volume content of (A) is about 12-15%; the gas flow rate of the reducing mixed gas when the reducing mixed gas is introduced into the atmosphere furnace is 3.0 +/-0.2L/min.
S6 performs cooling stage i. After step S5 is completed, the introduction of the reducing mixed gas into the atmosphere furnace is stopped, and simultaneously, a non-reducing gas containing no oxygen is introduced into the atmosphere furnace through another pipeline, wherein the non-reducing gas containing no oxygen may be N2Ar or a mixed gas of the two gases. When the step S6 is carried out, the temperature in the atmosphere furnace is reduced from 1100 ℃ to 1020-1030 ℃ by adopting a temperature reduction rate of 15-20 ℃/min under the condition that the non-reducing gas without oxygen is introduced into the atmosphere furnace.Preferably, in this embodiment 1, N is used2N as a non-reducing gas containing no oxygen2The gas flow rate during the introduction was 2.0. + -. 0.2L/min.
S7 performs cooling stage ii. After step S6 is completed, the introduction of the non-reducing gas containing no oxygen into the atmosphere furnace is stopped, and simultaneously, the introduction of the oxygen-rich mixed gas into the atmosphere furnace through another pipeline is stopped, wherein the oxygen-rich mixed gas may be O2And N2And at least one of Ar and He, wherein the volume content of oxygen in the mixed gas is 40-70%; meanwhile, the temperature of the atmosphere furnace is rapidly reduced from 1020-1030 ℃ to 720-750 ℃ at a cooling rate of 45-55 ℃/min. Preferably, O is selected in the embodiment 12And N2As the mixed gas, the volume content of oxygen in the mixed gas is 45-50%, and the flow rate when the gas is introduced is 4.0 +/-0.2L/min.
S8 carries out cooling stage iii. And after the step S7 is finished, stopping introducing the oxygen-rich mixed gas into the atmosphere furnace, closing a heating power supply of the atmosphere furnace, maintaining the state that the interior of the atmosphere furnace is communicated with the outside atmosphere, and naturally cooling the atmosphere furnace from 720-750 ℃ to room temperature.
It should be noted that the pipeline ports for introducing the external source gas into the atmosphere furnace are all on the same side of the furnace tube, and the pipeline inside the furnace tube and communicated with the external atmosphere is on the other side of the furnace tube, so that the introduced gas is exhausted from the other side of the furnace tube after passing through the inside of the furnace tube.
After the above steps of S1 to S8, the CCTO ceramic sintered body in embodiment 1 of the present invention is obtained.
In order to comparatively illustrate the beneficial effects of the technical scheme of the invention, the CCTO ceramic body is sintered by adopting the prior conventional technology and is taken as comparative example 1. In the preparation of the sample of the comparative example 1, the CCTO ceramic body and the atmosphere furnace which are the same as those of the example 1 are adopted for sintering the ceramic, wherein the sintering steps and the process parameters of the comparative example 1 are as follows:
(1) and putting the formed CCTO ceramic blank into an atmosphere furnace. In comparative example 1, the same CCTO ceramic green body as in example 1 was selected and sintered, and the CCTO ceramic green body used was in the form of a disc having a diameter of 10mm and a thickness of about 2 mm. In the operation process of the step, the CCTO ceramic body is placed on a corundum base plate and then placed in an atmosphere furnace.
(2) A temperature rise stage i is carried out. In this step, the temperature raising parameters set by the atmosphere furnace are exactly the same as step S2 in example 1.
(3) And (5) implementing a heat preservation stage I. In this step, the atmosphere furnace was set with exactly the same process parameters as in step S3 in example 1.
(4) A temperature rise stage II is carried out. In this step, the atmosphere furnace was set with exactly the same process parameters as in step S4 in example 1.
(5) And implementing a heat preservation sintering stage II. In the step, the inside of the atmosphere furnace is kept communicated with the outside atmosphere, and the atmosphere furnace is kept at the heat preservation temperature of 1100 ℃ for 10 hours.
(6) And implementing a cooling stage. In the step, the heating power supply of the atmosphere furnace is closed, the state that the inside of the atmosphere furnace is communicated with the outside atmosphere is maintained, and the temperature of the atmosphere furnace is naturally cooled from 1100 ℃.
The CCTO ceramic sintered body prepared in comparative example 1 was obtained after the above steps (1) to (6) were performed.
After the CCTO ceramic sintered bodies obtained in example 1 using the technical scheme of the present invention and comparative example 1 using the conventional technical scheme were respectively subjected to electrode fabrication, dielectric constants, dielectric losses, and impedance maps were measured, wherein the comparison result of the dielectric constants is shown in fig. 2, and the comparison result of the dielectric losses is shown in fig. 3.
As can be seen from the results of comparison of dielectric constants in FIG. 2, the dielectric constant of the CCTO ceramic obtained in example 1 was significantly higher than that of the CCTO ceramic obtained in comparative example 1 in the frequency range of 20Hz to 1 MHz. Particularly, at a frequency of 1 kHz, the dielectric constant of the CCTO ceramic obtained in example 1 is 58295, whereas the dielectric constant of the ceramic obtained in comparative example 1 is only 16857, and the dielectric constant of the CCTO ceramic obtained in example 1 using the technical solution of the present invention is increased by about 2.45 times compared to comparative example 1.
As can be seen from the results of comparison of dielectric loss in fig. 3, the dielectric loss of the CCTO ceramic obtained in example 1 is significantly lower than that of the CCTO ceramic in comparative example 1 in the frequency range of 20Hz to 1 MHz. Particularly at a frequency of 1 kHz, the dielectric loss of the CCTO ceramic obtained in example 1 was 0.018, whereas the dielectric loss of the ceramic obtained in comparative example 1 was as high as 0.159.
As can be seen from the comparison results of dielectric constant and dielectric loss in the attached drawings 2 and 3, compared with the prior art, the CCTO ceramic obtained by adopting the technical scheme of the invention not only has obviously improved dielectric constant, but also has synchronously and obviously reduced dielectric loss, and the dielectric comprehensive performance of the obtained CCTO ceramic is effectively improved.
The technical scheme of the invention has the following beneficial effects: with respect to CCTO ceramics, the sintered CCTO ceramics are composed of semiconducting grains with insulating grain boundaries. 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 grain boundaries and grains, thereby forming a large amount of barrier capacitors inside the ceramic to exhibit a high dielectric constant. The enhancement of the heterostructure of the conductive capability of the CCTO ceramic crystal grain and the crystal boundary is beneficial to improving the response of the internal blocking capacitor of the CCTO ceramic, thereby improving the dielectric constant; meanwhile, the increase of the grain boundary resistance at the surface of the crystal grains can also reduce the electric leakage among the crystal grains in the CCTO ceramic, thereby further reducing the dielectric loss of the CCTO ceramic. Based on the principle, in the technical scheme of the CCTO ceramic reduction-oxidation atmosphere co-sintering method provided by the invention, in the step S5 of implementing the heat preservation sintering stage II, the interior of the atmosphere furnace is in the reducing atmosphere at high temperature by introducing the reducing mixed gas into the atmosphere furnace, so that the oxygen vacancy concentration in the CCTO ceramic crystal grains and the grain boundaries is obviously improved relative to the heat preservation in the air atmosphere, and the improvement of the oxygen vacancy concentration can cause the increase of the conductivity of the crystal grains and the grain boundaries, namely the grain resistance and the grain boundary resistance are reduced. The reduction of the resistance of the crystal grains means the enhancement of the semi-conductive degree of the crystal grains, which is beneficial to improving the dielectric constant; however, the decrease of grain boundary resistance is not beneficial to the improvement of the CCTO ceramic performance. In order to avoid the problem, the technical scheme of the invention is provided with the step S7, namely in the process of implementing the cooling stage II in the step S7, mixed gas which is rich in oxygen and has higher oxygen content than the oxygen in the air is introduced into the atmosphere furnace, so that oxygen vacancies at the grain boundary of the CCTO ceramic can be effectively backfilled under the condition of high temperature, thereby reducing the conductive capability of the grain boundary, further reducing the electric leakage among the grains and reducing the dielectric loss of the CCTO ceramic; meanwhile, a fast cooling rate (about 40-60 ℃/min) is adopted in the process of the cooling stage II of the step S7, namely, the temperature of the atmosphere furnace is rapidly reduced to 720-750 ℃ from 1020-1030 ℃ by adopting the cooling rate which is obviously higher than that of the furnace during natural cooling. The purpose of employing the rapid cooling in step S7 is: the CCTO ceramic sintered body at high temperature is reduced to a relatively low temperature (720-750 ℃) in a relatively short time. Due to the rapid temperature decrease, the diffusion rate of oxygen atoms at the grain boundary will also decrease exponentially with the temperature decrease, and since the rapid temperature decrease will also result in a relative decrease in the total time that the CCTO ceramic sintered body is in the high temperature region, so that most of the oxygen atoms at the grain boundary cannot be effectively diffused into the interior of the grains due to the significant decrease in the diffusion rate and the relatively reduced diffusion time, and thus the oxygen vacancies in the interior of the grains are difficult to backfill, thereby effectively maintaining the high electrical conductivity formed by the CCTO ceramic grains when performing step S5. In addition, in order to achieve a better effect, the technical scheme of the invention designs a step S6, namely: in the process of implementing the cooling stage I of S6, the temperature of the atmosphere furnace is firstly reduced to 1020-1030 ℃ from the heat preservation temperature, and non-reducing gas without oxygen is introduced into the atmosphere furnace. The purpose of this is to reduce the temperature of the oxygen-enriched mixed gas introduced in the early stage of the cooling stage of S7, so as to reduce the diffusion rate of oxygen atoms and avoid or reduce the diffusion of oxygen atoms into the crystal grains, thereby maintaining the high conductivity of the crystal grains formed in step S5; on the other hand, the purpose is to eliminate the reducing mixed gas introduced in the step S5 in the atmosphere furnace in advance, so as to ensure the safety and effectiveness when the oxygen-enriched mixed gas with higher oxygen content than the air is introduced into the atmosphere furnace during the cooling stage II of the step S7. Therefore, in summary, in the technical solution of the present invention, it is implemented by the combination of the corresponding process schemes in the heat-preservation sintering stage ii, the cooling stage i of S6, and the cooling stage ii of S7 in the above step S5, that is, mainly by the method of co-sintering in the reducing-oxidizing atmosphere, so as to implement: the conductivity of CCTO ceramic crystal grains is enhanced, and simultaneously, the insulativity of the crystal boundary is effectively and synchronously improved, so that the response mechanism of a barrier layer capacitor in the CCTO ceramic is enhanced, and the dielectric constant of the CCTO ceramic is further improved; meanwhile, the electric leakage among crystal grains in the CCTO ceramic is effectively reduced due to the improvement of the crystal boundary resistance (insulativity), so that the dielectric loss of the CCTO ceramic is obviously reduced. In order to more clearly show the beneficial effects of the technical solution of the present invention achieved by the combined implementation of the step S5 and the step S7 in the technical solution of the present invention, the following description will be further made in combination with example 2 and comparative example 2, comparative example 3, and comparative example 4.
Another preferred embodiment 2 of the present invention comprises the following steps:
s1, putting the CCTO ceramic blank formed by pressing into an atmosphere furnace. In this embodiment 2, a tubular atmosphere furnace with an inner diameter of 20cm is used as the atmosphere furnace, and a circular CCTO green body pressed into a disc shape is selected for sintering, wherein the diameter of the circular ceramic green body is 10mm, and the thickness of the circular ceramic green body is about 2 mm; in the implementation process of the step, the CCTO ceramic body is placed on a corundum base plate, and then placed in an atmosphere furnace.
S2 performs a temperature raising stage i. In the implementation process of the step, a gas circuit switch communicated with the atmosphere furnace and the outside atmosphere is opened, so that the temperature of the atmosphere furnace is raised from room temperature to 600 ℃ in the air atmosphere, and the temperature raising rate of the atmosphere furnace is 5-8 ℃/min in the temperature raising process.
S3, carrying out an incubation stage I. During the implementation of the step, the inside of the atmosphere furnace is kept communicated with the outside atmosphere, and the heat is preserved for 30 min at the heat preservation temperature of 600 ℃.
S4 carries out a temperature raising stage ii. In the process of implementing the step, the inside of the atmosphere furnace is kept communicated with the outside atmosphere, and the temperature in the atmosphere furnace is increased from 600 ℃ to 1100 ℃ at the temperature increasing rate of 8-10 ℃/min.
S5, carrying out a heat preservation sintering stage II. After step S4 is completed, introducing the reducing mixed gas into the atmosphere furnace, and discharging the introduced reducing mixed gas from a gas path pipeline through which the furnace tube is communicated with the external atmosphere after the introduced reducing mixed gas passes through the interior of the furnace tube; in the process of implementing the step S5, the holding temperature of the atmosphere furnace is set to 1100 ℃, and the holding time is 10 h. Preferably, in this embodiment, the reducing mixed gas is CO, N2, and Ar, wherein the volume content of CO is 10%, the volume content of N2 is 70%, and the volume content of Ar is 20%; the gas flow rate when the reducing mixed gas is introduced is 2.0 +/-0.2L/min.
S6 performs cooling stage i. After step S5 is completed, the introduction of the reducing mixed gas into the atmosphere furnace is stopped, and simultaneously, a non-reducing gas containing no oxygen is introduced into the atmosphere furnace through another pipeline, wherein the non-reducing gas containing no oxygen is N2Ar or a mixed gas of the two gases. When the step S6 is carried out, the temperature in the atmosphere furnace is reduced from 1100 ℃ to 1020-1030 ℃ by adopting a temperature reduction rate of 15-20 ℃/min under the condition that the non-reducing gas without oxygen is introduced into the atmosphere furnace. Preferably, in this embodiment 1, N is used2The flow rate of the non-reducing gas containing no oxygen gas when N2 was introduced was 2.0. + -. 0.2L/min.
S7 performs cooling stage ii. After step S6 is completed, the introduction of the non-reducing gas containing no oxygen into the atmosphere furnace is stopped, and simultaneously, the introduction of the oxygen-rich mixed gas into the atmosphere furnace through another pipeline is stopped, wherein the oxygen-rich mixed gas is O2The mixed gas consists of Ar and oxygen, wherein the volume content of oxygen in the mixed gas is 50-55%, and the flow rate when the mixed gas is introduced is 3.0 +/-0.2L/min; meanwhile, the temperature of the atmosphere furnace is rapidly reduced from 1020-1030 ℃ to 720-750 ℃ at a cooling rate of 45-55 ℃/min.
S8 carries out cooling stage iii. And after the step S7 is finished, stopping introducing the oxygen-rich mixed gas into the atmosphere furnace, closing a heating power supply of the atmosphere furnace, maintaining the state that the interior of the atmosphere furnace is communicated with the outside atmosphere, and naturally cooling the atmosphere furnace from 720-750 ℃ to room temperature.
After the above steps of S1 to S8, the CCTO ceramic sintered body in embodiment 2 of the present invention is obtained.
In the preparation of the sample of comparative example 2, the same CCTO ceramic body as in example 2 was used, and the CCTO ceramic body was sintered in the same atmosphere furnace by the sintering method: referring to the process steps and process conditions of example 2, in comparative example 2, the process steps and process conditions were exactly the same as those of example 2 except that "introducing the reducing mixed gas into the atmosphere furnace" in step S5 was changed to "introducing air into the atmosphere furnace". Comparative example 2 is mainly used to demonstrate the effect of introducing the reducing mixed gas into the atmospheric furnace in step S5 in the technical solution of the present invention on improving the conductivity of the CCTO ceramic crystal grains.
In the preparation of the CCTO ceramic sample in the comparative example 3, the same CCTO ceramic green body as in the example 2 was used, and the CCTO ceramic green body was sintered in the same atmosphere furnace by the sintering method: referring to the process steps and process conditions of example 2, in comparative example 3, except that "introducing a mixed gas of O2 and Ar containing 50 to 55% by volume of oxygen into the atmosphere furnace" in step S7 was replaced with "introducing air into the atmosphere furnace", the other process steps and process conditions were completely the same as those of example 2. Comparative example 3 is mainly used for proving the effect of introducing the oxygen-rich mixed gas in the cooling stage II of S7 in the technical scheme of the invention on improving the grain boundary resistance of the CCTO ceramic.
In the preparation of the CCTO ceramic sample in the comparative example 4, the same CCTO ceramic green body as in the example 2 was used, and the CCTO ceramic green body was sintered in the same atmosphere furnace by the sintering method: referring to the process steps and process conditions of example 2, in comparative example 3, except that "the temperature of the atmosphere furnace is rapidly reduced from 1020 to 1030 ℃ to 720 to 750 ℃ at a cooling rate of 45 to 55 ℃/min" in step S7 is changed to "the temperature of the atmosphere furnace is reduced from 1020 to 1030 ℃ to 720 to 750 ℃ at a cooling rate of 15 to 20 ℃/min", other process steps and process conditions are completely the same as those of example 2. Comparative example 4 is mainly used to show the effect of the temperature reduction rate in the temperature reduction stage ii of S7 in the technical solution of the present invention on maintaining the conductivity of the CCTO ceramic grains.
Fig. 4 shows the results of grain resistance, grain boundary resistance, and dielectric constant and dielectric loss at a frequency of 1 kHz of CCTO ceramics obtained in example 2 and comparative examples 2, 3, and 4. As can be seen from the results shown in FIG. 4, the CCTO ceramic obtained in example 2 according to the present invention has a dielectric constant of 57986, a dielectric loss of 0.0192, a grain resistance of 8.8W, and a grain boundary resistance of 8.98X 108 W is added. Compared with the example 2, the CCTO ceramic obtained in the comparative example 2 is aerated into the atmosphere furnace in the S5 heat preservation sintering stage II in the sintering process, and the grain resistance of the obtained CCTO ceramic is 48.4W, which is obviously higher than that of the CCTO ceramic sample obtained in the example 2 by aerating reducing gas. The dielectric loss of the ceramic obtained in comparative example 2 is not much different from that of example 2, but the dielectric constant is only 9233, which is significantly lower than that of the CCTO ceramic obtained in example 2. It can be seen from the comparison result between example 2 and comparative example 2 that, in the technical scheme of the present invention, the conductivity of the CCTO ceramic crystal grains can be improved by introducing the reducing mixed gas into the atmospheric furnace in the S5 heat-preservation sintering stage ii, so as to achieve the beneficial effect of reducing the dielectric loss and simultaneously improving the dielectric constant.
As is apparent from the results of example 2 and comparative example 3 in FIG. 4, in comparative example 3, the grain boundary resistance of the CCTO ceramic obtained when air was introduced into the atmospheric furnace in the cooling stage II of S7 was 3.76X 107 W, is significantly lower than that of example 2, and the dielectric loss value is 0.9432, which is also correspondingly significantly higher than that of example 2. Therefore, in the technical scheme of the invention, the mixed gas rich in oxygen is introduced into the atmosphere furnace in the S7 temperature reduction stage II, so that the insulativity of the CCTO ceramic grain boundary can be improved, and the dielectric loss of the CCTO ceramic is effectively reduced.
As can be seen from the results of example 2 and comparative example 4 in fig. 4, the CCTO ceramic obtained in comparative example 4 has a grain resistance of 85.9W, which is significantly higher than that of example 2, and a dielectric constant of only 7348 when a temperature lowering rate is applied to the temperature lowering stage ii of S7, which is slower than that of example 2. The above comparison results show that the relatively high cooling rate adopted in the cooling stage ii of S7 in the technical scheme of the present invention can maintain the relatively high conductivity of the CCTO ceramic grains in the oxygen-rich atmosphere, so that the CCTO ceramic obtained in the technical scheme of the present invention has a high dielectric constant.
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 (7)
1. Copper calcium titanate CaCu based on reduction-oxidation atmosphere collaborative sintering3Ti4O12A method of (CCTO) ceramics, characterized by: the CCTO ceramic body is subjected to a heating stage I under the air atmosphere, a heat preservation stage I under the air atmosphere, a heating stage II under the air atmosphere, a heat preservation stage II under the atmosphere of introducing reducing mixed gas, a cooling stage I under the condition of introducing non-reducing gas without oxygen, a rapid cooling stage II under the condition of introducing mixed gas rich in oxygen and a furnace cooling stage III in an atmosphere sintering furnace to obtain the CCTO ceramic sintered body.
2. The method for co-sintering CCTO ceramics based on reduction-oxidation atmosphere according to claim 1, characterized in that the method comprises the following steps:
s1, placing the formed CCTO ceramic blank into an atmosphere furnace;
s2 implementing a temperature rise stage i: heating the temperature in the atmosphere furnace from room temperature to 600 ℃ in an air atmosphere, wherein the heating rate in the heating process is 5-8 ℃/min;
s3 implementation of incubation stage i: keeping the temperature of the atmosphere furnace at 600 ℃ for 30-50 min in the air atmosphere;
s4 implementing a temperature raising stage ii: raising the temperature in the atmosphere furnace from 600 ℃ to 1080-1120 ℃ in an air atmosphere, wherein the temperature raising rate in the temperature raising process is 8-10 ℃/min;
s5, implementing a heat preservation sintering stage II: after the step S4 is completed, introducing a reducing mixed gas into the atmosphere furnace, and preserving heat for 8-10 h at the heat preservation temperature of 1080-1120 ℃;
s6 implementation of cooling stage i: after the step S5 is completed, introducing non-reducing gas without oxygen into the atmosphere sintering furnace, and reducing the temperature in the atmosphere sintering furnace from the heat preservation temperature to 1020-1040 ℃ at a temperature reduction rate of 15-20 ℃/min;
s7 implementing cooling stage ii: after the step S6 is completed, introducing mixed gas rich in oxygen into the atmosphere sintering furnace, and rapidly reducing the temperature in the atmosphere sintering furnace from 1020-1040 ℃ to 720-750 ℃ by adopting a rapid cooling mode;
s8 implementation of cooling stage iii: and after the step S7 is finished, naturally cooling the furnace temperature of the atmosphere furnace from 720-750 ℃ at the air atmosphere.
3. A method for co-sintering CCTO ceramics based on a reducing-oxidizing atmosphere according to claim 1 and claim 2, wherein: the reducing mixed gas in the step S5 of carrying out the heat-preservation sintering stage II is formed by reducing gas H2At least one gas of CO and N2And at least one of Ar and He, wherein the volume content of the reducing gas in the reducing mixed gas is 10-20%.
4. A method for co-sintering CCTO ceramics based on a reducing-oxidizing atmosphere according to claim 1 and claim 2, wherein: the non-reducing gas containing no oxygen in the step S6 of performing the temperature reduction stage I is N2Ar, or N2And Ar, mixed gas.
5. A method for co-sintering CCTO ceramics based on a reducing-oxidizing atmosphere according to claim 1 and claim 2, wherein: step S7 is implemented by the mixed gas rich in oxygen in the cooling stage IIIs oxygen and N2And a mixed gas composed of at least one of Ar and He.
6. A method for co-sintering CCTO ceramics based on a reducing-oxidizing atmosphere according to claims 1 and 5, characterized in that: the volume content of oxygen in the oxygen-enriched mixed gas is 40-70%.
7. A method for co-sintering CCTO ceramics based on a reducing-oxidizing atmosphere according to claim 1 and claim 2, wherein: and the cooling rate of the rapid cooling mode in the cooling stage II implemented in the step S7 is 40-60 ℃/min.
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