Preparation method of low phase transition electric field NaNbO3-based antiferroelectric ceramic

Abstract

The application discloses a preparation method of a low phase change electric field NaNbO3-based antiferroelectric ceramic, which comprises the following steps: synthesizing the antiferroelectric ceramic from Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3; and adopting a double heat treatment technology to improve a traditional solid phase sintering method to obtain a columnar SrNb2O6 precipitated phase; on one hand, the precipitated phase is located in the ceramic, breaks long-range electric domains, refines the size of the antiferroelectric domains, and further reduces an antiferroelectric-ferroelectric (AFE- FE) phase change excitation electric field; on the other hand, micro stress is easily formed around the precipitated phase, which leads to a local unbalanced state, forms a phase change driving force, causes the AFE- FE phase change to easily occur, and further reduces the phase change excitation electric field; the application has simple process, and the lead-free antiferroelectric ceramic with a low phase change electric field at room temperature is easy to obtain, and has wide application prospects in the field of ferroelectric devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of lead-free antiferroelectric ceramics, and in particular to a method for preparing a NaNbO3-based antiferroelectric ceramic with low phase transition electric field. BACKGROUND

[0002] Antiferroelectric (AFE) materials are an important potential material for information storage devices and high power density energy storage devices. Antiferroelectric materials have a special feature of opposite arrangement of adjacent dipoles, resulting in zero spontaneous polarization. However, under an external electric field, an antiferroelectric-ferroelectric (AFE-FE) phase transition is induced, showing a characteristic hump-shaped polarization-electric field (P-E) hysteresis loop. With a large polarization difference (ΔP = P max -P r ), it shows excellent energy storage and information switching potential at low field.

[0003] NaNbO3 ceramic material belongs to perovskite structure, and its molecular formula is ABO3. At room temperature, the antiferroelectric P phase (space group Pbma) and the ferroelectric Q phase (space group P21ma) have similar free energies, so there is a phenomenon of unstable phase transition under the action of an external electric field. This transition is derived from the eccentric displacement of B-site Nb 5+ in the oxygen octahedron, which produces co-tipping and counter-tipping, and finally leads to an antiparallel Nb displacement configuration (Stabilization of the ferrielectric phase in NaNbO3-based lead-free ceramics for a wide-temperature large electrocaloric effect, Journal of Materials Chemistry A, 2022, 10: 18070-18077). It can be known from the existing literature that by reducing the tolerance factor and increasing the electronegativity, the antiferroelectric P phase can be effectively stabilized (for example: Na 0.96 Ca 0.04 Nb 0.96 Zr 0.04The hysteresis loop of the NaNbO3-based antiferroelectric ceramic is a typical pinched loop with antiferroelectric characteristics. However, the AFE-FE phase transition electric field of the NaNbO3-based antiferroelectric ceramic obtained by using the existing stable antiferroelectric method is too high (E≥160 kV / cm), so that the large polarization current generated is easy to cause the antiferroelectric ceramic to be electrically broken down, which is not conducive to the potential of the antiferroelectric material. Therefore, it is of great significance to develop NaNbO3 antiferroelectric ceramics with low phase transition electric field for practical application. In addition, SrNb2O6 belongs to the tetragonal tungsten bronze structure, has a wide band gap, a high breakdown field strength and the like. The crystal is connected by the niobium-oxygen octahedron in the form of common vertex, has a certain adaptability with the perovskite structure lattice, and is easy to develop into a columnar crystal along the C axis.

[0004] In metal materials, quenching and tempering processes are widely used to improve the structure and performance of metal materials, but are rarely used in ceramic materials. The present application changes the traditional solid phase sintering method and innovatively introduces a quenching and tempering double heat treatment process to improve (1-x)Na 0.96 Ca 0.04 Nb 0.96 Zr 0.04 O3-xSrNb2O6 ceramic sintering process, to obtain SrNb2O6 precipitated phase to reduce the antiferroelectric-ferroelectric phase transition electric field. The solid solubility between the tungsten bronze structure SrNb2O6 and the perovskite structure SrNb2O6-based ceramic two phases is limited, and through a suitable heat treatment method, the SrNb2O6 nano / micro columnar crystals can be uniformly precipitated from the NaNbO3-based ceramic grains / grain boundaries. The two phases can form a coherent phase boundary in some areas, which is different from simply preparing a composite of the two phases. On the one hand, the precipitated phase is located in the ceramic, and the columnar crystal cuts the long-range antiferroelectric domain, refines the antiferroelectric domain size, and further reduces the room temperature AFE-FE phase transition induced electric field. On the other hand, the precipitated phase forms a micro-stress around it, which causes a local imbalance, forming a phase transition driving force, further reducing the room temperature AFE-FE phase transition induced electric field. SUMMARY

[0005] The present application aims to solve the technical problems existing in the prior art and provide a preparation method of NaNbO3-based antiferroelectric ceramic with low phase transition electric field.

[0006] To achieve the above-mentioned purpose, the technical solution provided by the present application is as follows: a preparation method of NaNbO3-based antiferroelectric ceramic with low phase transition electric field, the preparation method comprising the following steps:

[0007] 1) Weigh the chemical pure Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3 according to the molar ratio of 0.48(1-x):(0.48+0.52x):0.04(1-x):0.04(1-x):x for synthesizing NaNbO3-based antiferroelectric ceramics, wherein x=0.02-0.15;

[0008] 2) Weigh the powder of NaNbO3-based antiferroelectric ceramics in step 1) into a ball mill tank for mixing, pre-sintering, secondary ball milling, granulation and cold isostatic pressing to obtain a ceramic blank;

[0009] 3) Sinter the ceramic blank obtained in step 2);

[0010] 4) Quenching and tempering treatment is performed during the sintering process in step 3) to obtain a NaNbO3-based antiferroelectric ceramic sample containing columnar SrNb2O6 precipitated phase;

[0011] 5) Polishing and electrode are performed on the NaNbO3-based antiferroelectric ceramic sample in step 4) for testing.

[0012] Preferably, the pre-sintering process in step 2) has a temperature rising rate of 3-4 ℃ / min, a pre-sintering temperature of 900-1000 ℃ and a holding time of 2 h.

[0013] Preferably, the powder size after pre-sintering and secondary ball milling in step 2) is uniform, and the particle size is less than 74 μm.

[0014] Preferably, the cold isostatic pressing in step 2) has a pressure of 200-300 MPa and a holding time of 0.5-3 min; and the thickness of the green body after cold isostatic pressing is controlled to be 2-4 mm.

[0015] Preferably, the sintering process in step 3) has a sintering temperature of 1250-1350 ℃, a sintering holding time of 2 h and an air atmosphere.

[0016] Preferably, the quenching process in step 4) is that when the sintering holding time ends, the kiln is opened, the NaNbO3-based antiferroelectric ceramic sample is taken out and air-cooled to room temperature, and the average rate of air-cooling is 5-30 ℃ / s.

[0017] Preferably, the tempering process in step 4) is that the quenched NaNbO3-based antiferroelectric ceramic sample is heated to 1050-1150 ℃ at a rate of 10-30 ℃ / min and held for 0.5-5 h.

[0018] The present application has the following beneficial effects:

[0019] (1) The SrNb2O6 nano / micropillar crystals can be uniformly precipitated from the ceramic grains / boundary by quenching and tempering heat treatment method, and the coherent phase boundary can be formed between the two phases (NaNbO3 phase and SrNb2O6 phase) in some areas, which is different from the simple composite preparation of the two phases.

[0020] (2) The SrNb2O6 precipitated phase obtained by the method can realize the division of long-range ferroelectric domains in the ceramic, reduce the domain size, and easily induce the anti-ferroelectric hysteresis loop characteristics under a low electric field.

[0021] (3) The SrNb2O6 precipitated phase obtained by the method can increase the local microstress, break the local energy balance, increase the driving force of the anti-ferroelectric phase change, and reduce the AFE-FE phase change electric field.

[0022] In summary, the quenching and tempering heat treatment method adopted in the method reduces the (1-x)NaNbO3-xSrNb2O6 room temperature AFE-FE phase change electric field, the process is simple, and it is of great significance to improve the performance of ferroelectric devices. 0.96 Ca 0.04 Nb 0.96 Zr 0.04 O3-xSrNb2O6 room temperature AFE-FE phase change electric field, the process is simple, and it is of great significance to improve the performance of ferroelectric devices. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. The detailed description of the application is set forth in the accompanying drawings.

[0024] Fig. 1 The drawing is the distribution diagram of the columnar SrNb2O6 precipitated phase in the x=0.08 ceramic sample heat treated in Example 1 of the application;

[0025] Fig. 2 The P-E curves of the ceramic samples before (x=0) and after (x=0.08) regulation in Example 1 of the application. DETAILED DESCRIPTION

[0026] This part will describe the specific embodiments of the application in detail, the preferred embodiments of the application are shown in the accompanying drawings, the role of the drawings is to supplement the description of the text part with figures, so that people can intuitively and visually understand each technical feature and the overall technical scheme of the application, but it cannot be understood as a limitation on the protection scope of the application.

[0027] Referring Figs. 1-2 , the preferred embodiments of the application, a preparation method of a low phase change electric field NaNbO3-based anti-ferroelectric ceramic, the preparation method comprises the following steps:

[0028] 1), weighing the chemical pure Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3 according to the molar ratio of 0.48(1-x):(0.48+0.52x):0.04(1-x):0.04(1-x):x for synthesizing NaNbO3-based antiferroelectric ceramics, wherein x=0.02-0.15;

[0029] 2), the powder of NaNbO3-based antiferroelectric ceramics in step 1) is weighed and loaded into a ball mill tank for mixing, pre-sintering, secondary ball milling, granulation, and cold isostatic pressing to obtain a ceramic blank;

[0030] The specific pre-sintering process is that the heating rate is 3-4 ℃ / min, the pre-sintering temperature is 900-1000 ℃, and the holding time is 2 h; the powder size after pre-sintering and secondary ball milling is uniform, and the particle size is less than 74 μm;

[0031] The cold isostatic pressing pressure is 200-300 MPa, and the holding time is 0.5-3 min; the thickness of the green body after cold isostatic pressing is controlled to be 2-4 mm;

[0032] 3), the ceramic blank obtained in step 2) is sintered; the specific sintering process is that the sintering temperature is 1250-1350 ℃, the sintering holding time is 2 h, and the atmosphere is air atmosphere;

[0033] 4), quenching and tempering are carried out during the sintering process in step 3) to obtain NaNbO3-based antiferroelectric ceramic samples containing columnar SrNb2O6 precipitated phase; the specific quenching process is that when the sintering holding is over, the kiln is opened, the NaNbO3-based antiferroelectric ceramic sample is taken out and air-cooled to room temperature, and the average rate of air-cooling is 5-30 ℃ / s;

[0034] The specific tempering process is that the quenched NaNbO3-based antiferroelectric ceramic sample is heated to 1050-1150 ℃ at a rate of 10-30 ℃ / min and held for 0.5-5 h;

[0035] 5), the NaNbO3-based antiferroelectric ceramic sample in step 4) is polished and electrode, and tested.

[0036] Example 1:

[0037] 1), weighing Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3 according to the molar ratio of 0.4416:0.5216:0.0368:0.0368:0.08 for synthesizing 0.92NaNbO3-0.08SrNb2O6 antiferroelectric ceramics; 0.96 Ca 0.04 Nb 0.96 Zr 0.04O3-0.08SrNb2O6, the chemicals were added into a ball mill pot with ethanol solvent for the first ball milling mixing, the ball milling was carried out at a rotation speed of 300 r / min for 24 h, then the ball milling slurry was dried at 80℃ for 18 h, and sieved with a 200 mesh screen;

[0038] 2) the sieved powder was heated to 950℃ at a rate of 3℃ / min, and held for 2 h for pre-sintering, then the pre-sintered powder was secondarily ball milled, dried, and sieved with a 200 mesh screen;

[0039] 3) the powder obtained above was granulated with 5wt% PVA solution, then shaped using a tabletting die, then a cold isostatic press was used to press at 250 MPa for 3 min to obtain a green compact with a thickness of 3 mm;

[0040] 4) the ceramic green compact was sintered, the process parameters were: a heating rate of 3℃ / min, a sintering temperature of 1300℃, and a holding time of 2 h;

[0041] 5) the sample at the end of sintering was taken out of the kiln at 1300℃, and air cooled to room temperature, maintaining an average cooling rate of 10℃ / s. Then the quenched sample was tempered, heated to 1100℃ at a rate of 20℃ / min, and held for 4 h;

[0042] 6) the sintered sample was polished and electrode, and tested to obtain an antiferroelectric-ferroelectric phase transition electric field of 80 kV / cm.

[0043] Example 2:

[0044] 1), Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3 were weighed according to the molar ratio of 0.456:0.506:0.038:0.038:0.05 for synthesizing 0.95Na 0.96 Ca 0.04 Nb 0.96 Zr 0.04 O3-0.05SrNb2O6, the chemicals were added into a ball mill pot with ethanol solvent for the first ball milling mixing, the ball milling was carried out at a rotation speed of 300 r / min for 24 h, then the ball milling slurry was dried at 80℃ for 18 h, and sieved with a 200 mesh screen;

[0045] 2) the sieved powder was heated to 900℃ at a rate of 3℃ / min, and held for 2 h for pre-sintering, then the pre-sintered powder was secondarily ball milled, dried, and sieved with a 200 mesh screen;

[0046] 3) The powder obtained above was granulated with 5wt% PVA solution, then shaped using a tablet die, followed by cold isostatic pressing at 250 MPa for 2 min, to obtain a green thickness of 2 mm;

[0047] 4) The ceramic green body was sintered with the process parameters of: heating rate of 3°C / min, sintering temperature of 1290°C, and holding time of 2h.

[0048] 5) The sample at the end of sintering was taken out of the kiln at 1290°C and air-cooled to room temperature, maintaining an average cooling rate of 20°C / s. The quenched sample was then tempered by heating to 1090°C at a rate of 20°C / min and holding for 2h.

[0049] 6) The sintered sample was polished and electrode, and tested to obtain an antiferroelectric-ferroelectric phase transition electric field of 120 kV / cm.

[0050] Example 3:

[0051] 1) Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3 were weighed according to the molar ratio of 0.432:0.532:0.036:0.036:0.1 to synthesize 0.9Na 0.96 Ca 0.04 Nb 0.96 Zr 0.04 O3-0.1SrNb2O6, and the chemicals were added to a ball mill tank containing anhydrous ethanol solvent for the first ball milling mixing, at a speed of 300 r / min, ball milling for 24h, and then the ball milling slurry was dried at 80°C for 18h and sieved using a 200 mesh screen;

[0052] 2) The sieved powder was pre-fired at 1000°C for 2h at a rate of 3°C / min, and then the pre-fired powder was secondarily ball milled, dried, and sieved using a 200 mesh screen;

[0053] 3) The powder obtained above was granulated with 5wt% PVA solution, then shaped using a tablet die, followed by cold isostatic pressing at 200 MPa for 3 min, to obtain a green thickness of 4 mm;

[0054] 4) The ceramic green body was sintered with the process parameters of: heating rate of 3°C / min, sintering temperature of 1320°C, and holding time of 2h;

[0055] 5) The sample at the end of sintering was taken out of the kiln at 1320°C and air-cooled to room temperature, maintaining an average cooling rate of 5°C / s. The quenched sample was then tempered by heating to 1120°C at a rate of 25°C / min and holding for 4h;

[0056] 6), the sintered sample is polished and electrode, the test gets the antiferroelectric-ferroelectric phase transition field of 115kV / cm.

[0057] The application can make SrNb2O6 nano / micropillar crystals uniformly separate out from ceramic grains / boundary by quenching and tempering, and form coherent phase boundary between the two phases (NaNbO3 phase and SrNb2O6 phase) in some areas, which is different from simply preparing the two phases.

[0058] The SrNb2O6 precipitated phase obtained by the application can split long-range ferroelectric domains in the ceramic, reduce the domain size, and easily induce antiferroelectric hysteresis loop characteristics under a low electric field.

[0059] The SrNb2O6 precipitated phase obtained by the application can increase local microstress, break local energy balance, increase the driving force of antiferroelectric phase transition, and reduce the AFE-FE phase transition electric field.

[0060] In summary, the quenching and tempering method adopted by the application reduces the (1-x)NaNbO3-xSrNb2O6 room temperature AFE-FE phase transition electric field, is simple in process, and is of great significance in improving the performance of ferroelectric devices. 0.96 Ca 0.04 Nb 0.96 Zr 0.04 O3-xSrNb2O6 room temperature AFE-FE phase transition electric field, is simple in process, and is of great significance in improving the performance of ferroelectric devices.

[0061] The above additional technical features can be freely combined and used by those skilled in the art without conflicts.

[0062] The above is only the preferred embodiment of the application, and any technical solution with basically the same means to achieve the purpose of the application falls within the protection scope of the application.

Claims

1. A method for preparing a low phase transition electric field NaNbO3-based antiferroelectric ceramic, characterized by: The preparation method comprises the following steps: 1) weighing chemical pure Na2CO3, Nb2O5, CaCO3, ZrO2 and SrCO3 in a molar ratio of 0.48(1-x):(0.48+0.52x):0.04(1-x):0.04(1-x):x for synthesizing NaNbO3-based antiferroelectric ceramics, wherein x=0.02-0.15; 2) weighing the powder of the NaNbO3-based antiferroelectric ceramics in step 1) into a ball mill tank for mixing, pre-sintering, secondary ball milling, granulation and cold isostatic pressing to obtain a ceramic blank; 3) sintering the ceramic blank obtained in step 2); 4) quenching and tempering during the sintering process in step 3) to obtain NaNbO3-based antiferroelectric ceramics containing columnar SrNb2O6 precipitated phases; the quenching process in step 4) is that when the sintering holding ends, the NaNbO3-based antiferroelectric ceramic sample is taken out, and air cooling is performed until the temperature of the sample is lowered to room temperature, and the average rate of air cooling is 5-30 ℃ / s; the tempering process in step 4) is that the quenched NaNbO3-based antiferroelectric ceramic sample is heated to 1050-1150 ℃ at a rate of 10-30 ℃ / min, and the temperature is kept for 0.5-5 h; 5) polishing and electrodeing the NaNbO3-based antiferroelectric ceramic sample in step 4) and testing.

2. The method of claim 1, wherein the low phase transition electric field NaNb03-based antiferroelectric ceramic is prepared by the steps of: the pre-sintering process in step 2) is that the heating rate is 3-4 ℃ / min, the pre-sintering temperature is 900-1000 ℃, and the holding time is 2 h. ​ 3. The method for preparing a low phase change electric field NaNbO3-based antiferroelectric ceramic according to claim 1, characterized in that: the powder size after pre-sintering and secondary ball milling in step 2) is uniform, and the particle size is less than 74 μm.

4. The method of claim 1, wherein the low phase transition electric field NaNb03-based antiferroelectric ceramic is prepared by the steps of: the cold isostatic pressing pressure in step 2) is 200-300 MPa, and the pressure holding time is 0.5-3 min; the thickness of the green body after cold isostatic pressing is controlled to be 2-4 mm. ​ 5. The method of claim 1, wherein the low phase transition electric field NaNb03-based antiferroelectric ceramic is prepared by the steps of: the sintering process in step 3) is that the sintering temperature is 1250-1350 ℃, the sintering holding time is 2 h, and the atmosphere is air atmosphere. ​

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