A na, ta co-doped potassium bismuth niobate antiferroelectric crystal material and a preparation and processing method thereof

Abstract

The application belongs to the field of functional material preparation, and particularly relates to a Na and Ta co-doped potassium boron niobate antiferroelectric crystal material and a preparation and processing method thereof. 3‑x Na x Nb 3‑y Ta y B2O 12 , wherein x=0.05-0.45, y=0.05-0.5, the Na and Ta co-doped potassium boron niobate antiferroelectric crystal material has a dielectric coefficient increased from 9.85K to 11K at the time of gamma to beta phase transition, and Pmax is increased to 3 times of the original value; through optimization of crystal growth and processing technology, cleavage of the potassium boron niobate antiferroelectric crystal is obviously improved, and no obvious cleavage phenomenon occurs at a temperature of 600 DEG C.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional material preparation, and particularly relates to a Na and Ta co-doped potassium boron niobate antiferroelectric crystal material and a preparation and processing method thereof. BACKGROUND

[0002] Dielectric materials are increasingly attracting people's attention due to their fast charge and discharge capability and high power density. However, in order to meet the requirements of miniaturization and integration, the energy storage density of dielectric materials needs to be improved.

[0003] Among dielectric materials, antiferroelectric (AFE) materials generally exhibit excellent energy density. Typical AFE materials are lead-based ceramics such as PbZrO3, (Pb 0.98 La 0.02 )(Zr 0.55 Sn 0.45 ) 0.995 O3, etc., but Pb is toxic and its use can cause many environmental problems. A new lead-free AFE crystal K3Nb3B2O 12 (KNBO) has recently been reported. The AFE phase of the KNBO crystal has an extremely low critical phase transition field, 20 kV / cm at room temperature and 4.5 kV / cm at 388 K, and a relatively wide temperature range, from 203 K to 676 K. The KNBO crystal has a high Curie temperature (753 K) and an extremely low critical phase transition field Ec, and exhibits a high EO response potential; the KNBO has a significantly wide transparent range (from 327 nm to 4.67 mm), spanning the entire visible and near-infrared spectrum.

[0004] Therefore, the KNBO single crystal is easy to grow in large size, but the KNBO crystal has a typical layered crystal structure, and thus the KNBO crystal is easy to cleave parallel to the (010) plane, which limits the practical application of the KNBO crystal. The present application proposes a growth and processing method of a KNBO-based crystal, which greatly reduces the cleavage of the KNBO crystal and improves the use efficiency and application range of the product. SUMMARY

[0005] The present application proposes a Na and Ta co-doped potassium boron niobate antiferroelectric crystal material and a preparation and processing method thereof, which can effectively reduce cleavage and improve the use efficiency and application range of the KNBO crystal.

[0006] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0007] A Na and Ta co-doped potassium boron niobate antiferroelectric crystal material, characterized in that it has a chemical general formula of K 3- xNa x Nb 3-y Ta y B2O 12 , wherein x = 0.05-0.45, y = 0.05-0.5.

[0008] As preferred, x = 0.25, y = 0.12, and the chemical formula of the antiferroelectric crystal material is K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 .

[0009] The preparation method of the Na and Ta co-doped potassium bismuth niobate antiferroelectric crystal material described above comprises the following steps:

[0010] S1, K2CO3, Na2CO3, Nb2O5, Ta2O5, and H3BO3 are selected as raw materials, and the raw materials are weighed according to the molar ratio K2CO3: Na2CO3: Nb2O5: Ta2O5: H3BO3 = (3-x): x: (3-y): y: 4, mixed uniformly, and then transferred to a crucible;

[0011] S2, the temperature is raised to 180-300℃ at a rate of 1-3℃ / min and kept for 8-10h, then the temperature is raised to 700-900℃ at a rate of 50-100℃ / h and kept for 24-30h, and then lowered to room temperature;

[0012] S3, the powder obtained in step S2 is fully ground and then calcined at 700-900℃ for 24-30h to lower to room temperature, to obtain K 3-x Na x Nb 3-y Ta y B2O 12 powder;

[0013] S4, the K 3-x Na x Nb 3-y Ta y B2O 12 powder obtained in step S3 is mixed with K2B4O7·5H2O in proportion, ground, and then transferred to a platinum crucible and placed in a growth furnace, the temperature is raised to 400-450℃ at a rate of 50-100℃ / h, kept for 24h, the temperature is raised to 1000-1100℃ at a rate of 50-60℃ / h, kept for 12-24h, to obtain K 3-x Na x Nb 3-y Ta y B2O 12 melt;

[0014] S5, after the melt obtained in step S4 is cooled to the growth temperature at a cooling rate of 10-12 ℃ / h, a seed crystal is immersed in the melt and subjected to cooling annealing, then slowly cooled to 850-800 ℃, the grown crystal is lifted from the liquid surface and cooled to room temperature, to obtain K 3-x Na x Nb 3-y Ta y B2O 12 antiferroelectric crystal.

[0015] As preferred, to improve the growth quality of the potassium boron niobate antiferroelectric crystal, reduce cracking, shorten the growth time and reduce the growth cost, in step S5, the seed crystal is immersed in the melt and subjected to cooling annealing, and the melt is cooled, which specifically comprises the following steps:

[0016] S51, from 1000 ℃ to the crystallization temperature at a cooling rate of 10-15 ℃ / h;

[0017] S52, from the crystallization temperature to 900 ℃ at a cooling rate of 0.5-1 ℃ / h; the cooling rate in this temperature range is as small as possible to inhibit the growth of other nucleation centers and improve the crystal quality;

[0018] S53, from 900 ℃ to the crystallization temperature at a cooling rate of 1-1.5 ℃ / h, and then the crystal is lifted from the melt after the crystal grows to a suitable size;

[0019] S54, from the temperature at which the crystal is lifted from the melt in step S53 to the melt solidification temperature at a cooling rate of 0.5-1 ℃ / h;

[0020] S55, after the melt solidifies, the crystal is lowered back to the surface of the solidified melt and then cooled to room temperature at a rate of 10-15 ℃ / h, to obtain K 3-x Na x Nb 3-y Ta y B2O 12 antiferroelectric crystal.

[0021] As preferred, the growth furnace in step S4 is a single crystal pulling furnace, the temperature gradient of the furnace cavity is set to 1-2 ℃ / cm in the high-temperature zone to effectively reduce the volatilization of raw materials, the gradient in the crystallization zone is set to 4-6 ℃ / cm to facilitate the crystallization of the crystal during the growth, and the gradient in the low-temperature zone is reduced to 1-2 ℃ / cm to reduce the thermal stress of the crystal.

[0022] As preferred, in step S4, the molar ratio of K2B4O7·5H2O to the powder obtained in step S3 is 1:1.

[0023] The above K 3-x Na x Nb 3-y Tay B2O 12 In the process of processing the anti-ferroelectric material, in order to avoid the cracking of the crystal when it is bonded to the processing disc, the MTI series heating platform is used in the process, and the temperature of the heating disc is set to 80-100 DEG C.

[0024] As preferred, the KNBO crystal is cut by using the SYJ-200 external circle cutting machine, a large amount of cooling water is used to cool the cutting machine knife edge, and the feeding speed is controlled to be 0.5-1 cm / min.

[0025] The above Na and Ta co-doped potassium boron niobate anti-ferroelectric crystal material can be applied to electrical devices or optical devices.

[0026] Compared with the prior art, the advantages and positive effects of the present application are that a Na and Ta co-doped potassium boron niobate anti-ferroelectric crystal material is provided, the dielectric coefficient of the crystal material increases from 9.85K to 11K when the gamma→beta phase transition occurs, and Pmax increases to 3 times of the original value.

[0027] Through the optimization of the crystal growth and processing technology, the cleavage phenomenon of the potassium boron niobate anti-ferroelectric crystal is obviously improved, and there is no obvious cleavage phenomenon when the temperature rises to 600 DEG C. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The photo of the anti-ferroelectric crystal material prepared in Example 1 of the present application;

[0029] Figure 2 The curve of the relationship between the dielectric property and the temperature of the crystal in Comparative Example 1 and Example 1 of the present application;

[0030] Figure 3 The polarization electric field (P-E) hysteresis loop of the anti-ferroelectric crystal prepared in Example 1 of the present application is measured at room temperature 1hz; DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0032] Comparative Example 1

[0033] K2CO3, Nb2O5and H3BO3 of 4N purity were mixed in a molar ratio of 3:3:4, transferred into a corundum crucible, and heated to 200°C at a rate of 1°C / min and held for 10 hours, and then heated to 700°C at a rate of 100°C / h and held for 24 hours, and then cooled to room temperature. The obtained powder was ground and calcined again at 700°C for 24 hours and cooled to room temperature to obtain K3Nb3B2O7 powder. 12 powder;

[0034] The obtained powder was mixed with flux K2B4O7-5H2O of 2.5N purity in a molar ratio of 1:1, ground, and transferred into a platinum crucible in a single crystal pulling furnace and heated to 400°C at a rate of 100°C / h and held for 24 hours, and then heated to 1000°C at a rate of 60°C / h and held for 12-24 hours. The seed crystal was immersed in the melt after cooling to the growth temperature at a rate of 10°C / h and slowly cooled to 850-800°C at a rate of 1.5°C / h, and then the grown crystal was lifted from the liquid surface and cooled to room temperature at a rate of 15°C / h.

[0035] Example 1

[0036] A paraelectric crystal of the chemical formula K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 was prepared, i.e. x is 0.25 and y is 0.12, by the following steps

[0037] K2CO3, Na2CO3, Nb2O5, Ta2O5and H3BO3 of 4N purity were mixed in a molar ratio of 2.75:0.25:2.88:0.12:4, transferred into a corundum crucible, and heated to 200°C at a rate of 1°C / min and held for 10 hours, and then heated to 700°C at a rate of 100°C / h and held for 24 hours, and then cooled to room temperature. The obtained powder was ground and calcined again at 700°C for 24 hours and cooled to room temperature to obtain K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 powder.

[0038] The above obtained K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12The powder and K2B4O7.5H2O with purity of 2.5N were mixed and ground in a molar ratio of 1:1, and then transferred into a platinum crucible and placed in a single crystal pulling furnace, and heated to 400℃ at a heating rate of 100℃ / h, and then kept constant for 24 hours, and then heated to 1000℃ at a heating rate of 60℃ / h, and kept for 12-24 hours, to obtain K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 melt.

[0039] After being reduced to the crystallization temperature at a rate of 10℃ / h, it was reduced to 900℃ at a rate of 0.5℃ / h; then it was reduced from 900℃ to 820℃ at a rate of 1℃ / h, and after the crystal grew to a suitable size, the crystal was pulled away from the melt; then the melt was reduced to the solidification temperature at a rate of 0.5℃ / h, and after the melt solidified, the crystal was lowered to the surface of the solidified melt, and then it was continuously reduced to room temperature at a rate of 10℃ / h, to obtain K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 antiferroelectric crystal, such as Figure 1 as shown.

[0040] The temperature gradient of the furnace chamber in the single crystal pulling furnace was set to be further reduced in the high-temperature zone and the low-temperature zone, and increased in the middle crystallization zone. In this embodiment, the temperature gradient was set to be 1-2℃ / cm in the high-temperature zone, which can effectively reduce the volatilization of the raw material; the gradient was set to be 4-6℃ / cm in the crystallization zone, which is conducive to the crystallization of the crystal during the growth process; and the gradient was reduced to 1-2℃ / cm in the low-temperature zone, which can reduce the thermal stress of the crystal.

[0041] The K3Nb3B2O 12 crystal of Comparative Example 1, and the K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 crystal of Example 1 were polished on both sides and plated with silver electrodes, and the dependence of the dielectric properties of the crystal on temperature was tested using a precision LCR tester E4980A (Agilent). As shown in Figure 2 , the KNB crystal has several dielectric anomalies during the heating process, which correspond to the φ→ε, ε→δ, δ→γ, and γ→β phase transitions, respectively. Through doping improvement, the dielectric coefficient of the γ→β phase transition is increased from 9.85K to 11K.

[0042] The polarization electric field (P-E) hysteresis loop was measured at room temperature at 1hz using a precision ferroelectric analyzer (TF analyzer 3000, Synerce), as shown inFigure 3 Typical double P-E hysteresis loop was observed when the applied electric field reached 4.5kv / cm. The maximum polarization of the doped K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 crystal was increased to 3 times of the original.

[0043] Example 2

[0044] Preparation of antiferroelectric crystal of chemical formula K 2.85 Na 0.15 Nb 2.75 Ta 0.25 B2O 12 , i.e. x is 0.15 and y is 0.25, is as follows:

[0045] K2CO3, Na2CO3, Nb2O5, Ta2O5 and H3BO3 with purity of 4N were mixed in a molar ratio of 2.85:0.15:2.75:0.25:4, and then transferred into a corundum crucible, heated to 200℃ at a rate of 1℃ / min and kept for 10h, then heated to 700℃ at a rate of 100℃ / h and kept for 24h, and then cooled to room temperature; the obtained powder was ground and calcined again at 700℃ for 24h and then cooled to room temperature, to obtain K 2.85 Na 0.15 Nb 2.75 Ta 0.25 B2O 12 powder.

[0046] The K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 powder obtained above was mixed with K2B4O7·5H2O with purity of 2.5N in a molar ratio of 1:1, ground, and then transferred into a platinum crucible, heated to 400℃ at a rate of 100℃ / h, kept for 24h, heated to 1000℃ at a rate of 60℃ / h, kept for 12-24h, to obtain K 2.85 Na 0.15 Nb 2.75 Ta 0.25 B2O 12 melt.

[0047] After the temperature is decreased to the crystallization temperature at a rate of 10°C / h, the temperature is decreased to 900°C at a rate of 0.5°C / h; then the temperature is decreased from 900°C to 830°C at a rate of 1°C / h, and after the crystal grows to a suitable size, the crystal is lifted from the melt; then the melt is decreased to the solidification temperature at a rate of 0.5°C / h, and after the melt solidifies, the crystal is lowered to the surface of the solidified melt, and the temperature is decreased to room temperature at a rate of 10°C / h, to obtain K 2.85 Na 0.15 Nb 2.75 Ta 0.25 B2O 12 antiferroelectric crystal.

[0048] Example 3

[0049] antiferroelectric crystal of the chemical formula K 2.55 Na 0.45 Nb 2.95 Ta 0.05 B2O 12 , i.e., x is 0.45 and y is 0.05; the specific steps are as follows

[0050] K2CO3, Na2CO3, Nb2O5, Ta2O5, and H3BO3 with a purity of 4N are mixed in a molar ratio of 2.55:0.45:2.95:0.05:4, and then transferred into a corundum crucible, and then increased to 200°C at a rate of 1°C / min and kept for 10h, and then increased to 700°C at a rate of 100°C / h and kept for 24h, and then decreased to room temperature; the obtained powder is ground thoroughly, and then calcined at 700°C for 24h and then decreased to room temperature, to obtain K 2.55 Na 0.45 Nb 2.95 Ta 0.05 B2O 12 powder.

[0051] The K 2.55 Na 0.45 Nb 2.95 Ta 0.05 B2O 12 powder obtained above is mixed with K2B4O7·5H2O with a purity of 2.5N in a molar ratio of 1:1, and then ground, and then transferred into a platinum crucible, and then increased to 400°C at a rate of 100°C / h, and then kept for 24h, and then increased to 1000°C at a rate of 60°C / h, and kept for 12-24h, to obtain K 2.55 Na 0.45 Nb 2.95 Ta 0.05 B2O 12 melt.

[0052] After the temperature is decreased to the crystallization temperature at a rate of 10°C / h, the temperature is decreased to 900°C at a rate of 0.5°C / h; then the temperature is decreased from 900°C to 800°C at a rate of 1°C / h, and after the crystal grows to a suitable size, the crystal is lifted from the melt; then the melt is decreased to the solidification temperature at a rate of 0.5°C / h, and after the melt solidifies, the crystal is lowered to the surface of the solidified melt, and the temperature is decreased to room temperature at a rate of 10°C / h, to obtain K 2.55 Na 0.45 Nb 2.95 Ta 0.05 B2O 12 antiferroelectric crystal.

[0053] Example 4

[0054] An antiferroelectric crystal of the general chemical formula K 295 Na 005 Nb 25 Ta 05 B2O 12 , i.e., x is 0.05 and y is 0.5, is prepared by the following steps:

[0055] K2CO3, Na2CO3, Nb2O5, Ta2O5, and H3BO3 with a purity of 4N are mixed in a molar ratio of 2.95:0.05:2.5:0.5:4, and then transferred into a corundum crucible, and then increased to 200°C at a rate of 1°C / min and kept for 10h, and then increased to 700°C at a rate of 100°C / h and kept for 24h, and then decreased to room temperature; the obtained powder is ground and then calcined at 700°C for 24h and then decreased to room temperature, to obtain K 2.95 Na 0.05 Nb 2.5 Ta 0.5 B2O 12 powder.

[0056] The K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 powder obtained above is mixed with K2B4O7·5H2O with a purity of 2.5N in a molar ratio of 1:1, and then ground, and then transferred into a platinum crucible, and then increased to 400°C at a rate of 100°C / h and kept for 24h, and then increased to 1000°C at a rate of 60°C / h and kept for 12-24h, to obtain K 2.95 Na 0.05 Nb 2.5 Ta 0.5 B2O 12 melt.

[0057] After the temperature is decreased to the crystallization temperature at a rate of 10°C / h, the temperature is decreased to 900°C at a rate of 0.5°C / h; then the temperature is decreased from 900°C to 850°C at a rate of 1°C / h, and after the crystal grows to a suitable size, the crystal is lifted from the melt; then the melt is decreased to the solidification temperature at a rate of 0.5°C / h, and after the melt solidifies, the crystal is lowered to the surface of the solidified melt, and the temperature is decreased to room temperature at a rate of 10°C / h, to obtain K 2.95 Na 0.05 Nb 2.5 Ta 0.5 B2O 12 antiferroelectric crystal.

Claims

1. A Na, Ta co-doped potassium bismuth niobate antiferroelectric crystal material, characterized in that, The chemical general formula of the antiferroelectric crystal material is K 3-x Na x Nb 3-y Ta y B2O 12 , wherein, x=0.05~0.45, y=0.05~0.

5. 2.The Na, Ta co-doped potassium doped bismuth niobate antiferroelectric crystal material of claim 1, wherein, x = 0.25, y = 0.12, the chemical formula of the antiferroelectric crystal material is K 2.75 Na 0.25 Nb 2.88 Ta 0.12 B2O 12 .

3. The method of any one of claims 1-2 for preparing Na, Ta co-doped potassium bismuth niobate antiferroelectric crystal material, comprising the following steps: S1. Selecting K2CO3, Na2CO3, Nb2O5, Ta2O5 and H3BO3 as raw materials, and weighing the raw materials according to the molar ratio K2CO3:Na2CO3:Nb2O5:Ta2O5:H3BO3=(3-x):x:(3-y):y:4, mixing uniformly, and then transferring to a crucible; S2. Raising the temperature to 180-200℃ at a rate of 1-3℃ / min and maintaining for 8-10h, and then raising the temperature to 700-900℃ at a rate of 50-100℃ / h, maintaining for 24-30h, and then lowering to room temperature; S3, grinding the powder obtained in step S2 thoroughly and calcining again at 700-900°C for 24-30h and then reducing to room temperature to obtain K 3- x Na x Nb 3-y Ta y B2O 12 powder; S4, K 3-x Na x Nb 3-y Ta y B2O 12 powder and K2B4O7.5H2O are mixed in proportion, ground and then transferred into a platinum crucible and placed in a growth furnace, heated to 400-450°C at a heating rate of 50-100°C / h, and then kept constant for 24 hours, heated to 1000-1100°C at a heating rate of 50-60°C / h, and kept for 12-24 hours; K 3-x Na x Nb 3-y Ta y B2O 12 melt; S5, after the melt obtained in step S4 is cooled to the growth temperature at a cooling rate of 10-12 °C / h, the seed crystal is immersed in the melt and subjected to cooling annealing, then slowly cooled to 850-800 °C, the grown crystal is lifted from the liquid surface and cooled to room temperature, to obtain K 3- x Na x Nb 3-y Ta y B2O 12 antiferroelectric crystal.

4. The method for preparing the Na and Ta co-doped potassium boroniobate antiferroelectric crystal material according to claim 3, characterized in that, In step S5, the seed crystal is immersed in the melt for annealing, and the melt is cooled, specifically including the following steps: S51. From 1000℃ to the crystallization temperature at a rate of 10-15℃ / h; S52. From the crystallization temperature to 900℃ at a rate of 0.5-1℃ / h; S53. From 900℃ at a rate of 1-1.5℃ / h, and after the crystal grows to a suitable size, the crystal is lifted away from the melt; S54. From the temperature at which the crystal is lifted away from the melt in step S53 to the melt solidification temperature at a rate of 0.5-1℃ / h; S55、After the melt is solidified, the crystal is lowered back to the surface of the solidified melt and is continued to be lowered to room temperature at a rate of 10-15°C / h to obtain K 3-x Na x Nb 3-y Ta y B2O 12 Antiferroelectric crystal.

5. The method for preparing the Na and Ta co-doped potassium boroniobate antiferroelectric crystal material according to claim 4, characterized in that, In step S4, the growth furnace is a single crystal pulling furnace, and the temperature gradient of the furnace cavity is set as follows: the high-temperature zone gradient is 1-2℃ / cm; the crystallization zone gradient is 4-6℃ / cm; and the low-temperature zone gradient is reduced to 1-2℃ / cm.

6. The method of producing Na, Ta co-doped potassium bismuth niobate antiferroelectric crystal material according to claim 3, characterized in that, In step S4, K2B4O7-5H2O is reacted with K2NbF7obtained in step S3 3-x Na x Nb 3-y Ta y B2O 12 The molar ratio of the powders is 1 :

1.

7. The method of processing a Na, Ta co-doped potassium bismuth niobate antiferroelectric crystal material according to any one of claims 1-2, characterized in that, An MTI series heating platform is used in the processing, and the heating disc temperature is set to 80-100℃.

8. The method of processing Na, Ta co-doped potassium bismuth niobate antiferroelectric crystal material according to claim 7, characterized in that, An SYJ-200 external circle cutting machine is used to cut the antiferroelectric crystal, a large amount of cooling water is used to cool the cutting machine knife edge, and the feed speed is controlled at 0.5-1cm / min.

9. Use of any of the Na, Ta co-doped potassium bismuth niobate antiferroelectric crystal materials according to claims 1-2, characterized in that, It is applied to electrical devices or optical devices.

Images