BISMUTH SODIUM POTASSIUM TITANATE-BARIUM TITANATE-BASED COMPOSITE CERAMIC MATERIAL WITH HIGH DEPOLARIZATION TEMPERATURE AND PREPARATION METHOD THEREOF

Abstract

Disclosed are a bismuth sodium potassium titanate-barium titanate (BNKT-BT)-based composite ceramic material with high depolarization temperature and a preparation method thereof, belonging to the technical field of piezoelectric ceramics of electronic materials. The chemical general formula of the BNKT-BT based composite ceramic material is: 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3-xZnO, where 0.1x0.3. The composite ceramic material takes BNKT-BT ceramics as the substrate, and single-phase ZnO is embedded in the middle of the substrate to form a 0-3 composite structure.

Claims

1. A bismuth sodium potassium titanate-barium titanate (BNKT-BT)-based composite ceramic material with high depolarization temperatures, comprising a chemical general formula of
0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3-xZnO, wherein 0.1x0.3.

2. A preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 1, comprising steps as follows: S1, mixing a bismuth source, a sodium source, a potassium source, a titanium source and a barium source according to a stoichiometric ratio, ball milling with an organic solvent as a medium, drying and dry-pressing for molding to obtain a raw material block; S2, pre-sintering the raw material block in an oxygen atmosphere to obtain a BNKT-BT pre-sintered block; S3, mixing the BNKT-BT pre-sintered block with ZnO nanoparticles according to the stoichiometric ratio, performing secondary ball milling, drying, adding adhesive, standing, and pressing to obtain a sample; S4, grinding the pressed sample and sieving to obtain powder, and then re-pressing the obtained powder to obtain a ceramic blank; S5, sequentially heating, sintering, grinding and polishing the ceramic blank to obtain ZnO composite BNKT-BT-based ceramics; and S6, coating silver paste on a surface of the ZnO composite BNKT-BT-based ceramics, and performing silver-firing to obtain BNKT-BT-based composite ceramic material with high depolarization temperatures.

3. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein the dry-pressing in the S1 is carried out under a pressure of 400 Mpa for a duration of 1-3 minutes.

4. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein the pre-sintering in the S2 is carried out under a temperature of 820-850 C. for a duration of 3-4 hours.

5. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein the ZnO nanoparticles in the S3 are in a diameter of 50-80 nm.

6. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein in the S3, the adhesive is a 5 wt % polyvinyl alcohol adhesive; the standing is lasted for 12-15 h, and the pressing to obtain the sample is carried out under pressure of 600 Mpa for a duration of 3-6 minutes.

7. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein the re-pressing in the S4 is carried out under a pressure of 400 Mpa for a duration of 1-3 minutes.

8. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein in the S5, the heating comprises a temperature of 550 C. and a duration of 2-3 hours; and the sintering comprises a temperature of 1,030-1,070 C. and a duration of 1-1.5 h, with a heating rate of 9 C./min.

9. The preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperatures according to claim 2, wherein the silver-firing in the S6 is carried out under a temperature of 550-600 C. for a duration of 40-50 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is an X-ray diffraction (XRD) diagram of composite ceramic materials prepared in Embodiments 1-3 and Comparative embodiment 1.

[0030] FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D illustrate results of scanning electron microscope (SEM) analysis of a 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3 (BNKT-BT)-0.3ZnO at x=0.3 in Embodiment 2, where FIG. 2A shows morphological phases, FIG. 2B shows Ti elemental distribution, FIG. 2C illustrates Bi elemental distribution, and FIG. 2D illustrates Zn elemental distribution.

[0031] FIG. 3A, FIG. 3B, FIG. 3C and FIG. 3D respectively show dielectric temperature spectrum and loss spectrum of the composite ceramic materials prepared in Embodiments 1-3 and Comparative embodiment 1 under alternating current loading of different frequencies, where the temperature at which a first dielectric abnormal peak appears corresponds to a depolarization temperature Td of a substrate.

[0032] FIG. 4 is a graph showing variations of a piezoelectric constant d.sub.33 against annealing temperature of the composite ceramic materials prepared in Embodiments 1-3 and Comparative embodiment 1.

[0033] FIG. 5 is a process illustrating a preparation method of a BNKT-BT-based composite ceramic material with high depolarization temperature according to the present application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Various exemplary embodiments of the present application are described in detail and this detailed description should not be considered as limiting the present application, but should be understood as a more detailed description of certain aspects, features and embodiments of the present application.

[0035] It is to be understood that the terms described in the present application are intended to describe particular embodiments only and are not intended to limit the application. Further, with respect to the range of values in the present application, it is to be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value within a stated range and any other stated value or intermediate value within a stated range is also included in the present application. The upper and lower limits of these smaller ranges may be independently included or excluded from the scope.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the field described in the present application. Although the present application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present application. All literature referred to in this specification is incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with said literature. In the event of conflict with any incorporated literature, the contents of this specification shall prevail.

[0037] Without departing from the scope or spirit of the present application, a variety of improvements and variations can be made to specific embodiments of the specification of the present application, as will be apparent to those skilled in the art. Other embodiments obtained from the specification of the present application are obvious to the skilled person. The present specification and embodiments are exemplary only.

[0038] The terms including, comprising, having and containing used in this specification are all open terms, which means including but not limited to.

[0039] A BNKT-BT-based composite ceramic material with high depolarization temperature, and the BNKT-BT-based composite ceramic material has a chemical general formula of 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3 (BNKT-BT)-xZnO, where 0.1x0.3.

[0040] According to the present application, a BNKT-BT substrate is firstly formed by solid solution of a tetragonal phase BKT and BT with a tripartite phase BNT at room temperature, and then mixed and sintered with ZnO nanoparticles to form a 0-3 type composite structure; the prepared composite ceramic material retains a tripartite-tetragonal quasi-homotypic phase boundary and has better piezoelectric properties.

[0041] Referring to FIG. 5, the present application also provides a preparation method of the BNKT-BT-based composite ceramic material with high depolarization temperature, including the following steps: [0042] S1, mixing a bismuth source, a sodium source, a potassium source, a titanium source and a barium source into a slurry according to a stoichiometric ratio by a wet ball milling method for a duration of 20-24 hours (h) with a rotating speed of 300-400 revolutions per minute (rpm), with an organic solvent as a medium; then taking out the slurry after ball milling, pouring the slurry into a glass culture dish and drying for 3 h, with a temperature of a drying box being 105 degrees Celsius ( C.), then obtaining dried raw material powder; pressing that raw material powder into a circular disc in a tablet press, where the circular disc has a diameter of 30 millimeters (mm) and a thickness of 10 mm, the pressing is carried out under pressure of 400 megapascal (MPa) with pressure being kept for a duration of 1-3 min, preferably 1 min, to obtain a raw material block; [0043] the ball milling uses ball of onyx material, with diameters of large, medium and small balls of 20 mm, 10 mm and 6 mm respectively, and the balls of three sizes are in a ratio of large balls:medium balls:small balls=1:20:60; [0044] the bismuth source is Bi.sub.2O.sub.3, the sodium source is Na.sub.2CO.sub.3, the potassium source is K.sub.2CO.sub.3, the titanium source is TiO.sub.2, the barium source is BaCO.sub.3, and the organic solvent is anhydrous ethanol (with an addition amount of 30-50 percent (%) of a total volume of the powder, preferably 40%); [0045] S2, putting the raw material block into a box-type low-temperature reaction furnace, increasing temperature to 820-850 C. at a rate of 3 C./min, and pre-sintering for 3-4 h, preferably 3 h, in an oxygen atmosphere to obtain a BNKT-BT pre-sintered block; [0046] S3, grinding the obtained BNKT-BT pre-sintered block to obtain BNKT-BT pre-sintered powder, then mixing the BNKT-BT pre-sintered powder with ZnO nanoparticles (with an average diameter of 50-80 nanometers (nm), preferably 50 nm) according to the stoichiometric ratio, performing secondary ball milling for 12 h (the ball ratio and ball milling parameters are the same as those in S1), and drying to obtain mixed powder; and [0047] adding 5 weight percentage (wt %) polyvinyl alcohol adhesive into the mixed powder at a speed of 2-3 drops per gram (drops/g), fully stirring, standing for 12-15 h, preferably for 12 h, and then pressing the powder into a disc with a diameter of 30 mm, a thickness of 10 mm at a pressure of 600 MPa for a duration of 3-6 min, preferably 5 min; [0048] S4, grinding the pressed sample and sieving to obtain powder with a sieve meeting requirements of GB/T6003.1-2012, with only the powder with a diameter of 75-106 micrometers (m) is reserved; pressing the obtained powder into a disc with a diameter of 13 mm, a thickness of 1 mm at a pressure of 400 Mpa for a duration of 1-3 min, preferably 1 min, and slowly depressurizing and demoulding to obtain a ceramic blank; [0049] S5, placing the ceramic blank in a low-temperature reaction furnace, raising the temperature to 550 C. at a rate not higher than 2 C./min and keeping the temperature for 2-3 h, and discharging water vapor and organic matters in the ceramic blank to obtain the ceramic blank after discharging water vapor and organic matters; and [0050] placing the ceramic blank after discharging water vapor and organic matters in a high-temperature reaction furnace for high-temperature sintering, rapidly raising the temperature to 1,030-1,070 C. at a rate of 9 C./min and keeping the temperature for 1-1.5 h, and then naturally cooling to room temperature to obtain a ceramic sheet; [0051] among them, the temperature is 1,050-1,070 C. when 0.1x<0.2, and the temperature is 1,030-1,050 C. when 0.2x0.3; [0052] polishing a surface of the ceramic sheet to obtain ZnO composite BNKT-BT-based ceramics; and [0053] S6, coating high-temperature silver paste on the surface of ZnO composite BNKT-BT-based ceramics, and performing silver-firing at 550-600 C. (preferably 560 C.) for 40-50 min, preferably 40 min to obtain BNKT-BT-based composite ceramic material with high depolarization temperature. [0054] In an optimized embodiment, the ZnO nanoparticles in the S3 are in a diameter of 50 nm.

[0055] The raw materials used in the present application are Bi.sub.2O.sub.3 (Alfa Aesar, 99.9%), Na.sub.2CO.sub.3 (Acros Organics, 99%), TiO.sub.2 (Acros Organics, 99%), BaCO.sub.3 (Alfa Aesar, 99%), K.sub.2CO.sub.3 (Acros Organics 99.9%), ZnO (Aladdin, 99.9% and 50 nm), and anhydrous ethanol.

Embodiment 1

[0056] A 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3-xZnO composite ceramic material is synthesized, where x=0.1, and the specific implementation method is as follows: [0057] S1, using Bi.sub.2O.sub.3, TiO.sub.2, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, and BaCO.sub.3 as initial raw materials, weighing according to the stoichiometric ratio, subjecting to wet ball milling at a rotating speed of 300 rpm for 20 h with anhydrous ethanol (40% of the total powder volume) as the medium to obtain a slurry, taking out the slurry after the ball milling, pouring the slurry into a glass culture dish and drying for 3 h, with a temperature of a drying box being 105 C., then obtaining dried raw material powder; [0058] the ball milling uses ball of onyx material, with diameters of large, medium and small balls of 20 mm, 10 mm and 6 mm respectively, and the balls of three sizes are in a ratio of large balls:medium balls:small balls=1:20:60; and [0059] pressing the raw material powder into a circular disc in a tablet press with a diameter of 30 mm and a thickness of 10 mm under pressure of 400 MPa, keeping the pressure for 1 min, then obtaining a raw material block; [0060] S2, putting the raw material block into a box-type low-temperature reaction furnace, increasing temperature to 820 C. at a rate of 3 C./min, and pre-sintering for 3 h in an oxygen atmosphere to obtain a BNKT-BT pre-sintered block; [0061] S3, grinding the obtained BNKT-BT pre-sintered block to obtain BNKT-BT pre-sintered powder, then mixing the BNKT-BT pre-sintered powder with ZnO nanoparticles (with an average diameter of 50 nm) according to the stoichiometric ratio, and performing secondary ball milling for 12 h (the ball ratio and ball milling parameters are the same as those in S1)), and after ball milling, putting the slurry into a drying oven to dry to obtain mixed powder; and [0062] adding 5 wt % polyvinyl alcohol adhesive into the mixed powder at a speed of 2 drops/g, fully stirring and standing for 12 h, then pressing the powder into a circular disc with a diameter of 30 mm and a thickness of 10 mm under a pressure of 600 MPa for a duration of 5 min; [0063] S4, grinding the pressed circular disc and sieving to obtain powder with a sieve meeting requirements of GB/T6003.1-2012, with only the powder with a diameter of 75-106 m is reserved; pressing the obtained powder into a disc with a diameter of 13 mm, a thickness of 1 mm at a pressure of 400 MPa for a duration of 1 min, and slowly depressurizing and demoulding to obtain a ceramic blank; [0064] S5, placing the ceramic blank in a low-temperature reaction furnace, raising the temperature to 550 C. at a rate not higher than 2 C./min and keeping the temperature for 3 h, and discharging the water vapor and organic matters in the ceramic blank to obtain the ceramic blank after discharging the water vapor and organic matters; [0065] placing the ceramic blank after discharging water vapor and organic matters in a high-temperature reaction furnace for high-temperature sintering, rapidly raising the temperature to 1,055 C. at a rate of 9 C./min and keeping the temperature for 1.2 h, and then naturally cooling to room temperature to obtain a ceramic sheet; polishing a surface of the ceramic sheet to obtain ZnO composite BNKT-BT-based ceramics; and [0066] S6, coating high-temperature silver paste on the surface of ZnO composite BNKT-BT-based ceramics, and performing silver-firing at 560 C. for 40 min to obtain BNKT-BT-based composite ceramics (piezoelectric ceramic vibrator) with high depolarization temperature.

Embodiment 2

[0067] A 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3-xZnO composite ceramic material is synthesized, where x=0.3, and the specific implementation method is the same as that in Embodiment 1, except that the temperature in S5 is 1,050 C.

Embodiment 3

[0068] Same as Embodiment 2, except that x=0.2.

Comparative Embodiment 1

[0069] A 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3 composite ceramic material is synthesized, x=0, and the specific implementation method is the same as that in Embodiment 1, except that the temperature in S5 is 1,060 C.

[0070] FIG. 1 is an X-ray diffraction (XRD) diagram of the composite ceramic materials prepared in Embodiments 1-3 and Comparative embodiment 1.

[0071] As can be seen in FIG. 1, the (003) and (021) peaks splitting at diffraction angles around 40 indicate the presence of tripartite symmetry, while the (002) and (200) peaks splitting around 46 suggest the presence of tetragonal symmetry. The XRD results demonstrate that the ZnO composite ceramics maintain the tripartite-tetragonal quasi-isotropic phase boundary well.

[0072] When x=0.1, there are a few ZnO diffraction peaks with wurtzite structure in the XRD diagram, which proves the existence of single-phase ZnO; [0073] when x=0.2 and x=0.3, the ZnO diffraction peak of wurtzite structure is obvious in the XRD diagram, and a small amount of impurities are produced; and [0074] when x=0, there is only one set of diffraction peaks of perovskite lattice in the XRD diagram, and no other impurities appear.

[0075] FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D illustrate results of scanning electron microscope (SEM) analysis of a 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.11(Bi.sub.0.5K.sub.0.5)TiO.sub.3-0.04BaTiO.sub.3-0.3ZnO at x=0.3 in Embodiment 2, where FIG. 2A shows morphological phases, FIG. 2B shows Ti elemental distribution, FIG. 2C illustrates Bi elemental distribution, and FIG. 2D illustrates Zn elemental distribution.

[0076] It can be seen from the figure that the ZnO-rich regions are isolated in the BNKT-BT substrate, forming a 0-3 composite structure (a piezoelectric ceramic specific structure).

[0077] FIG. 3A, FIG. 3B, FIG. 3C and FIG. 3D show the dielectric temperature spectrum and loss spectrum of composite ceramic materials under different frequency alternating current loading when x=0, 0.1, 0.2 and 0.3, in which the temperature at which the first dielectric abnormal peak appears corresponds to the depolarization temperature T.sub.d of the substrate; specifically, FIG. 3A shows the dielectric temperature spectrum and loss spectrum of composite ceramic material under different frequency alternating current loading when x=0, and FIG. 3B shows the results when x=0.1, FIG. 3C shows that when x=0.2, and FIG. 3D shows that when x=0.3 (the upper curve is the dielectric constant .sub.r denoted by the arrow, the lower curve is the loss tan denoted by the arrow and T.sub.d is the depolarization temperature).

[0078] FIG. 4 is a graph showing variations of a piezoelectric constant d.sub.33 against annealing temperature of the composite ceramic materials prepared when x=0, 0.1, 0.2 and 0.3.

[0079] As can be seen from FIG. 3A-FIG. 3D and FIG. 4, the depolarization temperature of the composite ceramic materials prepared in Embodiments 1-2 of the present application is above 120 C.; the piezoelectric constant d.sub.33 under room temperature is 123 picocoulombs per Newton (pC/N) when x=0.1 when x=0.1, with a depolarization temperature of 122 C., the piezoelectric constant d.sub.33 under room temperature is 110 pC/N when x=0.2 with a depolarization temperature of 127 C., and the piezoelectric constant d.sub.33 under room temperature decreases to a certain extent when x=0.3, only 100 pC/N, while the depolarization temperature increases slightly to 134 C. As compared to Embodiment 1 and Embodiment 2, the piezoelectric constant d.sub.33 at room temperature is higher at 132 pC/N when x=0, but the depolarization temperature is only 68 C.

[0080] The depolarization behavior of the composite ceramic materials prepared in Embodiments 1-3 of the present application is obviously improved, and d.sub.33 remains relatively stable below 110 C.

Comparative Embodiment 2

[0081] Same as Embodiment 1, with the difference that the ZnO nanoparticles are replaced by niobium oxide.

[0082] The results show that the depolarization temperature of the composite ceramic material is only 110 C., and the piezoelectric constant d.sub.33 at room temperature is 98 pC/N.

Comparative Embodiment 3

[0083] The difference from Embodiment 1 is that the ball milling method in step 1) is altered to stirring and mixing.

[0084] It is found that the depolarization temperature of the prepared composite ceramic material is only 53 C. and the room temperature piezoelectric constant d.sub.33 is 70 pC/N.

[0085] All the above mentioned are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application.