Potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with non-stoichiometric Nb.SUP.5+ and preparation method therefor

Abstract

The present invention discloses potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with non-stoichiometric Nb.sup.5+ and a preparation method therefor. A ceramic powder with a general formula of (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (?0.01?x?0.04) is prepared by a traditional solid phase method; and then piezoelectric ceramics are prepared by traditional electronic ceramic preparation processes such as granulating, molding, binder removal, sintering and silvering test. An excessive amount of Nb.sup.5+ doping improves the temperature stability of the ceramics by providing a domain wall pinning effect. This result demonstrates the promise of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics for a wide range of applications, including sensors, actuators, and other electronic devices.

Claims

1. A potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+, wherein the ceramics have the following formula:
(K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3, wherein x is 0.01.

2. The potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 1, wherein the ceramic comprises the following piezoelectric properties: a piezoelectric constant d.sub.33 is 450 pC/N, Curie temperature T.sub.C is 300? C., an electromechanical coupling factor k.sub.p is 0.516, a dielectric constant ?.sub.r is 1644, and a dielectric loss tan? is 0.024.

3. A preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 1, comprising the following steps: (1) preparing potassium sodium bismuth niobate tantalate zirconate ferrite ceramic powder by a solid phase method comprising weighing and proportioning raw materials respectively according to the formula, placing the raw materials in a polyurethane ball milling pot and adding a dispersion medium, placing the raw materials in a planetary ball mill, conducting ball milling until the raw materials are mixed uniformly to form a slurry, placing the uniformly mixed slurry in a stainless steel basin, baking the uniformly mixed slurry under a drying lamp to obtain a dried powder, putting the dried powder into a crucible, raising the temperature in a programmed temperature control box furnace to 850? C.-950? C., and pre-sintering the dried powder for 6 hours to obtain a pre-sintered powder; (2) secondary ball milling by placing the pre-sintered powder prepared in step (1) in the polyurethane ball milling pot and adding the dispersion medium again, placing the dispersed pre-sintered powder in a planetary ball mill and conducting secondary ball milling to form a second slurry, and baking the second slurry under a drying lamp to obtain a dried ceramic powder; (3) granulating and molding by fully mixing the dried ceramic powder prepared in step (2) with a 5-10 wt % PVA binder, conducting granulating to form uniformly distributed particles, and pressing the particles into preformed ceramic green pellets with a diameter of 10 mm and a thickness of 1 mm under a uniaxial pressure of 10-15 MPa; (4) binder removal and sintering by removing binder of the preformed ceramic green pellets prepared in step (3) at a temperature of 500? C.-550? C., and sintering the ceramic green pellets at a temperature of 1090? C.-1120? C. for 3-5 hours to prepare sintered ceramic pellets; and (5) silvering and polarization by brushing the sintered ceramic pellets with a silver paste with a concentration of 5-15 wt %, sintering the ceramic pellets again at 700? C.-800? C. for 10-15 minutes to prepare a sample, and conducting polarization in an oil bath at a temperature between room temperature and 120? C. to prepare piezoelectric ceramics.

4. The preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 3, wherein the raw materials in step (1) comprise doped elements that are each an oxide or carbonate thereof.

5. The preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 3, wherein during the ball milling in step (1) and step (2), the ratio of powder to zirconium balls is 1:2-3, the ratio of powder to dispersion medium is 1:2-3, the dispersion medium is absolute ethyl alcohol, the ball milling time is 15-20 hours, the rotational speed is 250-320 r/min, and the baking time is 2-3 hours.

6. The preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 3, wherein particle size distribution after the ball milling in step (1) is D50=0.7-0.8 ?m, D90=1.7-1.8 ?m, and D97=2.2-2.4 ?m.

7. The preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 3, wherein particle size distribution after the ball milling in step (2) is D50=0.3-0.4 ?m, D90=0.7-0.8 ?m, and D97=1.2-1.5 ?m.

8. The preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramic with non-stoichiometric Nb.sup.5+ according to claim 3, wherein during the polarization in step (5), polarization voltage is gradually increased from a low voltage to a predetermined polarization voltage, polarization field strength is 3-4 kV/mm, and voltage holding time is 10-15 minutes.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows X-ray diffraction (XRD) patterns of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(2) FIG. 2 is an enlarged view of FIG. 1;

(3) FIG. 3 shows scanning electron microscope (SEM) photographs of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(4) FIG. 4 shows piezoelectric force microscope (PFM) images of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+, and a scanning area is 4?4 ?m;

(5) FIG. 5 shows d.sub.33 and T.sub.C of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(6) FIG. 6 shows k.sub.p and tan? of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(7) FIG. 7 shows high-temperature dielectric-temperature curves of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(8) FIG. 8 shows low-temperature dielectric-temperature curves of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(9) FIG. 9 shows ferroelectric hysteresis loops of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+;

(10) FIG. 10 shows the in-situ temperature stability of d.sub.33 of potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with different contents of Nb.sup.5+, and an illustration shows the relationship between ?d.sub.33/d.sub.33RT and temperature.

DETAILED DESCRIPTION

(11) The present invention is further described in detail below. It should be noted that detailed implementation modes and specific operation procedures are given by the embodiments on the premise of the present invention, but the present invention is not limited to the embodiments.

Embodiment 1

(12) A preparation method for the potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with non-stoichiometric Nb.sup.5+, comprising the following steps:

(13) (1) Preparing the Potassium Sodium Bismuth Niobate Tantalate Zirconate Ferrite Ceramic Powder by a Traditional Solid Phase Method

(14) Weighing and proportioning raw materials respectively according to the general formulas: (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.59001Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=?0.01, numbered as 1.sup.#), (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.59958Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.00, numbered as 2.sup.#), (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.90915Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.01, numbered as 3.sup.#), (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.91872Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.02, numbered as 4.sup.#), (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.92829Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.03, numbered as 5.sup.#), and (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.93786Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.04, numbered as 6.sup.#), placing the raw materials in a polyurethane ball milling pot (powder:zirconium balls=1:2-3), using absolute ethyl alcohol as a dispersion medium (powder:absolute ethyl alcohol=1:2-3), placing the raw materials in a planetary ball mill and conducting ball milling for 15-20 hours (the rotational speed is 250-320 r/min), placing the uniformly mixed slurry in a stainless steel basin, baking the slurry under a drying lamp for 2-3 hours, putting the dried powder into a crucible, raising the temperature in a programmed temperature control box furnace to 900? C., and pre-sintering the dried powder for 6 hours to obtained preformed powders of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958s+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3.

(15) (2) Secondary Ball Milling

(16) Placing the preformed powders of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 in a polyurethane ball milling pot and conducting secondary ball milling (powder:zirconium balls=1:2-3), using absolute ethyl alcohol as a dispersion medium (powder:solvent=1:2-3), placing in a planetary ball mill and conducting ball milling for 15-20 hours (the rotational speed is 250-320 r/min), and baking the slurry under a drying lamp for 2-3 hours to obtained a ceramic powder. As tested by a laser particle size analyzer, the particle size distribution after the ball milling is D50=0.3-0.4 ?m, D90=0.7-0.8 ?m, and D97=1.2-1.5 ?m.

(17) (3) Granulating and Molding

(18) Fully mixing the dried ceramic powder with an 8 wt % PVA binder, conducting granulating to form uniformly distributed particles, and pressing the particles into preformed ceramic green pellets of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.9958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 with a diameter of 10 mm and a thickness of 1 mm under a uniaxial pressure of 10-15 MPa.

(19) (4) Binder Removal and Sintering

(20) Removing binder of the preformed ceramic green pellets of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 at a temperature of 520? C., and sintering the ceramic green pellets at a temperature of 1100? C. for 4 hours to prepare sintered ceramic pellets of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3.

(21) (5) Silvering and Polarization

(22) Brushing the sintered ceramic pellets of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 obtained after the sintering with a silver paste with a concentration of 10 wt %, and sintering the ceramic pellets again at 750? C. for 12 minutes to prepare a sample. After silver sintering, baking the ceramic pellets in a furnace at about 340? C. for about 30 minutes to make preparation for polarization. Conducting polarization in an oil bath at a temperature of 100? C. The polarization voltage is gradually increased from a low voltage to a predetermined polarization voltage, the polarization field strength is 3 kV/mm, and the voltage holding time is 12 minutes to prepare piezoelectric ceramics of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3.

Embodiment 2

(23) The electrical properties of the piezoelectric ceramics of 1.sup.#, 2.sup.#, 3.sup.#, 4.sup.#, 5.sup.#, and 6.sup.# (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 prepared in embodiment 1 are tested and characterized.

(24) After standing at room temperature (25? C.) in an environment with a humidity of 45%-65% RH for 24 hours, various electrical parameters (such as k.sub.p, d.sub.33, ?.sub.r, and tan?) of the sample are measured by relevant instruments, wherein the test frequency of the dielectric constant and the dielectric loss is 1 kHz. It should be noted that the above test methods are commonly used in the art and will not be repeated herein.

(25) (1) XRD Characterization

(26) FIG. 1 depicts the phase structure and phase purity of the six kinds of (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics, wherein the XRD patterns thereof show that the synthesized KNN-based ceramics have a single perovskite structure, and an excessive amount of Nb.sup.5+ can enter KNN lattices to form a solid solution. As shown in FIG. 2, to further characterize the phase structure evolution of the ceramics with the increase of Nb.sup.5+ content, the split peak changes with the increase of Nb.sup.5+ content.

(27) (2) SEM Characterization

(28) FIG. 3 shows SEM micrographs of polished and heat-etched (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics and shows the random orientations of densely packed cuboid grains. The surface topography of the ceramics shows that large grains are surrounded by small ones, which is the result of abnormal growth, and thereby results in a high bulk density. Non-stoichiometric Nb.sup.5+ with a proper content can greatly improve the densification and grain growth of the (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.59958+0.957xTa.sub.0.5742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics, but an excessive amount of Nb.sup.5+ is not conducive to the formation of a dense structure.

(29) (3) PFM Characterization

(30) FIG. 4 shows that the nanoscale domains and lamellar domain structure of non-stoichiometric (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.90915Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics (x=0.01) exhibit a more dense and uniform distribution than that of ceramics with the stoichiometric (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics (x=0). Such results indicate that Nb.sup.5+ with a proper content occupying the B-site can refine the size of polar nanoregions and increase the compactability of the ceramics.

(31) (4) Electrical Property Characterizations

(32) FIG. 5 shows d.sub.33 and T.sub.C of the (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics at different x contents. The d.sub.33 initially increased followed by a gradual decrease, reaching the maximum value of 450 pC/N at x=0.01. When the addition amount of Nb.sup.5+ is stoichiometric, the d.sub.33 value is 380 pC/N. Although the d.sub.33 value of 450 pC/N can usually be achieved in KNN-based ceramics, it is rarely reported that such a large d.sub.33 value is achieved at high T.sub.C, which indicates that the ceramics prepared by the present invention has a high stability at a high temperature.

(33) FIG. 6 shows that k.sub.p also exhibits an evolutionary trend similar to that of d.sub.33, and reaches the peak value of 0.516 at x=0.01. The tan? values decrease first, then increase gradually, and reach the minimum value of 0.024 at x=0.01.

(34) FIG. 7 shows the variation of ?.sub.r with temperature for (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics from room temperature to 500? C. As the measured temperature rises, the sample exhibits a significant phase transition from a ferroelectric tetragonal phase to a paraelectric cubic phase at T.sub.C. Interestingly, the T.sub.C values keep unchanged basically with the addition of Nb.sup.5+.

(35) Considering that the peak of relative dielectric constant observed at about 60? C. is related to an R-T phase transition, the temperature change observed at this peak indicates the structural transformation of the potassium sodium bismuth niobate tantalate zirconate ferrite ceramics after the addition of Nb.sup.5+. FIG. 8 depicts the relationship between the T.sub.R-T value and the Nb.sup.5+ content of the ceramics. When x<0.01, T.sub.R-T decreases with the increase of the Nb.sup.5+ content, which can be attributed to the decrease in the values of tolerance factor. However, when x>0.01, T.sub.R-T shows an opposite trend with the further increase of x, which is related to the formation of defect dipoles.

(36) FIG. 9 shows that the (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics has typical P-E loops, which indicates that all samples are ferroelectric. With the increase of Nb.sup.5+ concentration from ?0.01 to 0.02, the remanent polarization (P.sub.r) value of the ceramics first increases and then decreases, whereas the P.sub.r values of the (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.03 and 0.04) ceramics increase abnormally, which can be attributed to the increase of a leakage current. The leakage current in the (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.89958+0.957xTa.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 (x=0.03 and 0.04) ceramics may be caused by non-stoichiometry induced mobile charged defects.

(37) FIG. 10 shows that the introduction of non-stoichiometric Nb.sup.5+ leads to the presence of the defect dipoles, and thereby controlling the domain wall pinning effect. Stabilizing domain structure and reducing domain wall mobility may also be conducive to the temperature stability of the d.sub.33 value.

(38) Therefore, in the potassium sodium bismuth niobate tantalate zirconate ferrite ceramics with non-stoichiometric Nb.sup.5+ and the preparation method therefor of the present invention using the above structure, B-site is occupied by an excessive amount of Nb.sup.5+, which significantly affects the microstructure, dielectric properties, ferroelectric properties and piezoelectric properties of the piezoelectric ceramics. In addition, an excessive amount of Nb.sup.5+ doping improves the temperature stability of the ceramics by providing a domain wall pinning effect. The Curie temperature T.sub.C=300? C., the dielectric loss tan?=0.024, the electromechanical coupling factor k.sub.p=0.516, the piezoelectric constant d.sub.33=450 pC/N and the dielectric constant ?.sub.r=1644 can be simultaneously obtained in (K.sub.0.45936Na.sub.0.51764Bi.sub.0.023)(Nb.sub.0.90915Ta.sub.0.05742Zr.sub.0.04Fe.sub.0.003)O.sub.3 ceramics, which makes the potassium sodium bismuth niobate tantalate zirconate ferrite ceramics have a broad application prospect, including in sensors, actuators, and other electronic devices.

(39) Finally, it should be noted that the above embodiments are only used for describing, rather than limiting the technical solution of the present invention. Although the present invention is described in detail concerning the preferred embodiments, those ordinary skilled in the art shall understand that the technical solution of the present invention can still be amended or equivalently replaced. However, these amendments or equivalent replacements shall not enable the amended technical solution to depart from the spirit and the scope of the technical solution of the present invention.