Reactive Templated Grain Growth Method Research Articles

Ultrahigh electrostrain with excellent fatigue resistance in textured Nb 5+-doped (Bi 0.5Na 0.5)TiO 3-based piezoceramics

(Bi_0.5Na_0.5)TiO₃ (BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain (electrostrain) properties, but often suffer from large hysteresis and poor fatigue resistance, which strongly limit their applications. Here, &lt;00<i>l</i>&gt; textured Nb⁵⁺-doped 0.8(Bi_0.5Na_0.5)TiO₃–0.2(Bi_0.5K_0.5)TiO₃ (0.8BNT–0.2BKT) ceramics with a high degree of texturing (~80%) were prepared by the reactive template grain growth (RTGG) method using Bi₄Ti₃O₁₂ as a template. By the combination of donor doping in the B-site and the RTGG method, the electrostrain performance achieves a significant enhancement. A high electrostrain of 0.65% and a piezoelectric coefficient (<inline-formula> <math display="inline" id="MA1"><mrow><msubsup><mi>d</mi><mrow><mn>33</mn></mrow><mo>*</mo></msubsup></mrow></math></inline-formula>) of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained. No electrostrain performance degradation is observed after unipolar electric field loading of 10⁵ cycles, showing excellent fatigue endurance. These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

Microstructure and enhanced seebeck coefficient of textured Sr3Ti2O7 ceramics prepared by RTGG method

Textured Sr3Ti2O7 ceramics (abbreviated as S3T) with grain orientation degree higher than 0.7 were successfully prepared by reactive-templated grain growth (RTGG) technique combined with tape casting process, using plate-like Sr3Ti2O7 particles as templates. The phase transition, microstructure and thermoelectric properties were investigated. As the sintering temperature and soaking time increase, the density and texture fraction of ceramics increase. Textured Sr3Ti2O7 ceramics were sintered in air and annealed in argon + graphene carbon (Ar+C) atmosphere. The results showed that the resistivity of textured Sr3Ti2O7 ceramics annealed in Ar+C environment decreased significantly (seven orders of magnitude). After the annealing process, the texture fraction decreased, and Sr3Ti2O7 phase on the surface of textured ceramics decomposed to SrTiO3. The Seebeck coefficient was negative, and the absolute value of S increased with increasing temperature. Textured Sr3Ti2O7 ceramics showed the maximum Seebeck coefficient (−399μV/K) at 1073K, which is higher than those of non-textured Sr3Ti2O7-based materials.

Fabrication of textured CoFe2O4 ceramics by a novel RTGG method using rod-like α-FeOOH particles as templates

A textured CoFe2O4 ceramic was fabricated by reactive template grain growth (RTGG) method using rod-like α-FeOOH particles as templates. The template particles were synthesized by hydrothermal method, the particles showed good crystallization and rod-like shape with a diameter of 0.1–0.2 μm and an aspect ratio of 20–50. {ll0} oriented CoFe2O4 ceramic was obtained after a sintering process. The ceramic sintered at 1150 °C for 4 h showed dense and oriented structure with orientation degree of 0.89. Different magnetic hysteresis loops were observed along the in-plane and out-of-plane direction of the textured CoFe2O4, which was due to anisotropy properties of the sample. The textured ceramic exhibited an in-plane Ms enhancement (355 emu/cm3) compared to that of the non-textured ceramics (320 emu/cm3) in the same sintering conditions.

Fabrication, dielectric, and thermoelectric properties of textured SrTiO3 ceramics prepared by RTGG method

Textured SrTiO3 ceramics with extensive [100] orientation were fabricated with the reactive templated grain growth (RTGG) method, using tabular Sr3Ti2O7 (abbreviated as S3T) particles as the templates. The microstructure and texture development of the samples sintered in different atmospheres were investigated along with their electrical properties. The X-ray diffraction (XRD) pattern suggested that the ceramics were all single phase and had a relatively high Lotgering factor (f=0.9). Electron back-scatter diffraction (EBSD) results showed that the textured ceramics exhibited {100} preferred orientation. The samples sintered in air exhibited anisotropic dielectric properties. The green body was sintered in nitrogen and then annealed in a reducing atmosphere (nitrogen and graphite) to test its thermoelectric properties. The minimum thermal conductivity was 2.1Wm−1K−1 at 1073K, which is lower than that of non-textured SrTiO3-based thermoelectric materials that have been reported. The Seebeck coefficients were negative, and the value increased as the temperature and texture fraction increased. The Seebeck coefficients were much higher than those of non-textured SrTiO3-based materials. The maximum value was −328μV/K at 1073K, which amounts to ~76% of the value for a SrTiO3 single crystal.

Fabrication of [100]-oriented bismuth sodium titanate ceramics with small grain size and high density for piezoelectric materials

Abstract A layered titanate H1.07Ti1.73O4·nH2O (HTO) with a plate-like particle morphology was used as a template for the fabrication of [1 0 0]-oriented bismuth sodium titanate (Na0.5Bi0.5TiO3, or BNT) ceramics by a reactive-templated grain growth (RTGG) method. The oriented BNT ceramic with a high degree of orientation (95%), high density (98%), and small grain size (2 μm) was fabricated for the first time by the RTGG method using a HTO-TiO2-Bi2O3-Na2CO3 reaction system. The oriented BNT ceramic is formed by a topotactic transformation reaction of plate-like HTO template particles to plate-like BNT mesocrystal particles, and then epitaxial crystal growth of BNT on the BNT mesocrystal particles. The epitaxial crystal growth reaction is affected by TiO2/HTO mole ratio, chemical component of the starting material, and calcination temperature program. The fabricated oriented BNT ceramic shows a higher d33* value than the non-oriented BNT ceramic, suggesting the promising application to high performance Pb-free piezoelectric materials.

Fabrication and Thermoelectric Properties of Al-Doped (ZnO)&lt;sub&gt;5&lt;/sub&gt;In&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; by Microwave Heating

Various (ZnO)5In2O3ceramics were fabricated by microwave heating. Density, XRD pattern and microstructure were examined and those of Al-doped (ZnO)5In2O3were almost the same as Al-free one. Highly textured (ZnO)5In2O3ceramic was also fabricated by reactive templated grain growth (RTGG) method. The electrical conductivity was not improved by Al-doping; however it was improved slightly by microwave heating compared with conventional heating and especially improved by texturing using RTGG method. On the other hand, the absolute Seebeck coefficient in microwave heating was improved about 25% by Al-doped. Maximum electric power factor of textured specimen fabricated by RTGG method along ab-plane showed 5.76×10-4WK-2m-1(at 873K), which was attributed to high electrical conductivity.

Fabrication and Piezoelectric Properties of Textured (Bi1/2K1/2)TiO3 Ferroelectric Ceramics

Textured (Bi1/2K1/2)TiO3 (BKT) ceramics were prepared by a reactive templated grain growth (RTGG) method to improve their piezoelectric properties. Also, a hot-pressing (HP) method was modified on the basis of RTGG method to obtain dense ceramics and promote the grain orientation. The textured BKT ceramics prepared by the RTGG and HP methods exhibited a relatively high orientation factor F of 0.82 and a high density ratio of 95–99%. Scanning electron microscopy (SEM) micrographs of the textured HP-BKT indicated a textured and poreless microstructure. In addition, the resistivity of the textured HP-BKT was 1.73×1013 Ω·cm. The piezoelectric strain constant d33 determined by means of resonance and antiresonance method was 125 pC/N for the direction parallel to the sheet-stacking direction of the RTGG process. From the measurement of field-induced stain, the normalized d33* (=Smax/Emax) at 80 kV/cm were 127 and 238 pm/V on the randomly oriented and textured samples (F=0.82) for the (∥) direction, respectively.

Fabrication and Microstructure of Grain-Oriented (Bi&lt;sub&gt;1/2&lt;/sub&gt;K&lt;sub&gt;1/2&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt; Ceramics

Grain-oriented (Bi1/2K1/2)TiO3 (BKT) ceramics were prepared by the reactive templated grain growth (RTGG) method, and a hot-pressing (HP) method was modified on the basis of the RTGG method to obtain dense ceramics. The BKT ceramic sintered at 1060°C showed a single-phase perovskite structure. The grain-oriented BKT prepared by the HP method exhibited a relatively high orientation factor F of 0.82 and a high density ratio of 99%. SEM micrographs of the HP-grain-oriented BKT indicated a textured and poreless microstructure. On the basis of the density ratio of 87% for the grain-oriented BKT without HP, the HP method was considered very effective for improving the density ratio even for the RTGG sample. In addition, the resistivity of the HP-grain-oriented BKT was 1.73 x 1013 •cm.

Preparation and Characterization of High Textured KSr&lt;sub&gt;2&lt;/sub&gt;Nb&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;15&lt;/sub&gt; Lead-Free Piezoelectric Ceramics

Anisometric KSr2Nb5O15 (KSN) particles were synthesized by molten salt method with SrCO3, Nb2O5 and KCl as raw materials. With K2CO3, SrCO3 and Nb2O5 starting materials, KSN lead-free piezoelectric ceramics were prepared by conventional ceramics technique and reactive templated grain growth (RTGG) method, respectively. In the RTGG process, green compacts were fabricated by tapecasting using anisometric KSN as template particles. The KSN particles prepared by molten salt method were rodlike in shape and dense. The KSN ceramics prepared by RTGG not only had higher degree of grain orientation but higher sintered density compared with that prepared by solid-state reaction.

Reactive Templated Grain Growth법에 의해 제조된 (Bi0.5Na0.5)TiO3-BaTiO3세라믹스의 압전 특성

Crystallographically {h00}-oriented <TEX>$0.94(Bi_{0.5}Na_{0.5})TiO_{3}-0.06BaTiO_{3}$</TEX> (0.94BNT-0.06BT) ceramics was prepared by the Reactive Templated Grain Growth (RTGG) method using the <TEX>$Bi_{4}Ti_{3}O_{12}$</TEX> template. The sheets prepared by tape-casting of slurries containing the templates and starting materials are cut, laminated, and pressed. Then burn-out and sintering was conducted. Also, to compare with the 0.94BNT-0.06BT ceramics prepared by the RTGG method another 0.94BNT-0.06BT ceramics was prepared by the solid-state method. In the optimum of this experiments range, the degree of orientation of the 0.94BNT-0.06BT ceramics prepared by the RTGG method was texture fraction<TEX>${\approx}92%$</TEX> and the piezoelectric constant(<TEX>$d_{33}$</TEX>) and coupling factor(<TEX>$k_{p}$</TEX>) was obtained to <TEX>$d_{33}{\approx}205{\;}pC/N$</TEX>, <TEX>$k_{p}{\approx}0.33%$</TEX>, respectively.

Effect of Potassium Concentration on the Grain Orientation in Bismuth Sodium Potassium Titanate

Bi0.5(Na1‐xKx)0.5TiO3 (BNKT) bulk ceramics with a preferred &lt;100&gt; orientation were prepared using the reactive templated grain‐growth method with platelike Bi4Ti3O12 particles as templates for BNKT. The potassium concentration (x value) had a large effect on the degree of orientation, and highly oriented ceramics were obtained for the specimens with x= 0.10 and x= 0.15, whereas the specimen with x= 0.00 had a small degree of orientation. Increased potassium concentration from x= 0.00 to x= 0.15 decreased the grain‐growth rate and changed the grain shape from irregular to cubic. These factors were responsible for the increased degree of orientation.