Changlai Yuan

Origin of high piezoelectric activity in perovskite ferroelectric ceramics

Dense (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 (BNT-BTx%, x = 3, 5, 6, and 7) ceramics exhibit large piezoelectricity for electrical poling below coercive fields. In particular, the piezoelectric activity and permittivity frequency dispersion have been found to be closely related. The significantly increased piezoelectric constant and sharply decreased permittivity frequency dispersion are observed to occur for poled ceramics under the critical poling electrical fields. These results suggest that the high piezoelectric response stems from poling electrical fields-induced-ordered nanodomains.

Sintering behavior and refining grains of high density tin doped indium oxide targets with low tin oxide content

High density indium tin oxide (ITO) ceramic targets with low SnO2 content were prepared successfully by sintering co-precipitationally synthesized powders. The sintering behavior, properties and refining grains of the ITO targets were studied in normal pressure oxygen ambience. Higher sintering temperature promoted sintering densification, resulted in abnormal grain growth and decreased bending strength. By a two-step sintering method, the uniform and fine-grained microstructures were obtained. The sintered density of the ITO targets was further improved. Furthermore, the grain size was reduced, and the bending strength was also enhanced.

Normal-to-relaxor ferroelectric phase transition and electrical properties in Nb-modified 0.72BiFeO3-0.28BaTiO3 ceramics

Perovskite-type 0.72BiFeO3-0.28BaTi1-xNbxO3 (BF-BTNx) ceramics were fabricated via a conventional oxide-mixed method. The phase transition behaviors, composition-dependent grain size, dielectric, ferroelectric and piezoelectric properties were investigated as a function of Nb content. The temperature dependence of dielectric permittivity showed that thermally driven normal to diffuse ferroelectric transition and Nb-doping induced normal to relaxor ferroelectric transition. Simultaneously, the butterfly shape to sprout shape transition for electric-field-induced strain curves and saturation to slim P-E hysteresis loops transition were associated with the normal-to-relaxor transition. And the low hysteresis strain curves for relaxor BF-BTNx ceramics indicated that the system was a promising candidate for high precision actuation applications. In addition, XRD results revealed that Nb-doping induced a structural transition from rhombohedral phase to pseudo-cubic phase, which may be the origin of normal-to-relaxor ferroelectric phase transition.

Crystallization kinetics and temperature dependence of energy storage properties of niobate glass-ceramics

Abstract Glass-ceramic materials of strontium barium niobate system were prepared through a melt-quenching method. The effects of crystallization temperature on the microstructure, dielectric property, breakdown strength and energy storage density of barium strontium niobate glass-ceramics were studied. The crystallization mechanism of the glass-ceramics was discussed and should be one-dimensional interfacial growth. The results indicate that the breakdown strength remarkably increases with the increase of crystallization temperature. The glass-ceramic heat treated at 900 °C was found to possess optimal properties with breakdown strength of 1300 kV/cm and energy storage density of 2.8 J/cm3, which is promising dielectric materials for high energy storage density dielectrics.

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO3–xBaTiO3 [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x = 0.275 sintered at 990 °C exhibit enhanced electrical properties of d33 = 136pC/N and kp = 0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x = 0.275 is a promising lead-free high-temperature piezoelectric material.

Microstructures and microwave dielectric properties of (Ba 1− x Sr x ) 4 (Sm 0.4 Nd 0.6 ) 28/3 Ti 18 O 54 solid solutions

Abstract(Ba1−xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 (x = 0.02, 0.04, 0.06, 0.08, 0.1) solid solutions were prepared by the conventional solid-state reaction process. It was found that (Ba1−xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramics are fully composed of BaSm2Ti4O12 and BaNd2Ti5O14 phases for all the compositions. The increasing x value (0.02 ≤ x ≤ 0.1) in ((Ba1−xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramics can not only obtain high Q × f value but also effectively enhance the permittivity (εr). The (Ba1−xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramic with x = 0.08, sintered at 1440 °C for 4 h, shows excellent microwave dielectric properties of permittivity (εr) ≈ 93.19, quality factor (Q × f) ≈ 9770.14 GHz (at 3.415 GHz), and almost near-zero temperature coefficient of resonant frequency (τf) ≈ +4.56 ppm/°C.

Preparation and Properties of Sm 2 O 3 Doped (Ba 0.7 Ca 0.3 )TiO 3 -Ba(Zr 0.2 Ti 0.8 )O 3 Lead-free Piezoelectric Ceramics: Preparation and Properties of Sm 2 O 3 Doped (Ba 0.7 Ca 0.3 )TiO 3 -Ba(Zr 0.2 Ti 0.8 )O 3 Lead-free Piezoelectric Ceramics

采用固相合成法制备了Sm 2 O 3 掺杂的(Ba 0.7 Ca 0.3 )TiO 3 -Ba(Zr 0.2 Ti 0.8 )O 3 (BCZT)无铅压电陶瓷. 借助XRD、SEM等手段对该陶瓷的显微结构与电性能进行了研究. 结果表明, Sm 2 O 3 的掺杂降低了BCZT无铅压电陶瓷的烧结温度并使居里温度点 T c 从85℃提高到95℃. 当Sm 2 O 3 掺杂量为0.02wt%~0.1wt%时, 样品具有典型ABO 3 型钙钛矿结构. Sm 2 O 3 掺杂量为0.02wt%时, 所得陶瓷样品具有最优综合电性能, 其压电常数 d 33 、机电耦合系数 k p 、机械品质因子 Q m 、介电损耗tan δ 和介电常数 e r 分别为590 pC/N、0.52、43、1.3%和3372.采用固相合成法制备了Sm 2 O 3 掺杂的(Ba 0.7 Ca 0.3 )TiO 3 -Ba(Zr 0.2 Ti 0.8 )O 3 (BCZT)无铅压电陶瓷. 借助XRD、SEM等手段对该陶瓷的显微结构与电性能进行了研究. 结果表明, Sm 2 O 3 的掺杂降低了BCZT无铅压电陶瓷的烧结温度并使居里温度点 T c 从85℃提高到95℃. 当Sm 2 O 3 掺杂量为0.02wt%~0.1wt%时, 样品具有典型ABO 3 型钙钛矿结构. Sm 2 O 3 掺杂量为0.02wt%时, 所得陶瓷样品具有最优综合电性能, 其压电常数 d 33 、机电耦合系数 k p 、机械品质因子 Q m 、介电损耗tan δ 和介电常数 e r 分别为590 pC/N、0.52、43、1.3%和3372.

Enhanced energy storage properties of Bi0.5Li0.5TiO3 modified Sr0.1Bi0.45Na0.45TiO3 based ceramics

Lead-free (1−x)Sr0.1Bi0.45Na0.45TiO3−xBi0.5Li0.5TiO3 (x = 0−0.4) ceramics were successfully prepared by a solid-state reaction technique. The effects of amount of Bi0.5Li0.5TiO3 on structure and electrical properties were examined. The X-ray diffraction (XRD) analysis revealed that all the investigated specimens have a perovskite structure. An obvious change in microstructure with the increase of Bi0.5Li0.5TiO3 concentration was observed. This study demonstrated that relaxor could be stabilized in Sr0.1Bi0.45Na0.45TiO3 based ceramics by lowering the tolerance factor and electronegativity difference. Besides, a dielectric anomaly related to thermal evolution of crystallographic symmetry was emerged at the depolarization temperature. Upon incorporation of 26 mol% Bi0.5Li0.5TiO3, the specimens were able to withstand an electric field intensity of 106.9 kV/cm with an energy density of 0.88 J/cm3 and an energy efficiency of 65%.

Effects of LiF on microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics

The effects of LiF addition on sinterability, microstructure and microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics were investigated. The LiF addition enhanced the sintering temperature of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics from 1200 to 1300°C, because the LiF addition could compensate the evaporation of Li during the sintering process. It was found that the bulk density and dielectric constant ( εr) gradually decreased, the quality factor (Qf) greatly increased and the temperature coefficient of resonant frequency (τf) shifted to a near-zero value with the increase in LiF addition. Obviously, excess Li addition could efficiently improve the microwave dielectric properties. In addition, 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 + 4.0 wt% LiF ceramics sintered at 1350 ∘C for 4 h exhibited good microwave dielectric properties of εr∼123.4,Qf∼ 2209 GHz (at 2.43 GHz) and τf∼ 12.3 ppm ∘C–1.

Preparation and Magnetoelectric Coupling Effects of Ba0.85Ca0.15Zr0.1Ti0.9O3/CoFe2O4 Laminated Ceramics: Preparation and Magnetoelectric Coupling Effects of Ba0.85Ca0.15Zr0.1Ti0.9O3/CoFe2O4 Laminated Ceramics

以CoFe 2 O 4 压磁体、掺CuO和CeO 2 助烧剂的压电体Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 为基本叠层材料, 采用界面固相熔融渗透法制备了掺助烧剂Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 -CoFe 2 O 4 叠层复合陶瓷。叠层复合陶瓷的压电压磁相叠层界面结合良好。随着压磁相与压电相厚度比比率的增加, 叠层复合陶瓷的饱和磁致伸缩系数–λ从67×10 -6 增加到134×10 -6 、压电系数 d 33 从340 pC/N逐渐减小到205 pC/N; 磁电耦合系数先增大后减小, 在厚度比为2、外磁场为100 mT时得到最大值3200 mV/(cm·mT)。