Changrong Zhou

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.

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.

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%.

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)。

Effects of Sintering Temperature on Structure and Properties of 0.997(KNN-LS-BF)-0.003V2O5 Lead-Free Piezoelectric Ceramics

Abstract0.997(KNN-LS-BF)-0.003V2O5 lead-free piezoelectric ceramics were prepared by a traditional sintering method. The effects of sintering temperature on the structure and properties of the 0.997(KNN-LS-BF)-0.003V2O5 ceramics were studied. The results show that the sintering temperature exerts a distinct influence on the phase structure and properties. With the increase in sintering temperature from 1040°C to 1060°C, the main crystallographic phase changes from the orthorhombic symmetry to the tetragonal phase, and the optimum dielectric and piezoelectric properties of samples can be obtained when sintering at 1060°C. However, the dielectric and piezoelectric properties of the samples deteriorate when the sintering temperature exceeds 1060°C.

A new insight into structural complexity in ferroelectric ceramics

The structure of the ferroelectrics has been widely studied in order to pursuing the origin of high electromechanical responses. However, some experiments on structure of ferroelectrics have yielded different results. Here, we report that the controversial phase structure is due to the adaptive diffraction of nanodomains which hides the natural crystal structure, and the electric-field-induced phase transition is that the natural crystal structure reappears due to the coalescent nanodomains or ordering nanodomains by applying a high electric field. The temperature dependence of dielectric constant with different measurement frequencies and X-ray diffraction (XRD) patterns of unpoled, poled, and annealing after poled ceramics in Bi0.5Na0.5TiO3–BaTiO3 (BNT–BT) ceramics authenticate the statement. These results provide a new insight into the origin of structural complexity in ferroelectric ceramics, which is related to the key role of nanodomains.

Effect of Reoriented Nanodomains on Crystal Structure and Piezoelectric Properties of Polycrystalline Ferroelectric Ceramics

It has been widely accepted that electric fields induce a reversible structural phase transition and thus yield giant piezoelectric responses in ferroelectric ceramics. Based on detailed measurements of polycrystalline (Li0.5Nd0.5)2+-modified 0.95Bi0.5Na0.5TiO3-0.05BaTiO3 ceramics, we demonstrate in this study that coherent diffraction from nanodomains in ferroelectric ceramics masks the real crystal structure. The observed electric-field-induced phase transformation behavior is a consequence of relaxor-to-ferroelectric transformation caused by changes in the coherence length of the nanodomains. A driving mechanism of the structure–property relationship in which high piezoelectric properties originate from correlated ordering of nanodomains during poling is proposed.

Excellent optical, dielectric, and ferroelectric properties of Sr(In0.5Nb0.5)O3 modified K0.5Na0.5NbO3 lead-free transparent ceramics

High visible light transmittance (1 − x)(K0.5Na0.5)NbO3−xSr(In0.5Nb0.5)O3 (KNN−xSIN, x = 0.05, 0.10, 0.15, 0.20, 0.25) lead-free ceramics with excellent electrical properties were synthesized by traditional solid-state method. The effects of Sr(In0.5Nb0.5)O3 doping on the optical properties, microstructure, and electrical performance were analyzed. The results showed that light transmission in KNN−xSIN ceramics was induced by the dense and fine-grain microstructure, the high symmetry of the pseudo-cubic structure as well as typical relaxor behavior of KNN−0.25SIN ceramic. Moreover, KNN−xSIN transparent ceramics with relaxor characteristics possessed permittivity stability over a wide temperature range. Ferroelectric properties were deteriorated gradually with increasing SIN content in virtue of the strengthened relaxor behavior. Its energy storage property was also tailored by the increasing relaxor characteristic. The appearance of a non-Debye type of relaxation was detected through an impedance Cole–Cole plots.