Xi'an Fan

Large spontaneous polarization in polar perovskites of PbTiO3–Bi(Zn1/2Ti1/2)O3

PbTiO3–Bi(Zn1/2Ti1/2)O3 is considered to be a promising high-ferroelectric performance material in the Pb/Bi-based perovskite family. In the present study, a whole set of (1 − x)PbTiO3–xBi(Zn1/2Ti1/2)O3 (0 ≤ x ≤ 1) solid solutions have been prepared by the conventional solid-state and high-pressure vs. high-temperature methods. The effect of Bi(Zn1/2Ti1/2)O3 on the crystal structure has been investigated by synchrotron X-ray powder diffraction. Unlike most PbTiO3-based perovskites, the present system exhibits a continuously enhanced tetragonality (c/a) and large spontaneous polarization (PS) properties. The enhanced c/a is ascribed to the large spontaneous polarization displacements induced by the strong Pb/Bi–O hybridization and coupling interactions between Ti/Zn and Pb/Bi cations, which can be evidenced from the lattice dynamics study and first-principles calculations. Accordingly, the TC (i.e., x = 0.5) is expected to be approximately 1000 °C if its perovskite structure can be stabilized. The present study provides a route to obtain large-PS in PbTiO3-based ferroelectric materials by introducing isostructural perovskites with strong polarity.

Effect of Ba and Pb dual doping on the thermoelectric properties of BiCuSeO ceramics

Besides the thermoelectric properties, mechanically robust is also very important for applications in TEGs. Up to now, no studies have been reported to investigate the mechanical properties of BiCuSeO oxyselenides. In this work, the results of hardness test of pristine and Ba/Pb doped BiCuSeO are presented here. These data may help to further evaluate the mechanical properties of BiCuSeO based ceramics.

Microstructure and Properties of Fe-6.5wt%Si Alloys Cores with Core-Shell Structures Prepared by Mechanical Alloying and Spark Plasma Sintering Methods

In this work, the Fe-6.5wt%Si alloy cores with core-shell structures were prepared by Mechanical Alloying and Spark Plasma Sintering methods. The microstructure and magnetic properties of the samples were investigated with differential scanning calorimetry, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results show that the synthesis of the Fe-6.5wt%Si powder with core-shell structures can be completion during mechanical alloying process. And the coreshell structure, Fe-6.5wt%Si as core and SiO2 as shell, apparently exists in the sinter cores. The relative densities of sintered cores would ascend with increasing the sintering temperature. The Ms offered upgrade tendency with increasing the sintering temperature, while the Hc curves evolve with almost opposite phases. For the core sintered at 1050 °C, the following magnetic data were observed: Ms = 167.84 emu/g, Mr = 2.26 emu/g, Hc = 11.77 Oe, ρ = 2 μΩm and P15/400 = 2.47 W/kg.

Preparation and Microstructure Control of One-Dimension Core-Shell Heterostructure of Te/Bi, Te/Bi2Te3 by Microwave Assisted Chemical Synthesis

Microstructure engineering of thermoelectric materials can resolve the conflicts of electrical and thermal transports. Especially, one-dimensional structure can obviously improve the thermoelectric figure of merit because of its crystal anisotropy and strong quantum confinement effect. In this paper, the Te nanowires, one-dimensional core-shell heterostructure of Te/Bi and Te/Bi2Te3 were controlled synthesized by microwave assisted chemical synthesis. The effect of PVP concentration and reductant dropping rate on the microstructure of the Te nanowires were investigated. The experimental results showed that with increasing the amount of PVP, the Te nanowires got less crystallinity and its surface become more rough due to its steric hindrance effect. With decreasing reductant dropping rate, the longer and thiner Te nanowires were obtained. Epitaxial growth can describe the relation of core Te and shell Bi (or Bi2Te3). It has been found that Bi shell uniformly surrounded around Te nanowires core, but Bi2Te3 sheets were perpendicular to the c-axis of Te nanowires. The different core-shell heterostructure structure can be obtained by adjusting reaction conditions and controlling diffusion kinetics of Te and Bi.