Yuntao Liu

Structure and lattice dynamics in PbTiO3–Bi(Zn1/2Ti1/2)O3 solid solutions

(1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 solid solutions show a much enhanced tetragonality (c/a) and Curie temperature (TC). The detailed structure of (1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 is studied by means of neutron powder diffraction based on the Rietveld refinement. Zn exhibits a more polarizable property than Ti, resulting in a B-site cation splitting (0.27 A) between Zn and Ti along c-axis direction. The spontaneous polarization displacements are enhanced by the substitution of Bi(Zn1/2Ti1/2)O3. The lattice dynamics study of (1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 by Raman scattering spectroscopy reveals that the optical modes [A1 (1TO), A1 (2TO), and E (2TO)] are abnormally hardened by the substitution of Bi(Zn1/2Ti1/2)O3 for PbTiO3, indicating the enhanced PS and the strong hybridization between Pb/Bi and O. The ceramic of (1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 (x=0.3) exhibits a low dielectric loss (tan δ) due to the d0 electronic structure.

Neutron diffraction studies of structure and increasing splitting of LO-TO phonons in Pb1−xCdxTiO3

Pb1−xCdxTiO3 (0.0⩽x⩽0.08) compounds in the tetragonal phase were prepared by the solid state reaction. Neutron powder diffraction study revealed that Pb1−xCdxTiO3 exhibits an unusual structural property. Although the tetragonality (c∕a) is enhanced by Cd substitution for Pb, the cation displacement of spontaneous polarization unexpectedly decreases, which is associated with the reduced Curie temperature. The increasing of the LO-TO splitting in Pb1−xCdxTiO3 shows an anomalous behavior in comparison with other previously studied PbTiO3-based systems. It was interestingly found that a similarity exists in the behavior of the solubility dependence of the LO-TO splitting and the negative thermal expansion (NTE) in the PbTiO3-based systems, which suggests that Pb–O hybridization plays an important role in NTE mechanism of PbTiO3.

Thermal expansion properties of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (Ln = Er and Y)

Structures and thermal expansion properties of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (Ln = Er and Y) have been investigated by X-ray powder diffraction. Rietveld analysis results of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} indicate that compounds Er{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (0 {<=} x {<=} 0.3) and Y{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (0 {<=} x {<=} 0.2) crystallize in orthorhombic structure and exhibit negative thermal expansion, while both monoclinic and orthorhombic compounds Er{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (1.7 {<=} x {<=} 2.0) and Y{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (1.8 {<=} x {<=} 2.0) possess positive coefficient of thermal expansion. The coefficients of linear thermal expansion of orthorhombic Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} change from negative to positive with increasing chromium content. Thermogravimetric and differential scanning calorimetry have been used to study the hygroscopicity and the phase transition temperature.