Siyuan Zhang

Facile sonochemical synthesis of CePO4 : Tb/LaPO4 core/shell nanorods with highly improved photoluminescent properties

A simple, efficient and quick method has been established for the synthesis of CePO(4):Tb nanorods and CePO(4):Tb/LaPO(4) core/shell nanorods via ultrasound irradiation of inorganic salt aqueous solution under ambient conditions for 2xa0h. The as-prepared products were characterized by means of powder x-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra and lifetimes. TEM micrographs show that all of the as-prepared cerium phosphate products have rod-like shape, and have a relatively high degree of crystallinity and uniformity. HRTEM micrographs and SAED results prove that these nanorods are single crystalline in nature. The emission intensity and lifetime of the CePO(4):Tb/LaPO(4) core/shell nanorods increased significantly with respect to those of CePO(4):Tb core nanorods under the same conditions. A substantial reduction in reaction time as well as reaction temperature is observed compared with the hydrothermal process.

Mössbauer spectroscopy and chemical bonds in BaFe12O19 hexaferrite

Barium hexaferrite was synthesized by chemical co-precipitation. Its Mossbauer spectra were obtained. A semi-empirical model, based on the Phillips theory of bonding, has been developed for quantitative explanation of the Mossbauer isomer shifts of Fe ions in BaFe12O19 crystals. The results show that, using the relationship between isomer shifts and covalency, the site assignments in hexaferrites will be resolved easily. This paper provides a powerful tool for studying other members of the hexagonal ferrimagnetic oxides family.

Investigation of thermal expansion and compressibility of rare-earth orthovanadates using a dielectric chemical bond method

The chemical bond properties, lattice energies, linear expansion coefficients, and mechanical properties of ReVO 4 (Re = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y) are investigated systematically by the dielectric chemical bond theory. The calculated results show that the covalencies of Re-O bonds are increasing slightly from La to Lu and that the covalencies of V-O bonds in crystals are decreasing slightly from La to Lu. The linear expansion coefficients decrease progressively from LaVO 4 to LuVO 4; on the contrary, the bulk moduli increase progressively. Our calculated results are in good agreement with some experimental values for linear expansion coefficients and bulk moduli.

Bonding Characteristics, Thermal Expansibility, and Compressibility of RXO4 (R = Rare Earths, X = P, As) within Monazite and Zircon Structures

Systematically theoretical research was performed on the monazite- and zircon-structure RXO(4) (R = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; X = P, As) series by using the chemical bond theory of dielectric description. The chemical bond properties of R-O and X-O bonds were presented. In the zircon phase, the covalency fractions of X-O bonds increased in the order of V-O < As-O < P-O, which was in accordance with the ionic radii and electronegative trends, and the covalency fractions of R-O bonds varied slightly due to the lanthanide contraction. While in the monazite phase, both R-O and X-O bonds were divided into two groups by their covalency fractions. The contributions from the bond to the lattice energy, linear thermal expansion coefficient (LTEC), and bulk modulus were explored. The X-O bonds with short bond lengths and high chemical valence made greater contributions to the lattice energy and performed nearly rigidly during the deformation. A regular variation of lattice energy, LTEC, and bulk modulus with the ionic radii of the lanthanides was observed in both monazite and zircon phases.

Estimation thermal expansion coefficient from lattice energy for inorganic crystals

By using the study of the lattice energy and the structural parameters of binary inorganic crystals, a new parameter reflecting the thermal expansion property has been found, the relation between the linear expansion coefficient and new parameter has been established. A semiempirical method for evaluation of linear expansion coefficient from the lattice energy is presented, and developed to the complex crystals. The estimated values of the linear expansion coefficients of both simple and complex crystals are in good agreement with the experimental values.

Chemical bond properties and Mössbauer spectroscopy in REBa2Cu3O7 (RE = Eu, Y)

Abstract By using the chemical bond theory of complex crystals, the chemical bond properties of REBa2Cu3O7 (RE=Eu, Y) were calculated. The calculated covalencies for Cu(1)–O and Cu(2)–O bond in REBa2Cu3O7 compounds are 0.41 and 0.28 respectively. Mossbauer isomer shifts of 57 Fe doped, and 119 Sn doped in REBa2Cu3O7−x were calculated by using the chemical environmental factor, he, defined by covalency and electronic polarizability. Four valence state tin ion and iron ion sites were identified in 57 Fe and 119 Sn doped REBa2Cu3O7−x superconductors.

Investigation of Chemical Bond Characteristics, Thermal Expansion Coefficients and Bulk Moduli of alpha-R2MoO6 and R2Mo2O7 (R = rare earths) by Using a Dielectric Chemical Bond Method

Theoretical researches are performed on the α‐R2MoO6 (R = Y, Gd, Tb Dy, Ho, Er, Tm and Yb) and pyrochlore‐type R2Mo2O7 (R = Y, Nd, Sm, Gd, Tb and Dy) rare earth molybdates by using chemical bond theory of dielectric description. The chemical bonding characteristics and their relationship with thermal expansion property and compressibility are explored. The calculated values of linear thermal expansion coefficient (LTEC) and bulk modulus agree well with the available experimental values. The calculations reveal that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the lanthanides: the LTEC decreases from 6.80 to 6.62 10−6/K and the bulk modulus increases from 141 to 154 GPa when R goes in the order Gd, Tb Dy, Ho, Er, Tm, and Yb in the α‐R2MoO6 series; while in the R2Mo2O7 series, the LTEC ranges from 6.80 to 6.61 10−6/K and the bulk modulus ranges from 147 to 163 GPa when R varies in the order Nd, Sm, Gd, Tb and Dy.