Tao Qiang

Dielectric Properties of Eu-Doped CaCu 3 Ti 4 O 12 with Different Compensation Mechanisms

To get a better understanding of the influence of rare-earth element doping, CaCu3Ti4O12 (CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction. All the ceramics were single phase, while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO. Ca0.875Eu0.1Cu3Ti4O12 (CECT1) exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO, while Ca0.85Eu0.1Cu3Ti4O12 (CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance. The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects. The variation of permittivity is related to the localization of carriers, which, according to the XPS results, should be caused by the presence of oxygen vacancies. The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu+ and Cu2+, which is an important source of the polarization in grain boundaries.

High-pressure Raman study of MgV2O6 synthesized at high pressure and high temperature

A new structural phase of MgV2O6 was obtained by a high-pressure, high-temperature (HPHT) synthesis method. The new phase was investigated by the Rietveld analysis of X-ray powder diffraction data, showing space group Pbcn (No. 60) symmetry and a = 13.6113(6) A (1 A = 0.1 nm), b = 5.5809(1) A, c = 4.8566(3) A, V = 368.93(2) A3 (Z = 4). High pressure behavior was studied by Raman spectroscopy at room temperature. Under 22.5 GPa, there was no sign of a structural phase transition in the spectra, demonstrating stability of the HPHT phase up to the highest pressure.