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The structural properties of pyrochlore Eu2Zr2O7under high pressure have been studied by using Raman spectroscopy andin situangle-dispersive X-ray diffraction (ADXRD). The results of Raman spectra indicate that Eu2Zr2O7undergoes a reversible structural change around 21.2 GPa. The results of Rietveld refinements fromin situADXRD data indicate that the ordered pyrochlore structure (Fd-3m) transforms to the defect-cotunnite structure (Pnma) at 26.5 GPa. The phase transition is irreversible and the transformation process is mainly induced by the accumulations of anti-site defects of the cation sublattice and Frenkel defects on the anion sublattice. Besides, the bonds should play a more important role than the bonds in the process of the phase transformation. [ABSTRACT FROM AUTHOR]

Polycrystalline BiCuSeO oxides are prepared by solid-state reaction followed by pressureless sintering (PLS) and high pressure sintering (HPS) methods. Both the experimental results and the density functional theory calculations indicate that the crystal defect concentrations of BiCuSeO can be reduced under the effect of high pressure. By comparing with the PLS sample, a larger power factor and a lower thermal conductivity can be obtained for the HPS sample. The maximum figure of merit ZT∼0.4 @ 800 K was obtained for the HPS sample, which is about 3 times higher than the PLS sample. These results indicate that the effect of high pressure is beneficial to modifying the microstructure and improving the thermoelectric performance of BiCuSeO oxyselenide. [ABSTRACT FROM AUTHOR]