The temperature dependence of heat capacity of Bi 4 Ti 3 O 12 has been measured for the first time in the range from 7 to 346 K by precision adiabatic vacuum calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity, enthalpy H o (T) -H o (0), entropy S o (T) -S o (0), and Gibbs function G o (T) -H o (0), in the range from T ? 0 to 346 K. The structure of Bi 4 Ti 3 O 12 is refined by the Rietveld method (space group Fmmm, Z = 4) at temperatures of 173, 273, 373, 473 K. Thermal deformation model is proposed on the basis of structural data.

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In the present work, we report results of high-pressure Raman scattering spectroscopy, on the ionic conducting system KNbTeO 6 , as well as lattice dynamics calculations for this compound. From lattice dynamics calculation, we were able to do a definite assignment of modes for this system taking into account the disorder caused by random K occupation and shared occupation of Nb and Te ions. On the basis of the theoretical results, we discuss the changes observed in the high-pressure Raman spectra. We report a transformation occurring around 4.7 GPa, attributed it to a structural phase transition. The Raman spectra during the decompression process reveals that all changes undergone by the structure are reversible, and the Raman spectrum recovers its original signature.