負の熱膨張を有するZr_<1-x>Hf_xV_2O_7固溶体の相転移

概要

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The phase transition of Zr_<1-x>Hf_xV_2O_7 (x=0-1) solid solutions substituted for Zr (IV) sites was investigated using X-ray diffraction, TMA and DSC methods. X-ray diffraction experiments revealed that all compositions of Zr_<1-x>Hf_xV_2O_7 (x=0-1) were of a single phase having a cubic structure. Lattice parameters of Zr_<1-x>Hf_xV_2O_7 (x=0-1) at room temperature decreased linearly with increasing Hf content, due to the smaller ionic radius of the Hf (IV) ion than that of the Zr (IV) ion. Abrupt positive thermal expansions in TMA were observed for all samples at two phase transition temperatures in the vicinity of T_1=350K and T_2=375K, and negative thermal expansions were seen above about 380K. DSC measurements clearly showed that all of the Zr_<1-x>Hf_xV_2O_7 (x=0-1) samples also underwent two successive phase transitions between 330 and 390K. Two transition temperatures and phase transition enthalpies of Zr_<1-x>Hf_xV_2O_7 (x=0-1) samples decreased with the increase of x content, reflecting the decrease of superlattice structure. The sum of transition entropy for successive two phase transitions increased with increasing the normalized relative intensity of the superlattice line at room temperature.
社団法人日本セラミックス協会の論文
2006-07-01