第一原理計算によるペロブスカイト型非酸化物 ABX<font size="-1">3</font> (X = F, Cl, S) の構造・機能評価

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This study is concerned with the systematic investigation on crystal structures and material properties of perovskite nonoxides ABX<font size="-1">3</font> to discover novel lead-free piezoelectric materials. Biocompatible elements were applied to A and B, meanwhile halogen elements (F and Cl) and chalcogen element (S) were introduced into X. Firstly the combinations of constituent elements were specified with consideration for geometric and electric equilibrium conditions. Then the stable cubic structure was evaluated through first-principles calculations based on the pseudo-potential, linear augmented plane-wave method within the local density approximation (LDA). Next the band structure was estimated to differentiate conductors and insulators and the phonon were analyzed to identify the soft mode, which induce a structural phase transition to non-centrosymmetric crystal structures, according to the eigenfrequency and eigenvector. Focusing on perovskite nonoxides with tetragonal structure, we compared their spontaneous polarization and piezoelectric stress constant and discussed the possibility for the advent of novel piezoelectric materials.