First-Principles Study on Novel Lead-free Piezoelectric Materials

In this study, we investigated systematically on perovskite oxides ABO(3) through first-principles calculations based on density functional theory to find novel biocompatible lead-free piezoelectric materials. Biocompatible elements were picked out with HSAB ( Hard Soft Acids and Bases ) principle at the viewpoint of interaction energy with in-vivo molecules and they were applied to A and B of perovskite oxides ABO(3). The stable combinations of constituent elements were specified with consideration for geometric and electric equilibrium condition. Then the stable cubic structure and the phonon properties were analyzed for the paraelectric non-polar phase. The soft modes, which induce a structural phase transition to non-centrosymmetric crystal structures, were distinguished with the phonon eigenfrequency and eigenvector. Additionally, insulation properties were estimated from band structure. As a result, five perovskite oxides, MgSiO3, MnSiO3, FeSiO3, ZnSiO3 and CaSiO3, were discovered as probable materials, which have band gap and soft modes progressing into tetragonal structure of ferroelectric phases. After the stable tetragonal structures were evaluated through initial setting of atomic positions based on soft modes, their material properties such as spontaneous polarization and piezoelectric stress constant were analyzed. Computations indicated tetragonal MgSiO3 exhibits relatively-large piezoelectricity.