First-principles study of the negative thermal expansion of PbTiO3

Abstract

By using first-principles calculation and quasi-harmonic approximation method, we have systematically investigated the thermal expansion properties of tetragonal phase of PbTiO3, focusing on the correlation between the A1(TO) mode and negative thermal expansion (NTE). It is found that volume of the unit cell shows positive thermal expansion in a axis direction, and NTE in c axis direction from 0K to 900K. It is also found that the A1(TO) mode is softening when the volume shrinks by the phonon calculation. Calculating of Grüneisen parameters show that the A1(TO) mode makes a main contribution to the NTE, and this vibrational mode is the Pb, Ti and O atoms’ relative motion in c axis direction, which lead to a shrink of the unit cell in this direction. Our calculations clarify the correlation between the phonon mode and NTE of PbTiO3 in c axis direction at the atomic level, and provide an important theoretical basis for further understanding of the mechanism of the NTE.