Advances in First-Principles Studies of Transducer Materials

We have used first-principles linear response calculations and molecular dynamics to study the relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-x PT). First-principles calculations for ordered PMN show a low-symmetry monoclinic ground state. A new set of phase transitions to lower symmetry rhombohedral and monoclinic structures is predicted for PT at high pressures, showing predicted piezoelectric response as high as is seen in the giant coupling relaxor ferroelectrics. We have developed a transferable shell-model potential for PMN-x PT by fitting to first-principles data. The potential qualitatively reproduces the compositional phase diagram for PMN-x PT. A new exchange-correlation potential, which gives excellent predictions for ferroelectric materials, is discussed.