Intrinsic piezoelectric response in perovskite alloys: PMN-PT versus PZT

First-principles supercell calculations and the modem theory of polarizatio n are used to compute the e(33) piezoelectric coefficients of Pb(Zr0.5Ti0.5 O3) (PZT) and 0.60 Pb(Mg1/3Nb2/3)O-3 + 0.40 PbTiO3 (PMN-PT) alloys. A drast ic enhancement by a factor of 2.7 is found for e(33) when going from PZT to PMN-PT. The huge value of e(33) in PMN-PT comes from the large response of the internal coordinates of Pb, Ti, Nb, and O atoms to a macroscopic strai n. On the other hand, the Mg atoms contribute little to the piezoelectricit y for dielectric and elastic reasons.