Polarization rotation mechanism for ultrahigh electromechanical response in single-crystal piezoelectrics

Piezoelectric materials, which convert mechanical to electrical energy(and vice versa), are crucial in medical imaging, telecommunication and ultrason ic devices(1,2). A new generation of single-crystal materials(3), such as P b(Zn1/3Nb2/3) O-3-PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O-3-PbTiO3 (PMN-PT), ex hibit a piezoelectric effect that is ten times larger than conventional cer amics, and may revolutionize(4) these applications. However, the mechanism underlying the ultrahigh performance of these new materials-and consequentl y the possibilities for further improvements-are not at present clear. Here we report a first-principles study of the ferroelectric perovskite, BaTiO3 , which is similar(5) to single-crystal PZN-PT but is a simpler system to a nalyse. We show that a large piezoelectric response can be driven by polari zation rotation induced by an external electric field; Out computations sug gest how to design materials with better performance, and may stimulate fur ther interest in the fundamental theory of dielectric systems in finite ele ctric fields.