Room-Temperature Nonlinear Dielectric Constants and DielectricTunability in Poled Pb(Mg_1/3Nb_2/3) O₃-PbTiO₃ Single Crystals

The room-temperature second-, third- and fourth-order nonlinear dielectric constants of poled (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ single crystals were determined by measuring the dielectric response at a frequency of 10 kHz and under a dc bias of 0-1000 V/mm. Tunability of the apparent dielectric constant ε_r was also defined and examined. The results show the phase structure, domain state, composition and orientation dependences of the dielectric nonlinearity and tunability. It is also shown that the <011>-poled monodomain orthorhombic ferroelectric 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ single crystal has the largest nonlinear dielectric constants and the highest tunability of ε_r in the monodomain crystals. It could be a most promising candidate for applications where a high dielectric nonlinearity is needed.