E-field induced phase transition in 〈001〉-oriented rhombohedral 0.92Pb(Zn_1/3Nb_2/3)O₃-0.08PbTiO₃ crystals

E-field induced phase transformation and associated changes in dielectric/piezoelectric properties of 〈001〉-oriented rhombohedral 0.92Pb(Zn_1/3Nb_2/3)O₃-0.08PbTiO₃ crystals were investigated. The longitudinal strain level was found to abruptly increase at 20 kV/cm, corresponding to that where an induced phase appears within a multidomain matrix. Decreases in the dielectric constant (K ₃^T∼4000 to 500), transverse coupling (k ₃₁∼70% to 50%) and transverse piezoelectric coefficient (d ₃₁∼ - 1100 to -200 pC/N) associated with the induced phase were the result of increased crystal anisotropy. By contrast, the thickness coupling (k_T) increased from 53% at 0 kV/cm to 64% at 45 kV/cm, associated with this phase transition. The measured dielectric and piezoelectric properties found for the induced phase state were nearly identical to those of 〈001〉 poled tetragonal (1 - x)PZN-xPT (x>0.1) crystals. Based on these results, it is evident that the symmetry of induced phase is tetragonal, 4 mm.