The cubic-to-rhombohedral phase transition of Pb(Zn_1/3Nb_2/3)O₃: a high-resolution x-ray diffraction study on single crystals

The cubic-to-rhombohedral (C–R) phase transition of the ferroelectric relaxor Pb(Zn_1/3Nb_2/3O₃) is investigated by means of a high-resolution x-ray diffraction study on single crystals. The phase transition is diffuse and spreads over the temperature range T_CR = 385 ± 5 K to T_R = 325 ± 5 K. Below T_CR, the cubic phase transforms progressively into rhombohedral domains whose average size, about 60–70 nm in the [111] direction, remains unchanged as temperature is lowered, so no growth of the R-domains is observed. At T_R, the nanometric R-domains fully pave the crystal but structural mismatches between adjacent domains generate stresses, which increase as temperature is lowered. The anomalous broadening of diffraction peaks of the R-phase, which originates from size and strain effects, can be suppressed by applying a dc electric field, along the [111] direction, which transforms the polydomain state into a rhombohedral quasi-monodomain state.