X-ray diffraction studies on a $\mathrm{Pb}\left({\mathrm{Zn}}_{1∕3}{\mathrm{Nb}}_{2∕3}\right){\mathrm{O}}_3$ (PZN) single-crystal sample show the presence of two different structures. An outer layer exists in the outer most $\sim 10$ to $50\mu \mathrm{m}$ of the crystal, and undergoes a structural phase transition at the Curie temperature $T_C\approx 410\mathrm{K}$. The inside phase is, however, very different. The lattice inside the crystal maintains a cubic unit cell, while ferroelectric polarization develops below $T_C$. The lattice parameter of the cubic unit cell remains virtually a constant, i.e., much less variations compared to that of a typical relaxor ferroelectric, in a wide temperature range of 15 to $750\mathrm{K}$. On the other hand, broadening of Bragg peaks and change of Bragg profile line shapes in both longitudinal and transverse directions at $T_C$ clearly indicate a structural phase transition occurring.

• Received 24 March 2004

DOI:https://doi.org/10.1103/PhysRevB.70.064107