Raman spectroscopy study of ferroelectric modes in [001]-oriented 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 single crystals

This work investigates the evolution of micro-Raman spectra of a [001]-oriented 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 single crystal in the temperature range from −120 to 200 °C. For a poled sample, the T1u mode splits into an E mode (remaining at 51cm−1) and a new A1 mode (shifting to 95cm−1 at −120°C) at the tetragonal to rhombohedral phase transition (Tc∼70°C), while other modes remain the same. This A1 mode belongs to the rhombohedral phase. If the sample is depoled, this A1 mode persists for temperatures much above Tc on heating, implying that local regions with rhombohedral symmetry still exist in the tetragonal phase. The underdevelopment of long-range order in the depoled crystal causes the sample to have typical characteristics of a relaxor while poling will enhance the long-range order to make it into a regular ferroelectric.