Intermediate phases in [111]- and [001]-oriented PbMg1/3Nb2/3O3–29PbTiO3 single crystals

Resumo

Phase transformations in [111]- and [001]-oriented PbMg_1/3Nb_2/3O₃–29PbTiO₃ single crystals have been studied using dielectric and optical measurements before and after applying an electric field. It is shown that the subsequence of phase transitions rhombohedral (R)—tetragonal (T)—cubic (C) phases is observed in nonpolarized samples of both orientations as temperature increases. In the [111]-oriented crystal, an additional intermediate monoclinic phase (it is possible, M_a) is induced after preliminary polarization at room temperature and the R–M_a–T–C phase transitions are observed on heating. In the [001]-oriented crystal, after its polarization, the monoclinic phase forms instead of the rhombohedral phase even at room temperature and the M_a–T–C transitions occur on heating. The results are discussed from the point of view of the existence polar nanoregions with different local symmetries in a glasslike matrix.