Nanotwin and phase transformation in tetragonal Pb(Fe1/2Nb1/2)1-xTixO3 single crystal.

This work is a study of phase transformation in (001)-cut Pb(Fe_1/2Nb_1/2)_1-xTi_xO₃ (x=48%) single crystals by means of dielectric permittivity, domain structure, and in situ x-ray diffraction. A first-order T(T_NT)-C(T_NT) phase transition was observed at the Curie temperature T_C≅518 K upon zero-field heating. T, T_NT, and C are tetragonal, tetragonal nanotwin, and cubic phases, respectively. T(T_NT) and C(T_NT) indicate that minor T_NT domains reside in the T and C matrices. Nanotwins, which can cause broad diffraction peak, remain above T_C≅518 K and give an average microscopic cubic symmetry in the polarizing microscopy. Colossal dielectric permittivity (>10⁴) was observed above room temperature with strong frequency dispersion. This study suggests that nanotwins can play an important role in relaxor ferroelectric crystals while phase transition takes place. The Fe ion is a potential candidate as a B-site dopant for enhancing dielectric permittivity. [ABSTRACT FROM AUTHOR]