Phase evolution and dielectric/ferroelectric properties of KTa0.67Nb0.33O3 single crystal

High quality KTa0.67Nb0.33O3 (KTN) single crystal has been grown by the Czochralski method. Three phase transitions Rhombohedral-to-Orthorhombic (R–O), Orthorhombic-to-Tetragonal (O–T) and Tetragonal-to-Cubic (T–C) were observed using temperature-dependent Raman spectra, thermal expansion, and dielectric measurements. The phase transition temperatures determined by the Raman spectra are close to those determined by thermal expansion, i.e., R–O at 175 K, O–T at 210 K, and T–C at 250 K. While dielectric measurements showed that the R–O, O–T, and T–C phase transitions occur at 192, 223, and 265 K, respectively. The dielectric properties of KTN obeys the Curie–Weiss law (T0=260 K) above 265 K. At 77 K, typical polarization–electric (P–E) hysteresis loops were observed, and the largest remnant polarization is 15 μC/cm2.