Ferroelectric domains and phase evolution in (Fe:) KTa1−xNbxO3 crystals

The domain structures and phase evolution in mixed ferroelectric (Fe): KTa1−xNbxO3 (KTN) crystals were investigated. Temperature dependent Raman spectra show that Curie temperatures of KTN and Fe: KTN are far below room temperature, but the ferroelectric domain switching was still visualized by scanning probe microscopy at room temperature. These observed domains origin from the nano-regions near the grain boundaries. In addition, the intrinsic domains (triangle for KTN and straight line/stripe for Fe: KTN) could only be observed at low temperature by transmission electron microscopy. Three phase transitions in Fe: KTN crystals were found by Raman spectroscopy and dielectric testing: 175 K for Rhombohedral-to-Orthorhombic (R-O), 210 K for Orthorhombic-to-Tetragonal (O-T) and 250 K for Tetragonal-to-Cubic (T-C), which is consistent with the domain behavior.