Meso- To nano-scopic domain structures in high Curie-temperature piezoelectric BiScO₃-PbTiO₃single crystals of complex perovskite structure

Bismuth scandate-lead titanate (BS-PT) solid solution is of great interest as a promising piezoelectric material for high-temperature electromechanical applications due to its excellent comprehensive electric performance and high Curie temperature. However, the full understanding of the ferro-/piezo-electric properties of BS-PT has been strongly hindered by the lack of detailed investigation of microscopic domain structures and successful growth of high-quality crystals. In this work, detailed structural and meso-/nano-scopic domain studies of the BS-PT crystals near the morphotropic phase boundary have been carried out by various characterization techniques. The multi-scale domain structures in the 〈001〉_cub-cut 0.324BS-0.676PT single crystals were investigated by a unique combination of temperature-variable birefringence imaging microscopy and piezoresponse force microscopy, in conjunction with high-resolution X-ray diffraction in the temperature range of 30-500 °C. The crystal was found to exhibit tetragonal symmetry on average at room temperature and showed a transformation to cubic symmetry around 460 °C. Complex domain structures with small domain sizes (2-6 μm) and a high density of domain walls were imaged and analyzed from meso- to nano-scopic scale, and more interestingly, local crystal distortion was found in the vicinity of the dense domain walls. The domain evolution as a function of temperature and the correlation between the domain structure and the dielectric properties have been studied. These studies of domains, symmetries and phase transitions provide a better understanding of the structure of BS-PT crystals and other related ferro-/piezo-electric single crystals on multiple length scales, and help design novel high-T_C, high performance ferro-/piezo-electric materials.