Nucleation of Rhombohedral Regions Within a Tetragonal Matrix in Mn-Doped Na0.5Bi0.5TiO3 Crystals: Origins of a Diffuse Transformation, Thermal Hysteresis, and Isotropization


  • P. Davies—contributing editor

  • This work was supported by the National Science Foundation (Materials world network) DMR-0806592, by the Department of Energy under DE-FG02-07ER46480, by the Natural Science Foundation of China 50602047, and by the Shanghai Municipal Government 08JC1420500.

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Dielectric, X-ray diffraction, and domain structure evolution for Mn-doped sodium bismuth titanate (Na0.5Bi0.5TiO3) single crystals was investigated as a function of temperature. A notable thermal hysteresis was found at the tetragonal→rhombohedral transition between heating and cooling measurements for the structural and dielectric properties. Domain studies by polarized light microscopy (PLM) revealed a corresponding thermal hysteresis at an isotropization point, where the contrast in the images disappeared but reappeared both at higher and lower temperatures. The images below the isotropization point exhibited stripe-like color bands, whose contrast became more intense and whose formation temperature on cooling was increased under electric field. Studies by piezoelectric force microscopy revealed fine-scale ferroelectric domains of about 0.1–0.3 μm in size that existed within these color bands at room temperature.