Thermal and electric field induced phase transitions of Na0.5Bi0.5TiO3 single crystals

The phase transitions of unpoled and poled Na0.5Bi0.5TiO3 (NBT) single crystals were studied using structural, hysteresis loops, polarizing-microscope, dielectric, mechanical (the first measurement), thermal expansion strain and calorimetric measurements. It was found that phase transitions in NBT are first-order and clearly demonstrate ferroelastic aspects. Both rhombohedral-tetragonal and tetragonal-cubic transformations are accompanied by a softening of mechanical properties like in improper ferroelastic transitions. It was concluded that the difference in the internal friction between unpoled/poled states and between [001]c/[111]c poled states can be associated with a difference in the density of mobile ferroelastic twin walls in these states.