Thermal stability and phase transformation of barium orthotitanate (Ba2TiO4)

Barium orthotitanate (Ba2TiO4) was prepared by heating at 1250 degrees C for 2h. The thermal stability of Ba2TiO4 and the phase transformation between the low-temperature monoclinic polymorph (-Ba2TiO4) and the high-temperature orthorhombic polymorph (-Ba2TiO4) were examined by X-ray diffraction. Ba2TiO4 can be corroded by CO2 below 700 degrees C forming BaCO3 and BaTiO3, which is reversible above 750 degrees C. A martensitic transformation from -Ba2TiO4 to -Ba2TiO4 starts at approximate to 100 degrees C and ends at approximate to 220 degrees C in heating process. The transformation hysteresis loop is approximate to 200 degrees C. -Ba2TiO4 can be stabilized to room temperature by doping small amount of aliovalent ion Nd3+ (1.5 mole%) or relatively large amount of isovalent ion Sr2+ (10 mole%). After annealing the doped samples at low temperatures (e.g., below 1100 degrees C), for the Nd-doped sample, -Ba2TiO4 can be partially transformed to -Ba2TiO4, whereas the Sr-doped sample is stably kept as -Ba2TiO4.