Temperature-induced phase transitions in BaTbO3

The crystal structures of BaTbO3 have been investigated over a wide temperature range between 40 and 773 K using high-resolution time-of-flight neutron powder diffraction. Two-phase transitions were observed. Below about 280 K, BaTbO3 adopts an orthorhombic perovskite structure (space group Ibmm), which is characterized by rotation of TbO6 octahedra about the pseudocubic two-fold axis. Above 280 K, BaTbO3 undergoes a first-order phase transition to a tetragonal symmetry (space group 141/mcm), in which the tilting of the octahedra is around the pseudocubic four-fold axis. As the temperature is further increased, BaTbO3 adopts the primitive cubic aristotype at about 623 K. This later phase transformation is characterized by a gradual decrease of the rotation angle, indicating a continuous phase transition, which is described by a critical exponent beta = 0.35. (C) 2004 Published by Elsevier Inc.