Instability of oxygen vacancy ordering at the metal-insulator transition in the iron-doped TbBaCo2O5.5 layered perovskite

The TbBaCo1.92Fe0.08O5+δ layered perovskite, exhibiting a metal-insulator phase transition at TMI∼ 340 K, has been investigated by the Moessbauer spectroscopy method. It was found that the Fe3+ ions have two different positions in the low-temperature insulator phase (at T<TMI) and predominantly one position in the high-temperature metallic region above TMI. X-ray diffraction experiments have revealed an orthorhombic-to-tetragonal crystal structure transformation taking place at TMI. These results have been interpreted as favouring an oxygen vacancy order-disorder transition that occurs simultaneously with the metal-insulator one. (author)