Neutron Powder Diffraction Study of the Phase Transition in BaTi₂O₅

Abstract

The structural phase transition and crystal structure of BaTi ₂ O ₅ sol-gel powder have been studied by neutron powder diffraction. The crystal structure of BaTi ₂ O ₅ at high-temperature phase has symmetry with the space group of C2/m from an extinction rule and a disappearance of spontaneous polarization. Lattice parameters are a = 17.0040(4) Å, b = 3.9455(1) Å, c = 9.5236(2) Å, β = 102.941(2)° and V = 662.706(23) Å ³ at 900 K. There are two kinds of Ba (Ba1 and Ba2) and three kinds of TiO ₆ octahedra (Ti1O ₆ , Ti2O ₆ and Ti3O ₆ ), and the unit cell has six BaTi ₂ O ₅ molecules, Z = 6. All atoms are situated on the mirror planes with y coordinates of 0 of 1/2. The high-to-low temperature phase transition will be characterized by the atomic displacement of Ti and other oxygen atoms like a Slater mode, in Ti1O ₆ octahedron.

Keywords:

• BaTi₂O₅
• crystal structure
• structural phase transition
• neutron powder diffraction

Acknowledgment

The present work was partly supported by the collaborative research project of Materials and Structures Laboratory, Tokyo Institute of Technology, and by a Grant-in-Aid for Scientific Research from Electric Technology Research Foundation of Chugoku. This work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland.