Structural Change at Metal-Insulator Transition of Tb₂Ba₂Co₄O₁₁

Abstract

Temperature variation of the crystal structure has been investigated for Tb₂Ba₂Co₄O₁₁, which shows a metal-insulator (MI) transition at T_MI = 340 K. The compound has a layered-type double-perovskite structure along the c-axis, with alternating the CoO₆ octahedron and the CoO₅ pyramids along the a-axis. With decrease of temperature below T_MI, the distortion of the octahedral and pyramidal sites is fairly released, suggesting that spin state transition of the Co³⁺ ions is the origin for the MI transition.