On the role of intrinsic disorder in the structural phase transition of magnetoelectric EuTiO3

Up to now the crystallographic structure of the magnetoelectric perovskite EuTiO3 was considered to remain cubic down to low temperature. Here we present high resolution synchrotron X-ray powder diffraction data showing the existence of a structural phase transition, from cubic Pm-3m to tetragonal I4/mcm, involving TiO6 octahedra tilting, in analogy to the case of SrTiO3. The temperature evolution of the tilting angle indicates a second-order phase transition with an estimated Tc=235K. This critical temperature is well below the recent anomaly reported by specific heat measurement at TA\sim282K. By performing atomic pair distribution function analysis on diffraction data we provide evidence of a mismatch between the local (short-range) and the average crystallographic structures in this material. Below the estimated Tc, the average model symmetry is fully compatible with the local environment distortion but the former is characterized by a reduced value of the tilting angle compared to the latter. At T=240K data show the presence of local octahedra tilting identical to the low temperature one, while the average crystallographic structure remains cubic. On this basis, we propose intrinsic lattice disorder to be of fundamental importance in the understanding of EuTiO3 properties.Comment: 13 pages, 8 figures, 2 table

A study on the metal-insulator transition in perovskite-type titanates

報告番号: 乙13540 ; 学位授与年月日: 1997-09-22 ; 学位の種別: 論文博士 ; 学位の種類: 博士(理学) ; 学位記番号: 第13540号 ; 研究科・専攻: 理学系研究

ペロブスカイト型チタン酸化物の金属-絶縁体転移の研究

University of Tokyo (東京大学