First-Principles Study of Structural Trend of BiMO3 and BaMO3: Relationship between Tetragonal or Rhombohedral Structure and the Tolerance Factors

The relationship between a tetragonal or rhombohedral structure and the tolerance factors in BiMO3 and BaMO3 has been investigated using a first-principles calculation with optimized structures. BiMO3 and BaMO3, which consist of M ions with d(0)-state transition metals (TMs) or non-Ms, were optimized within frameworks of P4mm (tetragonal) and R3m (rhombohedral) structures, and their total energies (E-tetra and E-rhombo, respectively) were compared. In BiMO3, except for BiGaO3, the total energy difference Delta E (= E-rhombo -E-tetra) as a function of the tolerance factor t increases monotonically and smoothly, and the critical value from negative to positive in Delta E is about 1.00. In BiGaO3 with d(10)-state Ga ions, the tetragonal structure is more stable despite t < 1.00. This result is due to the strong Coulomb repulsion between Ga 3s, 3p, and 3d states and O 2p states, which is consistent with tetragonal BiZn0.5Ti0.5O3 recently reported. In BaMO3, on the other hand, the dependence of Delta E is more complicated, that is, positive, zero [i.e., cubic (Pm<(3)over bar>m)], negative, and positive, as t increases. The trend of the above calculated results is consistent with that of experimantal results, and can be a principal guideline for material design. The above crystal structures of AMO(3) (A = or Ba) are found to be closely related to the contribution of A ions to the local electric fields at M ions by the analysis of Lorentz corrections. (C) 2010 The Japan Society of Applied Physics