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Ab initio calculations of the atomic and electronic structure of layered Ba0.5Sr0.5TiO3 structures

2005; Elsevier BV; Volume: 118; Issue: 1-3 Linguagem: Inglês

10.1016/j.mseb.2004.12.012

1873-4944

Sergei Piskunov, E. A. Kotomin, David Fuks, Simon Dorfman,

Magnetic and transport properties of perovskites and related materials

Abstract Understanding of the atomic and electronic structure of Ba c Sr 1 − c TiO 3 (BST) solid solutions is important for several applications including the non-volatile ferroelectric memories (dynamic random access memory, DRAM). We present results of ab initio calculations of several spatial arrangements of Ba 0.5 Sr 0.5 TiO 3 solid solutions based on DFT-HF B3PW hybrid method. We calculate the atomic and electronic structure, the effective charges, interatomic bond populations, the electronic density distribution, and densities of states for three layered structures with the same composition. The suggested method reproduces experimental lattice parameters of both pure BaTiO 3 and SrTiO 3 . The calculated optical band gaps for the pure SrTiO 3 and BaTiO 3 are in a good agreement with experimental data, much better than those from the standard LDA or HF calculations. In the studied BST structures with the equiatomic composition ( c = 0.5) the gap is reduced by ca. 0.2 eV. The electron density maps demonstrate the covalency effects in the Ti–O bonding. The electron density near the Sr atoms is stronger localized, as compared with the Ba ions.