Abstract
We investigate the possibility of enhancing chemical order in the relaxor ferroelectric Na1/2Bi1/2TiO3 upon substitution of Na+ by other monovalent cations M+ using total energy calculations based on density functional theory. All chemically available monovalent cations M+, which are Li, Na, Ag, K, Tl, Rb and Cs, are considered and an analysis of the structurally relaxed structures in terms of symmetry-adapted distortion modes is given in order to quantify the chemically induced structural distortions. We demonstrate that the replacement of Na+ by other monovalent cations can hardly alter the tendency of chemical order with respect to Na1/2Bi1/2TiO3. Only Tl1/2Bi1/2TiO3 and Ag1/2Bi1/2TiO3 show enhanced tendency for chemical ordering. Both heavy metals behave similar to the light alkali metals in terms of structural relaxations and relative stabilities of the ordered configurations. Although a comparison of the Goldschmidt factors of components (M TiO3)− reveals for Tl a value above the upper stability limit for perovskites, the additional lone-pair effect of Tl+ stabilizes the ordered structure.
Published Version
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