Structure Relations of Hexagonal Perovskite-Like Compounds ABX3at High Pressure

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Abstract
Phase stability relations among four hexagonal perovskite-like structures as well as the cubic perovskite structure have been studied for several oxides (BaMnO 3 and SrMnO 3 ) and fluorides (CsMnF 3 , RbNiF 3 and TlNiF 3 ) at high pressure. A series of high pressure transformations are found to occur in the order of the packing sequence along the hexagonal c axis (or cubic 111 axis) of ( a b ), ( a b a b c b c a c ), ( a b a c ), ( a b c a c b ) and ( a b c ) with increasing pressure. This order is corresponding with the increasing order of the proportion of the cubic close-packed layers in the hexagonal close-packed structure. It is suggested that the tolerance factor of the perovskite structure and the Coulomb repulsive force play an important role in determining the crystal structure and its order in the series of phase transformations at high pressure.