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Full-Text Articles in Physical Sciences and Mathematics
Jahn-Teller Distortions, Cation Ordering And Octahedral Tilting In Perovskites, Michael W. Lufaso, Patrick M. Woodward
Jahn-Teller Distortions, Cation Ordering And Octahedral Tilting In Perovskites, Michael W. Lufaso, Patrick M. Woodward
Michael W. Lufaso
In transition metal oxides, preferential occupation of specific d orbitals on the transition metal ion can lead to the development of a long-range ordered pattern of occupied orbitals. This phenomenon, referred to as orbital ordering, is usually observed indirectly from the cooperative Jahn-Teller distortions (CJTDs) that result as a consequence of the orbital ordering. This paper examines the interplay between orbital ordering, octahedral tilting and cation ordering in perovskites. Both ternary AMX3 perovskites containing an active Jahn-Teller (J-T) ion on the octahedral site and quaternary A2MM'X6 perovskites containing a J-T ion on one-half of the octahedral sites have been examined. …
Structure Determination Of A2m3+Tao6 And A2m3+Nbo6 Ordered Perovskites: Octahedral Tilting And Pseudosymmetry, Paris W. Barnes, Michael W. Lufaso, Patrick M. Woodward
Structure Determination Of A2m3+Tao6 And A2m3+Nbo6 Ordered Perovskites: Octahedral Tilting And Pseudosymmetry, Paris W. Barnes, Michael W. Lufaso, Patrick M. Woodward
Michael W. Lufaso
The room-temperature crystal structures of six A2M3+M5+O6 ordered perovskites have been determined from neutron and X-ray powder diffraction data. Ba2YNbO6 adopts the aristotype high-symmetry cubic structure (space group Fm3̄m, Z = 4). The symmetries of the remaining five compounds were lowered by octahedral tilting distortions. Out-of-phase rotations of the octahedra about the c axis were observed in Sr2CrTaO6 and Sr2GaTaO6, which lowers the symmetry to tetragonal (space group = I4/m, Z = 2, Glazer tilt system = a0a0c-). Octahedral tilting analogous to that seen in GdFeO3 occurs in Sr2ScNbO6, Ca2AlNbO6 and Ca2CrTaO6, which lowers the symmetry to monoclinic (space group …
Structure Prediction Of Ordered And Disordered Multiple Octahedral Cation Perovskites Using Spuds, Michael W. Lufaso, Paris W. Barnes, Patrick M. Woodward
Structure Prediction Of Ordered And Disordered Multiple Octahedral Cation Perovskites Using Spuds, Michael W. Lufaso, Paris W. Barnes, Patrick M. Woodward
Michael W. Lufaso
The software package SPuDS has previously been shown to accurately predict crystal structures of AMX3 and A1 - xA'xMX3 perovskites that have undergone octahedral tilting distortions. This paper describes the extension of this technique and its accuracy for A2MM'X6 ordered double perovskites with the aristotype Fm3̄m cubic structure, as well as those that have undergone octahedral tilting distortions. A survey of the literature shows that roughly 70% of all ordered double perovskites undergo octahedral tilting distortions. Of the 11 distinct types of octahedral tilting that can occur in ordered perovskites, five tilt systems account for ~97% of the reported structures. …