Collective Rotations in Oxides
نویسندگان
چکیده
The tendency of oxygen atoms to form just two bonds with a bond angle smaller than 180 allows the appearance of low energy atomic motions related to internal rotational degrees of freedom which, in a first approximation, involve neither bending nor stretching of bonds (“rigid unit modes” in silicates, “floppy modes” in glasses). A huge variety of compounds exhibit the oxygenbridge X-O-X basic unit, X being a linking atom. Among the many silicates, β-cristobalite (a silica polymorph) shows these internal rotations most clearly. The perovskites are also interesting candidate materials, especially the CuO2 planes of the high Tc superconducting materials.
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