A new three-dimensional incommensurately modulated cubic phase (in ZrP2B7) and its symmetry characterization via temperature-dependent electron diffraction

摘要

A detailed electron diffraction study has been made of the ZrP2O7 member of the AM(2)O(7) family of framework structures and of its temperature-dependent structural phase transformations. The room-temperature phase corresponds to a primitive 3 x 3 x 3 superstructure phase of probable space group symmetry Pa3. An observed glide extinction condition when viewed down < 001 > ages could, however, also be compatible with resultant Pbca space group symmetry. The high-temperature phase corresponds to the normal unmodulated parent structure. An intervening intermediate phase that exists over a relatively narrow temperature window (similar to 5-10 degreesC) around 294 degreesC is shown to be a three-dimensional incommensurately modulated cubic phase characterized by incommensurate primary modulation wave vectors in the close vicinity of 0.31 < 100 >* and probable superspace group symmetry P: Pa (3) over bar: Ia (3) over bar. (C) 2001 Academic Press. [References: 18]