Polymorphism and crystal data of the rare-earth disilicates of type R.E.2Si2O7

TLDR: In this article, the properties of 14 rare-earth disilicate compounds are described by means of single-crystal and powder X-ray data, and the thermal stability areas of the 7 observed structure types at normal pressure, and transition characteristics of the polymorphs are discussed in terms of structural aspects.

Abstract: The polymorphism of 14 rare-earth disilicate compounds, in the temperature range 900 °–1800 °C, is described by means of single-crystal and powder X-ray data. The thermal stability areas of the 7 observed structure types at normal pressure, and the transition characteristics of the polymorphs are discussed in terms of structural aspects. A description of the rare-earth-oxygen coordination polyhedra and of the [Si 2 O 7 ] 6− configurations are given approximately by isostructural relations to other disilicate or diphosphate compounds. Complete crystal data and cell dimensions for 30 polymorphic forms, and d -spacings of one representative of each structure type, are provided.