Analysis of extended inorganic structures

Extended (polymeric) inorganic structures present different problems to crystallographers than molecular structures. The samples are often tiny crystals, atomic scattering powers vary widely, and structures are frequently disordered or twinned, strongly absorbing, or prone to temperature-induced phase transitions. Pseudo-symmetry is also a frequent problem. Disorder includes atomic substitution on a single site and partial occupancy by atoms of variable valency; some forms of disorder lead to diffuse scattering. Phase transitions may cause incommensurate structures to form. Extended...

Extended (polymeric) inorganic structures present different problems to crystallographers than molecular structures. The samples are often tiny crystals, atomic scattering powers vary widely, and structures are frequently disordered or twinned, strongly absorbing, or prone to temperature-induced phase transitions. Pseudo-symmetry is also a frequent problem. Disorder includes atomic substitution on a single site and partial occupancy by atoms of variable valency; some forms of disorder lead to diffuse scattering. Phase transitions may cause incommensurate structures to form. Extended structures require different approaches to testing and validation; these include bond valence calculations. This chapter illustrates the issues with two detailed case histories of mixed oxide materials.