Introduction

Characterization is an essential part of all investigations in solid state chemistry and materials science. The various aspects of characterization are: (i) chemical composition and compositional homogeneity of the specimen, (ii) impurities that may affect the properties, (iii) structure, revealing the crystallinity or otherwise of the specimen, crystal system, unit cell and where possible (or necessary) atomic coordinates, bonding and ultrastructure and (iv) the nature and concentration of imperfections (defects) influencing properties. While it may not be possible to achieve complete characterization of a given solid by a single investigator or at any given time, yet without a minimum level of characterization no investigation can be initiated or completed. The scope of ‘characterization’ is so vast that nearly all aspects of solid state chemistry can be included under its domain. According to the US Materials Advisory Board Committee, ‘characterization describes those features of the composition and structure (including defects) of a material that are significant for a particular preparation, study of properties or use, and suffice for reproduction of the material’. The subject of characterization has been reviewed sufficiently in the literature (Cheetham & Day, 1987; Meinke, 1973; Newnham & Roy, 1973; Honig & Rao, 1981; West, 1985) and we shall therefore recount the main essentials and highlight some of the recent developments. The advances made in the last few years in characterization techniques, especially in structure elucidation, have been truly remarkable and have opened new vistas in solid state chemistry.