Part 1. Te-125 NMR study of tellurite crystals

Te-125 static and magic-angle spinning (MAS) NMR spectra of tellurite cryst als with known crystal structures have been measured to determine the isotr opic chemical shift delta(iso), the chemical shift anisotropy Delta delta a nd the asymmetry parameter eta. On the basis of structural unit, tellurite crystals are classified for convenience into TeO3 type (isolated TeO3 and t erminal TeO3 type), TeO3+1 type and TeO4 type (alpha-TeO2 and beta-TeO2 typ e). As a result, the following relations were found: TeO3 greater than or e qual to TeO3+1 approximate to beta-TeO2 > alpha-TeO2 in delta(iso(MAS)), be ta-TeO2 greater than or equal to alpha-TeO2 > TeO3+1 > terminal TeO3 greate r than or equal to isolated TeO3 in \Delta delta\ and TeO4 greater than or equal to TeO3+1 greater than or equal to TeO3 in eta. It was also found tha t the combination of \Delta delta\ and eta, namely, the relative values of delta(1), delta(2) and delta(3), can elucidate the local structure around T e atoms more definitely than delta(iso). This diagram is useful for examini ng the structures of tellurite crystals and glasses. (Glasses are discussed in another paper.) (C) 1999 Elsevier Science B.V. All rights reserved.