A series of vibrational Raman and i.r. spectroscopic researches on inorganic glasses based on B2O3(B2O3, B2O3-xH2O, xB2O3-Na2O), As2O3(As2O3, xAs2O3-Na2O, xAs2O3-K2O) and P2O5(Na2O-P2O5, xNa2O-P2O5) is here resumed and discussed. Vitreous B2O3 has a structure containing B2O3(O)3 rings, where the boron atoms are trigonally coordinated with oxygen. The structure of As2O3 glass is mostly of the claudetitic type (formed by double indefinite chains) while the Graham salt (Na2O-P2O5) structure is of the linear polymeric type. An addition of alkaline oxide to glasses gives in the Na2O-B2O3 system an initial anomalous behaviour (boric anomaly), consisting in the transformation of the boron centers from trigonal to tetrahedral form. Subsequently a demolition of the structure with the opening of the B—O—B bonds takes place. In the case of As2O3 and Na2O-P2O5, the alkaline oxide addition allows a regular demolition of the structure, so that these glasses do not present the typical boric anomaly.
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Con il contributo del Ministero per i Beni e le Attività Culturali