Characterization studies of potassium phosphotungstate glasses and a model of structural units

Abstract

K₂O–WO₃–P₂O₅ glasses have been studied over a wide range of compositions. Their physical, thermal and spectroscopic properties, such as density, molar volume, microhardness, heat capacity, glass transition temperature and infrared special changes has been investigated. A structural model is presented to rationalize the experimental observations. According to this model, binary phosphotungstate glasses are built up of [WO_6/2] octahedral and [POO_3/2] tetrahedral units which share corners. Addition of K₂O to binary phosphotungstates breaks the various linkages present in them. Consequently, a number of structural units are formed and the resulting glasses may be characterized by a network of polyhedra with different numbers of unshared corners. These structural units are consolidated into a structural phase diagram. The colours of these glasses, due to the presence of W⁵⁺ ions and their stabilization in the network as [W⁵⁺O_6/2]^– and [PO_4/2]⁺ structural pairs, are also discussed.