Role of lead in lead phosphomolybdate glasses and a model of structural units

Selvaraja, U. ; Rao, K. J. (1988) Role of lead in lead phosphomolybdate glasses and a model of structural units Journal of Non-Crystalline Solids, 104 (2-3). pp. 300-315. ISSN 0022-3093

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PbO---MoO3---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 IR spectra have been investigated. Variation of Mo5+ concentration as a function of PbO concentration has also been studied using ESR spectroscopy. A structural model is presented to rationalize the experimental observations. According to this model, binary phosphomolybdate glasses are built up of [MoO6/2] octahedral and [POO3/2 tetrahedral units which share corner Further, PbO plays a dual strutural role, both as a network former and as a network modifier. This aspect is discussed in the light of various experimental results. When PbO enters into the network modifier, itis assuuned to be present as four coordinated tetrahedral [PbO4/2]2- units again with share corber. This is accompanied by the simulataneous conversion of [POO3/2] into [PO4/2]+ units which thereby achieves charge neutrality in the system. When PbO acts as a network modifier, glasses are characterized by the presence of a number of polyhedral structural units carrying a net charge, while lead remains in the structure as Pb2+ ions. The composition dependent structural changes are represented using a structural phase diagram.

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ID Code:43763
Deposited On:16 Jun 2011 05:47
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