The composition dependence of the transformation temperature, melting temperature, and thermal expansion of glasses prepared from melting MoO3 with P2O5 in open crucibles, is described. A purpose built apparatus was employed to allow the use of samples of sizes suitable for a number of other physical property measurements, especially ultrasonic analysis. By comparison with the results of ultrasonic measurements presented elsewhere, the data are explained largely in terms of the relative amounts of P2O5, MoO3, and meta-ortho- and pyro-phosphate groupings in the glasses, and the relative sizes of the atomic rings characteristic of each of these groupings, assuming a 3-dimensional network. However a layer network is required to explain the low values of transformation temperature in the MoO3 rich glasses. No dramatic variations in anharmonic effects or in ratios of bending to stretching force constants are needed to explain the expansion data, even though the composition dependence of the latter is rather striking.
