We have identified the crystallographic phases of the melt-quenched superionic composites (AgI)(0.7)-(NaPO3)(0.3) and (AgI)(0.8)- (NaPO3)(0.2) by X-ray diffraction. Measurements were made in a temperature range from 300 to 630 K. The materials have a glass phase and one or more crystalline phases. At 300 K and at 350 K, the crystalline phase contains a 30:70 mixture of betaAgI and gammaAgI. Above 350 K, the fraction of betaAgI increases and at 403 K it is the dominant phase with beta-gamma ratio of about 70:30 (slightly less in (AgI)(0.8)-(NaPO3)(0.2)). At 453, 523 and 623 K the crystalline material is mainly alphaAgI. Crystalline 16-silver dodecaiodide diphosphate (Ag16I12P2O7) is also present between 373 and 523 K at a 5-10% level. It disappears at 623 K because the crystal melts. (C) 2004 Elsevier Ltd. All rights reserved.