We report crystalline phases in the melt-quenched (AgI)(0.8)-(NaPO3)(0.2) and (AgI)(0.7)-(NaPO3)(0.3) superionic composites at room temperature as studied by VEGA powder neutron diffraction of KEK. (AgI)(0.8)-(NaPO3)(0.2) contains gammaAgI and betaAgI with a 70:30 ratio, which is similar to that found in pure AgI. On the other hand, (AgI)(0.7)-(NaPO3)(0.3) contains AgI and Ag5IP2O7 with a 53:47 ratio, without any indication of betaAgI presence. Due to the overall broad line widths and the hexagonal-related orthorhombic unit cell of Ag5IP2O7, VEGA was indispensable to probe its existence in (AgI)(0.7)-(NaPO3)(0.3) at room temperature. The disappearance of betaAgI in (AgI)(0.7)-(NaPO3)(0.3) in favour of Ag5IP2O7 containing more oxygens indicating that the phosphate chains have been oxidized to P2O7 pairs of phosphate tetrahedra. (C) 2004 Elsevier B.V. All rights reserved.