In our work single crystals of Mg4.5Na7(P2O7)4 were prepared, pulveriz
ed, pressed into pellets and sintered in order to measure the electric
al conductivity of polycrystalline specimens. The conductivity was als
o measured on glassy specimens obtained by the melting of previously p
repared crystals. The electrical conductivities at 25-degrees-C with v
alues of the order of 10(-16) OMEGA-1 cm-1 for polycrystalline samples
and a value of the order of 10(-14) OMEGA-1 cm-1 for glass, show that
the glassy phase of Mg4.5Na7(P2O7)4, because of its greater molar vol
ume and loosely packed structure, is a better matrix for ionic motion.