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Abstract. The conductivity of glasses in the P2Os-[(1-x) V205 -X Na20] system is studied as a function of temperature and composition. For all compositions, the conductivity variations as a function of temperature follow an Arrhenius type relationship: cy= A---exp(-~za ].T \ RTJ The activation energies and pre-exponential factors corresponding to the V205 richest compositions are lower than that corresponding to the ionic ones. Isothermal variations of the conductivity as a function of composition show a deep minimum for a molar ratio x near 0.65. On either side of this minimum, the conductivity is mainly electronic (x < 0.7) or ionic (x > 0.8). The variations are interpreted assuming a prevailing diluting effect of the non predominantly present oxide without any interactions between the electronic and ionic charge carriers.