LARGE ENHANCEMENT OF ELECTRICAL-CONDUCTIVITY IN MAGNESIUM PHOSPHATE-GLASSES BY ION-IMPLANTATION OF PROTON

Large enhancement of electrical conductivity has been observed in Mg(P O3)(2) glasses by ion implantation of protons at 120 keV to a fluence of 1 x 10(18) cm(-2). Upon implantation d.c. conductivity at 300 K was drastically increased from similar to 10(-15) S . cm(-1) to 5 x 10(-4 ) S . cm(-1) and the activation energy of the conduction was greatly r educed from similar to 1.3 eV to 0.18 eV. Observation of absorption cu rrent and the positive sign of Seebeck coefficient indicate that the p rimary charge carrier in H+-implanted Mg(PO3)(2) glasses is a cation. The same conductivity enhancement was observed in D+-implanted Mg(PO3) (2) glasses, but no significant change was seen in the He+-implanted g lasses. These results strongly suggest that fast protonic conduction o ccurs in the H+-implanted Mg(PO3)(2) glasses, No such a high conductiv ity was observed for H+-implanted SiO2 glasses. It was found that impl anted protons occur in the form of Si-OH and Si-H in SiO2 but exist as POH groups and molecular water H2O in Mg(PO3)(2) glasses. A quantitat ive discussion on the proton conductivity led to a hypothesis that the coexistence of acidic groups such as POH and molecular water H2O is a structural requirement for the emergence of fast proton transport in oxide glasses.