Energy landscapes in alkali aluminum germanium phosphate glasses as probed by alkali proton substitution

Abstract

The transport of native alkali ions in the energy landscape of alkali aluminum germanium phosphate (AAGP) glasses has been investigated by means of an alkali proton substitution (APS) experiment. This energy landscape is demonstrated to be dominated by the network former rather than the identity of the alkali ion. To this end AAGP glasses of composition A_1.5Al_0.5Ge_1.5(PO₄)₃ with A = Li, Na, K were subjected to APS, leading to a replacement of native alkali ions by foreign protons in a region reaching several 100 nm below the surface of the sample. Quantification of the concentration depth profiles by means of secondary ion mass spectrometry (SIMS) and modelling by means of Nernst–Planck–Poisson transport theory leads to the conclusion that the width of the site energy distributions (SED) only slightly varies from 114 meV, to 122 meV and 126 meV, FWHM, for the LAGP, the NAGP and the KAGP respectively.