Li⁺ Ion Site Energy Distribution in Lithium Aluminum Germanium Phosphate
2021
Wiemer, Jan L. | Schäfer, Martin | Weitzel, Karl-Michael
Lithium aluminum germanium phosphate of the stoichiometric formula Li₁.₅Al₀.₅Ge₁.₅(PO₄)₃ has been studied by means of the femtosecond laser plasma charge attachment induced transport (fs-plasma CAIT). The technique is based on attaching polarity selected charge carriers from a plasma to the front side of a sample, which induces transport of mobile charge carriers in the bulk of this sample. First, in a conductivity study, an activation energy of 0.73 eV for lithium ion transport has been measured by means of proton attachment. Second, a constant-voltage attachment experiment employing deuterium ions has been performed and subsequently analyzed by time-of-flight secondary ion mass spectrometry. The resulting concentration depth profile revealed a replacement of native lithium ions by deuterons in the first 350 nm of the sample. A theoretical analysis of the profile by means of the Nernst–Planck–Poisson equations provides access to the concentration dependent diffusion coefficient and the unique site energy distribution of the natively contained lithium ions. A full width at half-maximum of 113 meV for the SED of the Li⁺ ions is determined. The approach discussed can be applied to many more materials, where the potential energy landscape affects the function.
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