Li⁺ Ion Site Energy Distribution in Lithium Aluminum Germanium Phosphate

Abstract

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.

Opening Diffusion Pathways through Site Disorder: The Interplay of Local Structure and Ion Dynamics in the Solid Electrolyte Li6+xP1–xGexS5I as Probed by Neutron Diffraction and NMR

“… 26 Recently, Weitzel and co-workers significantly advanced this field by analyzing site energy distributions and energy landscapes in a variety of crystalline and amorphous solids. 27 − 30 …”

“…This view is in contrast to that of a rigid lattice framework with the Li + cations being regarded as random walkers carrying out completely uncorrelated jump processes with negligible lattice relaxation . Recently, Weitzel and co-workers significantly advanced this field by analyzing site energy distributions and energy landscapes in a variety of crystalline and amorphous solids. − …”

Manifestation of site energy landscapes for ion transport in borate glasses

“…In previous work we had derived widths of 280 meV for a sodium calcium phosphate glass, 31 320 meV for a sodium rubidium borate glass, 21 and 113 meV for lithium aluminum germanium phosphate glass. 62 Thus, the width of the SED is characteristic for a given glass system. With this result the goal of this work has been achieved.…”

Enhancing proton mobility and thermal stability in phosphate glasses with WO3: the mixed glass former effect in proton conducting glasses

“…S6 in the ESI †). Although it has recently been reported that the diffusion coefficient, i.e., mobility, of alkali ions is strongly dependent on the local structure, 33 it is not reasonable to attribute the partial conductivity due to nonproton contributions to Na + ions, taking into account the small C Na in the glasses after APS. The C Na in these glasses was less than 10% in the glasses before APS.…”