Deposition and Characterization of Li ₂ O–SiO ₂ –P ₂ O ₅ Thin Films

Abstract

Amorphous lithium electrolyte thin films, xLi 2 O·ySiO 2 ·zP 2 O 5 , were deposited by rf magnetron sputtering of pure and mixed‐phase lithium silicate, lithium phosphate, SiO 2 , Li 2 O, and Li 2 CO 3 targets, and their compositions were determined using proton‐induced y ‐ray emission spectroscopy, energy‐dispersive X‐ray analysis, Rutherford backscattering spectrometry, and atomic‐emission spectroscopy. The deposition conditions were chosen to assure thermalization of the sputtered flux, which proved to be necessary in order to obtain a homogeneous distribution of Si and P in the films. Optical absorption and ac impedance measurements showed that glass‐in‐glass phase separation occurred in a large SiO 2 ‐rich domain of the composition diagram. In contrast to bulk glasses, all of the Li 2 O–SiO 2 films were phase‐separated, including those with lithia contents larger than lithium disilicate. High‐performance liquid chromatography measurements revealed that, analogous to bulk glasses, the addition of SiO 2 to Li 2 O‐P 2 O 5 compositions reduced the number of phosphate anion dimers, trimers, and higher anion polymers in the films through the formation of ‐Si‐O‐P‐bonds. However, in contrast to bulk glasses, the distribution of phosphate anion polymers followed closely the Flory distribution, with the fraction of anion polymers decreasing monotonically with increasing chain length.