Identification and inspection of the vacancy site in Li doped BPO4 ceramic electrolyte by NMR

A study of the properties of the high temperature ceramic electrolyte LixB1−x/3PO4 (lithium boron phosphate) is reported. XRD and NMR are used to investigate changes of the material as a function of heat treatment. It was found that after synthesis at 450 °C the material contains a phase of Li4P2O7 in addition to the BPO4 phase. This second phase is removed by heat treatment at temperatures higher than 600 °C. Boron vacancies are present, REDOR and CPMAS techniques are used to investigate this defect site and show that for the heat treated material Li ions are present at the vacancy site.