Thermal variation of local structure in LiTa2PO8 solid electrolytes

Lithium tantalum phosphate LiTa2PO8 is a new Li+ ion conducting solid electrolyte that shows high room temperature Li+ ion conductivity. Our initial neutron diffraction studies at room temperature have confirmed changes in the lithium ion distribution depending on synthesis conditions. This is further confirmed by high resolution 31P solid state NMR results which suggest a number of local structural motifs are present, despite the crystallography showing only a single phosphorus site. The complex 31P spectrum observed at room temperature collapses into a single broad resonance at around 350 K, suggesting a significant change in the local structure, but this is not accompanied by a significant change in the average crystal structure. A total neutron scattering study of this system is proposed to establish how the Li+ ion distribution and local structure varies with temperature.