We report the results of a combined computational and experimental study of the structural and ion migration properties of this material as a function of temperature. Using first principles methods to calculate the idealized static structures together with estimations of the phonon free energies in the quasi-harmonic approximation, the simulations predict several phases at low temperature including tetragonal and orthorhombic structures. The predicted orthorhombic phases are similar to experimental X-ray analysis performed at temperatures 15 K < T < 300 K as well as with literature reports, while the tetragonal phase may be difficult to experimentally realize. Additionally, the disordered cubic phase was investigated using first-principles molecular dynamics to determine the lithium tracer diffusion and several order parameters in the temperature range of ~350-650 K.
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Jason Howard was supported by NSF grant DMR-1507942. Computations were performed on
the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the University. A portion of this research was supported by the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, which is a U.S. Department of Energy (DOE) Office of Science User Facility. Zachary Hood was supported by a Graduate Research Fellowship award from the National Science Foundation (DGE-1148903) and the Georgia Tech-ORNL Fellowship.