Abstract
Li3PS4 is an attractive solid-electrolyte material that possesses high RT ionic conductivity (10(-4) S.cm(-1) ) but the effects of specific synthesis parameters on the material's local structure and transport properties still demand clarifications. Herein, we highlight the substantial effects of cooling breaks in the mechanochemical synthesis procedure on the formation of a variety of PxSya- moieties and on the transport properties of Li3PS4, through Raman and impedance spectroscopy measurements. We show that ball-milled Li3PS4 (with no subsequent annealing), which is often regarded as ``amorphous/glass/glassy Li3PS4 ``, is not fully amorphous using X-ray diffraction and transmission electron microscopy. Upon subsequent annealing for 1 h above 190 degrees C, beta-Li3PS4 is crystallized and our P-31 magic angle spinning nuclear magnetic resonance spectra suggest that 3 distinct PS43- moieties form, which we refer to as amorphous-, beta-and gamma-type units. Herein, we present a hypothesis to explain the correlation between the ionic conductivity and the distinct PS43- units as a function of the annealing temperature. Our results consolidate the recent reports noting that crystallization of beta-Li3PS4 is not necessary to obtain a high conductivity in ball-milled Li3PS4. Finally, we introduce a phase mixture between beta-Li3PS4 and gamma-Li3PS4 synthesized at 200 degrees C, which is the lowest synthesis temperature yet for gamma-Li3PS4.