On processing structure-conductivity relations in NASICON-type LiSn2(PO4)3

The present investigation focuses on understanding the structure-electric conductivity correlation in NASICON-type LiSn2(PO4)(3) (LSP) powders prepared via solid-state reaction method. LSP powders synthesized at different temperatures were characterized for their structural and electrical properties using lab source powder X-ray diffraction (XRD), high-resolution synchrotron X-ray diffraction (SXRD) and complex impedance spectroscopy. LSP powders prepared in 900-1000 degrees C temperature crystallize in triclinic structure (space group, P (1) over bar) along with the small amount of SnO2(P4(2)/mnm) impurity phase. Samples prepared at temperatures in 1050-1250 degrees C range showed a mixed rhombohedral (R (3) over barc) and triclinic structure with the fraction of the triclinic phase decreasing with an increase in calcination temperature. On further increase in the calcination temperature to 1300 degrees C, LSP transformed to the rhombohedral structure. Moreover, temperature-dependent SXRD confirmed that the LSP powder exhibits a martensitic behaviour, where a pure triclinic structure transforms into a pure rhombohedral phase at 170 degrees C and retains a partial rhombohedral phase on cooling back to room temperature. The highest value of conductivity was found to be similar to 1.06 x 10(-6) Scm(-1) for the LSP powder with triclinic structure calcined at 900 degrees C, with an associated activation energy of similar to 0.24 eV. Rhombohedral LSP calcined at 1300 degrees C exhibits the lowest conductivity and highest activation energy at room temperature similar to 1.12 x 10(-8) Scm(-1) and similar to 0.39 eV, respectively. This decrease in conductivity for the supposedly high-conducting rhombohedral phase is attributed to the drastic increase in the fraction of the SnO2 impurity phase, as confirmed by the XRD analysis.

Automated summary

The study reveals a significant correlation between the structure and electrical conductivity of NASICON-type LiSn2(PO4)(3) (LSP) powders, with the calcination temperature affecting both the crystalline structure and conductivity. LSP powders prepared at different temperatures exhibit variations in their structural phases and electrical conductivities.