Lithium conductivity in an Li-bearing double-ring silicate mineral, sogdianite

The crystal structure of an Li-bearing double-ring silicate mineral, sogdianite ((Zr1.18Fe3+0.55Ti0.24Al0.03)(ϒ1.64,Na0.36)K0.85[Li3Si12O30], P6/mcc, a≈10.06 Å, c≈14.30 Å, Z=2), was investigated by neutron powder diffraction from 300 up to 1273 K. Rietveld refinements of displacement parameters revealed high anisotropic Li motions perpendicular to the crystallographic c-axis, indicating an exchange process between tetrahedral T2 and octahedral A sites. AC impedance spectra of a sogdianite single crystal (0.04×0.09×0.25 cm3) show that the material is an ionic conductor with conductivity values of σ=4.1×10−5 S cm−1 at 923 K and 1.2×10−3 S cm−1 at 1219 K perpendicular to the c-axis, involving two relaxation processes with activation energies of 1.26(3) and 1.08(3) eV, respectively.