Preparation, characterization, and impedance studies of LiSbM(PO4)3 (M=Al, Fe, and Cr)

Lithium containing sodium superionic conductors of composition LiSbM(PO4)3 (M=Al, Cr, and Fe) were prepared by solid-state method and were characterized by powder x-ray diffraction and infrared spectroscopy. All compounds were found to crystallize in rhombohedral lattice with space group R3¯c. They show characteristic PO4 vibrational bands. The dc conductivity and ac impedance studies of all these samples correlate well in terms of activation energy of conduction Ea. The Cole-Cole plots do not show any spikes on the lower frequency side, indicating negligible electrode effects. The activation energies obtained from the plots of logσdc vs 1∕T and logσ(0) vs 1∕T are approximately the same suggesting conducting species to be mobile lithium ions. The peak width at half maximum for modulus plots (logf vs M″) is ∼1.34 decades for LiSbM(PO4)3 (M=Al, Cr, and Fe), which is close to 1.14 decades observed for a Debye solid. The heights of M″ obtained from the experimental plots are close to that of M″(max)=C0∕2C, co...