Structural investigation and Li-ion transport properties of LiYbP2O7 as lithium solid electrolyte

Solid-state lithium-ion batteries are expected to be the next-generation batteries with high energy densities, highly stable and safe properties. Recently, the exploration of new solid electrolyte materials with high-ion conductivity has been accelerated. In this context, the present work focuses on a novel solid electrolyte LiYbP₂O₇ which has been prepared by the conventional high temperature solid-state method. It was characterized by X-ray powder diffraction, thermal analysis, IR, Raman, complex impedance spectroscopies. The crystalline phase of the synthesized compound was carried out by X-ray diffraction proving its crystallization in the monoclinic structure with the space group P21/c. The differential scanning calorimetry analysis discloses the existence of an endothermic peak around T = 571 ± 5 K indicating the existence of a phase transition. Vibrational spectroscopies reveal all bending and stretching modes of the P₂O₇ group and confirm the presence of P–O–P. Ionic transport inside the LiYbP₂O₇ compound was investigated using impedance spectroscopy. Nyquist plots were explored with an equivalent circuit including a parallel combination of resistance and fractal capability. Dc conductivity is assured only by grains. The frequency and temperature behavior of the conductivity is explained by correlated barrier hopping and Non-overlapping small polaron Elliot models in phases I and II, respectively.