Isotropic Negative Thermal Expansion of Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 Solid-State Electrolyte

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability
• Main Authors: Ghosh, Sayan, Sudakar, Chandran
• Format: Journal Article
• Language: English
• Published: 2024
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D4TA03772C

Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) is a promising solid-electrolyte for Li-ion batteries with a favorable open structural framework made up of corner shared LiO 6 and TiO 6 octahedra and PO 4 tetrahedra network. Here we report the temperature dependence of this interconnected polyhedral network of LATP, leading to an isotropic negative thermal expansion (NTE) with an estimated lattice thermal expansion along a and c axis to be -1.07×10 -5 (±0.08×10 -5 ) K -1 and -2.56×10 -5 (±0.25×10 -5 ) K -1 in the temperature range of 93 K and 303 K, respectively. The change in bond lengths and bond angles of LiO 6 , TiO 6 octahedra and PO 4 tetrahedra are estimated as a function of temperature by Rietveld refining the X-ray diffraction patterns recorded in the temperature range of 93 K to 303 K. The overall shrinkage of LiO 6 octahedra results in the contraction of lattice along c axis. Local distortion in the lattice is also observable through the temperature dependent change of bond angles and bond lengths for TiO 6 octahedra and PO 4 tetrahedra. The existence of phosphate rotational/ librational motion is identified to be the underlying reasons for the occurrence of NTE along a -axis. The isotropic thermal contraction with temperature results in decrease lattice volume with temperature with volume expansion coefficient of -4.82×10 -5 (±0.37×10 -5 ) K -1 . Estimation of distortion indices such as quadratic elongation and bond angle variance suggests Li-occupied 6 b polyhedral site undergoes greater degree of distortion than other polyhedral units in LATP. Quadratic elongation and bond angle variance parameters for all the polyhedral units also suggest larger extent of distortion in LiO 6 and absence of any Jahn-Teller distortion in the framework. With further increase in temperature beyond 80 °C, a gradual switch over to a positive thermal expansion behavior becomes observable.