Temperature-dependent local structure and lattice dynamics of 1T-TiSe$_2$ and 1T-VSe$_2$ probed by X-ray absorption spectroscopy

The local atomic structure and lattice dynamics of two isostructural layered transition metal dichalcogenides (TMDs), 1T-TiSe$_2$ and 1T-VSe$_2$, were studied using temperature-dependent X-ray absorption spectroscopy at the Ti, V, and Se K-edges. Analysis of the extended X-ray absorption fine structure (EXAFS) spectra, employing reverse Monte Carlo (RMC) simulations, enabled tracking the temperature evolution of the local environment in the range of 10-300 K. The atomic coordinates derived from the final atomic configurations were used to calculate the partial radial distribution functions (RDFs) and the mean-square relative displacement (MSRD) factors for the first ten coordination shells around the absorbing atoms. Characteristic Einstein frequencies and effective force constants were determined for Ti-Se, Ti-Ti, V-Se, V-V, and Se-Se atom pairs from the temperature dependencies of MSRDs. The obtained results reveal differences in the temperature evolution of lattice dynamics and the strengths of intralayer and interlayer interactions in TiSe$_2$ and VSe$_2$.