Lattice and phonon properties in semiconductors FeSb₂ and RuSb₂

The family of transition-metal dipnictides, MX₂ (M: metal, X: N, P, As, Sb, and Bi), has emerged as an important quantum material system due to its unique physical properties, such as large magnetoresistance, colossal Seebeck coefficients, and Weyl semimetal characteristics. In order to study the M-site ions effect on the lattice structure and the related dynamics, we compared two isostructural compounds, FeSb₂ and RuSb₂. Neutron diffraction, specific heat, and Raman scattering spectra of RuSb₂ were measured. We found that the thermal expansion coefficients are isotropic for RuSb₂, in contrast to the anisotropic behavior reported previously in FeSb₂. Moreover, the specific heat of RuSb₂ shows a boson-like anomaly around 25 K. Four of the six predicted vibrational modes were identified by polarized Raman scattering spectra and successfully simulated by ab initio calculations. Meanwhile, the temperature-dependent linewidths reveal that phonon–phonon interactions might dominate above 50 K, while electron–phonon coupling remains relatively weak.