First-Principles Study of the Superconductivity of Ti₃VH₁₂ and TiV₃H₁₂ Under 200 GPa

Hydrogen-rich compounds under high pressure are promising for high-temperature superconductivity, but many high-Tc hydrides rely on rare-earth or alkaline-earth elements and remain difficult to tune chemically. Transition-metal hydrides offer an alternative platform because partially filled d states can modify the electronic density of states, metal-hydrogen hybridization, and electron-phonon coupling. Here, VH3 is used as a parent high-pressure transition-metal hydride framework, and Ti substitution is introduced as a chemically compatible way to tune the d-derived states near the Fermi level. Two ternary hydrides, Ti3VH12 and TiV3H12, are therefore constructed from the VH3 lattice and investigated by first-principles calculations at 200 GPa. Both compounds are thermodynamically and dynamically stable under this pressure condition, as indicated by formation energies, the Ti-V-H convex hull, and phonon spectra. Within the same ultrasoft-pseudopotential computational framework, Ti3VH12 and TiV3H12 yield Allen-Dynes Tc values of 42.1 K and 36.8 K, respectively, higher than the corresponding VH3 value. A norm-conserving cross-check for VH3 gives a different absolute value, indicating that the Tc estimates are method-dependent. Electronic structure analysis indicates that Ti incorporation shifts pronounced van Hove singularities close to the Fermi level, enhances the density of states, and changes the Fermi surface topology. These results suggest that Ti-V-H hydrides are a useful model system for examining how transition-metal substitution can couple structural stability with electronic tuning in compressed hydride superconductors.