Accessing the high-pressure scheelite phase of SmVO4 at ambient conditions via mechanical alloying synthesis

We report the first successful mechanical alloying synthesis of the high-pressure scheelite phase of SmVO 4 under ambient pressure and near-room-temperature conditions. High-energy ball milling of Sm 2 O 3 and V 2 O 5 precursors enabled the direct stabilization of both scheelite ( I4 1 /a ) and zircon ( I4 1 /amd ) polymorphs in a single processing step. Structural evolution was tracked by ex situ X-ray diffraction combined with Rietveld refinement, revealing time-dependent phase transformation kinetics and a final phase assemblage dominated by the scheelite polymorph (82.7%). Raman spectroscopy corroborated this polymorphic coexistence, displaying distinct vibrational fingerprints for each phase, while linewidth analysis exposed substantial structural disorder within the metastable scheelite structure. Thermal analysis identified an irreversible exothermic event near 790 °C, corresponding to the complete scheelite-to-zircon transformation accompanied by significant crystallite growth from ∼12 nm to 130 nm. This structural evolution drives a pronounced band-gap shift, increasing from 2.15 eV in the as-milled state to 3.56 eV after annealing. First-principles DFT+U calculations support these observations, confirming the higher thermodynamic stability of the zircon phase and providing insight into the electronic structure of both polymorphs. Altogether, this work demonstrates mechanochemistry as a robust and low-cost route to access high-pressure polymorphs of functional materials under ambient conditions, offering new opportunities for polymorph engineering and property tuning in rare-earth vanadates.