Deviation from bulk in the pressure-temperature phase diagram of V2O3 thin films

We found atypical pressure dependence in the transport measurements of the metal to insulator transition (MIT) in epitaxial thin films of vanadium sesquioxide (${\mathrm{V}}_{2}{\mathrm{O}}_{3}$). Three different crystallographic orientations and four thicknesses, ranging from 40 to 500 nm, were examined under hydrostatic pressures $({\mathrm{P}}_{h})$ of up to 1.5 GPa. All of the films at transition exhibited a four order of magnitude resistance change, with transition temperatures ranging from 140 to 165 K, depending on the orientation. This allowed us to build pressure-temperature phase diagrams of several orientations and film thicknesses. Interestingly, for pressures below 500 MPa, all samples deviate from bulk behavior and show a weak transition temperature $({T}_{c})$ pressure dependence $(d{T}_{c}/d{P}_{h}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.28em}{0ex}}\mathrm{K}/\mathrm{MPa}),$ which recovers to bulklike behavior $(3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.28em}{0ex}}\mathrm{K}/\mathrm{MPa})$ at higher pressures. Furthermore, we found that pressurization leads to morphological but not structural changes in the films. This indicates that the difference in the thin film and bulk pressure-temperature phase diagrams is most probably due to pressure-induced grain boundary relaxation, as well as both plastic and elastic deformations in the film microstructure. These results highlight the difference between bulk and thin films behaviors.