Structure and transport properties of HoNiO₃ under high pressure

Rare-earth nickelate (ReNiO₃, with Re ≠ La) constitutes a paradigmatic class of strongly correlated electron systems, exhibiting a remarkable tunability of the metal–insulator transition (MIT) in response to external stimuli such as hydrostatic pressure, temperature, and chemical doping. This tunability arises from the competitive interplay among charge, spin, and orbital degrees of freedom. However, the fundamental mechanisms governing the effective control of the MIT under extreme conditions, particularly the intricate coupling between lattice dynamics and electronic localization, remain elusive. This knowledge gap poses a significant challenge to both fundamental research and practical applications of these materials. Herein, we present a systematic investigation of the structural phase transitions and electrical transport properties of HoNiO₃ under extreme conditions. In situ high-pressure x-ray diffraction (XRD) analysis uncovers a structural evolution pathway: an initial transition from a monoclinic insulating phase (P2₁ / n) to an orthorhombic metallic phase (Pbnm) at approximately 17 GPa, followed by the emergence of a mixed-phase region (Pbnm and $R\overline{3}c$) at approximately 35 GPa. Complementary electrical transport measurements reveal a pronounced sensitivity of the metal–insulator transition temperature (T_MIT) to the synergistic effects of high pressure and low temperature. These findings not only provide crucial experimental evidence for elucidating the structure–property relationship in HoNiO₃ under extreme conditions, but also lay a conceptual foundation for designing advanced functional devices based on ReNiO₃ materials, with promising applications in high-sensitivity pressure sensors and temperature-responsive switches featuring tunable activation thresholds.