  Transition-metal honeycomb compounds are capturing scientific attention due
to their distinctive electronic configurations, underscored by the
triangular-lattice spin-orbit coupling and competition between multiple
interactions, paving the way for potential manifestations of phenomena such as
Dirac semimetal, superconductivity, and quantum spin liquid states. These
compounds can undergo discernible pressure-induced alterations in their
crystallographic and electronic paradigms, as exemplified by our high-pressure
(HP) synthesis and exploration of the honeycomb polymorph of ReO3 (P6322). This
HP-P6322 polymorph bears a phase transition from P6322 to P63/mmc upon cooling
around Tp = 250 K, as evidenced by the evolution of temperature-dependent
magnetization (M-T curves), cell dimension, and conductivity initiated by an
inherent bifurcation of the oxygen position in the ab plane. Insightful
analysis of its band structure positions suggests this HP-P6322 polymorph being
a plausible candidate for Dirac semimetal properties. This phase transition
evokes anomalies in the temperature-dependent variation of paramagnetism
(non-linearity) and a crossover from semiconductor to temperature-independent
metal, showing a temperature independent conductivity behavior below ~200 K.
Under increasing external pressure, both the Tp and resistance of this
HP-polymorph is slightly magnetic-field dependent and undergo a "V"-style
evolution (decreasing and then increasing) before becoming pressure independent
up to 20.2 GPa. Theoretical calculations pinpoint this anionic disorder as a
probable catalyst for the decrement in the conductive efficiency and muted
temperature-dependent conductivity response.
