Abnormal high-pressure structural transitions; the curious case of GaFeO$_{3}$

High pressure studies have been carried out in the antiferromagnetic-insulator GaFeO$_{3}$ (SG\textit{ Pc2}$_{1}n) $to 90 GPa using XRD at RT, Moessbauer spectroscopy, [MS(P,T)], and resistance measurements [R(P,T)]. Both MS(P,T) and R(P,T) studies reveal a \textit{Mott-Hubbard} correlation breakdown, starting at 50 GPa and culminating at 65 GPa, manifested by loss of paramagnetism concurring with a insulator-metal transition. XRD studies reveal a sluggish 1$^{st}$-order phase transition in the 25 -- 38 GPa range characterized by a discontinuous volume change ( 5{\%}) and formation of a perovskite structure (\textit{Pc2}$_{1}n \quad >$ \textit{Pbnm}). At $\sim $50 GPa an isostructural transition with 3.5{\%} volume decrease is observed, consistent with the MS and R(P,T) findings. At decompression the EOS follows a non-hysteretic curve down to 24 GPa, below which a 1$^{st}$-order transition occurs forming an ilmenite state (\textit{Pbnm$>$R3}), with a slight increase in V ($\sim $1{\%}), stable down to ambient pressure. The perovskite stability beyond 25 GPa and the peculiar \textbf{perovskite -ilmenite} will be discussed.