Pressure-induced high-spin to low-spin transition inCaFeO3

In situ ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy and x-ray diffraction on ${\mathrm{CaFeO}}_3$ (${\mathrm{Fe}}^4$:${\mathit{t}}_2^3$ ${\mathit{e}}^1$) under pressure have revealed a first-order high-spin (S=2) to low-spin (S=1) transition near 30 GPa. The spin and structure transition is an laternative manifestation of the electronic instabilities of the σ-bonding Fe-O-⇆${\mathrm{Fe}}^{4\mathrm{-}\mathrm{\delta }}$+${\mathrm{Fe}}^{4+\mathrm{\delta }}$, 0≤δ≤1, occurs at a ${\mathit{T}}_{\mathit{t}}$≊290 K. Such instabilities found at the transition from localized to itinerant ${\mathrm{\sigma }}^{\mathrm{*}}$-band electrons reflect a sensitivity to interactions with the lattice.