High-pressure neutron-diffraction study of the metallization process in PrNiO3

Abstract

The modifications of the crystallographic and magnetic structures of PrNi${\mathrm{O}}_{3}$ associated with the decrease of the metal-insulator transition temperature, ${T}_{\mathrm{MI}}$, with external pressure (${P}_{\mathrm{ext}}\ensuremath{\approx}5$ kbar) have been investigated by means of neutron powder diffraction. Our results indicate that the symmetry of the unit cell (orthorhombic $\mathrm{Pbnm}$ at ambient pressure), is preserved in the pressure range studied. The changes observed in the Ni-O distance and the Ni-O-Ni superexchange angle are, however, similar in sign but very different in magnitude from those obtained by applying an equivalent "internal" pressure. The antiferromagnetic ordering observed at ambient pressure for $T<{T}_{\mathrm{MI}}$ remains unchanged for ${P}_{\mathrm{ext}}<5$ kbar. This finding is in strong contrast with the results of high-pressure electrical resistance measurements, where a reentrant metallic behavior was observed for $P>4$ kbar and $T<65$ K.