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

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 ($P_{\mathrm{ext}}\approx 5$ 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 $T<\mathrm{}{T}_{\mathrm{MI}}$ remains unchanged for $P_{\mathrm{ext}}<5\mathrm{}$ kbar. This finding is in strong contrast with the results of high-pressure electrical resistance measurements, where a reentrant metallic behavior was observed for $P>\mathrm{}4\mathrm{}$ kbar and $T<\mathrm{}65\mathrm{}$ K.