PRESSURE-DEPENDENCE (INTERNAL AND EXTERNAL) OF THE METALLIZATION PROCESS AND THE MAGNETIC-ORDERING OF PRNIO3 - A NEUTRON POWDER DIFFRACTIONSTUDY

The modifications of the cystallographic and magnetic structures of Pr NiO3 associated to the decrease of the metal-insulator transition temp erature T-M-I With external pressure have been investigated by means o f neutron powder diffraction. The changes observed in the average Ni-O distances and Ni-O-Ni superexchange angles at 4.7 kbar are similar in sign but different in magnitude from those reported for the applicati on of an equivalent internal pressure. The low temperature phase (T < T-M-I) is magnetic (and probably insulating) at 4.7 kbar.