Pressure-induced breakdown of a correlated system: The progressive collapse of the Mott-Hubbard state in RFeO3 - art. no. 094411

Mossbauer spectroscopy, resistance, and synchrotron x-ray-diffraction (XRD) methods were combined for detailed studies of the pressure-induced breakdo wn of the strongly correlated perovskite RFe3+O3 (R=La. Pr) systems. The XR D studies have shown that in the range 30-50 GPa both orthorhombic perovski tes undergo a first-order phase transition to a new high-pressure (HP) phas e accompanied by a similar to3% volume contraction. The HP phases at P<50 G Pa are characterized by the coexistence, with equal abundance, of high (S = 5/2. (6)A(1g)) and low-spin (S = 1/2, T-2(2g)) Fe3+ sublattices. With furt her pressure increase a gradual high- to low-spin transition occurs, fully converting to an S = 1/2 state at <similar to>65 GPa for both La and Pr. Fo r PrFeO3 up to 90 GPa, the highest pressure reached with MS in this compoun d, and for LaFeO3 between 70-120 GPa, magnetic spin-spin relaxation spectra are observed suggesting the presence of a weak magnetic exchange. This coi ncides with a drastic decrease in the resistance. The observation of spin-l attice paramagnetic relaxation in spectra in the 120- to 170-GPa range for LaFeO3 Concurs with the onset of a metallic state with noninteracting momen ts as evidenced by R(P,T) studies. It is predicted that a normal metal, wit h no moments, will be established in LaFeO3 at similar to 240 GPa. A detail ed analysis of the magnetic interactions in an antiferromagnetic insulator at very high pressures and a Mott-Hubbard phase diagram are presented in te rms of the pressure versus the magnetic moment.