Electronic and structural transitions in NdFeO3 orthoferrite under high pressures

The effect of high pressure up to 65 GPa on the crystal structure and optical absorption spectra of NdFeO3 orthoferrite single crystals is studied in diamond anvil cells. At P similar to 37.5 GPa, an electronic transition at which the optical absorption edge jumps from similar to2.2 to similar to0.75 eV is observed. The equation of state V(P) is studied on the basis of the X-ray diffraction data obtained under pressure. This study reveals a first-order structural phase transition at P similar to 37 GPa with a jump of similar to4% in the unit cell volume. It is shown that the phase transition observed in rare-earth orthoferrites at 30-40 GPa is a transition of the insulator-to-semiconductor type. (C) 2003 MAIK "Nauka / Interperiodica".