Transport and optical properties of iron borate FeBO3 under high pressures

The optical absorption spectra of iron borate FeBO3 were measured in diamond anvil cells at high pressures up to P=82 GPa. The electronic transition with an abrupt jump in the absorption edge from similar to3 to 0.8 eV was observed at Papproximate to46 GPa. The resistance and its temperature dependence were directly measured for FeBO3 at high pressures up to 140 GPa. It was established that the electronic transition at Papproximate to46 GPa was accompanied by the insulator-semiconductor transition. In the high-pressure phase, the thermoactivation gap decreases smoothly at 46