Pressure-induced melting of charge-order in the self-doped mott insulator yttrium nickelate

The stability under pressure of the charge-density-wave in the insulating phase of YNiO₃ was studied by infrared spectroscopy and synchrotron diffraction techniques up to 23 GPa. YNiO₃ undergoes a pressure induced insulator-to-metal transition at approximately 15 GPa in the pressure domain, coinciding with the melting of the charge ordered phase. The optical band gap is non-zero above 15 GPa, as is the case above the reported insulator-metal transition (585 K) in the temperature-domain. There is a similarity between the infrared spectral profile around 15 GPa and the infrared spectral profile above ca. 700 K. We conclude therefore that the pressure-induced structural/electronic transition induced around 15 GPa, probably having an as-yet unreported counterpart in the temperature domain at a temperature in excess of 585 K.