Pressure-induced oxidation state change of ytterbium in YbGa2

The crystal structure and the electronic properties of YbGa2 realising a Ca In2 type atomic arrangement were characterised at ambient conditions using single crystal X-ray diffraction data and magnetic susceptibility measureme nts at ambient pressure. Pressure-induced changes of structural and electro nic properties of YbGa2 were measured by means of angle-dispersive X-ray po wder diffraction and XANES at the Yb L-III threshold. At pressures above 22 (2) GPa, YbGa2 undergoes a structural phase transition into a high pressure modification with a UHg2 type crystal structure. Parallel to the pressure- induced structural alterations, ytterbium in YbGa2 undergoes an increase of the oxidation state from +2 at ambient conditions to +3 in the high-pressu re phase. Quantum chemical calculations of the Electron-Localisation-Functi on confirm that the phase transition is associated with a conversion of the three-dimensional gallium network of the low-pressure crystal structure in to two-dimensional gallium layers in the high-pressure modification.