Structural phase transition of TmGa₂ at high pressure

We have investigated the structural properties of the intermetallic compound TmGa2 under hydrostatic pressures up to 45 GPa by means of X-ray powder diffraction in diamond anvil cells. The orthorhombic low-pressure modification of the KHg2 (CeCu2) type undergoes a structural phase transition at 21(3) GPa into a high-pressure modification of the AlB2 structure type. TB-LMTO-ASA calculations and use of the electron localization function confirm that the structural change from a three-dimensional gallium network to a layered structure is associated with a transition from a tetrahedral homonuclear gallium network to a trigonal planar one