CRYSTAL-STRUCTURE AND BAND-GAP OF RUBIDIUM HYDRIDE TO 120 GPA

Energy dispersive x ray diffraction measurements were performed on RbH to 120 GPa. RbH was observed to transform from the B2 phase to the or thorhombic, CrB, phase at 85 GPa. The equation of state for the B2 pha se and the CrB phase are reported. Transmission measurements were made to 120 GPa to determine the band gap versus pressure in RbH. We repor t here the first measurement of the band gap of RbH at zero pressure a t 4.91 eV. At 120 GPa, the band gap closed to 2.68 eV. Extrapolating t he present band gap data leads to a zero gap at about 310 GPa.