The valence state of Yb ion in YbInAu2 compound at high pressure determined by x-ray diffraction and x-ray absorption near edge structure measurements

X-ray diffraction patterns and LIII-edge x-ray absorption near edge structure (XANES) spectra of YbInAu2 and LuInAu2 compounds have been measured at high pressure and room temperature using a diamond anvil cell and a synchrotron radiation at SPring-8. YbInAu2 is more compressible at pressures lower than 4 GPa than above it; the evaluated bulk modulus by Birch-type equation of state is 54.7 GPa which is one-half of that of the LuInAu2 (112.5 GPa). The mean valence v¯ of Yb ion in YbInAu2 determined by the XANES measurement is an increasing function of pressure: 2.71(2) at normal pressure and 2.94(2) at 10 GPa. The rate of increase in v¯ with pressure is two times larger at pressures below 4 GPa than that above 4 GPa. However, the v¯ is described by a linear increasing function of the lattice compression: v¯ =v¯0+2.9|ΔV/V0| where v¯0 is 2.71. The extrapolation to the trivalent state gives the critical pressure of 13 GPa