Pressure-induced valence change of YbNiGe3investigated by resonant x-ray emission spectroscopy at the YbL3edge

Abstract

Pressure dependence of the Yb valence in YbNiGe${}_{3}$ has been investigated up to 15.6 GPa at 300 K and up to 7.7 GPa at 17 K by means of x-ray absorption spectroscopy in $L{\ensuremath{\alpha}}_{1}$ partial fluorescence yield mode and resonant x-ray emission spectroscopy around the Yb ${L}_{3}$ absorption edge. The Yb valence in YbNiGe${}_{3}$ at ambient pressure strongly fluctuates with the mean valence of $v=2.52\ifmmode\pm\else\textpm\fi{}0.01$ at 300 K. The Yb valence rapidly changes toward a trivalent state with pressure up to $\ensuremath{\sim}$5 GPa, slowly increases up to $\ensuremath{\sim}$10 GPa, and then reaches a saturated value of $v\ensuremath{\sim}2.87$ at 15.6 GPa. The Yb valence at 17 K slightly decreases compared to that at 300 K; $v\ensuremath{\sim}2.45$ at ambient pressure and $\ensuremath{\sim}$$2.72$ at 7.7 GPa. We found that the pressure-induced change in the intensity of a quadrupole component in the x-ray absorption spectra shows the same trend as the Yb valence in YbNiGe${}_{3}$. In contrast to YbNiGe${}_{3}$, the Yb valence in YbNiSi${}_{3}$ is nearly 3 at ambient pressure with almost no temperature dependence.