Origins of Phase Transitions in Valence Fluctuating YbPd

Abstract

The cubic YbPd compound undergoes two first-order phase transitions at \(T_{1}=125\) K and \(T_{2}=105\) K. We report the experimental results of the X-ray diffraction (XRD) and electron diffraction of single crystals of YbPd at low temperatures. Below \(T_{1}\), the \((h00)\) Bragg peaks (\(h\): an integer) are split into two subpeaks. Below \(T_{2}\), the superlattice reflections of \((n/2,0,0)\) (\(n\): an odd number) in the XRD patterns and the superlattice spots of \((1/2,0,0)\), \((0,1/2,0)\), and \((1/2,1/2,0)\) in the electron diffraction profile appear, which suggests the valence order of YbPd. We discuss two possible structures, assuming a tetragonal symmetry below \(T_{1}\). The origins of the transitions at \(T_{1}\) and \(T_{2}\) are probably the band Jahn–Teller effect and the valence order, respectively.