Tunable thermal expansion behavior in the intermetallic YbGaGe

We investigate the effects of carbon and boron doping on the thermal expansion of the hexagonal (P6{sub 3}/mmc) intermetallic YbGaGe. X-ray powder diffraction was used to measure the lattice constants on pure and doped (C or B at nominal levels of 0.5%) samples from T{approx}10 K to T{approx}300 K. Also measured were resistivity, specific heat, and magnetic susceptibility. While the pure YbGaGe samples exhibit positive thermal volume expansion (V{sub 300K}-V{sub 10K})/V{sub 300K}=0.94, the volume expansion in the lightly C- or B-doped samples changes slope and tends toward zero-volume expansion. Such a strong response to light doping suggests that the underlying mechanism for the reported zero-volume expansion is substitutional disorder, and not the previously proposed valence fluctuations.