Bulk properties of YbGaGe: A question of zero thermal expansion

Despite the recent report of zero thermal expansion in YbGaGe, our extensive studies of the physical properties of pure YbGaGe failed to find anomalous behavior of the thermal expansion of both X-ray and dilatometry measurements. Instead, the temperature dependence of the lattice constants can be simply explained in terms of the Debye model with the cutoff frequency of 226 K, which was estimated from heat capacity measurement. Additionally, susceptibility measurements have not revealed any sign of a change of the Yb valency from 2 to 700 K, but magnetic correlations develop at low temperatures. Important findings of further interest are that YbGaGe has very strong low-lying optic phonons, 1.7 oscillator strength with an energy of 80 K, and shows strong increase of Grüneisen parameter below 20 K.