Anomalies in the bulk properties of single crystalline Niobium*

The thermodynamic properties of single crystal Niobium are presented. Anomalies in thermal expansion, specific heat, elastic constants, and electrical resistivity are observed. The linear coefficient of thermal expansion, $\alpha$, exhibits a large, broad peak in the range 200 K $<$ T $<$ 280 K, with a nearly two-fold increase in $\alpha$. The elastic constants show anomalies over a similar temperature range, while anomalies in heat capacity and resistivity are much narrower. This is surprising since crystalline Nb is a simple system, with only one naturally occurring isotope and a body centered cubic structure. Measurements on a second single crystal and on high purity polycrystalline Nb will also be presented.