Thermodynamics of the charge-density-wave transition in blue bronze.

Specific heat, Young's moduli, and magnetic susceptibility have been measured on pieces of a single crystal of blue bronze (for which thermal expansivity was previously measured) at its 180 K charge-density-wave (CDW) transition. All quantities were analyzed using a free energy appropriate for a three-dimensional $\mathrm{XY}$ model. Although not all parameters can be readily interpreted, the resulting fits permit quantification of the magnitudes of the anomalies at the phase transition in a systematic way that does not require guessing of the background variation.