We reexamine the thermodynamic properties such as specific heat, thermal expansion, and elastic constants at the charge density wave (CDW) phase transition in several one- and two-dimensional materials. The amplitude of the specific heat anomaly at the CDW phase transition TCDW increases with increasing TCDW and a tendency to a lineal temperature dependence is verified. The Ehrenfest mean field theory relationships are approximately satisfied by several compounds such as the rare earth tritelluride compound TbTe3, transition metal dichalcogenide compound 2H-NbSe2, and quasi-one-dimensional conductor K0.3MoO3. In contrast inconsistency exists in the Ehrenfest relationships with the transition metal dichalcogenide compounds 2H-TaSe2 and TiSe2 having a different thermodynamic behavior at the transition temperature TCDW. It seems that elastic properties in the ordered phase of most of the compounds are related to the temperature dependence of the order parameter which follows a BCS behavior.

中文翻译：

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电荷密度波系统的热力学性质调查

我们重新研究了几种一维和二维材料中电荷密度波 (CDW) 相变时的热力学特性，例如比热、热膨胀和弹性常数。CDW 相变 TCDW 处的比热异常幅度随着 TCDW 的增加而增加，并证实了线性温度依赖性的趋势。稀土碲化物化合物TbTe3、过渡金属二硫属化物化合物2H-NbSe2和准一维导体K0.3MoO3等几种化合物近似满足Ehrenfest平均场论关系。相反，在 Ehrenfest 关系中存在与过渡金属二硫属化物化合物 2H-TaSe2 和 TiSe2 在转变温度 TCDW 下具有不同热力学行为的不一致。