Advances in Condensed Matter Physics

Review Article

Survey of the Thermodynamic Properties of the Charge Density Wave Systems

Table 2

Materials (2D CDW) transition metal dichalcogenides 2H-NbSe₂, TiSe₂, 2H-TaSe₂, and 2H-TaS₂. Molar volumes are given in cm³, specific heat discontinuities in J/molK, thermal expansion discontinuities in K⁻¹, elastic velocity discontinuities in , and measured and calculated elastic constants in GPa. Discrepancies exist among the experimental values of the Young modulus; the largest values are only indicated. Ratio = calculated /experimental elastic constant.


Materials	Molar volume cm³	T_CDW K	Specific heat J/molK	Thermal expansion coefficient ∆α K⁻¹	Elastic velocity decrease ∆V/V	Elastic constant GPa	calculated GPa	Ratio

2H-NbSe₂	40	30	0.5 [19]	axis -3x10⁻⁶ [19] axis -2x10⁻⁷ [18]	axis -5x10⁻⁴ [16, 17]	C₁₁=108 [17] C₃₃=460	35	~0.3

TiSe₂	39.6	200	1.15 [22] 0.5 [23]	axis -2.5x10⁻⁶ [19]	along the axis -0.05 [19]	axis C₁₁~ 190 [20]	1800 800	~10 ~4

2H-TaSe₂		120	4 [24]	axis -8x10⁻⁶ [25]	axis -0.0005 [16, 17]	Young modulus ( axis) [16]	16	~0.1

2H-TaS₂	35.7	78	2.8 [24]		no discountin.