Elastic constants of 2H-MoS2 and 2H-NbSe2 extracted from measured dispersion curves and linear compressibilities

Recent neutron data on the dispersion curves and X-ray measurements of the linear compressibilities of the 2H polytypes of MoS₂ and NbSe₂ have been used to obtain approximate values of the five independent elastic constants of these materials. In the case of NbSe₂ sufficient information is available to over-determine the elastic constants and the results are self consistent within estimated uncertainties, although the uncertainties are especially large for c₃₃ and c₁₁. Additional related considerations such as Debye temperatures and model calculations of c₃₃, and c₄₄ are also made. It is found that there is significant and unexplained disagreement between the value of the low temperature specific heat Debye temperature of NbSe₂ and the value determined on the basis of the elastic constants, but that the model predictions of c₃₃ and c₄₄ are in satisfactory agreement with the values extracted from the neutron data for both MoS₂, and NbSe₂.