Heat Capacity of Isotopically Enriched 28Si, 29Si and 30Si
  The heat capacity of isotopically enriched 28Si, 29Si, 30Si samples has been measured in the temperature range between 4K and 100K. The heat capacity of Si increases with isotopic mass. The values of the Debye temperature for the three isotopic varieties of silicon have been determined. Good agreement with the theoretical dependence of the Debye temperature on isotopic mass has been found. 
A. Gibin, G.G. Devyatykh, A.V. Gusev, R.K. Kremer, M. Cardona, H.-J.   Pohl