The heat capacity of three pure (n, p≤2×1016
cm-3) germanium crystals with different isotopic compositions was measured in
the temperature range from 2.8 K to 100 K. These samples, one made of enriched
70Ge (95.6%), Ge of natural isotopic composition and n, p < 1014 cm-3, and
one of the largest possible isotopic mass variance 70/76Ge (43%/48%) with n,
p<1014 cm-3, show a change of the molar heat capacity (and corresponding
Debye temperature, θD) as expected from the average mass variation,
corresponding to θD∝M-0.5 (M = molar mass) at low temperatures. The mass
effect is best visible around 21.5 K, at the minimum of the corresponding Debye
temperatures θD, and amounts to ΔθD = 5.3 K for the difference between the Debye
temperatures of 70Ge and 70/76Ge. The specific heat capacity of the natural Ge
crystal agrees within 2% with the best data available in the literature taken
on much larger masses of Ge.
Source:IOPscience
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