Specific heat studies of small KDP crystals at low temperatures

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Abstract
Specific heat measurements 1.7-25 K are reported on small KDP crystals with surface-to-volume ratios (S/V) between 11 and 44 cm-1. The studies involved as-grown crystals which were measured under essentially zero-strain conditions. All crystals display C/T3 maxima describable by a single Einstein term. and neither the Debye temperature (364 K ± 2.6%) nor the Einstein temperature (80.0 K ± 5.8%) depend on S/V. A T3/2 specific heat contribution appears below ∼4 K, and the amplitude of this term goes through a minimum at S/V ≈ 25 cm-1 where it is essentially zero. A surface excitation is indicated because the T3/2 amplitude increases rapidly with S/V > 25 cm-1, and a bulk excitation is also indicated by the increase in the amplitude for S/V < 20 cm-1.