Specific heat measurements in pure and in (Cu, Mn, Fe, Ni)-doped single-crystals of l-arginine phosphate monohydrate Original Research Article

The influence of highly diluted impurities (Cu, Mn, Fe, Ni) on the temperature (T) dependence of the specific heat (cp) of l-arginine phosphate monohydrate (LAP) was investigated in the temperature range 1.8–300 K. The doped samples yielded values for cp in excess to those obtained for a pure LAP sample. The melting temperatures (Tm≈420 K) obtained by differential scanning calorimetry for pure and doped LAP samples were found not to be significantly affected by the impurities. The T-dependence of cp was fully accounted for by taking into consideration the Debye contribution, an Einstein term and a contribution due to both Frenkel and Schottky defects. The model fit all cp versus T data using a single value for both the Debye (θD=160 K) and the Einstein (TE=376.8 K) temperatures, and for the energy (εd=157.9 meV) required to create the defects.