Order-Disorder Transition in NH4Cl. III. Specific Heat

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Abstract
The ac technique for measuring heat capacities is explained, and a model is presented to show the effects that the thermal properties of the heat link have on the observed temperature modulation. The ac technique is used to measure the heat capacity of ammonium chloride near the order-disorder transition at 242 °K. The measured heat capacities are analyzed using the theory presented in the first paper of this series. There is a strong sample dependence in the data that is not understood, but agreement with the theory is obtained for the sample with the sharpest transition. The critical exponents obtained from the fitting procedure are much closer to 1 than the theoretical values obtained from various model calculations.