LOW-TEMPERATURE SPECIFIC HEAT OF KC1 - OH

In KCl containing OH- ions with small concentration nOH, a low-temperature specific-heat anomaly is observed which peaks at 0.3°K and whose entropy is close to nOHk ln6. This anomaly is interpreted with the model in which the OH- ion in the Cl- cavity has six equilibrium positions among which it can tunnel. Assuming a Devonshire potential, a best fit to the data is obtained for a splitting between the A1g and T1u states of 6.2 × 10-5 eV (0.5 cm-1), and between the T1u and Eg states of 3.1 × 10-5 eV. The observed anomaly is somewhat broader than the predicted one, which indicates that the potential of octahedral symmetry is only an approximation. From the rise of the anomaly at low temperatures, a splitting of 4.1 × 10-5 eV (0.33 cm-1) 10% is determined, in agreement with the value determined by paraelectric resonance. At concentrations exceeding 10-4 mole ratio, the anomaly changes its shape in a way similar to that in KCl:Li. Our interpretation is that the tunneling states are perturbed by an electric interaction between the OH- ions. Specific evidence for an ordered state has not been found. © 1969 The American Physical Society.