CONDUCTION AND DIFFUSION IN CRYSTALS CONTAINING HYDROGEN BONDS .2. AMMONIUM DIHYDROGEN PHOSPHATE

Electrolysis measurements on crystals of ammonium dihydrogen phosphate (ADP) have confirmed the results of Murphy, showing that protons are mobile in the solid. The ac conductance of ADP crystals along the c axis over the temperature range 40-150°C has been shown to fit the expression σ = 1.26×102 × exp[- (11.08±0.02 kcal mole -1)-1, and the conductance results are discussed in terms of the simultaneous formation and migration of proton defects. The diffusion of tritium along the c axis of ADP crystals has been measured as a function of temperature and the results expressed as D = 6.63×10-5× exp[- (9.3±0.8 kcal mole-1)/9.3±0.8 kcal mole -1. A comparison of the conductance and diffusion results has shown that the Einstein relation is not obeyed, and the deviations have been interpreted in terms of correlated proton jumps in the crystal. The value of the pre-exponential factor in the diffusion equation suggests that there is a small negative entropy factor in the diffusion process.