Direct current conduction in ammonium and potassium dihydrogen phosphate

Abstract

Experiment, plus critical discussion of previous work, suggests the following. Conductivity is primarily due to the migration of L defects (proton vacancies), the enthalpy for L‐defect mobility being 0.53 eV in KDP and 0.46 eV in ADP. Such L defects are produced by impurities, but there is an additional tendency towards incipient decomposition in both crystals. This leads to a high‐temperature conductivity which, in KDP, is associated with the formation of water molecules and the thermal generation of L defects and, in ADP, with the formation of ammonia molecules and the thermal generation of proton vacancies in the ammonium lattice (A defects). The enthalpy of L‐defect formation in KDP is 0.46 eV; that for A‐defect formation in ADP is 0.19 eV. Previously reported overheating effects are spurious. The conductivity is independent of field.