Direct current conduction in ammonium and potassium dihydrogen phosphate

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.