Measurement of an electrical potential induced by normal stress applied tothe interface of an ionic material at elevated temperatures

The measurement of a potential difference between two surfaces of zirconia is reported, when a normal stress is applied to one surface, leaving the ot her surface stress free. The potential difference is proportional to the ap plied stress over a wide range. The proportionality constant represents a n ew thermo-dynamic measurement of the interfacial state because the measurem ent is reversible and independent of temperature. In zirconia, the proporti onality constant is related to the volume and the charge on the oxygen ion by considering thermodynamic equilibrium among the electrochemical potentia ls of the oxygen ion at the stressed and unstressed interfaces. The agreeme nt with theory is within 10% for specimens made of polycrystalline zirconia , or single crystal cubic zirconia of (100) orientation. The proportionalit y constant changes by up to 20% for other orientations of the single crysta l; this change is attributed to differences in the effective charge on the oxygen ion on different surface orientations. The kinetics of the voltage r esponse was also investigated in detail; it is consistent with the diffusio n of the oxygen ion along the interface formed between the metal electrode and the zirconia surface. The present measurements provide the first experi mental confirmation of the fundamental relationship between the chemical po tential, the normal traction, and the atomic volume of species at interface s of crystalline materials. The measurement has implications in further und erstanding of diffusional creep, creep cavitation and sintering in ionic (o r partially ionic) solids. (C) 1999 Acta Metallurgica Inc. Published by Els evier Science Ltd. All rights reserved.