Anelastic Relaxation of Protonic Defects in M³⁺-Doped BaCeO₃

Abstract
When perovskite-structured BaCeO₃ is doped with M³⁺ ions (e.g., Nd³⁺, Gd³⁺, Yb³⁺) that substitute on Ce⁴⁺ sites, oxygen-ion vacancies are created for charge compensation. However, when treated in water vapor, the vacancies are replaced by protons, which take the form of OH ions. This treatment makes the materials a good protonic conductor. Questions about the defect structure of the protons are here investigated by means of internal friction measurements, at frequencies ≈6kHz. As many as three broadened Debye peaks have been found in the temperature range from 200 - 500 K, the relaxation strengths of which vary as the square of the dopant concentration. Defect clusters considered responsible include the M(OH) pair and the M₂(OH) triplet.