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The temperature dependence of the dielectric properties and ac conduction of YMnO3 ceramics annealed under different atmospheres is investigated from 25 to 700 °C. The origin of the dielectric anomalies is clarified. Two dielectric peaks in the permittivity accompanied by a single anomaly in the dielectric losses characterize the dielectric response. Simultaneously, three different regions can be distinguished in the temperature dependence of ac conductivity. Oxygen vacancies with an activation energy for the conduction of 1.13 eV are suggested to be responsible for the dielectric anomaly observed at < 400 °C. For temperatures > 400 °C, the dielectric data are influenced by conductivity and no ferroelectric anomaly is obvious. [ABSTRACT FROM AUTHOR]