Thermally stimulated depolarization current properties of Co4Nb2O9 ceramics

Thermally stimulated depolarization current in magnetoelectric antiferromagnet Co₄Nb₂O₉ were investigated above Néel temperature, and five current peaks (denoted as P0 ~ P4 in the order of ascending temperature) were observed. These peaks are related to holes which can be trapped by cobalt vacancies, their surrounding medium (self-trapped), internal, and surface barrier layers. In low-temperature range, the holes are bound to cobalt vacancies. The polarization caused by bound holes yields P0 peak at 46 K. In middle-temperature range, the holes are localized by the surrounding medium forming polarons. The hopping motions of the self-trapped holes create P2 peak at ~120 K. The microdisplacements around their locating positions for the self-trapped holes lead to P1 peak, whose peak temperature strongly depends on the poling temperature but lower than that of P2 peak. In high-temperature range, the holes are trapped by internal and surface barrier layers giving rise to P3 peak at ~150 K and P4 peak at ~230 K, respectively.