Origin Of Colossal Dielectric Behavior In Double Perovskite Ba_2CoNbO_6

摘要

Ba_2CoNb0_6 ceramic samples were synthesized by solid-state reaction technique. X-ray photoemission spectroscopy reveals the coexistence of mixed-valent structure of Co~(2+) /Co~(3+) in the sample. Dielectric measurements reveal that the sample shows colossal dielectric behavior. This behavior is contributed by two thermally activated dielectric relaxations: the low-temperature relaxation is a polaron relaxation resulting from the hopping motions of self-trapped holes; the high-temperature relaxation is a Maxwell-Wagner relaxation caused by the grain-boundary response. Our results indicate a multirelaxation mechanism, i.e., the coupling of the polaronic relaxation and the Maxwell-Wagner relaxations might be a common origin of the colossal dielectric behavior found in different materials.