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首页> 外文期刊>Physica Scripta: An International Journal for Experimental and Theoretical Physics >Octahedral distortion and correlated electrical conduction of corundum type Co4Ta2O9 and Co4Nb2O9
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Octahedral distortion and correlated electrical conduction of corundum type Co4Ta2O9 and Co4Nb2O9

机译：八面体变形和刚玉型CO4TA2O9和CO4NB2O9的相关电导

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The structural, elemental and electrical conductivity properties along with the relaxor phenomena are studied for corundum type Co4Ta2O9 and Co4Nb2O9 ceramics. The refined x-ray diffraction results confirm that the unit cells of both the ceramics are isostructural to Mg4Ta2O9. A comparative study of polyhedral distortion shows that (Ta/Nb)O-6 octahedra are more distorted than CoO6 octahedra. X-ray photoelectron spectra of Co4Ta2O9 and Co4Nb2O9 compositions reveal that the majority of Co ions possess high spin 2+ oxidation state, whereas both Ta and Nb ions exhibit reduction in their oxidation state to 4+ suboxide state on the surface, because of the generation of oxygen vacancies along with trapped electrons in (Ta/Nb)(2)O-9 species. The effects of defect chemistry, ionic vacancies and crystal distortion on the charge transport and relaxor phenomenon are analyzed using impedance measurement over a wide range of temperature (30 degrees C-275 degrees C) and frequency (100 Hz-1 MHz). The frequency exponent eta versus T plot of Co4Ta2O9 proposes that both correlated barriers hopping and small polaron tunneling are the principal charge transport mechanisms at high and low-temperature regimes respectively. In this composition, at high-temperature regime vacancy trapped electrons are the major charge carriers, whereas at low-temperature regime the charge carriers are small polarons. For Co4Nb2O9, a single conduction process is observed above 5 kHz frequency where overlapping large polarons tunneling is the predominant conduction mechanism and below this frequency, electrode polarization prevails.
机译：研究了刚玉型CO 4TA2O9和CO4NB2O9陶瓷的结构，元素和电导率以及松弛剂现象。精制的X射线衍射结果证实，陶瓷的单位细胞是IsoScrontuctuctory至Mg4ta2O9。多面体畸变的比较研究表明（Ta / Nb）O-6八面体的o-6八面体比CoO6八面乳糖更扭曲。 CO 4TA2O9和CO 4NB2O9组合物的X射线光电胞组合物揭示了大部分CO离子具有高旋转2+氧化状态，而由于产生氧气空位与捕获的电子（Ta / Nb）（2）O-9种。使用受阻测量在宽范围的温度（30摄氏度-275摄氏度）和频率（100Hz-1MHz）上，分析缺陷化学，离子空位和晶体变形对电荷传输和弛豫现象的影响。 CO4TA2O9的频率指数ETA与T图表提出了两个相关的障碍跳跃和小极化子隧道的频率分别是高温和低温方案的主要电荷传输机制。在该组合物中，在高温调节空位中被捕获的电子是主要电荷载流子，而在低温调节器中，电荷载体是小极化子。对于CO4NB2O9，观察到在5kHz频率高于5kHz的频率之上，其中重叠大的极性隧道是主要的传导机构和低于该频率，电极极化占上去。

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