Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: I, Electrical Conductivity

Abstract

The electrical behavior of NaNbO3 ceramic samples with different relative densities was investigated by ac impedance spectroscopy in a range of 13 MHz to 10−3 Hz between 400° and 800°C in dry air. Measurements were performed during heating and cooling cycles. The Nyquist impedance diagrams of dense sodium niobate exhibit only one semicircle representing the grain contribution with depression angles as small as 1°, indicating a high homogeneity of the specific electrical properties. In the case of porous samples, the data reveal an additional low‐frequency semicircle related to microstructure. For all studied samples, the Arrhenius conductivity plots show a change in the activation energy around 640°C, attributed to the tetragonal‐cubic phase transition. The electrical conductivity of porous samples appears to be higher than that of dense ones.

Effect of γ-Irradiation on the Dielectric and Conductivity Properties of Nano-Wollastonite

“…In semiconducting SrTiO 3 doped with Y 2 O 3 , it is reported that increase in porosity has resulted in decrease in conductivity [19]. However, in polycrystalline NaNbO 3 ceramic, porous counterpart is known to exhibit higher bulk conductivity than dense ones [20]. In any case, exposure of ceramic powders to γ-radiation has resulted in modifications in the dielectric and electrical properties of nano-β-CaSiO 3 .…”

Dielectric and AC conductivity studies of CdSe nanocrystals doped sol–gel silica matrices

“…It can be seen that R b, C b and increases with increase in concentration of the samples. The presence of spike at low frequencies is typical of polarization effects at the electrodes and indicates the presence of an ionic contribution to the electrical conductivity [27,28]. …”

Comportamento elétrico a alta temperatura de termistor cerâmico alfa-Fe2O3 com coeficiente de temperatura negativo

“…Como exemplo, a 573 K, a contribuição da cauda na modelagem do comportamento pode ser desprezada para efeitos de modelagem, uma vez que sua magnitude (4,72x10 3 W) é muito inferior à resistência total determinada pela soma das resistências de grão e contorno de grão (2,36x10 5 W), o que corresponde a 2% da resistência total. Este comportamento tem sido identificado em outros materiais, onde a cauda foi associada a um componente regular do contorno de grão [24] devido a eventual distribuição de características de contorno de grão como estado de oxidação, orientação de grão, tensão da rede, etc.. Não foi observado nos diagramas de impedância fenômeno relacionado à contribuição do eletrodo, caracterizado por meio de retas representando difusão de espécies iônicas na região de baixas freqüências [25].…”