Transport properties and dielectric response of Pr0.8Na0.2-xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) ceramics synthesized by sol-gel method

The effect of substituting sodium by potassium on electrical and dielectric properties is investigated in details for the GdFeO3-type Pr0.8Na0.2-xKxMnO3 (x = 0.00, 0.05, 0.1, 0.15 and 0.2) manganites. The electrical measurements indicate that the parent compound exhibits a metal behavior. When introducing potassium, all samples show a metal-semiconductor transition. Then, the increase of K content reduces the resistivity in the whole temperature range but doesn't affect the metal-semiconductor temperature transition (T-MS). At a specific temperature T-S, a saturation region was marked in the resistivity curve. It is found that T-S values shift toward lower temperatures when the potassium content rises. The T-S value approaches to room temperature for x = 0.2. The temperature coefficient of resistance (TCR) of the investigated manganites shows significant value, especially for x = 0, indicating that these ceramics can be used for a specific application such as bolometer technology. The frequency dependence of conductance was investigated through Jonscher's universal power law and the electrical conduction mechanism well interpreted by the correlated barrier hopping (CBH) model. Impedance spectroscopy measurements indicate that the electrical behavior of these perovskites is primarily dominated by the grain boundary response. The dependence of the dielectric constant on the frequency and the temperature confirms that the investigated samples are of a classical dielectric type.