Effect of Strontium and Cobalt Co-doping on the Structural and Electrical Properties of PrAlO_3 Perovskite Oxides

Novel Sr-and Co-codoped(Pr,Sr)(Al,Co)O3-δ perovskite oxide conducting ceramics were prepared by citrate process combined with subsequent high-temperature sintering.The phase composition,microstructure and electrical properties of the obtained ceramics were characterized by XRD,SEM and direct current four-wire method.The experimental results show that all the as-prepared Pr0.9Sr0.1Al1-yCoyO3-δ(y=0.1~0.5) ceramics are a single-phase rhombohedral perovskite structure,and their unit cell volumes,relative densities and electrical conductivities increase with increasing y in the doping range,while the increasing rate in electrical conductivity progressively decrease.Furthermore,these samples are a mixed conductor of oxygen ion and hole in air and their electrical conductivities are absolutely dominated by p-type conduction.The temperature dependence of electrical conductivity for Pr0.9Sr0.1Al1-yCoyO3-δ can be described by the small polaron hopping mechanism.For the as-prepared Pr1-xSrxAl0.5Co0.5O3-δ(x=0.1~0.4) ceramics,a second phase(Pr,Sr)CoO3obviously precipitates when x=0.2,indicating that the solid solubility limit of Sr on A site in this system is between 10at% and 20at%,and the(Pr,Sr)CoO3phase in samples increases gradually and finally becomes the main phase with further increase in Sr content.It is found that the electrical conductivity of Pr1-xSrxAl0.5Co0.5O3-δ ceramics roughly exhibits a trend of first increase and then decrease with increasing x in the whole examined temperature range,and reaches the maximum value at around x= 0.3.Additionally,the semiconductor-to-metal transition in the conduction behavior is obviously observed for the samples with x≥0.2,and the transition temperature gradually decreases with increasing Sr content.