Synthesis and electrical conductivity of perovskite-type PrCo1-xMgxO3

Oxides in the system PrCo1-xMgxO3 (x=0.0, 0.05, 0.10, 0.15, 0.20, 0.25) were synthesized by citrate technique and characterized by powder X-ray diffraction and scanning electron microscope. All compounds have a cubic perovskite structure (space group Oh1-Pm3-bar m). The maximum ratio of doped Mg in the system PrCo1-xMgxO3 is x=0.2. Further doping leads to the segregation of Pr6O11 in PrCo1-xMgxO3. The substitution of Mg for Co improves the performance of PrCoO3 as compared to the electrical conductivity measured by a four-probe electrical conductivity analyzer in the temperature range from 298 to 1073K. The substitution of Mg for Co on the B site may be compensated by the formations of Co4+ and oxygen vacancies. The electrical conductivity of PrCo1-xMgxO3 oxides increases with increasing x in the range of 0.0-0.2. The increase in conductivity becomes considerable at the temperatures >=673K especially for x>=0.1; it reaches a maximum at x=0.2 and 1073K. From x>0.2 the conductivity of PrCo1-xMgxO3 starts getting lower. This is probably a result of the segregation of Pr6O11 in PrCo1-xMgxO3 , which blocks oxygen transport, and association of oxygen vacancies. A change in activation energy for all PrCo1-xMgxO3 compounds (x=0-0.25) was observed, with a higher activation energy above 573K and a lower activation energy below 573K. The reasons for such a change are probably due to the change of dominant charge carriers from Co4+ to Vo in PrCo1-xMgxO3 oxides and a phase transition mainly starting at 573K