Physical and Chemical Properties of (Sr,Mg)FeO<sub>3-y</sub> System Heat-treated in N<sub>2</sub>

The perovskite solid solutions of the $Sr_{1-x}Mg_xFe{^{3+}}_{1-{\tau}}Fe{^{4+}}_{\tau}O_{3-y}$ system (x=0.0, 0.1, 0.2, and 0.3) were synthesized in $N_2$ at $1,150^{\circ}C$. X-ray powder diffraction study assured that all the four samples had cubic symmetries(SM-0: $3.865{\AA}$, SM-1: $3.849{\AA}$, SM-2: $3.833{\AA}$, and SM-3: $3.820{\AA}$) and that the lattice volumes decreased steadily from $57.7{\AA}^3$ to $55.7{\AA}^3$ with x values. The nonstoichiometric chemical formulas were determined by Mohr salt analysis and with the increase of x values the amounts of $Fe^{4+}$ ion and oxygen were decreased simultaneously. Thermal analysis showed that SM-0 started to lose its oxygen at $450^{\circ}C$ and SM-1, Sm-2, and SM-3 began to lose their oxygen at around $350{\sim}400^{\circ}C$. SM-0 showed almost reversible weight change in the cooling process. All the samples exhibited semiconducting behaviors in the temperature range of $10{\sim}400^{\circ}C$. Conductivities of the 4 samples were decreased in the order of SM-0, SM-1, SM-2, and SM-3 at constant temperature. The activation energies of the conductions were in the range of 0.176 eV~0.244 eV.