Effect of sintering temperature on the structure and transport properties of La4/3Sr5/3Mn2O7

La4/3Sr5/3Mn2O7 polycrystalline samples are prepared by the sol-gel method followed by sintering treatments at various temperatures (Ts). The sample sintered at lower Ts has higher insulator-metal transition temperature (Tp). But for the case of higher Ts, the sample has higher Tp and lower resistivity at the layer near the surface, but lower Tp and larger resistivity inside the sample. Based on the structure analysis, we propose that although a higher Ts favors the formation of Sr3Ti2O7 phase, it is likely for the segregation of (La, Sr)MnO3 phase to the surface layer, resulting in a higher Tp and lower resistivity at the layer near the surface.