In this thesis, the La 0.80 Ba 0.20 Mn 1-x Al x O 3 ( micrometer sized samples were synthesized by sol jel method, and their structural, magnetic, and electrical properties have been investigated. Rietveld refinement of X-ray diffraction patterns indicates a rhombohedral structure with the ace group for all the samples. In all samples with 1350 o C and 750 o C sintering temperature, the unit cell volume does decrease regularly with Al content i (the Al ion has a smaller size of 0.535? than that of a Mn ion of 0.645 ?), but it increases by the further increase in Al doping level up to x=0.25. SEM images shows that grains being closer together by making the tablets, and the grain size increased and are more homogeneous by increasing annealing temperature. Ac susceptibility measurements show that for doping x=0 in 750 o C and 1350 o C annealing temperature, an increase of annealing temperature, reduces the Curie temperature, which is may be related to oxygen defects that result from reducing the ratio of Mn 3+ / Mn 4+ ions. Furthermore, ac susceptibility measurements shows that, the Curie temperature decreases with increasing aluminum doping. According to an ac magnetic susceptibility measurements on tablets, we have seen deviation from the Currie Weiss which may indicate the presence of Griffith’s phase in the samples. Moreover, spin-glass behavior was observed for x=0.15 doping. Electrical resistance measurements showes that, the behaviors of samples are insulator due to increasing aluminum doping, and only samples x=0 and x=0.10 showed insulator- metal transition. Also, the effects of grain boundaries with increasing aluminum doping, the effect of annealing temperature and the duration of annealing was studied by using SPH, percolation, and CCDC models. Finally, the phase diagram of La 0.80 Ba 0.20 Mn 1-x Al x O 3 composition in the range of was drawn by using the all results of the experiments in this study.
