Grain boundary modification in La0.67Ca0.33MnO3 manganites with additives: impact on magneto-transport properties

La0.67Ca0.33MnO3 manganite sample was synthesized using a sol-gel technique, and it was subsequently mixed with 1% of the additives Li2CO3, Bi2O3 and ZrO2, respectively. X-ray diffraction studies confirmed all the four samples were formed in single phase having an orthorhombic perovskite structure with the space group pnma. The estimated average grain size varies between 0.944 mu m and 1.245 mu m, and well-defined grains were observed in the additive samples with significant grain morphology in Li2CO3 additive, using morphological analysis. The magnetic and electrical behaviors of prepared samples were investigated in the temperature range (5-325 K) under constant applied magnetic field. The ferromagnetic to paramagnetic transition temperature (T-C) was found to be more than 300 K and exhibiting 50% of ferromagnetic fraction at room temperature. The metal-insulator transition temperature (T-P) is found to be in the neighborhood of the T-C. The study expounds the role of 1% addition of additives: Li2CO3 acts as conduction barrier at the grain boundaries and hence an increase in the magnitude of resistivity, whereas Bi2O3, ZrO2 act as conduction channel at grain boundaries as a result the decrease in resistivity when compared with the pure sample. The ZrO2 additive sample exhibiting highest MR% includes extrinsic and intrinsic nature, whereas the Li2CO3 additive sample exhibiting extrinsic nature only. The conduction mechanism was explained in ferromagnetic metallic phase and paramagnetic insulator phase using electron-magnon scattering model and small polaron hopping model, respectively.