In this paper we report the investigation of transition metal oxide compound, La_0.67Ca_0.25Sr_0.04Ba_0.04MnO₃ (LCSBMO), along with La_0.67Ca_0.33MnO₃ (LCMO), synthesized by sol–gel route under identical conditions. The effect of simultaneous low level substitution of large size ions such as Sr²⁺ and Ba²⁺ for Ca²⁺ ions on the electronic transport and magnetic susceptibility properties are analysed and compared apart from microstructure and lattice parameters. The temperature dependent electrical transport of the polycrystalline pellets of LCSBMO and LCMO when obeying the well studied law, ρ = ρ₀ + ρ₂ 𝑇² for 𝑇 < 𝑇_MI, is observed to differ by more than 50% from the values of ρ₀ and ρ₂, with the former compound showing enhanced electrical conductivity than the latter. Similarly in fitting the adiabatic small polaron model for resistivity data of both the samples for 𝑇 > 𝑇_MI, the polaron activation energy is found to differ by about 11%. In addition, the temperature dependent a.c. magnetic susceptibility study of the compounds shows a shift of about 6% in the paramagnetic to ferromagnetic transition temperature (285 K for LCSBMO and 270 K for LCMO).

Electrical resistivity and magnetoresistive behaviour of bismuth-substituted lanthanum manganites La_0.4Bi_0.1Ca_0.5–𝑥Sr_𝑥MnO₃ (𝑥 = 0.1 and 0.2) were systematically studied by varying the temperature from 2 to 300 K and the magnetic field up to 12 T. The samples were found to crystallize in rhombohedral structure and their morphology shows near-spherical nanosize crystallites. Charge ordering was observed in both the samples under zero field conditions and corresponding transition temperature 𝑇_CO was found to decrease with the increase of 𝑥. Resistivity measurements with magnetic field also showed suppression of magnetoresistivity (MR) with the increase of 𝑥 and the maximum MR was found to be 98 and 93% for 𝑥 = 0.1 and 0.2, respectively, at 10 T. In the high-temperature domain, the electronic transport was observed to be dominated by the variable range hopping mechanism for both the samples, whereas in the low-temperature domain the electrical conduction of 𝑥 = 0.1 sample was observed to be contributed by various other electron scattering mechanisms.