Oxides of the type (La_2/5Ba_2/5Ca_1/5)(Mn_(2/5)–𝑥Ni_𝑥Ti_3/5)O₃ (0 ≤ 𝑥 ≤ 0.4) have been synthesized by the ceramic route. All the above oxides have been found to crystallize in the cubic perovskite structure. Rietveld refinement of the Ni-based oxide, (La_2/5Ba_2/5Ca_1/5)(Ni_2/5Ti_3/5)O₃ gave rise to a composition (La_0.44Ba_0.38Ca_0.18) (Ni_0.42Ti_0.58)O_2.85(6) and the refined lattice parameter obtained was 3.9411(2) Å (space group 𝑃𝑚$\bar{3}$𝑚; 𝑅(𝐹²) = 0.026, 𝑅_p = 0.074, 𝑤𝑅_p = 0.087). A shift from antiferromagnetic to paramagnetic behaviour is observed with increase in nickel concentration, the Mn-rich phases showing antiferromagnetism around 5 K. There is a systematic decrease in the dielectric constant, 𝜀 and loss tangent with increase in Ni concentration (from 𝜀 = 592 for 𝑥 = 0 to 𝜀 = 78 for 𝑥 = 0.4).

The present study describes the synthesis of ZnMn₂O₄ nanoparticles with the spinel structure. These oxide nanoparticles are obtained from the decomposition of metal oxalate precursors synthesized by

Our studies reveal that the shape, size and morphology of precursors and oxides vary significantly with the method of synthesis. The oxalate precursors prepared from the reverse micellar synthesis method were in the form of rods (micron size), whereas the coprecipitation method led to spherical nanoparticles of size, 40–50 nm. Decomposition of oxalate precursors at low temperature (∼ 450°C) yielded phase pure ZnMn₂O₄ nanoparticles. The size of the nanoparticles of ZnMn₂O₄ obtained from reverse micellar method is relatively much smaller (20–30 nm) as compared to those made by the co-precipitation (40–50 nm) method. Magnetic studies of nanocrystalline ZnMn₂O₄ confirm antiferromagnetic ordering in the broad range of ∼ 150 K. The photocatalytic activity of ZnMn₂O₄ nanoparticles was evaluated using photo-oxidation of methyl orange dye under UV illumination and compared with nanocrystalline TiO₂.