Sol-Gel Synthesis, Crystal Structure, Magnetic and Optical Properties in ZnCo2O3 Oxide

Synthesis of ZnCo2O3 oxide is performed by sol-gel method via nitrate-citrate route. Powder X-ray diffraction (XRD) study shows monoclinic unit cell having lattice parameters: a = 5.721(1) angstrom, b = 8.073(2) angstrom, c = 5.670(1) A, beta = 93.221(8)degrees, space group P-2/m and Z = 4. Average crystallite sizes determined by Scherrer equation are the range similar to 14-32 nm, whereas SEM micrographs show nano-micro meter size particles formed in ZnCo2O3. Endothermic peak at similar to 798 K in the Differential scanning calorimetric (DSC) trace without weight loss could be due to structural transformation and the endothermic peak similar to 1143 K with weight loss is due to reversible loss of O-2 in air atmosphere. Energy Dispersive X-ray (EDX) analysis profile shows the presence of elements Zn, Co and O which indicates the purity of the sample. Magnetic measurements in the range of +12 kOe to -12 kOe at 10 K, 77 K, 120 K and at 300 K by PPMS-II Physical Property Measurement System (PPMS) shows hysteresis loops having very low values of the coercivity and retentivity which indicates the weakly ferromagnetic nature of the oxide. Observed Xband EPR isotropic lineshapes at 300 K and 77 K show positive g-shift at g(iso) similar to 2.230 and g(i)(so) similar to 2.217, respectively which is in agreement with the presence of paramagnetic site Co2+(3d(7)) in the oxide. DC conductivity value of 2.875 x10(-8) S/cm indicates very weakly semiconducting nature of ZnCo2O3 at 300 K. DRS absorption bands similar to 357 nm, similar to 572 nm, similar to 619 nm and -654 nm are due to the d-d transitions T-4(1g)(F-4)-> E-2(g)((2)G), T-4(1g)(F-4)-> T-4(1g)(P-4), T-4(1g)(F-4)->(4)A(2g)(F-4), T-4(1g)(F-4) -> T-4(2)g(F-4), respectively in octahedral ligand field around Co2+ ions. Direct band gap energy, E-g similar to 1.5 eV in the oxide is obtained by extrapolating the linear part of the Tauc plot to the energy axis indicates fairly strong semiconducting nature of ZnCo2O3.