Intermediate-spin state of Co ions in magnetic and thermoelectric properties of double perovskite Ba2CoNbO6.

Double perovskite Ba 2 CoNbO 6 , obtained by pyrolysis of nitrate-organic mixtures, was studied by XRD, XRF, DFT, AC/DC-magnetization, specific-heat, thermoelectric, and ESR methods. The sample has cubic symmetry space group Pm 3 m with a = b = c = 4.0074(11) Å. Deficiency in oxygen ions shows the presence of Co ions in both 3+ and 2+ valency. According to AC-magnetization and specific-heat data, Ba 2 CoNbO 6 demonstrates spin-glass ordering at T SG = 30 K at external field value of 0.1 kOe. This temperature of spin glass transition drops with field power increase down to complete suppression at 10 kOe. The effective magnetic moment determined using the Curie-Weiss approximation is 4.29 μ B , which is consistent with the theoretical estimation for Co ions in the intermediate-spin state. The peak at T = 90 K, observed in the temperature dependence of the specific heat and accompanied by a peak in the ESR linewidth, is possibly due to the structural transition at this temperature. The Seebeck coefficient of the compound is S = 4–6.5 μ V/K and the band gap obtained within the small-polaron-jump conductivity model is Δ E = 0.284 eV in the temperature range of 350–550 K connected with DFT calculation. An intensity ESR line, related to Co2+ ions, was observed in ESR spectra. • Double perovskite Ba 2 CoNbO 6 shows presence of two sublattices. • Co3+ ions present in the compound in intermediate- and low-spin states (S = 1 and S = 0, respectively). • Measurements show transitions in canonical spin-glass state at 30K for Ba 2 CoNbO 6. • The effective magnetic moment per unit cell is μ eff = 4.29 μ B. • Band gap is ΔE = 0.284eV. [ABSTRACT FROM AUTHOR]