Ferrimagnetic transition, relaxor ferroelectric and optical properties in tungsten bronze Ba6MnNb9O30 ceramics

•The sample BMNO exhibited a ferrimagnetic transition at 43 K.•The sample BMCNO showed a cluster glass state.•Both samples exhibited the relaxor ferroelectric nature.•The sample BMCNO showed a superior energy storage with U = 1.58 J/cm3 and η = 74.5 %.•Two different optical absorption edges were achieved in both samples. The structural, magnetic, ferroelectric, dielectric and optical properties of Ba6MnNb9O30 (BMNO) and Ba6Mn0.5Co0.5Nb9O30 (BMCNO) ceramics were investigated. The samples can be indexed by a tetragonal lattice and the space group of P4bm with the presence of a tiny amount of impurity phase Ba1.04NbO3. The sample BMNO undergoes a short-range ferrimagnetic-like transition at 43 K originating from the spin canting of the antiferromagnetic coupling between the adjacent Mn2+ and Mn3+ based sublattices via the Dzyaloshinskii-Moriya interaction, whereas the sample BMCNO exhibits a local short-range antiferromagnetic state with the presence of weak ferromagnetic ordering. Both samples show the relaxor ferroelectric nature. The sample BMCNO possesses a superior energy storage property with a total energy density of 1.58 J/cm3 and a conversion efficiency of 74.5 %, which can be mainly ascribed to the improved densification and the reduced oxygen vacancies. Two different dielectric relaxations are discussed in term of the Vogel-Fulcher law. In addition, all samples have two different absorption edges and the optical band gaps are determined to be about 2.2 eV and 2.8 eV.