Crystal Structure, Ionic Conductivity, Dielectric Properties and Electrical Conduction Mechanism of the Wyllieites Na1.5Mn3.5(AsO4)(3) and Na1.5Mn3Fe0.5(AsO4)(3)

(Na1.5Mn3MnIII)-Mn-II (0.5)(AsO4) (3) and Na1.5MnII Fe-3(III) (0.5)(AsO4) (3) compounds were synthesized via a high-temperature solid-state combustion reaction. The obtained samples were submitted to structural, morphological, and electrical characterizations. X-ray diffraction measurements revealed that both compounds crystallize in the monoclinic system with the space group P21/c. The lattice parameters were determined to be a = 6.78344 angstrom, b = 12.93830 angstrom, c = 11.22825 angstrom, and beta = 98.5374 angstrom for Na1.5Mn(II) Mn-3(0.5)III(AsO4)(3), and a = 6.76723 angstrom, b = 12.9864 angstrom, c = 11.256 angstrom, and beta = 98.8636 degrees for Na1.5Mn(2+) (3)Fe3+0.5(AsO4)(3). The structures consist of octahedral Mn-II and Mn-III or Fe-III ions connected by sharing edges, forming infinite chains. These chains are further connected by AsO4 tetrahedra, resulting in a three-dimensional anionic framework with tunnels parallel to the a-direction and cavities according to the c-direction. The structural models were validated using bond valence and charge distribution analyses. In addition to the structural characterization, the electric results depended on the crystal structures, indicating the potential of the studied materials for being used in several applications.