Magnetic and Electrical Properties of CoRE 2 W 2 O 10 Ceramic Materials.

Microcrystalline samples of CoRE 2 W 2 O 10 tungstates (RE = Y, Dy, Ho, Er) were prepared by a high-temperature solid-state reaction and then sintered into a ceramic form for unique properties and potential applications. For this purpose, structural, microscopic, ultraviolet-visible (UV-vis), magnetic, electrical, and thermoelectric measurements were performed. These studies showed a monoclinic structure, paramagnetism, short-range antiferromagnetic interactions in all samples, long-range ferrimagnetic interactions only in CoY 2 W 2 O 10 , poor n -type conductivity of 6.7 × 10 -7 S/m at room temperature, strong thermal activation ( E a1 = 0.7 eV) in the intrinsic region, a strong increase in the power factor ( S 2 σ) above 300 K, a Fermi energy ( E F ) of 0.16 eV, and a Fermi temperature ( T F ) of 1800 K. The above studies suggest that anion vacancy levels, which act as doubly charged donors, and to a lesser extent, the mixed valence band of cobalt ions (Co 2+ , Co 3+ ), which are located below the bottom of the conduction band and below the Fermi level, are responsible for electron transport.