Structural, elemental, and electrical conduction properties of corundum-type Mg2Co2Nb2O9

ABSTRACT is a new member of the corundum-type family. Its crystal structure is trigonal with space group . and ions share the A-site with fifty-fifty occupancy. In , exhibits a 2 + oxidation state, whereas shows a reduction in the charge state from 5 + to 4 + due to the presence of vacancy-trapped electrons in dimmer. The conductivity spectra analysis in view of various transport models states that overlapping large polaron tunneling is the predominant transport process (polaron radius 10.65 Å) in the low-temperature range (303-473 K), while for the high-temperature range (573-673 K), the conduction is intrinsic, and the carriers are primarily small polarons. The proximity between optical bandgap (∼1.60 eV) and conduction activation energy (1.64 eV) is due to the formation of intermediate energy bands near the Fermi level and their participation in high-temperature intrinsic conduction.