Enhancement of dielectric constant in transition metal doped ZnO nanocrystals

We have presented dielectric studies on Zn1−xCoxO, Zn1−xFexO, and Zn1−xFex/2Cox/2O (x = doping level) semiconducting nanoparticles (∼2–40 nm). For all those samples, dielectric constant (є) is found to exhibit a maximum with x. Enhancement of є is found to be ∼250 times for Zn0.85Co0.15O and ∼400 times for Zn0.8Fe0.1Co0.1O from that of ZnO. Presence of effective higher oxidation state of transition metals ions in ZnO due to Fe/Co doping resulting in space charge polarization possibly yields this effect. The simultaneous existence of high є, semiconducting, and ferromagnetic like behaviour at 300 K seems to propose Zn0.8Fe0.1Co0.1O, promising for technological application.