Direct correlation between the band gap and dielectric loss in Hf doped BaTiO₃

Effect of Hf doping at Ti site in BaTiO₃ on the optical band gap (E_g), Urbach energy (E_u), dielectric constant (ε) and dielec-tric loss i.e. loss tangent (tanδ) have been investigated. It has been observed that with Hf doping, the value of E_g and E_u systematically increases whereas; the value of dielectric constant and dielectric loss systematically decreases. The decrease in the value of dielectric constant has been explained in terms of reduction in the tetragonality i.e. by c/a ratio. In the present investigation, it has been proposed that increase in the value of E_g and E_u, leads to decrease in the tunneling probability of electron from valence band to the conduction band which may result in decrease in the value of the dielectric loss. Present investigations clearly suggest that the value of dielectric loss is effectively controlled by E_g. Thus, through present studies, a new methodology has been proposed for understanding the origin of dielectric loss. Moreover, a possible correlation between the E_g and tanδ in terms of tunneling probability has been provided.