Dielectric Response of Ta2O5, NbTaO5 and Nb2O5 from First-Principles Investigations

High-κ dielectrics are intensively investigated as a replacement for SiO2 in integrated nanoelectronics. Ta and Nb based oxides are among the list of interesting candidates that display a relatively large dielectric constant with a band gap larger than 3 eV. In this paper, we show that it is possible to modulate the dielectric response of the Ta2O5 by admixing it with Nb2O5. The dynamical charges and dielectric constants of Ta2O5 and of Nb2O5 were calculated at the Density Functional Theory (DFT) level for different crystal phases. The averaged dielectric constants range between 27(38) and 42(77) for Ta2O5 (Nb2O5) in the hexagonal and orthorhombic varieties. Interestingly, a mixed NbTaO5 composition exhibits a directionally averaged dielectric constant of 54 and a relatively large band gap, close to the arithmetic mean value of the binary species. The origins of the dielectric permeability are discussed and confronted to experimental measurements.