Electronic structure and light-induced conductivity in a transparent refractory oxide

Combined first-principles and experimental investigations reveal the underlying mechanism responsible for a drastic change of the conductivity (by 10 orders of magnitude) following hydrogen annealing and UV-irradiation in a transparent oxide, 12CaO.7Al2O3, found by Hayashi et al. The charge transport associated with photo-excitation of an electron from H, occurs by electron hopping. We identify the atoms participating in the hops, determine the exact paths for the carrier migration, estimate the temperature behavior of the hopping transport and predict a way to enhance the conductivity by specific doping.Comment: 4 pages including 4 figure

Electronic band structure and carrier effective mass in calcium aluminates

First-principles electronic band structure investigations of five compounds of the CaO-Al2O3 family, 3CaO.Al2O3, 12CaO.7Al2O3, CaO.Al2O3, CaO.2Al2O3 and CaO.6Al2O3, as well as CaO and alpha-, theta- and kappa-Al2O3 are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p-states and, although the band gap in Al2O3 is almost twice larger than in CaO, the s-states of both cations. Such a hybrid nature of the conduction band leads to isotropic electron effective masses which are nearly the same for all compounds investigated. This insensitivity of the effective mass to variations in the composition and structure suggests that upon a proper degenerate doping, both amorphous and crystalline phases of the materials will possess mobile extra electrons

Hopping versus bulk conductivity in transparent oxides: 12CaO∙7Al2O3

First-principles calculations of the mayenite-based oxide, [Ca12Al14O32]{2+}(2e-), reveal the mechanism responsible for its high conductivity. A detailed comparison of the electronic and optical properties of this material with those of the recently discovered novel transparent conducting oxide, H-doped UV-activated Ca12Al14O33, allowed us to conclude that the enhanced conductivity in [Ca12Al14O32]{2+}(2e-) is achieved by elimination of the Coulomb blocade of the charge carriers. This results in a transition from variable range hopping behavior with a Coulomb gap in H-doped UV-irradiated Ca12Al14O33 to bulk conductivity in [Ca12Al14O32]{2+}(2e-). Further, the high degree of the delocalization of the conduction electrons obtained in [Ca12Al14O32]{2+}(2e-) indicate that it cannot be classified as an electride, originally suggested.Comment: submitte