Electronic band structure and carrier effective mass in calcium aluminates

Abstract

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 α-, θ-and κ-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.

Composition-dependent oxygen vacancy formation in multicomponent wide-band-gap oxides

“…In marked contrast to Zn, Ca does not exhibit a preference for fourfold coordination being sixfold-coordinated with oxygen in the ground state (rocksalt structure) as well as in most CaO-Al 2 O 3 structures [54]. Thus, in InAlCaO 4 , the difference between the formation energies in site-1 and site-5 is large, 1.4 eV, and is mainly determined by the differences in the metal-oxygen interaction in the corresponding binary oxides, Table I.…”

“…The corundum Al 2 O 3 has octahedrally coordinated Al atoms, but there are many stable oxide phases where Al is in fourfold coordination with oxygen [54]. Ga 2 O 3 has two nonequivalent Ga atoms in the ground-state monoclinic phase -one being fourfold coordinated and the other in sixfold coordination.…”

Secondary electron emission and glow discharge properties of 12CaO·7Al2O3electride for fluorescent lamp applications

“…Figure 6 schematically illustrates the electronic structure of the C12A7 electride [8][9][10][11][12][13][21][22][23][24][25]. The vertical axis indicates the energy measured from the vacuum level and the horizontal axis corresponds to the density of states.…”

“…A part of these cages can clathrate an electron as depicted in figure 1. Owing to the mobility of these cage electrons, C12A7 exhibits a high electrical conductivity of up to 1500 S cm −1 , and the low work function of this electride originates from the midgap states created by these electrons [21][22][23][24][25]. The operating voltage of the fluorescence lamp is known to be closely related to the work function of the cathode material, and the work function is much smaller for C12A7 (2.4 eV) than for Ni (5.0 eV), Mo (4.6 eV) or W (4.5 eV).…”

Combining Optical Transparency with Electrical Conductivity: Challenges and Prospects

“…For example, for ZnO in rocksalt (octahedral coordination) or wurtzite (tetrahedral coordination) structures, and for In 2 O 3 in Ia 3 (byxbyite), R 3c (corundum) or I2 1 3 structures, the effective masses vary by about 15%. Moreover, the effective mass remains nearly isotropic in all phases of the oxides -including those with irregular atomic arrangements or large structural voids [31,32].…”