Structural, electronic, thermodynamic and optical properties of alkaline earth oxides MgO, SrO and their alloys

Abstract

The structural, electronic, optical and thermodynamic properties of Mg1−xSrxO ternary alloys in NaCl structures at various Sr concentrations are presented. The calculations were performed using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the local density approximation (LDA) and two developed refinements, namely the generalized gradient approximation (GGA) of Perdew et al (1996 Phys. Rev. Lett. 77 3865) for the structural properties and Engel and Vosko (1993 Phys. Rev. B 47 13164) for the band structure calculations. Deviation of the lattice constants from Vegard's law and the bulk modulus from the linear concentration dependence (LCD) were observed for the alloys. The microscopic origins of the gap bowing were explained by using the approach of Bernard and Zunger (1986 Phys. Rev. Lett. 34 5982). The refractive index and optical dielectric constant for the alloys of interest were calculated by using different models. In addition, the thermodynamic stability of the alloys was investigated by calculating the critical temperatures of alloys.

Cation Size Mismatch and Charge Interactions Drive Dopant Segregation at the Surfaces of Manganite Perovskites

“…Even if the feature is geometrically protruding from the surface, it appears depressed if the feature is less conducting or insulating compared to the rest of the film surface. This observation is supported by the drastically different energy gaps between the pristine LSM film and insulating SrO phases; 2.1–2.6 eV for LSM films from our previous work , and 5.7–5.9 eV for SrO . Therefore, this image contrast provides a direct evidence that the secondary phases formed upon dopant segregation are electronically more insulating than the rest of the film surface.…”

Optical properties of transition metal oxide quantum wells

“…STO has an experimental gap of 3.2 eV, 31,34 while the DFT calculation using local-density approximation (LDA) gives a gap of 1.7 eV. SrO has an experimental gap of 5.8 eV, 35 while LDA calculation only leads to a gap of 3.0 eV. The gap underestimation is typical for this approximation.…”

Off-centre motion in doped cubic oxides: A general view on the instability

“…Table 2 Calculated values of the f = DR/DR 0 quantity derived for the five considered impurities from the R values collected in Table 1 According to the criterion presented above we expect that it would be easier to find an off-centre instability using SrO as host lattice than in a stiffer lattice like MgO. This difference is well seen when comparing the bulk modulus of SrO (B = 91 GPa) with that of MgO which is 70% higher [49]. On the other hand, if we place the same impurity in the three cubic oxides the impurity-ligand distance, R, increases following the R 0 value of the host lattice.…”