The results of a theoretical study on the point defects of monoclinic ␤-Ga 2 O 3 are reported here. The point defects considered here are vacancies, interstitials together with dopant ions such as Be, Mg, In, Cr, Si, Ge, Sn, and Zr. Since the low symmetry of the monoclinic lattice does not provide an unambiguous location of interstitial sites and migration paths, we propose a unique way for their identification in terms of the electron density topology. Special attention has also been given to the preference among the lattice and interstitial sites for the impurity defects, and its explanation in terms of structural, electrostatic, and electron density arguments. The calculated results find the most prominent features in the lattice to be the existence of ͑i͒ empty channels along the b direction, and ͑ii͒ atomic layers perpendicular to them. Their interplay governs the stability and mobility of the point defects in ␤-Ga 2 O 3. The anionic Frenkel pair consisting of the oxygen vacancy and oxygen interstitial is predicted to dominate the defect structure in the lattice. The dopants considered here are likely to be stabilized at the octahedral gallium sites, except for Be +2 , which prefers a tetrahedral gallium site in the lattice. Some of the possible migration paths have been determined, and the pseudoactivation energies for the intrinsic, oxygen-rich, and oxygen-deficient conditions are computed as a function of temperature. It is suggested that tuning the concentration of oxygen can lead to a change in the anisotropy of the ionic conductivity in ␤-Ga 2 O 3 .

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Single phase X type Fe2CoGa Heusler alloy nanoparticles with average crystallite sizes of 56 nm, 26 nm, and 21 nm have been synthesized using a refined template-less chemical route. Size...

The structural stabilities, elastic, electronic and magnetic properties of the Heusler-type shape memory alloy Ni(2)FeGa are calculated using density functional theory. The volume conserving tetragonal distortion of the austenite Ni(2)FeGa find an energy minimum at c/a = 1.33. Metastable behaviour of the high temperature cubic austenite phase is predicted due to elastic softening in the [110] direction. Calculations of the total and partial magnetic moments show a dominant contribution from Fe atoms of the alloy. The calculated density of states shows a depression in the minority spin channel of the cubic Ni(2)FeGa just above the Fermi level which gets partially filled up in the tetragonal phase. In contrast to Ni(2)MnGa, the transition metal spin-down states show partial hybridization in Ni(2)FeGa and there is a relatively high electron density of states near the Fermi level in both phases.

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