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Detailed structural and optical properties of α-(AlxCr1−x)2O3 (0 ≤ x ≤ 1) synthesized by the solid state reaction method have been investigated. Single phase α-(AlxCr1−x)2O3 with space group R 3 ¯ c is obtained for the full composition range of 0 ≤ x ≤ 1. Variations in the lattice parameters a and c have been determined. Lattice parameter c follows Vegard's law, while the lattice parameter a shows a clear deviation with a bowing parameter of −0.035 Å. This behavior of the lattice parameters of α-(AlxCr1−x)2O3 with x is explained in detail by studying the local structure. Extended x-ray absorption fine structure spectroscopy shows a reduction in the values of Cr–O bond lengths with composition x. Optical absorption measurements of α-(Al1−xCrx)2O3 for 0 ≤ x ≤ 1 show a large bandgap tunability of 1.9 eV (from 3.4 eV to 5.3 eV). The photoemission spectroscopy data and the analysis of partial density of states obtained from first principles electronic structure calculations suggest that the valence band maxima is mainly composed of Cr 3d levels, which hybridize with the O 2p levels. Increased contribution of O 2p partial density of states is observed with Al substitution, which is expected to enhance p-type carrier conduction in the α-(AlxCr1−x)2O3 system as compared to the parent α-Cr2O3 system. Thus, the large bandgap, its tunability in the UV region, and the predicted enhancement of p-type conductivity in the α-(AlxCr1−x)2O3 system make it a potential candidate for application in UV based photo-detectors and transparent electronics. [ABSTRACT FROM AUTHOR]

Abstract We report the structural and optical properties of ternary α-(Ga x Cr (1- x)) 2 O 3 with 0 ≤ x ≤ 0.45 which is synthesized by solid state reaction method. Single phase with space group R-3c is obtained for the gallium composition range of 0 ≤ x ≤ 0.45 and further increase in Ga concentration results in appearance of secondary C 2/ m phase corresponds to Ga 2 O 3. Variations in the in-plane ’ a’ and out of plane ’ c’ lattice parameters shows a clear daviation from the Vegard's law with the bowing parameters of −0.0510 Å and 0.0305 Å respectively. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows larger values of Ga-O bond lengths, which elucidate the deviation in lattice parameters from the Vegard's law and immisibility of Ga in Cr 2 O 3 lattice. Diffuse reflectance spectroscopy (DRS) confirms a blue shift of 0.5 eV in the band gap of α-(Ga x Cr (1- x)) 2 O 3. It has also observed that Cr 3d level shifted towards the O 2p level in the valence band which has been reconfirmed by photo electron spectroscopy. The observed shift indicates enhancement of mixing between these levels which can leads to further delocalization of hole states in the valence band responsible for p-type conduction in the α-Cr 2 O 3. These results suggest that ternary α-(Ga x Cr (1- x)) 2 O 3 (0 ≤ x ≤ 0.45) can be useful in the field of UV transperant electronics and photodetectors. Highlights • Synthesis of α-(Ga x Cr (1- x)) 2 O 3 (0 ≤ x ≤ 0.45) by solid sate reaction method. • Deviation of lattice parameters from the Vegard's law and immiscibility of Ga is discussed. • Tunability of ∼0.5 eV in the bandgap of α-Cr 2 O 3 as a function of Ga composition. • Enhancement in the mixing of Cr d and O 2p states in the valance band. [ABSTRACT FROM AUTHOR]

Abstract Polycrystalline NiCrGa half Heusler alloy, which is predicted to be a half-metallic ferromagnet from first principles calculations, has been synthesized by arc meting technique and its structural, magnetic as well as the electronic properties have been studied. The measured x-ray diffraction (XRD) pattern shows the signature of a disordered structure. Magnetization and magnetoresistance measurements indicate a competition between ferromagnetic and antiferromagnetic correlations in the sample, with no evidence of long range magnetic order down to the lowest temperature (2 K) and highest magnetic field (70 kOe) studied. The experimentally observed structural and magnetic properties are found to be significantly different from the theoretically predicted properties of the ordered cubic C1 b structure. To probe into the possibility of the presence of atomic disorder in the system, we have performed theoretical calculations using the spin-polarized-relativistic Korringa-Kohn-Rostoker method (SPR-KKR). By comparing the experimental data from XRD, magnetization, photoelectron spectroscopy measurements and theoretical calculations, we conclude that NiCrGa has significant amount of atomic disorder. Although, the ordered structure is energetically more stable than the disordered structures, we find that after synthesis, the system tends to stabilize in a disordered structure. The nature of the disorder has been ascertained from experiments and the corresponding electronic structure and magnetic properties have been obtained. With this atomic disorder present in the sample, the ferromagnetic ordering is disturbed and the spin polarization is consequently reduced. [ABSTRACT FROM AUTHOR]