https://ri.ufs.br/jspui/handle/riufs/552 2026-04-26T03:15:39Z 2026-04-26T03:15:39Z Lima, Adilmo Francisco de Dantas, Jeânderson de Melo Lalic, Milan https://ri.ufs.br/jspui/handle/riufs/644 2024-11-01T00:32:25Z 2012-11-01T00:00:00Z

Título: An ab-initio study of electronic and optical properties of corundum Al2O3 doped with Sc, Y, Zr, and Nb Autor(es): Lima, Adilmo Francisco de; Dantas, Jeânderson de Melo; Lalic, Milan Abstract: Ab-initio calculations based on density functional theory have been employed to study the structural, electronic, and optical properties of yttrium (Y), scandium (Sc), zirconium (Zr), and niobium (Nb) doped α-Al2O3 with corundum structure. Exchange and correlation effects between electrons have been treated by generalized gradient approximation within the Perdew-Burk-Ezrenhof parameterization and by recently developed Tran-Blaha modified Becke-Johnson approach. Most attention in the work has been paid to the impurity d states, whose energy splitting has been analyzed in terms of the crystal field theory and whose influence on the gap size and the offset of the bands around it has been carefully evaluated. The influence of these states on modification of the optical absorption edge and the static dielectric constant of the doped systems has been also studied. It is concluded that only the Y doped α-Al2O3 (1) preserves the size of the band gap of the pure alumina, (2) does not change significantly the band offset around it, and (3) elevates the value of the static dielectric constant of the compound. These three conditions, necessary for usability of the doped material as a high-ε dielectric gate, are not satisfied by the Sc-, Zr-, and Nb-doped alumina compounds. Therefore, only the Y-doped α-Al2O3 exhibits potential to be further explored for employment in the semiconductor industry.

2012-11-01T00:00:00Z Lima, Adilmo Francisco de Lalic, Susana de Souza Lalic, Milan https://ri.ufs.br/jspui/handle/riufs/643 2013-07-16T05:00:09Z 2009-07-01T00:00:00Z

Título: Electronic structure and optical absorption of the Bi4Ge3O12 and the Bi4Si3O12 scintillators in ultraviolet region: an ab initio study Autor(es): Lima, Adilmo Francisco de; Lalic, Susana de Souza; Lalic, Milan Abstract: Ab initio calculations based on density-functional theory have been employed to study structural and electronic properties of Bi4Ge3O12 (BGO) and Bi4Si3O12 (BSO), as well as their optical characteristics in ultraviolet region, up to 40 eV. The electronic structure around the band gap is found to be similar in both compounds, dominated by the O p- and the Bi s-states (valence band top) and the Bi p-states (conduction band bottom). The gap is found to be indirect in both BGO and BSO. The optical spectra are analyzed, compared, and interpreted in terms of calculated band structures. It is shown that the absorption process involves significant energy flow from the O ions to the Bi ions. This fact stresses importance of the first neighborhood of the Bi (six O’s forming an octahedron), which is more distorted in the BSO than in the BGO. The latter difference is mainly responsible for the different absorption characteristics of the BGO and BSO.

2009-07-01T00:00:00Z Lima, Adilmo Francisco de Lalic, Milan https://ri.ufs.br/jspui/handle/riufs/642 2013-07-16T05:00:07Z 2010-10-01T00:00:00Z

Título: Structural, electronic, and optical aspects of Cr doping of the Bi4Ge3O12: an ab initio study Autor(es): Lima, Adilmo Francisco de; Lalic, Milan Abstract: Ab initio calculations based on density functional theory have been employed to study energetic, structural, electronic, and optical properties of Cr doped Bi4Ge3O12 (BGO). Two possible accommodations of Cr impurity have been taken into account: at the Ge (Cr4+) and the Bi (Cr3+) substitution site. For each accommodation the local structure around the Cr has been determined, and in the Cr3+ case the Cr off-site displacement was analyzed. The Cr d-states are positioned at the bottom of the conduction band and within the gap in form of two deeplike (Cr4+) and shallowlike (Cr3+) bands, exhibiting magnetic moments of +1.58 μB and −2.44 μB, respectively. The Cr dominated part of absorption spectrum is calculated and analyzed in terms of Cr band arrangement. Comparison with the experimental BGO:Cr absorption spectrum suggests that it consists of both Cr3+ and Cr4+ contributions, indicating the Cr simultaneous presence at both substitution sites

2010-10-01T00:00:00Z Lima, Adilmo Francisco de Farias, Sérgio Antônio de Souza Lalic, Milan https://ri.ufs.br/jspui/handle/riufs/641 2013-07-16T05:00:10Z 2011-10-01T00:00:00Z

Título: Structural, electronic, optical, and magneto-optical properties of Bi12MO20 (M5Ti, Ge, Si) sillenite crystals from first principles calculations Autor(es): Lima, Adilmo Francisco de; Farias, Sérgio Antônio de Souza; Lalic, Milan Abstract: The structural, electronic, optical, and magneto-optical properties of the three Bi12MO20 sillenites (BMO; M = Ti, Ge, and Si) have been investigated on the basis of the first-principles calculations performed by the full potential augmented plane wave method. The BMO’s linear optical responses are found to be very similar, but their optical rotatory powers and Faraday ellipticities exhibit notable differences in both visible and ultraviolet parts of the spectra. These differences originate from the subtle differences within the BMO’s electronic structures, such as different band-gaps and different offsets of the valence band tops. The latter are found to be caused not by the influence of the M ion electronic states, but by particular behavior of the M–O and the Bi–O chemical bonds.

2011-10-01T00:00:00Z