Papers by Jailton Souza de Almeida
Physics and Chemistry of Minerals, 2006
Combined X-ray powder diffraction, Mo¨ssbauer, and XANES spectroscopy in situ experiments reveale... more Combined X-ray powder diffraction, Mo¨ssbauer, and XANES spectroscopy in situ experiments revealed the transformation of cubic (Mg 0.8 Fe 0.2 )O ferropericlase to a rhombohedrally distorted phase at 35(1) GPa and room temperature. The Mo¨ssbauer spectroscopy results show that the rhombohedral distortion does not involve magnetic ordering. Combined with data from the literature, our results imply that the cubic to rhombodedral transition occurs in (Mg,Fe)O under conditions of non-hydrostatic stress over a wide range of composition (0.2 £ x Fe £ 1).
Physics and Chemistry of Minerals, 2006
Combined X-ray powder diffraction, Mo¨ssbauer, and XANES spectroscopy in situ experiments reveale... more Combined X-ray powder diffraction, Mo¨ssbauer, and XANES spectroscopy in situ experiments revealed the transformation of cubic (Mg 0.8 Fe 0.2 )O ferropericlase to a rhombohedrally distorted phase at 35(1) GPa and room temperature. The Mo¨ssbauer spectroscopy results show that the rhombohedral distortion does not involve magnetic ordering. Combined with data from the literature, our results imply that the cubic to rhombodedral transition occurs in (Mg,Fe)O under conditions of non-hydrostatic stress over a wide range of composition (0.2 £ x Fe £ 1).
Chinese Science Bulletin, 2001
The single-phase sample of MgB2 was prepared successfully at the temperature of 900°C and under t... more The single-phase sample of MgB2 was prepared successfully at the temperature of 900°C and under the pressure of 3 GPa. The structure of the sample was investigated using powder X-ray diffraction and Rietveld analysis. The results show that the structure of the sample belongs to the hexagonal structure with space group of P6/mmm, a=3.0861(5) Å, c=3.5222(8) Å. The magnetic and
Journal of Physics: Condensed Matter, 2008
... least squares polynomial approximations. It is worth noting that the first and third strain i... more ... least squares polynomial approximations. It is worth noting that the first and third strain in table 1, although not being volume conserving, have tetragonal symmetry together with the volume conserving second strain. The ci j:s ...
Journal of Physics-condensed Matter, 2008
... least squares polynomial approximations. It is worth noting that the first and third strain i... more ... least squares polynomial approximations. It is worth noting that the first and third strain in table 1, although not being volume conserving, have tetragonal symmetry together with the volume conserving second strain. The ci j:s ...
Journal of Physics-condensed Matter, 2004
We report on a density functional theory calculation of the electronic structure and optical prop... more We report on a density functional theory calculation of the electronic structure and optical properties of γ -Al 2 O 3 . We have made a comparison between the optical and electronic properties of the α and γ phases of alumina. The calculated bulk modulus of the γ phase is slightly lower than that of the α phase. The calculated static dielectric function and the optical constant of the γ phase are very close to those of the α phase.
Journal of Applied Physics, 2003
... density-of-states as functions of composition The imaginary part of the dielectric function w... more ... density-of-states as functions of composition The imaginary part of the dielectric function was calculated from the joint density-of-states and the optical matrix elements, whereupon the real part of the dielectric function was obtained by using the KramerKronig dispersion relation ...
Journal of Applied Physics, 2002
The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated... more The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.
Applied Physics Letters, 2009
We report on the behavior of structural and electronic properties of yttrium trihydride under pre... more We report on the behavior of structural and electronic properties of yttrium trihydride under pressure using first principles calculations. We show that YH3 undergoes a structural transformation and its high pressure phase is dynamically stable under pressure since the peak at the imaginary frequencies of the phonon density of states, which account for the structural instability disappears at high pressure. Additionally, our GW calculations indicate a metallization of the high pressure cubic phase of YH3.
Physical Review B, 2000
The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepar... more The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepared by ion implantation, was investigated theoretically and experimentally at room temperature. The calculations were carried out within a framework of the random-phase approximation and the temperature and different manybody effects were taken into account. The experimental data were obtained with photoconductivity measurements. Theoretical and experimental results fall closely together in a wide range of donor concentration.
Physical Review Letters, 2007
In a series of experiments in externally electrically heated diamond anvil cells we demonstrate t... more In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above 240 GPa gold adopts a hexagonal -close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.
Solid-state Electronics, 1999
We report measurements of the optical band gap of Si 1Àx Ge x , by photoacoustic spectroscopy tec... more We report measurements of the optical band gap of Si 1Àx Ge x , by photoacoustic spectroscopy technique. The material has been obtained by a mechanical alloying process. Due to its technological application, in highperformance bipolar transistors and integrated circuits, the interest in the physical properties of Si 1Àx Ge x has recently increased. The metal±nonmetal transition (for x = 0.2) is determined to be 3.2 Â 10 18 cm À 3 . The optical band gap estimated from the absorption data at high boron concentration shows band gap narrowing when compared to the undoped alloy. #
Physical Review B, 2006
We report first principles self-consistent electronic structure calculations of RuO2 and IrO2 usi... more We report first principles self-consistent electronic structure calculations of RuO2 and IrO2 using the full-potential linearized augmented plane wave method. Our electronic properties are in good agreement with x-ray photoelectron spectroscopy data regarding the bandwidths and peak positions. Additionally, we probe our electronic structures by calculating the dielectric functions and comparing them with optical measurements. Our calculations show that intraband
Physical Review B, 2004
High-pressure synthesis is a powerful method for the preparation of novel materials with high ela... more High-pressure synthesis is a powerful method for the preparation of novel materials with high elastic moduli and hardness. Additionally, such materials may exhibit interesting thermal, optoelectronic, semiconducting, magnetic, or superconducting properties. We report on the new high-pressure, high-temperature synthesis of platinum carbide. The experiments were performed in a laser-heated diamond anvil cell and data were collected using the synchrotron X-ray diffraction method at pressures O75 GPa at high-temperatures. The new platinum carbide has a rock-salt type structure, with space group Fm3m and cubic symmetry. It was confirmed to remain stable to at least 120 GPa. This structure is the same as that of other metal carbides reported in previous studies. After decompression, the new high-pressure phase was recoverable at ambient pressure. The Birch-Murnaghan equation of state for this new phase was determined from the experimental unit cell parameters, with K 0 Z 301 (G15) GPa, and K 0 0 Z5.2 (G0.4).
Physical Review B, 2000
The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepar... more The band-gap shift of the heavily single and double-donor doped systems Si:Bi and Si:P,Bi, prepared by ion implantation, was investigated theoretically and experimentally at room temperature. The calculations were carried out within a framework of the random-phase approximation and the temperature and different many-body effects were taken into account. The experimental data were obtained with photoconductivity measurements. Theoretical and experimental results fall closely together in a wide range of donor concentration.
Applied Physics Letters, 2002
The effect of the transition energy of three-donor clusters on far infrared absorption in n-type ... more The effect of the transition energy of three-donor clusters on far infrared absorption in n-type semiconductor materials has been investigated by a multiconfigurational self-consistent-field model calculation and applied to GaAs and GaN systems. We show that it is crucial to consider the many-particle correlation effects within three-donor clusters. With electron correlation taken into account, the present results support the interpretation of a very recent unidentified peak energy observed in absorption measurement of GaN as due to electronic transitions in these clusters. We also corroborate the suggestion that the X line in GaAs arises from such transitions.
Journal of Applied Physics, 2006
We report the series of ruthenate-cuprates RuSr 2 LnCu 2 O 8 (Ru-1212Ln; Ln ¼ Y, Dy, Ho, Er), whi... more We report the series of ruthenate-cuprates RuSr 2 LnCu 2 O 8 (Ru-1212Ln; Ln ¼ Y, Dy, Ho, Er), which were prepared at 1200-1300°C under 6 GPa. High-purity sample could be obtained for every system with the ÔRu-poorÕ starting composition, Ru 0:9 Sr 2 LnCu 2 O 7:8 . It was confirmed that a solid solution of (Ru 1Àx Cu x )Sr 2 YCu 2 O y exists and its range terminates at x $ 0:1 without formation of the stoichiometric phase of RuSr 2 YCu 2 O y . Many Y-based samples were prepared varying the Ru/Cu ratio and the oxygen contents. According to DC susceptibility measurements, ferromagnetism and superconductivity looked to coexist below approximately 40 K in some samples. However, DC resistivity was always quite high even when a sample showed a large diamagnetism in a low temperature region. These results may suggest phase separation regarding the Ru/Cu ratio in the solid solution of (Ru 1Àx Cu x )Sr 2 YCu 2 O y , casting doubt for the coexistence of superconductivity and ferromagnetism.
Physical Review B, 2002
We have studied the effects of disorder, correlation, external electric field, impurity concentra... more We have studied the effects of disorder, correlation, external electric field, impurity concentration, and impurity location near and at the Si-SiO2 interface of a metal-oxide-semiconductor field-effect transistor, in the range of experimental interest. We show that the intraimpurity correlation energy and the binding energy have strong dependence with the applied electric field and the impurity location on the interface. Taking
Physical Review B, 2002
We have studied the effects of disorder, correlation, external electric field, impurity concentra... more We have studied the effects of disorder, correlation, external electric field, impurity concentration, and impurity location near and at the Si-SiO2 interface of a metal-oxide-semiconductor field-effect transistor, in the range of experimental interest. We show that the intraimpurity correlation energy and the binding energy have strong dependence with the applied electric field and the impurity location on the interface. Taking into account all the above effects the Hubbard-Mott scenario is presented. As a result we obtain a critical concentration of about 1011 cm-2, which can be discussed in terms of recent experimental findings.
Applied Physics Letters, 2006
A series of first principles calculations have been carried out to investigate structural, electr... more A series of first principles calculations have been carried out to investigate structural, electronic, and optical properties of BexZn1-xTe alloys for five beryllium compositions. Our results show that the lattice constant scales linearly with beryllium composition and there is a direct-to-indirect band gap crossover nearly at the composition of 20%. It is also found that no bowing effect in the absorption edge is observed unlike other II-VI semiconductor alloys. Our results are in good qualitative agreements with experimental observations.
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Papers by Jailton Souza de Almeida