Triclinic CdSiO 3 structural, electronic, and optical properties from first principles calculations (original) (raw)
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Chemical Physics Letters, 2006
The CaSiO 3 triclinic crystal was studied using a quantum mechanical first principles approach. Unit cell parameters have been optimized using the local density approximation (LDA) within the density functional theory (DFT) formalism in order to minimize the total energy. A comparison was made between these theoretical results and X-ray data. We also have calculated the electronic band structure, density of states, and optical absorption. Indirect band gaps E(Q ! C) = 5.43 eV and E(B ! C) = 5.44 eV, and a direct gap E(C ! C) = 5.52 eV were obtained, as well as effective masses for electrons and holes at the maximum and minimum of valence and conduction bands, respectively.
CdXO3 (X = C, Si, Ge, Sn, Pb) electronic band structures
Chemical Physics Letters, 2009
Electronic properties for a set of CdXO 3 (X = C, Si, Ge, Sn, Pb) crystals were investigated using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Hexagonal CdCO 3 and triclinic CdSiO 3 have indirect main energy band gaps while orthorhombic CdGeO 3 and CdSnO 3 exhibit direct interband transitions. Orthorhombic CdPbO 3 has a very small indirect band gap. The Kohn-Sham minimum electronic band gap oscillates as a function of the X ns level, changing from 2.94 eV (hexagonal CdCO 3 ; LDAÞ to 0.012 eV (orthorhombic CdPbO 3 ; LDA).
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Physics Procedia, 2013
The charge compensation effects induced by aliovalent doping were studied in the monoclinic CdSiO 3. An interstitial oxide ion may be feasible in this host to provide the extra negative charge required by the R 3+ doping. The oxide was studied in CdSiO 3 using density functional theory (DFT) calculations and synchrotron radiation (SR) luminescence spectroscopy. The crystal structure of this host was significantly modified by the interstitial oxide. The experimental band gap energy (E g) was perfectly reproduced by the calculations and intrinsic electron traps were revealed. Defect levels were found also in the interstitial oxide containing host, however their role has to be studied further.
Physical Review B, 2008
Soft x-ray emission spectroscopy ͑XES͒ and x-ray absorption spectroscopy ͑XAS͒ are employed to investigate the occupied and unoccupied electronic structures in rocksalt-phase single-crystal CdO. Resonant XES at the OK edge reveals a clear Cd 4d -O 2p hybridized peak and momentum-dependent coherent contributions to the resonant emission spectra. Good agreement is obtained between the above-threshold XES and XAS spectra, and the calculated O 2p local partial density of states ͑PDOS͒. Calculation of the O 2p PDOS was performed within the GW framework of many-body perturbation theory.
Low temperature synthesis of CdSiO3 nanostructures
Journal of the Brazilian …, 2011
Descreve-se a síntese de nanoestruturas de CdSiO 3 cristalino como fase única a 580 °C; ao que sabemos, esta é a mais baixa temperatura de formação observada até o presente para este composto. A formação da fase desejada ocorre somente a partir de de 580 °C, já que a 570 °C os picos de difração estão deslocados para menores ângulos em relação ao padrão JCPDS 85-0310. A fonte de silício influencia diretamente a morfologia do material: Na 2 SiO 3 leva à formação de nanopartículas na forma de agulhas, ao passo que sílica mesostruturada de alta área superficial leva a partículas coralóides. A difratometria de raios X em baixo ângulo mostra que o caráter mesosestruturado da sílica precursora não se mantém no CdSiO 3 resultante. A microscopia eletrônica de varredura sugere que, neste caso, haja uma transição da morfologia esférica do precursor para a morfologia em forma de agulhas do material obtido a partir de Na 2 SiO 3. A área superficial do precursor de sílica utilizado tem influência direta na formação de CdSiO 3 , pois o uso de sílica comercial de menor área superficial não resulta no produto desejado. We report the synthesis of single-phase, crystalline CdSiO 3 nanostructures at 580 °C; to the best of our knowledge, this is the lowest temperature at which this material is reported to form. The desired phase does not form below 580 °C, since the diffraction peaks are shifted to lower angles in the material treated at 570 °C when compared to JDPDS Card No. 85-0310. The source of silicon has strong influence on the product morphology: Na 2 SiO 3 yields single-phase CdSiO 3 in needle-shaped nanostructures, while high surface area mesostructured SiO 2 yields coralloidshaped particles. Low angle X-ray diffractometry reveals that the mesostructured nature of the silica precursor is not maintained in the resulting CdSiO 3. Scanning electron microscopy suggests that in this case a transition occurs between the spherical morphology of the precursor and the needle-shape morphology of the material prepared from Na 2 SiO 3. The surface area of the silica precursor has a strong influence in the reaction, since the use of commercial silica with a lower surface area does not yield the desired product.
Structural, electronic and optical properties of spinel oxides: Cadmium gallate and cadmium indate
The European Physical Journal Applied Physics
The structural, electronic and optical properties of two principal representatives of spinel oxides CdGa{2}O{4} and CdIn{2}O{4} have been investigated using the full-potential augmented plane-wave plus local orbitals method within density functional theory. We used the generalized gradient approximation (GGA) for the exchange-correlation (XC) potential. Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for the band structure calculations. The equilibrium lattice constants and the internal parameters are in agreement with the available experimental results. Results obtained for band structure using GGA-EV show a significant improvement over other theoretical work and are closer to the experimental data. The pressure dependence of band gaps is investigated. The dielectric function, reflectivity spectra and refractive index are calculated up to 50 eV. Pressure and volume dependence of the static refractive index have been also calculated.
Physical Review B, 2014
N-type CdO is a transparent conducting oxide (TCO) which has promise in a number of areas including solar cell applications. In order to realize this potential a detailed knowledge of the electronic structure of the material is essential. In particular, standard density functional theory (DFT) methods struggle to accurately predict fundamental material properties such as the band gap. This is largely due to the underestimation of the Cd 4d binding energy, which results in a strong hybridization with the valence-band (VB) states. In order to test theoretical approaches, comparisons to experiment need to be made. Here, synchrotron-radiation photoelectron spectroscopy (SR-PES) measurements are presented, and comparison with three theoretical approaches are made. In particular the position of the Cd 4d state is measured with hard x-ray PES, and the orbital character of the VB is probed by photon energy dependent measurements. It is found that LDA + U using a theoretical U value of 2.34 eV is very successful in predicting the position of the Cd 4d state. The VB photon energy dependence reveals the O 2p photoionization cross section is underestimated at higher photon energies, and that an orbital contribution from Cd 5p is underestimated by all the DFT approaches.
Physical Review B, 2009
The valence-band density of states of single-crystalline rock-salt CdO͑001͒, wurtzite c-plane ZnO, and rocksalt MgO͑001͒ are investigated by high-resolution x-ray photoemission spectroscopy. A classic two-peak structure is observed in the VB-DOS due to the anion 2p-dominated valence bands. Good agreement is found between the experimental results and quasi-particle-corrected density-functional theory calculations. Occupied shallow semicore d levels are observed in CdO and ZnO. While these exhibit similar spectral features to the calculations, they occur at slightly higher binding energies, determined as 8.8 eV and 7.3 eV below the valence band maximum in CdO and ZnO, respectively. The implications of these on the electronic structure are discussed.
Journal of Physics-condensed Matter, 2002
We report on first-principles band-structure calculations of the semiconducting CuAlO 2 delafossite compound in the pure form and also with Cd impurity occupying either a Cu or Al position. The computational tool was a fullpotential linear augmented plane-wave method, with the generalized gradient approximation accounting for the exchange and correlation effects. The changes caused by the presence of Cd are studied by the analysis of the electronic structure and the electric field gradient (EFG) in both Cd-doped and pure CuAlO 2 systems. Good agreement between the calculated and measured EFGs at Cd substituting for Cu or Al atoms in CuAlO 2 indicates that the calculations were able to correctly describe the ground state of the system containing the impurity. It is shown that a specific hybridization scheme, involving Cu (and Cd) s and d z 2 orbitals and neighbouring O p z orbitals, takes place at the Cu sites in CuAlO 2 as proposed earlier. The results of the calculations indicate that the Cd-doped system changes its electrical properties when Cd replaces Cu atoms (producing an n-type semiconductor), but not when it substitutes for Al atoms.
(X=C, Si, Ge, Sn, Pb) electronic band structures
Chemical Physics Letters, 2009
Electronic properties for a set of CdXO 3 (X = C, Si, Ge, Sn, Pb) crystals were investigated using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Hexagonal CdCO 3 and triclinic CdSiO 3 have indirect main energy band gaps while orthorhombic CdGeO 3 and CdSnO 3 exhibit direct interband transitions. Orthorhombic CdPbO 3 has a very small indirect band gap. The Kohn-Sham minimum electronic band gap oscillates as a function of the X ns level, changing from 2.94 eV (hexagonal CdCO 3 ; LDAÞ to 0.012 eV (orthorhombic CdPbO 3 ; LDA).