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The present work aims at investigating the electronic, optical, photovoltaic and thermoelectric properties of AgBiS2 compound using the density functional theory (DFT) and the modified Becke-Johnson exchange-correlation potential (mBJ). Both hexagonal Matildite and cubic Schapbachite polymorphs were considered. The hexagonal phase is found to be indirect gap semiconductor with band gap energy of about 1.07 eV and high absorption coefficient of 106 cm−1, whereas the cubic phase were metallic. The analysis of band alignment of Matildite with some binary oxides and sulfides revealed interesting results. The photovoltaic properties of AgBiS2 confirmed that Matildite phase could achieve a short-circuit current of 22 mA/cm2 and conversion efficiency of 20%. Also, we demonstrated that including photon recycling with a proper solar cell design could improve the conversion efficiency. Moreover, interesting thermoelectric performance has been confirmed.

In this study, first-principles investigations were performed using the full-potential linearized augmented plane-wave method of the structural and optoelectronic properties of thorium germinate (ThGeO4), a high-K dielectric material. Under ambient conditions, the structural properties calculated for ThGeO4 in the zircon phase were in excellent agreement with the available experimental data. Furthermore, using the modified Becke -Johnson correction method, the calculated band gaps and optical constants accurately described this compound. Finally, the thermal properties were predicted over a temperature range of 0–700 K and pressures up to 11 GPa using the quasi-harmonic Debye model, where the variations in the heat capacity, primitive cell volume, and thermal expansion coefficients were determined successfully.

To find a seemly solution to the problems of efficiency dependency of the hybrid PV/TE devices, on important factors like “high-absorbance with high-ZT materials” and improving the performance of existing devices, are essential research topics nowadays. In this regard, we report here optical coating, and thermoelectric features of the kesterite-structured Ag2CdSnS4 and Ag2CdSnSe4 compounds. These investigations are performed at the level of “full-potential linearized augmented plane wave plus local orbital method, FP-L(APW + lo)” framed within the “density functional theory (DFT)” method comprised with relativistic effects. Our study of the optical coating shows that both the investigated materials have a good level of absorbance (A), approximately 80% in the visible part of the spectra. Further, we found that the magnitude of reflectance (R) of the Ag2CdSnX4 (X = S, Se) thin films increase with increasing film thickness, while the response of the transmittance (T) spectra is reverse to it. These results are corroborated by the study of the transport properties by employing the Boltztrap code, and correspondingly electrical conductivity, Seebeck coefficient, electronic thermal conductivity as well as the figure of merit parameters were evaluated and analyzed as a function of the chemical potential for both investigated compounds at five values of the temperatures. Hence our obtained results show that both the investigated semiconductor materials exhibit strong potential for the application of hybrid PV/TE systems.

First principles calculations were carried out on the SrMoO4 compound which has been of interest owing to its technologically important physical properties. The structural, electronic, optical and thermal properties of this compound have been investigated under low pressure (LP) through the full potential linearized augmented plane wave method (FP-LAPW) within the framework of density functional theory. It is found that the phase transition from zircon to scheelite type structure occurs at negative pressure. The calculated ground state properties in scheelite structure are found to be in good accord with previously published data. Using the recently developed Tran Blaha-modified Becke Johnson approach, we have also studied the electronic band structure of this compound which shows the semiconducting behavior with a direct band gap of 4.30 eV in the scheelite phase, whereas the band gap is found to be 2.18 eV in the zircon phase. Various thermodynamic properties including the thermal volume expansion coefficient and heat capacities at constant volumes and pressures were calculated via the quasi-harmonic Debye model at different temperatures (0–1000 K). Furthermore, optical properties such as complex dielectric function, refractive index, and reflectivity spectra of the titled compound were studied for incident electromagnetic waves in an energy range up to 16 eV. The contributions to various transitions peaks in the optical spectra are analyzed and discussed with the help from the energy dependent imaginary part of the dielectric function.

In this paper, we present the results of a detailed computational study of the structural, electronics, optical, thermodynamic, and thermoelectric properties of the AgXO2 (X = In, Y) materials with delafossite-type structure, by using the “full-potential linearized augmented plane wave (FP-LAPW)" method. The calculated structural parameters of the title compounds are in excellent agreement with the available theoretical data. We have explored the dynamical stability of the AgXO2 compounds by investigating the phonon dispersion curves. The optoelectronic characteristics of the studied compounds were accurately described at the level of the “Trans Blaha modified Becke-Johnson (TB-mBJ)" approach to model the exchange-correlation potential. On the other hand, the optical characteristics of the AgInO2 and AgYO2 thin films were investigated in the wavelength range 200–750 nm for three different thicknesses: 300, 600 and 1300 nm on a transparent substrate (glass: nglass = 1.5, kglass = 0). Thermodynamic and thermoelectric properties of the considered compounds were predicted by employing the “quasi-harmonic Debye model” and the Boltzmann transport theory.

The optical absorbance of four ternary thin films, i.e. MgSiP2, MgGeP2, MgSiAs2, MgGeAs2 have been theoretically examined over a wide range of wavelength from 300 nm to 800 nm. The combination of first-principle electronic structure calculations and the optical matrix approach for modeling the multilayer assembly have been employed for theoretical studies. The analysis of the calculated absorbance spectra at room temperature with unpolarized light and normal incidence, revealed that MgGeAs2 with a direct energy band gap of 1.6 eV exhibit a considerable high optical absorption, where a thickness of 3.2 μm of this thin film is sufficient to absorb 90% of the incident light and generates a maximum photocurrent of ∼23 mA/cm2.

We theoretically investigate the possibility of enhancing light absorption in graphene-based one dimensional photonic crystal. We demonstrate that it is possible to achieve total light absorption at technologically important wavelengths using one-dimensional graphene-based photonic crystals. By means of the transfer matrix method, we investigate the effect of refractive indices and layer numbers on the optical response of the structure. We found that it is possible to achieve one peak, multi-peak or broadband, and complete optical absorption. As a result, the proposed photonic structures enable myriad potential applications such as photodetection, shielding and optical sensing.

A first principles study of structural, electronic and optical properties of zinc aluminum oxide (ZnAl 2 O 4 ) by means of the full potential linear augmented plane wave method is presented. The local density approximation is used for the exchange-correlation potential. A direct band gap of 4.19 eV, in agreement with experiment ( E g =3.9 eV), was determined. ZnAl 2 O 4 is transparent in the visible spectral region; the excitonic transition associated with the fundamental band gap is 4.17 eV. The refractive index value is 1.74 in the ultraviolet spectral region.

Refractive indices and birefringences for some representative uni-axial crystals such as II- SiP 2 and II- GeP 2 have been determined over a wide range of wavelengths by the use of first-principles electronic structure calculations. First, the calculated refractive indices are fitted usually by a generalized Sellmeier equation which consists of several oscillation terms involve in its parameters more direct information about material such as electronic transitions or resonance wavelengths. Then, in contrast to all other semiconductors under discussion our spectra show a negative birefringence for CdSiP 2 in agreement with the experimental data, and they exhibit a considerable dispersion near the band gap.

In this paper we focus on the novel solar material, namely cubic TiO2. The full potential linearized augmented plane wave method in combination with the local density approximation (LDA) and the generalized gradient approximation (GGA) have been used. We calculated structural parameters, elastic constants, wave velocities and thermal properties of the material assuming the fluorite structure. The obtained values were in good agreement with the available theoretical and experimental data. Moreover, the pressure and temperature dependences of the bulk modulus, Debye temperature, Heat capacity and linear expansion coefficient have been addressed for the first time.

In order to get a good overall description of the structural, electronic and optical properties of ternary chalcopyrite semiconductors especially for ZnSiAs2 and CdSiAs2, they have been calculated self consistently using the full potential augmented plane wave plus local orbital method (FPAPW+lo). The calculations are presented within the local density approximation (LDA), where we clarify the electronic and optical properties for both compounds. Since, we prove the existence of the direct band gap and also the efficiency of the method to give more details about the optical properties. We found that the most important features of the band gap is pseudo-direct for ZnSiAs2, and direct for CdSiAs2; then the contribution of the different transitions peaks are analyzed from the imaginary part of the dielectric function and the reflectivity spectra.

Full Potential Augmented Plane Wave plus local orbital method ( FAPW+lo) calculations were performed for ZnSiP2, ZnGeP2, and ZnSnP2 in the chalcopyrite structure in order to investigate the optical properties and to show the origin of the different optical transitions and their correspondence in the band structure. It is found that the most important features of the band gap is pseudo-direct for ZnSiP2, indirect for ZnGeP2, and direct for ZnSnP2. Then the contribution of the different transitions peaks are analyzed from the imaginary part of the dielectric function and the reflectivity spectra.

We investigated the pressure dependence of the excitation energies of the ternary CdXP2 (with X=Si, Ge and Sn) pnictide semiconductors in the chalcopyrite structure. Using a new full potential augmented plane wave plus local orbitals method, we have studied the effect of high pressure on the band structure and on the optical properties. We show that the pseudodirect band gap of CdSiP2 narrows with increasing pressure and the direct band gap of CdGeP2 changes to a pseudo-direct band gap. Furthermore, we find that the magnitude of the pressure coefficients for this series of materials changes from the pseudodirect to a direct band gap.

The optical properties of a ternary CdSnP 2 semiconductor have been studied in the chalcopyrite structure using the full potential augmented plane wave plus local orbital method (FPAPW + lo ). First, we present the main features of the structural and electronic properties of this compound, where the electronic band structure shows that the fundamental energy gap is direct at the centre of the Brillouin zone. The contribution of the different bands were analysed from the total and partial density of states curves. Moreover, our calculated optical properties suggest that there is an anisotropic optical conductivity of this crystal along both principal directions E ⊥ c axis and E ∥ c axis. The different direct interband transitions have been determined from the imaginary part of the dielectric function.

New structured mesoporous catalysts TiSBA15 were synthesised by grafting titanium atoms on the pore surface of various SBA15 materials by means of titanium tetrachloride in the gas phase. Site counting allowed us to optimise the experimental conditions in order to get the best selectivity and reactivity in the epoxidation of alkenes by various hydroperoxides in mild conditions (343–353 K). The silica based materials lead, in any case, to the selective formation of the epoxides with a high level of conversion over four catalytic runs.

Equilibrium lattice constants, bulk modulus, electronic band structure, and different optical transitions calculated by means of the full potential linearized augmented plane wave method are presented for BeCN2 in the chalcopyrite structure. Analysis of the band structure suggests a pseudo-direct band gap, which refers to an indirect band gap in binary compounds. We also discuss the relationships of the principal band gaps of the c-BN zinc-blende analogs. We investigate the assignment of the different optical transitions that are discussed in more detail from the reflectivity spectra. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; New mesoporous catalysts with a mean pore size of 65 Å have been synthesised by grafting titanium on a mesoporous silica SBA15 (Santa BArbara) by means of titanium tetrachloride in the gas phase. These catalysts have been tested for the green epoxidation of cyclooctene, cyclohexene, (R)-limonene and -pinene by hydrogen peroxide, tert-butyl hydroperoxide or cumyl hydroperoxide. The selectivity is 100% and epoxide yields can reach almost 100% in the case of organic hydroperoxides without any leaching of titanium species. Here we show that cyclohexene epoxidation could be used as the first step of a greener synthesis of adipic acid.

We have studied structural, electronic and optical properties of some A II B IV C 2 V ternary semiconductors, precisely CdSiP 2 and CdGeP 2 with chalcopyrite structure which are investigated using the full potential linearized augmented plane wave (FPLAPW) method. For treating the correlation term, we have choosen the local density approximation (LDA). The total-energy approach is used to determine the c / a ratio and the equilibrium volume. On the one hand, we have analyzed electronic properties such as band structures, electronic charge densities and density of states. On the other hand, optical properties are also derived.

New catalysts TiO2–SiO2 (Ti–SBA) with pore sizes of 37 and 65 A have been synthesized by grafting titanium on a structured mesoporous SBA15 (SBA for Santa BArbara and 15 for hexagonal structure) by means of titanium tetrachloride in the gas phase. These catalysts have been tested in the selective epoxidation of cyclooctene, cyclohexene, (R)-limonene and α-pinene. Whatever the oxidant, hydrogen peroxide (H2O2), tert-butyl hydroperoxide (TBHP) or cumyl hydroperoxide (CHP), the selectivity is 100%. However, the yield is low with H2O2 and the catalyst is partially leached out. In the case of TBHP and CHP the epoxide yields can reach practically 100% and no leaching of titanium is observed after four successive reaction cycles. An effect of pore size on the epoxidation kinetics of α-pinene and cyclooctene has been found.

The electronic structure, mechanical and thermodynamic properties of Fe2VX, (with X = Al and Ga), have been studied self consistently by employing state-of-the-art full-potential linearized approach of augmented plane wave plus local orbitals (FP-LAPW + lo) method. The exchange-correlation potential is treated with the local density and generalized gradient approximations (LDA and GGA). Our predicted ground state properties such as lattice constants, bulk modulus and elastic constants appear more accurate when we employed the GGA rather than the LDA, and these results are in very good agreement with the available experimental and theoretical data. Further, thermodynamic properties of Fe2VAl and Fe2VGa are predicted with pressure and temperature in the ranges of 0–40 GPa and 0–1500 K using the quasi-harmonic Debye model. We have obtained successfully the variations of the heat capacities, primitive cell volume and volume expansion coefficient.

The incorporation of aluminium into the framework of mesostructured SBA15 silica either by direct synthesis or by post-synthesis followed by titanium grafting using titanium tetrachloride as Ti precursor leads to bifunctional Ti–AlSBA15 catalysts very active in the “one-pot” synthesis of adipic acid. Depending on the mode of preparation, the reaction between cyclohexene and tert-butyl hydroperoxide (TBHP), under mild, stoichiometric conditions (353 K), can lead to an adipic acid yield better than 80%. trans-1,2-Cyclohexandiol, 2-hydroxycyclohexanone, glutaric and succinic acids are the main by-products of the reaction. Moreover, recycling and reuse of the catalysts do not show any loss of activity, proving that there is no leaching of aluminium or titanium, which is confirmed by elementary analysis.

New structured mesoporous catalysts TiSBA15 and Ti-A1SBA15 were synthesised by grafting titanium on the pore internal surface of various SBA15 and A1-SBA15 materials by means of titanium tetrachloride in the gas phase. These catalysts were tested in the oxidation of alkenes by alkyl hydroperoxides in mild conditions (343-353 K). The silica based materials lead, in any case, to the selective formation of the epoxides with a high level of conversion over four catalytic runs. Al-based supports afford an efficient acid-catalysed ring opening of oxiranes and allow the direct conversion of cyclohexene to adipic acid with a yield of 80%.

Functionnalization of mesoporous silica SBA15 with titanium oxide was carried out under gas phase conditions with TiCl4 as titanium source, between 473 and 673 K, followed by hydrolysis at ambient temperature. Spectroscopic characterisations (X-ray diffraction, XPS, IR, UV-Vis.) and porosimetry measurements showed that part of TiO2 is grafted on the internal surface of the pores. Catalytic activity was tested in selective oxidation of bulky alkenes. Several cycles of reaction showed that any leaching of Ti species is observed in the liquid phase. © 2002 Elsevier Science B.V. All rights reserved.

International audience; VOx–TiO2 catalysts with vanadium loading less than that of a monolayer have been prepared either by impregnation in aqueous media from solutions of V(V) or V(IV) at different concentrations and pH, or by grafting in anhydrous media on anatase supports with surface areas of 10, 150 and 350m2 g−1. Their characterisation by XPS, DRIFT and Raman spectroscopy, compared to that of EUROCAT EL10V1 and V8 reference catalysts, shows that the dispersion of the load depends on the mode of preparation and is not necessarily equal to 1.

We propose the use of a pattern search optimization technique in combination with a seed preprocessing procedure to determine the optical constants and thickness of thin films using only the transmittance spectra. The approach is quite flexible, straightforward to implement, and efficient in reaching the best fitting. We demonstrate the effectiveness of the method in extracting optical constants, even when the films are not displaying interference fringes. Comparison to a real-coded genetic algorithm shows that the modified pattern search is fast, almost accurate, and does not need any parameter adjustments. The approach is successfully applied to extract the thickness and optical constants of spray pyrolyzed nanocrystalline CdO thin films.