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Tin (IV) disulfides (SnS 2 ) doped with Fe ions are prepared through the molten salt solid state reaction at 280 °C and the effect of the Fe-doping on their structural and optical properties is reported. They were found to be nanocrystalline hexagonal structure with nanoflakes morphology with an average size 30 nm. The analysis of the optical data showed that all the samples are indirect semiconductors. Two absorption bands are observed in their optical diffuse reflectance spectra which indicate setting of two photons absorption processes due to formation of Fe intermediate band. The band gaps E g H I n d and E g L I n d that correspond to the two photons absorptions are found to vary from 1.49 to 1.09 eV and 0.76 to 0.93 eV, respectively. The most significant findings is that the sum of E g H I n d and E g L I n d has values between 2.25 and 2.02 eV which reproduces or slightly enhances the band gap value of the parent SnS 2 (2.01 eV). This finding is directly related with the perseveration of the output voltage ( V o ) which is a major condition required for realization of intermediate band solar cells with high solar conversion efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Successful preparation of double perovskite oxides of chemical formula ALaFeTiO6 (A=Ba, Sr and Ca) has been achieved by following the precursor method. The samples were studied by means of X-ray diffraction and Mössbauer spectroscopy. The Rietveld analysis of the X-ray diffraction data showed that all the samples have anti-site disorder. The presence of anti-site disorder has altered the electronic environment around the Fe ion sites which creates electric field gradient between two different sites. Observation of quadruple splitting in the ideal cubic perovskite BaLaFeTiO6 (its tolerance factor equals 1) is the evidence of this anti-site generated electric field gradient. The valence state of the Fe atom determined from the measurements of the Mössbauer effect of 57Fe at room temperature and 80K showed that the iron ion has the Fe3+ high spin state as extracted from the values of the isomer shift for all the samples. It is evidenced that the anti-site disorder has no appreciable effect on the spin state of the Fe ion, but alters the charge densities at the Fe sites and influences the hyperfine parameters of the present samples. Weak ferromagnetism is observed in CaLaFeTiO6 and SrLaFeTiO6 and is related to both the internal pressure and the anti-site effect which facilitate the occurrence of the antiferromagnetic interaction with canted spin. [Copyright &y& Elsevier]

Abstract: We have systematically investigated the electronic structure and magnetic properties of the double perovskite oxides Sr2CrZrO6, Sr2MnNbO6, Sr2FeMoO6 and Sr2NiRuO6 in terms of band filling of different t2g and eg orbitals. Calculations of density of the states (DOS) were performed within the frame of the local spin density approximation and Hubbard potential (LSDA+U) employed in the Linear Muffin Tin Orbitals with Atomic Sphere Approximation (LMTO-ASA) method. The DOS of Sr2FeMoO6 was obtained and found to agree very well with published reports. Half-metallic character through the spin-down channel and the ferrimagnetic ordering was observed with notable hybridization among the 3d, p and 4d orbitals within Fermi level. A difference between the theoretically expected values and the calculated ones for the magnetic moment (Δm) of the 3d orbitals is determined and had been found to increase on going from Sr2CrZrO6 to Sr2NiRuO6. This increment in Δm indicates increment in the hybridization strength, which leads to long range ordering in Sr2FeMoO6 and Sr2NiRuO6 compounds. In comparison with reported experiments, the frustrated magnetism and weak ferrimagnetism states are the most possible ones in Sr2CrZrO6 in Sr2MnNbO6, respectively. The half-metallic character was also seen in Sr2MnNbO6 and Sr2CrZrO6 compounds while Sr2NiRuO6 shows normal metallic conduction and ferromagnetism in accordance with the superexchange interaction eg 2–o–eg 0 of Goodenough–Kanamori–Anderson (GKA). [Copyright &y& Elsevier]

Abstract: The electronic structure and magnetic properties of pseudo-cubic and tetragonal double perovskite oxides Sr2MnNbO6, Sr2FeMoO6 and Sr2NiRuO6, have been determined by using the full potential linear augmented plane wave method (FP-LAPW) employing the LSDA+U scheme. The spin–orbit coupling (SOC) has been taken into consideration. These calculations showed that all the three compounds in their two crystalline structures are half metallic. The values of the total energy have indicated that first two compounds prefer the tetragonal structures while the third one prefers the pseudo-cubic structure. The obtained magnetic moments indicate that Sr2MnNbO6 and Sr2NiRuO6 are ferromagnetic while Sr2FeMoO6 has ferrimagnetic ordering. The effect of the spin–orbit coupling was seen to grow from quenched to weakly unquenched to unquenched as going from Nb to Ru and from Mn to Ni as signified by the values of the orbital magnetic moments of the 3d and 4d orbitals. Sr2NiRuO6 shows half-metallic conduction and ferromagnetism in accordance with the superexchange interaction of Goodenough–Kanamori–Anderson (GKA). [ABSTRACT FROM AUTHOR]

Abstract: The paramagnetic susceptibility measured on La1−x Y x Sr2−y Ca y Mn2O7 (x, y or z=0, 0.03 and 0.1) manganites does not obey the Curie–Weiss law. The Curie constant exceeds the expected values by more than order of magnitude. Based on strong disorder we have compared the experimental data with predictions based on Griffith''s singularity model. We find that this model allows for consistent interpretation of the data in contrary to a model assumes that magnetic polarons make contribution akin to cluster to susceptibility. In particular the values of Curie constant agree excellently with those theoretically expected, whereas the magnetic polarons model is less satisfactory. [Copyright &y& Elsevier]

Abstract: Blends made of poly[2-methyl-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) conducting polymer and cresyl violet 670 (CV) and coumarin 460 (C460) have been utilized for preparation of organic Schottky diodes. The I–V characteristics of these diodes are then determined and interpreted in terms of thermoionic emission (TIE) conduction process. Upon blending MEH-PPV with CV and C460 dyes, the conduction is seen to completely be through TIE conduction. The turn on voltage for MEH-PPV diode is found to be 2.0V and decreases with CV blending in contrast to the blend of MEH-PPV-C460. The Schottky parameters are determined where the potential barrier is found to be around 0.75V which is consistent with reported values. The charge densities of the respective blends are calculated and found to reduce by in MEH-PPV-C460 blends while it has been enhanced in the CV samples by an order of magnitude compared that of MEH-PPV. The correlation between the ideality factor with the dielectric constant and the charge density is inspected. It is found that the ratio between the charge density of the polymeric blend and the charge density of the Al-electrode is crucial for obtaining low ideality factor. [Copyright &y& Elsevier]

First principles calculations based on density functional theory (DFT) using TB-mBJ and SCAN + U methods were used to study the electronic and optical properties of the monoclinic VO 2 (M1) phase. TB-mBJ gives values of the energy gap (E g) and Δd || band splitting in agreement with experiments. Systematic investigation of SCAN + U, U varies from 0 to 10 eV, shows that agreement with experimental values of both E g and Δd || was achieved at U * = 5.75 eV. Moreover, TB-mBJ and SCAN + U * were able to reproduce frequency and polarization dependence of the optical constants that agree with the reported experimental results of the monoclinic VO2 (M1) phase. The high value of U needed to reproduce the experimental values of electronic and optical parameters of the monoclinic VO 2 (M1) phase is a strong indication that VO 2 is a Mott insulator and the Mott-Hubbard scheme plays an important role in the metal-insulator transition. • The electronic and optical properties of the insulating monoclinic VO 2 (M1) phase were studied using TB-mBJ and SCAN+ U. • The size of the energy gap (E g) and d || band splitting and some optical constants of the VO 2 (M1) phase were calculated. • TB-mBJ and SCAN+U gave E g and Δd|| band splitting values in agreement with experiments. • TB-mBJ and SCAN+U were able to predict the frequency and polarization dependence of n , a , ε 1 , ε 2 of the VO 2 (M1) phase. • The current calculations reveal that Mott-Hubbard electron correlation is dominant in the metal-insulator transition in VO 2. [ABSTRACT FROM AUTHOR]

Polycrystalline Sn 1−x Fe x S 2 samples with (x=0, 0.125, 0.250 and 0.375) have been prepared by the molten salt solid state reaction method. The X-ray diffraction (XRD) shows that all the samples crystallize in the hexagonal structure, with P-3m1 space group in preferred orientation of (011). The electrical properties have been studied by complex impedance spectroscopy over the frequency range (20 Hz up to 1 MHz) at room temperature. The Nyquist plot for all samples have been fitted using ZMAN software. The impedance analysis showed that all samples exhibit both bulk and grain boundary contributions and it was found that by increasing the iron content, the resistance increases, but, the dielectric constant and dielectric loss tangent decrease which leads to decrease in conduction. The absorption coefficient (α) has been calculated from the complex dielectric constant. Interestingly, there was a significant correlation between the electromagnetic wave absorption and the reduction in the peak intensity of the XRD patterns indicating that when the iron content increases the sample seems to be a good absorber of electromagnetic waves. [ABSTRACT FROM AUTHOR]