A DFT computational design and exploration of novel direct band gap silver-thallium double perovskites

Researchers have addressed the non-traditional power generation schemes as alternatives to the traditional fossil-fuel methods enormously since the scientific community has serious concerns about shortages of energy on our planet for future generations. In this scenario, the innovative materials for photovoltaic and thermoelectric device applications are required by addressing current issues of instability and efficiency. Perovskites are very popular in this regard particularly having higher power conversion efficiency of 25.2% in the case of solar cells. In the current article, we investigated innovative small direct band gap double perovskites (elapsolite) Cs$_2$AgTlX$_6$ (X= Cl, Br) with a comprehensive discussion on structural, electronic, optical, and thermoelectric properties using a first-principles approach. The compounds under investigation are found stable, efficient, and economical with alluring optical and thermoelectric properties. The higher absorption peaks in the visible range, substantial optical conductivities (~10$^{16}$ sec$^{-1}$), and a lower percentage of reflection in the visible range make these compounds fascinating for solar cell applications. Whereas large values of Seebeck coefficients, electrical conductivities, the figure of merits (greater than unity), and small values of thermal conductivities suggest the applications of these compounds in thermoelectric generators.Comment: 24 pages, 8 figure

Modeling and Simulation of Monolithic AlGaAs/InGaAs Tandem Solar Cell

Employing conventional III-V junctions we report a classical calculation of conduction and valence band edge and the electron and hole densities. It is shown that the optimum performance can be achieved by employing AlGaAs /AlGaAs/InGaAs monolithic cascade solar cells, we have established these calculations by solving the Poisson equation within the framework of the Nextnano

X-ray Diffraction Study of Aquamarine from Shigar Deposits, Skardu Valley, Northwest Pakistan

Samples of aquamarine collected from pegmatite rocks in Shigar mines, Skardu valley were investigated by powder X-ray diffraction method. Qualitative phase analyses of the samples showed the presence of aquamarine as major phase with quartz, talc and magnesite as minor phases. Lattice parameters were determined by employing CuKα radiations in step-scan mode using a computer program ‘Powder’. The lattice parameters of the Shigar specimens (with CuKα wavelength = 0.15418 nm) are a = 9.214 ± 0.002 (Å), c = 9.202 ± 0.002 (Å) compared to NBS (National Bureau of Standards) beryl data a = 9.215 Å, c =9.192Å. The deviations in the unit cell dimensions (especially the increase in a) of the samples are attributed to the presence of additional components (Cr, Fe, Na and Mg) detected by X-ray fluorescence method

Optical anomaly in near-end-member grossular garnet from the Jeffrey mine, Asbestos, Quebec, Canada

The optical anomalies, surface and lamellar textures of a birefringent grossular garnet crystal from the Jeffrey mine Canada have been investigated by optical polarizing microscope, electron-probe micro-analyzer (EPMA) and infrared spectrometer from the stand point of crystal growth. This grossular shows one-to-one correlation between surface features and its internal textures. The average chemical composition measured by EPMA is Grs97.4Alm1.2Sps1.2Pyr0.1 as a near-end-member grossular. The surface features correspond to the internal textures observed under crossed polarizers. Two growth hillocks with regular growth steps elongated parallel to [001] vertical direction of the (110) face, produce sectoral twins. Such growth steps indicate the orthorhombic symmetry of the crystal correlated with the growth direction. Some irregular or curved growth steps appearing as lamellae in (110) thin section are parallel to the sides of (110) face but inclined to the [001] growth direction; this suggests the monoclinic symmetry. The crystal is optically biaxial (+) and its 2Vx angle being close to 90° could not be measured. Infrared spectroscopy data revealed the presence of [(OH)4] group substitution at [SiO4], the tetrahedral site. Optical birefringence of the grossular is about 0.002. Back-scattered electron imaging could not detect any zonation and compositional differences of the lamellar texture

Theoretical Study of Hydrogen- and Halide-Terminated Germanium Nanowires

We present a density functional theory (DFT) study of ultra-thin finite hydrogen and halogen passivated germanium nanowires implies that surface effects significantly influence their structural, cohesive and electronic properties, which plays important role in the fabrication of nanodevices such as field effect transistors and sensors. We show that full coverage of halogen passivations i.e. with fluorine (F), chlorine (Cl) and bromine (Br) in particular, reduces the band gap of the [1 1 0] GeNWs drastically. Moreover, we find that, Halide-terminated especially chlorine and bromine terminated Ge nanowires show greater ambient stability with increasing molecular weight of the halogen species

Structural and dielectric properties of doped ferrite nanomaterials suitable for microwave and biomedical applications

The sol–gel auto-combustion method was adopted to synthesize nanomaterials of single-phase X-type hexagonal ferrites with the composition of Sr2−xGdxNi2Fe28−yCdyO46 (x=0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and y=0, 0.1, 0.2, 0.3, 0.4, 0.5). The structural properties were carried out by XRD analysis and the lattice parameters show variation with the doping of Gd–Cd. The average particle size measured by TEM was in the range of 8–10 nm which is beneficial in obtaining suitable signal-to-noise ratio in recording media and biomedical applications. The room temperature resistivity enhanced with the increase of the dopant concentration. The increase in resistivity indicates that the synthesized materials can be considered good for the formation of the multilayer chip inductors (MLCIs) as well as for the reduction of eddy current losses. The dielectric constant decreased with the increase in the frequency which is the general reported trend of the hexagonal ferrites and can be explained on the basis of Koop׳s theory and Maxwell–Wagner polarization-model. The abnormal dielectric behavior indicates the formation of small polarons in the material. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF)