IR Studies of Impurities in In-Se-Tl Bulk Chalcogenide Glassy System

Chalcogenide glasses with composition In10Se90-xTlx (7≤x≤15) and In15Se85-xTlx (2≤x≤10) are synthesized by melt quenching technique. The FT-IR transmission spectroscopy studies using KBr pellet method in the wavelength range 400-4000 cm-1 has been carried out. The In-Se-Tl glasses studies shows good transparency in the entire spectral range. There is an increase in percentage of transmittance values with increase in the Tl content. In the transmittance curve various absorption bands are seen, which are related to chemical bonds of different extrinsic impurities present in the glassy material. The vibrational properties of the impurities in the powdered samples are measured. Vibrational modes attributed to O-H hydroxyl groups, molecular H2O and carbon impurity atoms were detected in the mid-IR spectra

Effect Of Thallium Additive On Heat Capacities Of In-Se Bulk Chalcogenide Glasses

Chalcogenide glasses are promising materials for optoelectronic device applications. Heat capacity of such materials is the essential physical parameter to estimate the energy/data storage capacity. In the present work, the effect of Tl incorporation on heat capacities ΔCpg, ΔCpc and ΔCpm of In10Se90-xTl x (7≤x≤15) and In15Se85-xTlx (2≤x≤10) bulk glasses have been investigated by analyzing the Differential scanning calorimetry (DSC) thermogram plots. Composition dependence of heat capacities of In-Se-Tl glassy systems have been obtained at the peaks of the glass transitions, crystallizations and melting temperatures (Tg, Tc and Tm). It is found that the heat capacities of In10Se90-xTl x and In15Se85-xTlx glasses increases initially with the incorporation of thallium (up to x≤13 and x≤6) and reaches to maximum at x=13 and x=6 respectively beyond which it decreases. This behavior seems to follow the change in network connectivity and rigidity and may be explained with the help of chemical bond theory of solids. Further in these glassy materials, at the average coordination =2.46 (x=13) and = 2.42 (x=6) a sharp slope change is seen in the composition dependence of heat capacity of both the series which is attributed to the rigidity percolation threshold

Throughflow and Quadratic Drag Effects on Thermal Convection in a Rotating Porous Layer

A linear stability analysis is implemented to study thermal convective instability in a horizontal fluid-saturated rotating porous layer with throughflow in the vertical direction. The modified Forchheimer-extended Darcy equation that includes the time-derivative and Coriolis terms is employed as a momentum equation. The criterion for the occurrence of direct and Hopf bifurcations is obtained using the Galerkin method. It is shown that if a Hopf bifurcation is possible it always occurs at a lower value of the Darcy–Rayleigh number than the direct bifurcation. Increase in the throughflow strength and inertia parameter is to decrease the domain of Prandtl number up to which Hopf bifurcation is limited but opposite is the trend with increasing Taylor number. The effect of rotation is found to be stabilizing the system, in general. However, in the presence of both rotation and Forchheimer drag a small amount of vertical throughflow as well as inertia parameter show some destabilizing effect on the onset of direct bifurcation; a result of contrast noticed when they are acting in isolation. The existing results in the literature are obtained as limiting cases from the present study

Defects, Dopants and Sodium Mobility in Na₂MnSiO₄

Sodium manganese orthosilicate, Na2MnSiO4, is a promising positive electrode material in rechargeable sodium ion batteries. Atomistic scale simulations are used to study the defects, doping behaviour and sodium migration paths in Na2MnSiO4. The most favourable intrinsic defect type is the cation anti-site (0.44 eV/defect), in which, Na and Mn exchange their positions. The second most favourable defect energy process is found to be the Na Frenkel (1.60 eV/defect) indicating that Na diffusion is assisted by the formation of Na vacancies via the vacancy mechanism. Long range sodium paths via vacancy mechanism were constructed and it is confirmed that the lowest activation energy (0.81 eV) migration path is three dimensional with zig-zag pattern. Subvalent doping by Al on the Si site is energetically favourable suggesting that this defect engineering stratergy to increase the Na content in Na2MnSiO4 warrants experimental verification

Li2SnO3 as a Cathode Material for Lithium-ion Batteries:Defects, Lithium Ion Diffusion and Dopants

Tin-based oxide Li2SnO3 has attracted considerable interest as a promising cathode material for potential use in rechargeable lithium batteries due to its high- capacity. Static atomistic scale simulations are employed to provide insights into the defect chemistry, doping behaviour and lithium diffusion paths in Li2SnO3. The most favourable intrinsic defect type is Li Frenkel (0.75 eV/defect). The formation of anti-site defect, in which Li and Sn ions exchange their positions is 0.78 eV/defect, very close to the Li Frenkel. The present calculations confirm the cation intermixing found experimentally in Li2SnO3. Long range lithium diffusion paths via vacancy mechanisms were examined and it is confirmed that the lowest activation energy migration path is along the c-axis plane with the overall activation energy of 0.61 eV. Subvalent doping by Al on the Sn site is energetically favourable and is proposed to be an efficient way to increase the Li content in Li2SnO3. The electronic structure calculations show that the introduction of Al will not introduce levels in the band gap

Synergistic ecoclimate teleconnections from forest loss in different regions structure global ecological responses

ABSTRACT: Forest loss in hotspots around the world impacts not only local climate where loss occurs, but also influences climate and vegetation in remote parts of the globe through ecoclimate teleconnections. The magnitude and mechanism of remote impacts likely depends on the location and distribution of forest loss hotspots, but the nature of these dependencies has not been investigated. We use global climate model simulations to estimate the distribution of ecologically-relevant climate changes resulting from forest loss in two hotspot regions: western North America (wNA), which is experiencing accelerated dieoff, and the Amazon basin, which is subject to high rates of deforestation. The remote climatic and ecological net effects of simultaneous forest loss in both regions differed from the combined effects of loss from the two regions simulated separately, as evident in three impacted areas. Eastern South American Gross Primary Productivity (GPP) increased due to changes in seasonal rainfall associated with Amazon forest loss and changes in temperature related to wNA forest loss. Eurasia’s GPP declined with wNA forest loss due to cooling temperatures increasing soil ice volume. Southeastern North American productivity increased with simultaneous forest loss, but declined with only wNA forest loss due to changes in VPD. Our results illustrate the need for a new generation of local-to-global scale analyses to identify potential ecoclimate teleconnections, their underlying mechanisms, and most importantly, their synergistic interactions, to predict the responses to increasing forest loss under future land use change and climate change