Key Engineering Materials Vol. 875

Abstract: Perovskite solar cells are emerging as highly potent and efficient devices as sustainable energy source. The stability issue of hybrid perovskite methyl ammonium lead bromide can be improved by all inorganic perovskites like cesium lead bromide (CsPbBr₃). The present work is about the synthesis and characterization of CsPbBr₃ for efficient perovskite solar cells. The synthesis is carried out using hot injection method. The resulting nanocrystals (NCs) are characterized using XRD, SEM, AFM, UV/Vis Spectroscopy, PL spectroscopy and Hall Effect measurements. The NCs are tested for their performance in solar cells.

Abstract: BiScO₃-xPbTiO₃ (BS-PT) of perovskite type structure (with x~0.64) were prepared by solid state ceramic process with addition of calcium fluoride (CaF₂) in different molar ratios (0.5, 1.0 and 4.0 mol%). The doped compositions were found to have different symmetry compared with parent material. The 0.5 mol% doped sample was found to possess enhanced rhombohedral phase as compared to other compositions while he Curie temperature (T_c) was not affected appreciably. Small dielectric peaks were observed, indicating phase transition, at temperature lower than T_c in all the samples except 4.0% doped composition. At room temperature doping reduced the loss factor. d₃₃ and P_r reduced rapidly with doping. The characteristics of BS-PT ferroelectric ceramics became harder with the addition of CaF₂.

Abstract: High temperature ternary Ti₅₀Ni₂₅Pd₂₅ and quaternary Ti₅₀Ni₂₀Pd₂₅Cu₅ shape memory alloys were developed in vacuum arc melting furnace using high purity constituent elements. Half numbers of samples were solution treated at 900 °C for 2 hrs and remaining were aged at 600 °C for 3 hrs. Both alloys were characterized for microstructure analysis and mechanical properties. After aging the alloys, no significant change in microstructure was observed in ternary alloy however, fine precipitates of bright color were found along the grain boundaries in quaternary alloy. The mechanical properties of ternary and quaternary alloys were found to be improved significantly. Microhardness of ternary alloy was increased by 18 Hv whereas for quaternary alloy the same property was improved by 24 Hv. Yield stress of ternary and quaternary was observed to be enhanced by 10 MPa and 9 MPa respectively. Similarly the fracture stress was observed to be increased by 9 MPa and 13.4 MPa. Conversely, the fracture strain of ternary and quaternary alloys was reduced by 0.5% and 0.35% respectively. From these results it can be established that aging at 600 °C is beneficial to improve the mechanical properties of both alloys however, quaternary alloy responded more actively as compared to ternary alloy.

Abstract: Development of multifunctional flame retardant (FR) polymer composite was done. Flame retardant polymer composite was prepared by modifying diglycidylether of bisphenol-A (DGEBA) epoxy. Modification involved two types of FR. Reactive type FR used was phosphoric acid and additive type FR used was magnesium hydroxide. Composite was fabricated using resin infusion under flexible tooling (RIFT) process. Different FR epoxy samples were evaluated by compression test, UL 94. The carbon fiber reinforced polymer composite with attributes of flame retardancy were characterized using in-plane shear test, to estimate the structural properties, and UL-94 test, to estimate the fire performance. FR composite exhibited UL-94 rating of V-1 and a shear modulus of 9.7 GPa, which proved it to multifunctional.

Abstract: Surface structuring on the nano/micro level is important for a huge range of areas. A critical bottle neck for many industrial applications is upscaling; that is to say it must be possible to do the structuring in a comparatively simple and inexpensive manner. However, this is a challenge for many industrially important materials, including sapphire. A few years ago, solid state conversion was introduced as a relatively simply nanoscale structuring method for sapphire. Here we show that the method, by careful choice of parameters, can be extended to work also on the micron scale. We show that a microstructured aluminium film deposited on a Al₂O₃ (0001) surface is converted into a crystalline Al₂O₃ surface, when thermally annealed in air, using optimized parameters.

Abstract: Flat spiral coil for electromagnetic forming system has been modelled in FEMM 4.2 software. Copper strip was chosen as material for designing the actuator coil. Relationship between height to width ratio (S-factor) of the copper strip and coil’s performance has been studied. Magnetic field intensities, eddy currents and Lorentz force were calculated for the coils that were designed using six different 'S-factor' values (0.65, 0.75, 1.05, 1.25, 1.54 and 1.75), keeping the cross-sectional area of strip same. Results obtained through simulation suggest that actuator coil with S-factor ~ 1 shows optimum forming performance as it exerts maximum Lorentz force (84 kN) on work piece. The same coils was fabricated and used for electromagnetic sheet forming experiments. Aluminum 6061 sheets of thickness 1.5 mm have been formed using different voltage levels of capacitor bank. Smooth forming profiles were obtained with dome heights 28, 35 and 40 mm in work piece at 800, 1150 and 1250 V respectively.

Abstract: The quest to research the new engineering materials for energy applications is increasing day by day due to decrease in fossil fuel materials. Moreover, the management of municipal solid waste (MSW) by converting it to the energy is need of our society to address the energy shortage as well as environmental issues. Refused derived fuel (RDF) material is one of the energy products of MSW, whose reliability and quality with respect to the energy is analyzed in this work. Three different RDF materials (RDF-A, RDF-B and RDF-C) have been characterized by thermal analysis techniques to suggest best RDF based on energy efficiency. The results showed that the RDF-A contains higher amounts of carbon (52.44%) and hydrogen (4.184%) contents and good calorific value (5278 kcal/kg), which leads to a better fuel quality. TGA analysis revealed that with the increase in volatile matter fraction of RDF materials, the retention time under combustion atmosphere has also been increased accordingly. In the light of all results RDF-A was suggested to be a good candidate for energy applications and can be used as fuel for various combustion reactions.

Abstract: In the applications of renewable energy; use of energy in the electric vehicles and many other electronic devices such as mobile devices and computers; electrical energy storage is essential. Batteries are used to store electrical energy but have low power density and lower cycle life. Using extremely porous electrode materials for supercapacitors, based on quick ion transport, are specialized to provide high power density, long stability and effective energy storage. Using graphene-based electrode is the best way to boost the energy density of supercapacitor. Graphene synthesized by chemical exfoliation, ultrasonic exfoliation and solution based chemical reduction suffers agglomerations that tends to restack the graphene sheets. In the present work, we studied the option of hydrogen gas annealing to obtain graphene from amorphous carbon film, coated on Cu substrate using sputtering. For electrochemical assessment, in situ developed film was compared with graphene applied from other methods of graphene synthesis. Atomic force microscopy (AFM) results revealed that annealed carbon sputtered electrode has high route mean square (RMS) roughness i.e 181.5 nm, most probably because of graphene formation. Cyclic voltammogram (CV) results show less area curve for annealed electrode which depicts high active area for charge storage and enhanced conductivity due to deposited graphene layer.

Abstract: The capacitance of (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) [001]-oriented single crystal was examined as a function of temperature and applied external dc electric field. The phase transition temperatures under the applied electric field were measured upon cooling the crystal (zero-field heating field-cooling condition) from paraelectric cubic phase. From these data, temperature versus electric field phase diagram of PMN-xPT crystal have been constructed and discussed.