A compact multi-source multi-substrate evaporator for thin film studies of rare earth sulphides

To facilitate materials research by thin film techniques, we have built a compact multi-source multi-substrate evaporator. We have successfully prepared crystalline binary EuS (T_c = 16 K), SmS and Sm₂S₃ as well as ternary Sm_1?xLn_xS (Ln = Tm, Yb) compounds by tenchnique of co-evaporation. Special precautions were taken to avoid sulphur contamination. The X-ray, optical and magnetic properties of these films confirmed the good quality of the samples. Optical data obtained on Sm_1?xYb_xS indicate a stable valency of 2 for Sm and Yb for all values of x.     

Electrochemistry of metals and semiconductors in fluoride media

The electrochemical surface transformations and diverse applications of a variety of metals and semiconductors in a wide range of fluoride media such as aqueous, non-aqueous media, liquid HF media, room temperature fluoride melts and molten fluoride media with a melting range covering 50–1000°C are reviewed. Nickel shows excellent corrosion resistance in the absence of water. The anodic performance of this metal in electrochemical perfluorination and NF₃ production is discussed. Compact carbon materials serve as anodes in fluorine generators. In high temperature melts, they perform as consumable anodes. Graphitic carbon undergoes intercalation/de-intercalation process and related battery applications. Cu/CuF₂ couple is a good reference electrode. Pt and vitreous carbon materials are the inert electrodes of choice for electro analytical applications. Electrodeposition of Lithium as a non-dendritic uniform phase is important in Lithium metal based secondary batteries. High temperature fluoride melts are used in electro-deposition of valve metals such as Nb, Ta, and Ti. The stability and decomposition of fluoride complexes in these media are of interest.     

Voltammetric investigations on the transition between dissolution, passivation and deposition characteristics of Ni, Cu and their alloys in fluorine based ionic liquid

Multisweep cyclic voltammetric (CV) responses of nickel, copper, Monel and nickel–copper alloy had been extensively studied and compared in a variety of non-aqueous solvents such as acetonitrile (AN), propylene carbonate (PC) and sulfolane containing triethylamine trishydrogen fluoride (TEA·3HF) ionic liquid. The quantity of dissolution as well as surface morphological transformation on the electrode surfaces as a result of anodic polarization were investigated using atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM) respectively. The nature of crystallites formed on the polarized electrode was characterized using X-ray diffraction (XRD). The voltammetric study clearly indicates that Ni, Monel and Ni–Cu alloy are passive and stable in neat TEA·3HF medium in the recorded potential region of CV. Surface morphology of Ni after polarization, reveals the generation of pits, whereas the evolution of small crystallites of CuF₂ are noted on the polarized alloy material, as evidenced by SEM pictures. Copper electrode shows reversible voltammetric characteristics with high charge recovery ratio (q_c/q_a) suggesting that in this medium, Cu can certainly serve as reference electrode. Addition of water in TEA·3HF medium increases the solubility and stability of these metal fluoride film. In solvents such as PC, AN and sulfolane containing TEA·3HF, Ni and their alloys exhibit remarkable passivity and the charge recovery ratio decreases to some extent for Cu. In TEA·3HF/AN medium, the dissolution of Cu is very high. The present investigation suggests that the relative stability of all the four electrodes in neat TEA·3HF and solvents containing 0.1 M TEA·3HF decreases in the order: Ni > Monel > Ni–Cu alloy > Cu and relative solubility of metal fluoride films in the three solvents increases in the order: PC < sulfolane < AN.     

The influence of surface morphology of TiO2 coating on the performance of dye-sensitized solar cells

The optimization of solar energy conversion efficiency of dye-sensitized solar cells (DSSCs) was investigated by the tuning of TiO₂ photoelectrode's surface morphology. Double-layered TiO₂ photoelectrodes with four different structures were designed by the coating of TiO₂ suspension, incorporated with low and high molecular weight poly(ethylene glycol) as a binder. Among these four systems, P2P1, where P1 and P2 correspond to the molecular weight of 20,000 and 200,000, respectively, showed the highest efficiency under the conditions of identical film thickness and constant irradiation. This can be explained by the larger pore size and higher surface area of P2P1 TiO₂ electrode than the other materials as revealed by scanning electron microscopic (SEM) and Brunauer–Emmett–Teller (BET) analyses. Electrochemical Impedance Spectroscopy (EIS) analysis shows that P2P1 formulation displayed a smaller resistance than the others at the TiO₂/electrolyte interface. The best efficiency (η) of 9.04% with the short-circuit photocurrent density (J_sc) and open-circuit voltage (V_oc) of 18.9 mA/cm² and 0.74 V, respectively, was obtained for a solar cell by introducing the light-scattering particles to the TiO₂ nanoparticles matrix coated on FTO electrode having the sheet resistivity of 8 Ω/sq.     

Structural,electrical and magnetic properties of Y-Sr-Cu-O

Preparation, resistivity (ρ), field-cooled (FC) and zero field-cooled (ZFC) susceptibility (χ) of YSrCuO are reported. Zeroρ is observed at 72K. FCχ shows a superconducting transition at 68 K and also an antiferromagnetic transition at 15 K which is due to Y₂Cu₂O₅ as deduced from electron diffraction and composition analyses. It is tentatively proposed that the Y-rich phase could be responsible for the observed superconductivity.     

Interpretation of Mössbauer spectra of YBa2Cu3−x Fe x O7−d

We have studied the Mössbauer spectra of YBa₂Cu_3?x Fe _x O_7?d (11 compositions) and present here the results obtained from quantitative analyses of the paramagnetic and magnetic spectra.