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In the present work, $$\hbox {Al}_{65}\hbox {Cu}_{20}\hbox {Fe}_{15}$$ alloy has been synthesized by melting of pure elements (e.g., Al (99.96%), Cu (99.99%) and Fe (99.98%)), using a radiofrequency induction melting furnace. The as-prepared alloy was subjected to rapid solidification by melt spinning technique at $$\sim $$ 3500 rpm speed on a copper disk of diameter 14 cm. As a result of the melt spinning, nearly 2 mm wide, $$30{-}40\,{\upmu }\hbox {m}$$ thick and 4–5 cm long ribbons were formed. The structural and microstructural characterizations were carried out by X-ray diffraction and transmission electron microscopy techniques. We have performed leaching operation using 10 mol NaOH aqueous solution on the surface using a pipette. Leaching was performed for various durations ranging from 30 min to 8 h. After leaching, the reflectivity reduces and the surface looks reddish brown. The microstructure of the 8 h leached sample shows a breakdown of the quasicrystalline phase but with the evolution of other metallic phases. Copper (Cu) particles are found to be present on the surface of quasicrystal after 4 h of leaching and relatively more iron (Fe) evolves during further leaching of 8 h. This low-cost method to prepare a distribution of nano-Cu/Fe metal particles encourages their uses in catalytic reactions, indicating the possibility of use of quasicrystals as the industrial catalysts.

The macroscopic coaxial carbon cylinders (dia. ∼0.5 cm with varying lengths, ∼ 7–10 cm) consisting of aligned carbon nanotube (CNT) stacks have been prepared by controlled spray pyrolysis method. The coaxial carbon cylinders of CNT stacks have been formed directly inside the quartz tube. Another study is done on multi-walled CNTs (MWNTs)-polymer (e.g. polyethylene oxide (PEO), polyacrylamide (PAM)) composite films. We have investigated the structural, electrical and mechanical properties of MWNTs-PEO composites. Composites with different wt% (between 0 and 50 wt% of MWNTs) have been prepared and characterized by the scanning electron microscopic technique. Enhanced electrical conductivity and mechanical strength were observed for the MWNTs-PEO composites. We have also studied the electrical property of MWNTs-PAM composite films.

Nanocrystalline semiconducting materials are attracting much attention due to their potential applications in solar energy conversion, nonlinear optics, and heterogeneous photocatalysis. In the present investigation, we have synthesized nanostructured TiO2 photocatalysts, which have been used in the photocatalytic degradation of phenol (one of the most common water pollutants). These catalysts have been prepared through sol-gel technique using titanium tetra-isopropoxide as a raw material for synthesis. Characterization techniques such as XRD, SEM and TEM have been employed for structural/microstructural investigations. XRD results show that the as synthesized TiO2 nanopowder exhibit anatase phase, TiO2. The average sizes of the TiO2 nanopowders are ∼ 5–10 nm. The optical properties of the samples were investigated through UV-visible and fluorescence techniques. It has been observed that absorption edge corresponds to ∼ 410 nm (bandgap, ∼ 3.02 eV). The emission peak in the fluorescence spectrum at ∼ 418 nm corresponds to the bandgap energy of ∼ 2.97 eV. Concentration of phenol (initial concentration, ∼ 100 ppm) with illumination time was monitored by measuring the absorbance of pure and illuminated phenol through UV-visible spectrophotometer. Salient feature of this study relates to the fact that the present sol-gel synthesized TiO2 nanopowders have been found to be better photocatalysts for phenol degradation than the presently employed commercial TiO2 (P-25, Degussa) photocatalyst. Thus, whereas phenol concentration, with the presently synthesized TiO2 nanopowders, the concentration of phenol decreases up to ∼ 32% but for commercial TiO2 nanopowder (P-25, Degussa), it decreased only up to ∼ 25%. The improved surface area is considered as an important factor for the aforesaid decrease in phenol concentration.

In the present study, we report the synthesis, characterization and application of nanostructured oxide materials. The oxide materials (Cu2O and ZnO) have been synthesized by electrolysis based oxidation and thermal oxidation methods. Cuprous oxide (Cu2O) nanostructures have been synthesized by anodic oxidation of copper through a simple electrolysis process employing plain water (with ionic conductivity, ∼6 μS/m) as electrolyte. In this method no special electrolytes, chemicals and surfactants are needed. The method is based on anodization pursuant to the simple electrolysis of water at different voltages. Two different types of Cu2O nanostructures have been found. One type got delaminated from copper anode and was collected from the bottom of the electrochemical cell and the other was located on the copper anode itself. The nanostructures collected from the bottom of the cell are either nanothreads embodying beads of different diameters, ∼ 10–40 nm or nanowires (length, ∼ 600–1000 nm and diameter, ∼ 10–25 nm). Those present on the copper anode were nanoblocks with preponderance of nanocubes (nanocube edge, ∼ 400 nm). The copper electrode served as a sacrificial anode for the synthesis of different nanostructures. Aligned ZnO nanorod array has been successfully synthesized by simple thermal evaporation catalyst free method. Detailed structural characterizations revealed that the as synthesized aligned ZnO nanorods are single crystalline, with a hexagonal phase, and with growth along the [0001] direction. The room-temperature photoluminescence spectra showed a weak ultraviolet emission at 380 nm, a broad blue band at 435 nm and a strong orange-red emission at 630 nm. Structural/microstructural characterization of these nanomaterials have been carried out employing scanning (XL-20) and transmission electron microscopic (Philips EM, CM-12 and Technai 20G2) techniques and X-ray diffraction techniques having graphite monochromater with CuKα radiation (λ =1.54439 A) (X’Pert PRO PAN analytical). The UV-visible absorption spectra were recorded on Model-VARIAN, Cary 100, and Bio UV-visible spectrophotometer. The photoluminescence (PL) measurement was carried out at room temperature with a He-Cd, a laser excited at 325 nm.

In order to get good quality reproducible films of Tl : HTSC system, we have studied the different annealing conditions to finally achieve the optimized annealing condition. In the present investigation, Tl -Ca- Ba-Cu-O superconductin g films have been prepared on YSZ (100) and MgO (100) single crystal substrates via precursor route followed by thallination. The post deposition heat treatments of the precursor films were carried out for various annealing temperatures (870°C, 890°C) and durations (1 and 2 min). The optimized thallination procedure occurred at 870°C for 2 min into good quality films with Tc (R = 0) ~ 103 K for YSZ and Tc (R = 0) ~ 98 K for MgO substrates, respectively. Further we have correlated the stru ctural/microstructural characteristics of the films.

The synthesis of high temperature superconducting films of Y : 247 (T c ∼ 73 K) have been successfully achieved. The difficulty in synthesis owing to narrow range of stability of Y : 247 has been taken care of through several quenching modes, e.g. quenching of the films synthesized at ∼850°C, in air or in liquid nitrogen. The energy dispersive analysis of X-rays (EDAX) and transmission electron microscopy (TEM) studies of the as processed film, Y2Ba4Cu7O14+x, exhibit nearly correct cationic stoichiometry of 2 :4 :7; also narrow regions (< 50 A) of minority Y : 124 phase and stacking faults capable of working as flux pinning sites have been invariably found to be present. In addition to Y : 247, Ag admixed films have also been investigated. TheT c here is ∼ 70–75 K which is similar to that of the film without silver. Representative estimates of transport critical current density (J c) for Y : 247 films is ∼103 A/cm2, and with silver corresponding to Y2Ba4Cu7O14+x (Ag0.1) is found to be ∼ 104 A/cm2.

X-ray diffraction, transmission electron microscopy and differential scanning calorimetry were carried out to study the transformation from amorphous to icosahedral/crystalline phases in the rapidly quenched Al50Cu45Ti5 and Al45Cu45Ti10 alloys. In the present investigation, we have studied the formation and stability of amorphous phase in Al50Cu45Ti5and Al45Cu45Ti10 rapidly quenched alloys. The DSC curve shows a broad complex type of exothermic overlapping peaks (288- 550†C) for Al50Cu45Ti5 and a well defined peak around 373†C for Al45Cu45Ti10 alloy. In the case of Al50Cu45Ti5 alloy amorphous to icosahedral phase transformation has been observed after annealing at 280†C for 73 h. Large dendritic growth of icosahedral phase along with α-Al phase has been found. Annealing of Al50Cu45Ti5 alloy at 400†C for 8 h results in formation of Al3Ti type phase. Al45Cu45Ti10 amorphous alloy is more stable in comparison to Al50Cu45Ti5 alloy and after annealing at 400†C for 8 h it also transforms to Al3Ti type phase. However, this alloy does not show amorphous to icosahedral phase transformation.

In this paper we have reported investigations on the effect of simultaneous substitution of Bi and Tl at the Hg site in the oxygen deficient HgOδ layer of HgBa2Ca2Cu3O8+δ cuprate superconductor. Bulk polycrystalline samples have been prepared by the two-step solid state reaction process (precursor route). It has been observed that the as grown HgBi0.2−xTIxBa2Ca2Cu3O8+δ (withx = 0.00, 0.05, 0.10, 0.15, 0.20) corresponds to the 1223 phase. It has been found that the Tc varies with the average cationic size of the dopant cations. The optimumTc of ∼ 131 K has been found for the composition HgBi0.15TI0.05Ba2Ca2Cu3O8+δ This composition leads to the average dopant cation size of ∼1.108 a which is very close to the size of Hg2+ (∼ 111 a). The microstructure for HgBi0.15TI0.05Ba2Ca2Cu3O8+δ has been found to be most dense and this phase exhibits the highest stability. The Jc of the optimum material HgBi0.15TI0.05Ba2Ca2Cu3O8+δ is found to be ∼ 1.29 × 103 A/cm2 at 77 K.

We have investigated Fe substituted versions of the quasicrystalline (qc) alloy corresponding to Al65Cu20(Cr, Fe)15 with special reference to the possible occurrence of various quasicrystalline and related phases. Based on the explorations of various compositions it has been found that alloy compositions Al65Cu20Cr12Fe3 and Al65Cu20Cr9Fe6 exhibit interesting structural phases and features at different quenching rates. At higher quenching rates (wheel speed ∼ 25 m/sec) all the alloys exhibit icosahedral phase. For Al65Cu20Cr12Fe3 alloy, however, both the icosahedral and even the decagonal phases get formed at higher quenching rates. At higher quenching rate, alloy having Fe 3 at % exhibits twobcc phases,bccI (a = 8.9 a) andbccIIa = 15.45 a). The orientation relationships between icosahedral and crystalline phases are: Mirror plane ∥ [001] bcc I and [351] bcc II, 5-fold ∥ [113] bcc II and 3-fold ∥ [110]inbcc II. At lower quenching rate, the alloy having Fe 6 at % exhibits orthorhombic phase (a = 23.6 a,b = 12.4 a,c = 20.1 a). Some prominent orientation relationships of the orthorhombic phase with decagonal phase have also been reported. At lower quenching rate (∼ 10 m/sec), the alloy (Al65Cu22Cr9Fe6) shows the presence of diffuse scattering of intensities along quasi-periodic direction of the decagonal phase. For making the occurrence of the sheets of intensities intelligible, a model based on the rotation and shift of icosahedra has been put forward.

Synthesis of Hg(Tl)Ba 2Ca2Cu3O8+δ superconducting tapes have been accomplished by annealing the precursor tape, Ba2Ca2Cu3Oy (fabricated by doctor blade tape casting technique) in an environment of Hg(Tl) vapour. Characterization of superconducting HTSC tape sample was carried out through XRD, TEM, SEM and R-T measurements. Surface morphological investigations of the as -synthesized Hg(Tl)Ba2Ca2Cu3O8+δ HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small crystal like grains of superconducti ng material Hg(Tl)Ba2Ca2Cu3O8+δ. The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence of growth fronts formed from Hg(Tl):1223 and Hg(Tl):1234 nuclei.

In this paper we have shown that polycrystalline films corresponding to Tl-2223 phase can be grown by employing high thalliation temperatures and short thalliation times. Ultrasonically deposited precursor films corresponding to Ba2Ca2.2Cu3.3Ox(Agy) have been thalliated under high vacuum (∼ 10-5 torr) at 890°C to obtain single phase Tl-2223 films. An off-stoichiometric and unreacted pellet of composition Tl2.05Ba2Ca2Cu3Oz has been used as source of Tl. We have shown that oxygen ambient is not necessary for the growth of Tl-2223 phase. The as-thalliated films have Tc’s in the range 123 K ±0.70 K. TheT c has been found to be independent of the addition of AgNO3 to the precursor. The zero field transportJ c has been observed to be > 1.2 X 105 A/cm2 at 77 K. NearT c (110 K-122 K),J c has been observed to follow the power lawJ c ∞ (1-T/T c )p,p 2. A power law withp tt 1.4 has been observed for the temperature range 70 K-110 K. An optimum doping of Ag has been observed to induce about 25% increase inJ c and it also leads to uniform and enlarged grain growth. The surface morphology of Ag free samples contains plate like grains having arbitrary shapes. In contrast to this 0.35 Ag doped sample exhibits nearly rectangular plate like grains

The quasicrystals being based on quasiperiodic order other than crystal like periodic translational order and embodying self similarity, present unique condensed matter phases. In addition to their curious structural characteristics the paucity of translational periodicity leads to drastic deviations in their electronic behaviour as compared to crystalline counterparts. This paper describes and discusses some new developments in regard to structural and electronic aspects of quasicrystalline materials. In regard to the structural aspects, two comparatively newer features will be described. One of them relates to the observation of variable strain approximants (VSA) first found in Ti68Fe26NiSi5, qc alloys; the other relates to the structure of decagonal phases. The variable strain approximants correspond to qc phases exhibiting variable strain for the different diffraction spots for the same reciprocal lattice row (possessing linear shifts). The VSA is thought to result from variable phason strain mode locking; this in contrast to RAS which results due to linear phason mode locking. The results obtained in our laboratory on VSA will be described and discussed. Another interesting structural feature emanating in the last few years relate to the development of structural models for the decagonal phases which have nearly answered the question ‘Where are the atoms?’ for this qc variant. High resolution electron microscopy has revealed the existence of two types of atom cluster columns with a diameter of 20A; a pentagonal cluster column and a decagonal one. The decagonal quasicrystals can be classified into three types of structures according to the space groups and symmetries and arrangements of the cluster columns. These three deca structures have been typified by: deca Al-Co-Cu, deca Al-Mn and deca Al-Fe-Pd types. Some basic features on the structures of decagonal phases as obtained recently will be outlined.

The second generation of high temperature superconductors typified by Bi2Sr2Can−1CunO2n+4 and Tl2Ba2Can−1CunO2n+4 exhibits curious structural properties which have direct relevance to the superconducting behaviour particularly transition temperature (Tc). The present paper reports on investigations of structural properties at microlevel in Bi-bearing HTCS. We have found curious structural characteristics which manifests itself in the form of transformation fromap×ap×c to (2)1/2ap×(2)1/2ap×c through the loss of calcium atoms and the formation of five-fold modulated phase alongb through the loss of Ca and Sr atoms. We have also found the evidence of high periodicities (n=4) Bi2Sr2Ca3Cu4O12. The microstructural characteristics of HTCS showing the higherTc(R=0) ∼ 120 K exhibits unusual characteristics.

High temperature superconducting films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O have been deposited on different substrates using conventional techniques, like flash evaporation and spray pyrolysis. The microstructural investigation of the films by SEM technique reveals the partially oriented nature of the crystallites. In the case of spray-deposited Bi-Sr-Ca-Cu-O HTSC films it has been found that film/substrate mismatch is not the decisive factor for the superconducting transition temperatureTc.

Rare earth trialuminides (RAl3) exhibit an interesting series of structures changing from 2H to 3C in the bulk form. Many of the rare earth trialuminides have been recently found to exhibit curious structural characteristics such as the occurrence of the modulated phases. A detailed investigation of the formation synthesis and characterization of some binary and ternary alloys of the rare earth-aluminium system has been carried out. High resolution microscopic technique has been employed to study the modulated phases for some alloyse.g. HoAl3, Er0·5Gd0·5Al3 and Y0·91Er0·09Al3. With the help of lattice imaging technique, several new modulated phases have been investigated. A possible mechanism for the formation of these phases has been suggested. The details of the results obtained by lattice imaging technique are discussed.