Himanshu Narayan | National University of Lesotho (original) (raw)
Papers by Himanshu Narayan
In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and e... more In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and environment friendly resources rather than just being a waste material. A number of novel applications have been identified and are being exploited as well. The pozzolanic properties of FA make it a suitable candidate for cement replacement, as well as for the production of ceramics and glasses to be used as construction material. It can be utilized in the construction of embankments and structural fill; waste stabilization and solidification; mine reclamation; road sub-base; aggregate and mineral filler in asphalt concrete; soil amendment of soft soil and to increase bioavailability of nutrients in the soils, as well as adsorbent for heavy toxic metals. Other applications include production of roofing tiles, paints, metal casting, and as filler in wood and plastic products. Alkali rich FA can be used to neutralize the waste water from Acid Mine Drainage (AMD). Most of the current applica...
![Research paper thumbnail of Role of particle size in visible light photocatalysis of Congo Red using TiO2·[ZnFe2O4] x nanocomposites](https://attachments.academia-assets.com/45529613/thumbnails/1.jpg)
](Bulletin of Materials Science, Nov 25, 2009
x (x = 0⋅0-0⋅5) nanocomposites (NCs) with an average particle size of 72⋅4 nm were synthesized by... more x (x = 0⋅0-0⋅5) nanocomposites (NCs) with an average particle size of 72⋅4 nm were synthesized by the method of co-precipitation/hydrolysis (CPH). For the comparison of particle-size dependent effects, a set of polycrystalline samples with similar compositions was also prepared by solid state reaction (SSR) route. Average particle size for SSR prepared samples was about 3⋅0 μm. All the samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer, Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Their visible light photocatalytic activity was tested for the degradation of Congo Red dye. Maximum photodegradation was observed for the NC with x = 0⋅1 synthesized by CPH (particle size, 71 nm). Similar composition prepared by SSR method (particle size, 6⋅19 μm) showed lower photoactivity in comparison even with that observed for pure TiO 2 (particle size, 4⋅03 μm). It was, therefore, concluded that enhanced photodegradation is directly related to the reduced particle size of the composites, which implies that photosensitization is the process primarily involved. Although, doping of TiO 2 with ZnFe 2 O 4 does extend the cut-off wavelength towards visible parts of the spectrum, its contribution in the enhancement is not as significant as that due to the photosensitization.
Physical Review B, 2002
The grain boundaries ͑GB's͒ in the intermetallic superconductor MgB 2 , interestingly, do not sho... more The grain boundaries ͑GB's͒ in the intermetallic superconductor MgB 2 , interestingly, do not show suppression of supercurrent density. This unexpected behavior has been investigated by a scanning tunneling microscopy/spectroscopy technique at atomic resolution. The GB in MgB 2 is seen as an amorphous region extending from ϳ50 to 200 Å and has a metallic character. This observation supports proximity coupling between the grains, which explains why supercurrent density does not degrade in this material. The results for another intermetallic superconductor YNi 2 B 2 C having GB's ͑average width ϳ30 Å͒ that are quasi-insulating in nature have also been presented and compared with the former.
One possible approach for the treatment of wastewater is the photocatalytic oxidative degradation... more One possible approach for the treatment of wastewater is the photocatalytic oxidative degradation of the pollutants. The wide band gap (Eg = 3.2 eV), semiconducting titanium oxide (TiO2) is one of the materials most extensively investigated for its photocatalytic properties. Even in the pure form, it shows considerable degradation efficiency, but only under UV irradiation. With some appropriate structural and compositional modifications, not only its degradation efficiency could be enhanced, but the visible-light induced photocatalysis could also be made possible, which is rather cost-effective. The overall understanding about the synthesis of TiO2 based catalysts is more or less consistent; however there is still a lack of general consensus regarding the mechanisms involved in the process of photocatalysis. In an attempt to improve our insight on this subject, we present in this chapter, a comparative report on the photocatalytic degradation mediated by two TiO2 based materials, on...
We have investigated two MgB 2 superconductor thin films, prepared by two different methods, name... more We have investigated two MgB 2 superconductor thin films, prepared by two different methods, namely, pulsed laser deposition (PLD) and electron beam evaporation (EVE), by scanning electron microscopy (SEM) before and after 200 MeV 107 Ag ions irradiation. Severe degradation of superconducting properties in irradiated PLD film and absence of the same in EBE film correlates well with the observed changes in their micrstructures. It has been noted that the microsctructural changes observed in the PLD film is due to significant irradiation induced mass-transfer at the film surface, which is evident from the SEM pictures (figure 1). This has been supported quantitively using the viscoelastic model originally developed for amorphous solids subjected to irradiation.
In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and e... more In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and environment friendly resources rather than just being a waste material. A number of novel applications have been identified and are being exploited as well. The pozzolanic properties of FA make it a suitable candidate for cement replacement, as well as for the production of ceramics and glasses to be used as construction material. It can be utilized in the construction of embankments and structural fill; waste stabilization and solidification; mine reclamation; road sub-base; aggregate and mineral filler in asphalt concrete; soil amendment of soft soil and to increase bioavailability of nutrients in the soils, as well as adsorbent for heavy toxic metals. Other applications include production of roofing tiles, paints, metal casting, and as filler in wood and plastic products. Alkali rich FA can be used to neutralize the waste water from Acid Mine Drainage (AMD). Most of the current applica...
Two types of TiO 2 based nanocomposites (NC's) were synthesized using the co-precipitation/hy... more Two types of TiO 2 based nanocomposites (NC's) were synthesized using the co-precipitation/hydrolysis (CPH) method. NC's with average particle size of 72.4 nm were produced when Zn 2+ /Fe 3+ ions were co-doped into TiO 2 , and that of 74.0 nm resulted when Y 3+ ions were doped. The composition of the first set (TZF) of NC's was: TiO 2 .[ZnFe 2 O 4 ] x (with x = 0.1 to 0.5), and that of the second set (TY) was: TiO 2 .[Y 2 O 3 ] x (x = 0.1 to 0.4). Moreover, polycrystalline samples of both TZF and TY sets with similar compositions were also prepared by solid state reaction (SSR) route. This method produced average particle size of more than 1.0 µm for both the sets, and thus enabled the comparison of particle-size dependent effects. Characterization of all the samples was done by scanning electron microscopy (SEM), x-ray diffraction (XRD) and particle size analyzer. Further, visible light photocatalytic degradation of the dye Congo Red (CR) was investigated in the presenc...
We report the synthesis, characterization and ac-conductivity (σ ac ) results of some polyaniline... more We report the synthesis, characterization and ac-conductivity (σ ac ) results of some polyaniline (PAni) based composites. These materials were synthesized through incorporation of various fractions (20 to 60% by weight) of insulating fly-ash (FA) or clinker (Ck) in semiconducting PAni host. The synthesis was carried out for two different polymerization times (t p ) of 8 and 14 h, at 5 °C through oxidative polymerization, using ammonium-persulfate as initiator. Characterization of samples was done using x-ray diffraction (XRD), electron microscopy (SEM), and infrared spectroscopy (FTIR). Electrical conductivity analysis showed that synthesis for longer t p produced more conducting samples because it allowed the formation of longer and thicker polymer chains. In general, σ ac of the composites further increased with the fraction of FA or Ck, at least up to their maximum concentration studied in this work. Uniformly dispersed particles of FA or Ck apparently occupied the vacant spaces within the intertwined bundles of several polymer chains in such a way that continuity of the latter was not broken. Consequently, their presence pushed the bundles, and thus the individual chains, closer to each other, making the polymer parts more compact. The increased compactness of these conductive parts facilitated better mobility of charge carriers and therefore, the electrical conductivity increased.
Superconductor Science and Technology, 2001
We report an investigation of structure by x-ray diffraction, microstructure by atomic force micr... more We report an investigation of structure by x-ray diffraction, microstructure by atomic force microscopy (AFM) and broadening of resistive transitions in high dc magnetic fields (0-20 kOe) in Er 1−y Ca y Ba 2 Cu 3−x (Fe, Zn) x O 7−δ (y = 0.1, 0.2; and 0 x 0.20) ceramic superconductors. The XRD shows that the presence of Ca does not alter the known effect of Fe/Zn substitution on the structure of the pure (y = 0) system. Substitution of both Fe and Zn leads to a decrease in the grain size and micro-hardness. Interesting results were obtained on the influence of various dopants on the broadening of resistive transitions in dc magnetic fields, in general: (1) an increase in Ca content suppresses it; (2) Zn substitution has no effect; and (3) Fe substitution enhances it. We show that these results can be interpreted in terms of a thermally activated flux motion (TAFM), and the effect of various dopants on the properties like pinning barrier and anisotropy.
Physica E: Low-dimensional Systems and Nanostructures, 2015
Nanosized powders of rare-earth metal-ions doped potassium hexacyanoferrate have been investigate... more Nanosized powders of rare-earth metal-ions doped potassium hexacyanoferrate have been investigated. KRFe(CN) 6 Á 3H 2 O (with R ¼Y, Gd and Yb) powders were synthesized through precipitation. X-ray diffraction data has been analyzed with FullProf software suite. All samples were found to crystallize in the Orthorhombic unit-cell with P mmm space group. Crystal parameters were determined and refined with FullProf.
American Journal of Condensed Matter Physics, 2012
A simple method for the determination of temperature dependent second order elastic constants (SO... more A simple method for the determination of temperature dependent second order elastic constants (SOEC) of MgO, CaO, Mg 2 SiO 4 and Grossular garnet[Ca 3 Al 2 (SiO 4 ) 3 ] using a potential free model based on thermodynamical relationships, has been proposed. The equations developed here are based on the linear relationship between elastic constants at temperatures higher than the Debye temperature. The extrapolated data for elastic constants at very high temperatures obtained in the present study are useful to understand the thermoelastic properties of given solids. It is found that the calculated values of elastic constants, in general, decrease with temperature. The theoretical predictions incorporating the concept of Debye temperature, reported in this paper, are well supported by the available experimental data. The proposed emp irical relationship provides a method to estimate the thermoelastic properties of geophysical minerals and solids at high temperature range.
Nanoscience and Nanotechnology, 2012
A simple equation of state (EoS) has been derived and used to study the volume expansion of some ... more A simple equation of state (EoS) has been derived and used to study the volume expansion of some nanomaterials under the effect of pressure. Only two input parameters, namely, the bulk modulus and its first pressure derivative are required for calculations. We have considered a wide variety of nanomaterials, such as, metals [Ni (20 nm), α-Fe (nanotubes), Cu (80nm) and Ag (55nm)], semiconductors [Ge (49 nm), Si, CdSe (rock-salt phase), MgO (20nm) and ZnO], and carbon nanotube (CNT) to analyze the effects of pressure on them. The results have been compared with the available experimental data as well as with those obtained through other theoretical approaches. Excellent agreement between theoretical and experimental data, throughout the range of pressure under investigation, supports the validity of present approach.
Nanotechnology Development, 2011
We report fast and complete destruction of the dye Congo red (CR) under visible light in the pres... more We report fast and complete destruction of the dye Congo red (CR) under visible light in the presence of Nd 3+ and Er 3+ doped TiO 2 nanocomposites (NCs). TiO 2 NCs with general composition TiO 2 [R 2 O 3 ] x , {x=0.1, 0.2; R≡ Nd, Er} and particle size 12-16 nm were synthesized through co-precipitation/hydrolysis (CPH). A set of similar composites was also prepared through solid state reaction (SSR) route, which produced 31-47 nm particles. After characterization, visible light photocatalytic activity of all the samples was recorded for the degradation of CR. NCs with molar concentration x=0.2 of both doping types produced close to 100% degradation in 180 min. The apparent rate constant (k obs ) was found to be 2.91×10 -2 min -1 and 2.36×10 -2 min -1 , for these Nd 3+ and Er 3+ doped NCs, respectively. The other NCs with x=0.1, also showed significant degradation of CR, but the samples prepared through SSR performed worse. The excellent degradation obtained with the NCs may be attributed to their small particle size. Moreover, the doping of Nd 3+ and Er 3+ ions further supported the photocatalysis through formation of intermediate energy levels within the band gap of TiO 2 . These new levels not only acted as electron traps for efficient suppression of the undesired e -/h + recombination, but also facilitated to a certain extent the absorption of visible irradiation.
ISRN Physical Chemistry, 2012
Rare earth (R) ion-doped TiO 2 nanocomposites (NCs) with general composition [R 2 O 3 ] x · [TiO ... more Rare earth (R) ion-doped TiO 2 nanocomposites (NCs) with general composition [R 2 O 3 ] x · [TiO 2 ] 1−x (R: Y, Yb, Gd; x = 0.1, 0.2) were synthesized through co-precipitation/hydrolysis (CPH). NC particles with average size of approximately a few tens of nm were obtained. Similar compositions of polycrystalline (PC) samples with larger particle size were also prepared employing solid state reaction (SSR) method. Visible light photocatalytic activity of all samples was investigated for degradation of Congo red (CR) dye. Both in terms of apparent rate constant (k obs ) and percent degradation after 180 min (C 180 ), all NCs produced significantly enhanced degradation as compared to pure TiO 2 and PC samples. Best degradation of 95% (C 180 value) resulted with x = 0.2 composition of Y 3+ doped NC with k obs = 2.6 × 10 −2 min −1 . This was followed by C 180 of 85 and 80%, produced with Yb 3+ and Gd 3+ doped, x = 0.1 NCs, at k obs around 1.0 × 10 −2 and 0.9 × 10 −2 min −1 , respectively. The observations clearly suggest that enhanced photocatalytic degradation of CR is directly related to smaller particle size of the catalysts. Moreover, the presence of rare earth ions in the composites facilitates further improvement of degradation efficiency through effective suppression of e − /h + recombination.
Superconductor Science and Technology, 2003
We report magnetization studies on MgB 2 superconducting thin films in a temperature range 4.240... more We report magnetization studies on MgB 2 superconducting thin films in a temperature range 4.240 K and magnetic field range 06 T. Thin films prepared by both pulsed laser deposition (PLD) and electron beam evaporation (EBE) methods were investigated. In ...
Superconductor Science and Technology, 2004
MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evapo... more MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evaporation (EBE), have been investigated by scanning electron microscopy (SEM) before and after 200 MeV 107Ag ion irradiation. The severe degradation of superconducting properties in irradiated PLD film and the absence of the same in EBE film correlates with the observed changes in their microstructures. The micrographs of the PLD film show an overall smoothing, flow pattern and reduction in size of the bigger agglomerates after irradiation. On the other hand, the microstructure of the EBE film does not show any significant change after irradiation. The flow pattern observed in the PLD film can be understood on the basis of the viscoelastic model for irradiation induced shear flow in amorphous solids. The observed degradation of the PLD film may thus be attributed primarily to its disordered nature under irradiation, whereas the radiation hardness of the EBE film may be due to its higher crystallinity.
Solid-State Electronics, 2008
We have studied the effect of white light on hopping conduction and the effectiveness of non-equi... more We have studied the effect of white light on hopping conduction and the effectiveness of non-equilibrium phonon detection in Zndoped GaAs bolometers over the temperature range 1.35 K 6 T 6 2.15 K. The temperature dependence of the low electric field resistance indicates that the mechanism of conduction is due to variable range hopping. Using a heat-pulse technique we show that the sensitivity of a GaAs:Zn bolometer with an acceptor concentration, n a = 4.2 Â 10 17 cm À3 is significantly enhanced in the presence of suitably applied irradiation, despite the value of its temperature coefficient of resistance, aðT Þ ¼ ð1=RÞðoR=oT Þ, actually being decreased by light. It is proposed that the effect of light is to populate excited states of the acceptors, which have larger wave functions and hence show enhanced hopping.
physica status solidi (a), 2004
metallic glasses (MGs) resulting from 130 MeV 28 Si ion irradiation has been investigated. Resist... more metallic glasses (MGs) resulting from 130 MeV 28 Si ion irradiation has been investigated. Resistivity as a function of temperature has been measured off-line and in situ before and after irradiation, and on-line as a function of ion fluence. The results show that for the 2605SC MG electrical resistivity increases by 5.2% (fluence = 3.7 × 10 14 ions/cm 2 ) and 4.5% (fluence = 1.6 × 10 14 ions/cm 2 ). This has been explained on the basis of the 'two-hit model'. For the 2705M MG, however, an unexpected decrease of electrical resistivity of about -9.6% (fluence = 1.1 × 10 16 ions/cm 2 ) and -8.7% (1.3 × 10 14 ions/cm 2 ) is observed, which has been attributed to irradiation-induced structural modification.
Physica C: Superconductivity, 2002
We have presented here the results of SEM and STM/STS investigations carried out on MgB 2 superco... more We have presented here the results of SEM and STM/STS investigations carried out on MgB 2 superconductor. The SEM pictures show porous surface and well-linked granular structure in which bigger grains (few micrometer size) seem to be agglomeration of smaller, nearly hexagonal grains (size nearly 100 nm). Hexagonal structure of Mg and B layers have been directly observed in atomically resolved STM images. The lattice constants have been determined to be a Mg ¼ 3:1 A A, a B ¼ 1:7 A A and c ¼ 3:5 A A. Grain boundaries (GB) of width ranging from 50 to 200 A A have been observed. Absence of weak link effects despite wide GBs has been attributed to the metallic nature of the amorphous region of the GB interior as inferred from STS analysis. Irradiation with 200 MeV 107 Ag ions gives tracks of about 65 A A in the bulk of the sample. This is expected to give higher value of critical current density owing to the flux pinning mechanism, which is related to possibility of wide practical application of this material.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Self supporting samples of Metglass 2204 (Ti 50 Be 40 Zr 10 ) and substrate bound samples of Metg... more Self supporting samples of Metglass 2204 (Ti 50 Be 40 Zr 10 ) and substrate bound samples of Metglass 2705M (Co 69 B 12 Si 12 Fe 4 Mo 2 Ni 1 ) have been irradiated with 260 MeV 107 Ag and 130 MeV 28 Si ions, respectively at liquid nitrogen temperature. The surfaces have been examined by Scanning Electron Microscopy prior to and after irradiation. It is found that the surfaces have been smoothened after irradiation in both cases. The heights of the ÔhillsÕ have been decreased and the ÔvalleysÕ have been ®lled, without any detectable mass loss. The observed surface smoothing has been explained on the basis of shear¯ow mechanism within the framework of the viscoelastic model. Ó
In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and e... more In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and environment friendly resources rather than just being a waste material. A number of novel applications have been identified and are being exploited as well. The pozzolanic properties of FA make it a suitable candidate for cement replacement, as well as for the production of ceramics and glasses to be used as construction material. It can be utilized in the construction of embankments and structural fill; waste stabilization and solidification; mine reclamation; road sub-base; aggregate and mineral filler in asphalt concrete; soil amendment of soft soil and to increase bioavailability of nutrients in the soils, as well as adsorbent for heavy toxic metals. Other applications include production of roofing tiles, paints, metal casting, and as filler in wood and plastic products. Alkali rich FA can be used to neutralize the waste water from Acid Mine Drainage (AMD). Most of the current applica...
Bulletin of Materials Science, Nov 25, 2009
x (x = 0⋅0-0⋅5) nanocomposites (NCs) with an average particle size of 72⋅4 nm were synthesized by... more x (x = 0⋅0-0⋅5) nanocomposites (NCs) with an average particle size of 72⋅4 nm were synthesized by the method of co-precipitation/hydrolysis (CPH). For the comparison of particle-size dependent effects, a set of polycrystalline samples with similar compositions was also prepared by solid state reaction (SSR) route. Average particle size for SSR prepared samples was about 3⋅0 μm. All the samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer, Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Their visible light photocatalytic activity was tested for the degradation of Congo Red dye. Maximum photodegradation was observed for the NC with x = 0⋅1 synthesized by CPH (particle size, 71 nm). Similar composition prepared by SSR method (particle size, 6⋅19 μm) showed lower photoactivity in comparison even with that observed for pure TiO 2 (particle size, 4⋅03 μm). It was, therefore, concluded that enhanced photodegradation is directly related to the reduced particle size of the composites, which implies that photosensitization is the process primarily involved. Although, doping of TiO 2 with ZnFe 2 O 4 does extend the cut-off wavelength towards visible parts of the spectrum, its contribution in the enhancement is not as significant as that due to the photosensitization.
Physical Review B, 2002
The grain boundaries ͑GB's͒ in the intermetallic superconductor MgB 2 , interestingly, do not sho... more The grain boundaries ͑GB's͒ in the intermetallic superconductor MgB 2 , interestingly, do not show suppression of supercurrent density. This unexpected behavior has been investigated by a scanning tunneling microscopy/spectroscopy technique at atomic resolution. The GB in MgB 2 is seen as an amorphous region extending from ϳ50 to 200 Å and has a metallic character. This observation supports proximity coupling between the grains, which explains why supercurrent density does not degrade in this material. The results for another intermetallic superconductor YNi 2 B 2 C having GB's ͑average width ϳ30 Å͒ that are quasi-insulating in nature have also been presented and compared with the former.
One possible approach for the treatment of wastewater is the photocatalytic oxidative degradation... more One possible approach for the treatment of wastewater is the photocatalytic oxidative degradation of the pollutants. The wide band gap (Eg = 3.2 eV), semiconducting titanium oxide (TiO2) is one of the materials most extensively investigated for its photocatalytic properties. Even in the pure form, it shows considerable degradation efficiency, but only under UV irradiation. With some appropriate structural and compositional modifications, not only its degradation efficiency could be enhanced, but the visible-light induced photocatalysis could also be made possible, which is rather cost-effective. The overall understanding about the synthesis of TiO2 based catalysts is more or less consistent; however there is still a lack of general consensus regarding the mechanisms involved in the process of photocatalysis. In an attempt to improve our insight on this subject, we present in this chapter, a comparative report on the photocatalytic degradation mediated by two TiO2 based materials, on...
We have investigated two MgB 2 superconductor thin films, prepared by two different methods, name... more We have investigated two MgB 2 superconductor thin films, prepared by two different methods, namely, pulsed laser deposition (PLD) and electron beam evaporation (EVE), by scanning electron microscopy (SEM) before and after 200 MeV 107 Ag ions irradiation. Severe degradation of superconducting properties in irradiated PLD film and absence of the same in EBE film correlates well with the observed changes in their micrstructures. It has been noted that the microsctructural changes observed in the PLD film is due to significant irradiation induced mass-transfer at the film surface, which is evident from the SEM pictures (figure 1). This has been supported quantitively using the viscoelastic model originally developed for amorphous solids subjected to irradiation.
In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and e... more In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most cost-effective and environment friendly resources rather than just being a waste material. A number of novel applications have been identified and are being exploited as well. The pozzolanic properties of FA make it a suitable candidate for cement replacement, as well as for the production of ceramics and glasses to be used as construction material. It can be utilized in the construction of embankments and structural fill; waste stabilization and solidification; mine reclamation; road sub-base; aggregate and mineral filler in asphalt concrete; soil amendment of soft soil and to increase bioavailability of nutrients in the soils, as well as adsorbent for heavy toxic metals. Other applications include production of roofing tiles, paints, metal casting, and as filler in wood and plastic products. Alkali rich FA can be used to neutralize the waste water from Acid Mine Drainage (AMD). Most of the current applica...
Two types of TiO 2 based nanocomposites (NC's) were synthesized using the co-precipitation/hy... more Two types of TiO 2 based nanocomposites (NC's) were synthesized using the co-precipitation/hydrolysis (CPH) method. NC's with average particle size of 72.4 nm were produced when Zn 2+ /Fe 3+ ions were co-doped into TiO 2 , and that of 74.0 nm resulted when Y 3+ ions were doped. The composition of the first set (TZF) of NC's was: TiO 2 .[ZnFe 2 O 4 ] x (with x = 0.1 to 0.5), and that of the second set (TY) was: TiO 2 .[Y 2 O 3 ] x (x = 0.1 to 0.4). Moreover, polycrystalline samples of both TZF and TY sets with similar compositions were also prepared by solid state reaction (SSR) route. This method produced average particle size of more than 1.0 µm for both the sets, and thus enabled the comparison of particle-size dependent effects. Characterization of all the samples was done by scanning electron microscopy (SEM), x-ray diffraction (XRD) and particle size analyzer. Further, visible light photocatalytic degradation of the dye Congo Red (CR) was investigated in the presenc...
We report the synthesis, characterization and ac-conductivity (σ ac ) results of some polyaniline... more We report the synthesis, characterization and ac-conductivity (σ ac ) results of some polyaniline (PAni) based composites. These materials were synthesized through incorporation of various fractions (20 to 60% by weight) of insulating fly-ash (FA) or clinker (Ck) in semiconducting PAni host. The synthesis was carried out for two different polymerization times (t p ) of 8 and 14 h, at 5 °C through oxidative polymerization, using ammonium-persulfate as initiator. Characterization of samples was done using x-ray diffraction (XRD), electron microscopy (SEM), and infrared spectroscopy (FTIR). Electrical conductivity analysis showed that synthesis for longer t p produced more conducting samples because it allowed the formation of longer and thicker polymer chains. In general, σ ac of the composites further increased with the fraction of FA or Ck, at least up to their maximum concentration studied in this work. Uniformly dispersed particles of FA or Ck apparently occupied the vacant spaces within the intertwined bundles of several polymer chains in such a way that continuity of the latter was not broken. Consequently, their presence pushed the bundles, and thus the individual chains, closer to each other, making the polymer parts more compact. The increased compactness of these conductive parts facilitated better mobility of charge carriers and therefore, the electrical conductivity increased.
Superconductor Science and Technology, 2001
We report an investigation of structure by x-ray diffraction, microstructure by atomic force micr... more We report an investigation of structure by x-ray diffraction, microstructure by atomic force microscopy (AFM) and broadening of resistive transitions in high dc magnetic fields (0-20 kOe) in Er 1−y Ca y Ba 2 Cu 3−x (Fe, Zn) x O 7−δ (y = 0.1, 0.2; and 0 x 0.20) ceramic superconductors. The XRD shows that the presence of Ca does not alter the known effect of Fe/Zn substitution on the structure of the pure (y = 0) system. Substitution of both Fe and Zn leads to a decrease in the grain size and micro-hardness. Interesting results were obtained on the influence of various dopants on the broadening of resistive transitions in dc magnetic fields, in general: (1) an increase in Ca content suppresses it; (2) Zn substitution has no effect; and (3) Fe substitution enhances it. We show that these results can be interpreted in terms of a thermally activated flux motion (TAFM), and the effect of various dopants on the properties like pinning barrier and anisotropy.
Physica E: Low-dimensional Systems and Nanostructures, 2015
Nanosized powders of rare-earth metal-ions doped potassium hexacyanoferrate have been investigate... more Nanosized powders of rare-earth metal-ions doped potassium hexacyanoferrate have been investigated. KRFe(CN) 6 Á 3H 2 O (with R ¼Y, Gd and Yb) powders were synthesized through precipitation. X-ray diffraction data has been analyzed with FullProf software suite. All samples were found to crystallize in the Orthorhombic unit-cell with P mmm space group. Crystal parameters were determined and refined with FullProf.
American Journal of Condensed Matter Physics, 2012
A simple method for the determination of temperature dependent second order elastic constants (SO... more A simple method for the determination of temperature dependent second order elastic constants (SOEC) of MgO, CaO, Mg 2 SiO 4 and Grossular garnet[Ca 3 Al 2 (SiO 4 ) 3 ] using a potential free model based on thermodynamical relationships, has been proposed. The equations developed here are based on the linear relationship between elastic constants at temperatures higher than the Debye temperature. The extrapolated data for elastic constants at very high temperatures obtained in the present study are useful to understand the thermoelastic properties of given solids. It is found that the calculated values of elastic constants, in general, decrease with temperature. The theoretical predictions incorporating the concept of Debye temperature, reported in this paper, are well supported by the available experimental data. The proposed emp irical relationship provides a method to estimate the thermoelastic properties of geophysical minerals and solids at high temperature range.
Nanoscience and Nanotechnology, 2012
A simple equation of state (EoS) has been derived and used to study the volume expansion of some ... more A simple equation of state (EoS) has been derived and used to study the volume expansion of some nanomaterials under the effect of pressure. Only two input parameters, namely, the bulk modulus and its first pressure derivative are required for calculations. We have considered a wide variety of nanomaterials, such as, metals [Ni (20 nm), α-Fe (nanotubes), Cu (80nm) and Ag (55nm)], semiconductors [Ge (49 nm), Si, CdSe (rock-salt phase), MgO (20nm) and ZnO], and carbon nanotube (CNT) to analyze the effects of pressure on them. The results have been compared with the available experimental data as well as with those obtained through other theoretical approaches. Excellent agreement between theoretical and experimental data, throughout the range of pressure under investigation, supports the validity of present approach.
Nanotechnology Development, 2011
We report fast and complete destruction of the dye Congo red (CR) under visible light in the pres... more We report fast and complete destruction of the dye Congo red (CR) under visible light in the presence of Nd 3+ and Er 3+ doped TiO 2 nanocomposites (NCs). TiO 2 NCs with general composition TiO 2 [R 2 O 3 ] x , {x=0.1, 0.2; R≡ Nd, Er} and particle size 12-16 nm were synthesized through co-precipitation/hydrolysis (CPH). A set of similar composites was also prepared through solid state reaction (SSR) route, which produced 31-47 nm particles. After characterization, visible light photocatalytic activity of all the samples was recorded for the degradation of CR. NCs with molar concentration x=0.2 of both doping types produced close to 100% degradation in 180 min. The apparent rate constant (k obs ) was found to be 2.91×10 -2 min -1 and 2.36×10 -2 min -1 , for these Nd 3+ and Er 3+ doped NCs, respectively. The other NCs with x=0.1, also showed significant degradation of CR, but the samples prepared through SSR performed worse. The excellent degradation obtained with the NCs may be attributed to their small particle size. Moreover, the doping of Nd 3+ and Er 3+ ions further supported the photocatalysis through formation of intermediate energy levels within the band gap of TiO 2 . These new levels not only acted as electron traps for efficient suppression of the undesired e -/h + recombination, but also facilitated to a certain extent the absorption of visible irradiation.
ISRN Physical Chemistry, 2012
Rare earth (R) ion-doped TiO 2 nanocomposites (NCs) with general composition [R 2 O 3 ] x · [TiO ... more Rare earth (R) ion-doped TiO 2 nanocomposites (NCs) with general composition [R 2 O 3 ] x · [TiO 2 ] 1−x (R: Y, Yb, Gd; x = 0.1, 0.2) were synthesized through co-precipitation/hydrolysis (CPH). NC particles with average size of approximately a few tens of nm were obtained. Similar compositions of polycrystalline (PC) samples with larger particle size were also prepared employing solid state reaction (SSR) method. Visible light photocatalytic activity of all samples was investigated for degradation of Congo red (CR) dye. Both in terms of apparent rate constant (k obs ) and percent degradation after 180 min (C 180 ), all NCs produced significantly enhanced degradation as compared to pure TiO 2 and PC samples. Best degradation of 95% (C 180 value) resulted with x = 0.2 composition of Y 3+ doped NC with k obs = 2.6 × 10 −2 min −1 . This was followed by C 180 of 85 and 80%, produced with Yb 3+ and Gd 3+ doped, x = 0.1 NCs, at k obs around 1.0 × 10 −2 and 0.9 × 10 −2 min −1 , respectively. The observations clearly suggest that enhanced photocatalytic degradation of CR is directly related to smaller particle size of the catalysts. Moreover, the presence of rare earth ions in the composites facilitates further improvement of degradation efficiency through effective suppression of e − /h + recombination.
Superconductor Science and Technology, 2003
We report magnetization studies on MgB 2 superconducting thin films in a temperature range 4.240... more We report magnetization studies on MgB 2 superconducting thin films in a temperature range 4.240 K and magnetic field range 06 T. Thin films prepared by both pulsed laser deposition (PLD) and electron beam evaporation (EBE) methods were investigated. In ...
Superconductor Science and Technology, 2004
MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evapo... more MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evaporation (EBE), have been investigated by scanning electron microscopy (SEM) before and after 200 MeV 107Ag ion irradiation. The severe degradation of superconducting properties in irradiated PLD film and the absence of the same in EBE film correlates with the observed changes in their microstructures. The micrographs of the PLD film show an overall smoothing, flow pattern and reduction in size of the bigger agglomerates after irradiation. On the other hand, the microstructure of the EBE film does not show any significant change after irradiation. The flow pattern observed in the PLD film can be understood on the basis of the viscoelastic model for irradiation induced shear flow in amorphous solids. The observed degradation of the PLD film may thus be attributed primarily to its disordered nature under irradiation, whereas the radiation hardness of the EBE film may be due to its higher crystallinity.
Solid-State Electronics, 2008
We have studied the effect of white light on hopping conduction and the effectiveness of non-equi... more We have studied the effect of white light on hopping conduction and the effectiveness of non-equilibrium phonon detection in Zndoped GaAs bolometers over the temperature range 1.35 K 6 T 6 2.15 K. The temperature dependence of the low electric field resistance indicates that the mechanism of conduction is due to variable range hopping. Using a heat-pulse technique we show that the sensitivity of a GaAs:Zn bolometer with an acceptor concentration, n a = 4.2 Â 10 17 cm À3 is significantly enhanced in the presence of suitably applied irradiation, despite the value of its temperature coefficient of resistance, aðT Þ ¼ ð1=RÞðoR=oT Þ, actually being decreased by light. It is proposed that the effect of light is to populate excited states of the acceptors, which have larger wave functions and hence show enhanced hopping.
physica status solidi (a), 2004
metallic glasses (MGs) resulting from 130 MeV 28 Si ion irradiation has been investigated. Resist... more metallic glasses (MGs) resulting from 130 MeV 28 Si ion irradiation has been investigated. Resistivity as a function of temperature has been measured off-line and in situ before and after irradiation, and on-line as a function of ion fluence. The results show that for the 2605SC MG electrical resistivity increases by 5.2% (fluence = 3.7 × 10 14 ions/cm 2 ) and 4.5% (fluence = 1.6 × 10 14 ions/cm 2 ). This has been explained on the basis of the 'two-hit model'. For the 2705M MG, however, an unexpected decrease of electrical resistivity of about -9.6% (fluence = 1.1 × 10 16 ions/cm 2 ) and -8.7% (1.3 × 10 14 ions/cm 2 ) is observed, which has been attributed to irradiation-induced structural modification.
Physica C: Superconductivity, 2002
We have presented here the results of SEM and STM/STS investigations carried out on MgB 2 superco... more We have presented here the results of SEM and STM/STS investigations carried out on MgB 2 superconductor. The SEM pictures show porous surface and well-linked granular structure in which bigger grains (few micrometer size) seem to be agglomeration of smaller, nearly hexagonal grains (size nearly 100 nm). Hexagonal structure of Mg and B layers have been directly observed in atomically resolved STM images. The lattice constants have been determined to be a Mg ¼ 3:1 A A, a B ¼ 1:7 A A and c ¼ 3:5 A A. Grain boundaries (GB) of width ranging from 50 to 200 A A have been observed. Absence of weak link effects despite wide GBs has been attributed to the metallic nature of the amorphous region of the GB interior as inferred from STS analysis. Irradiation with 200 MeV 107 Ag ions gives tracks of about 65 A A in the bulk of the sample. This is expected to give higher value of critical current density owing to the flux pinning mechanism, which is related to possibility of wide practical application of this material.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Self supporting samples of Metglass 2204 (Ti 50 Be 40 Zr 10 ) and substrate bound samples of Metg... more Self supporting samples of Metglass 2204 (Ti 50 Be 40 Zr 10 ) and substrate bound samples of Metglass 2705M (Co 69 B 12 Si 12 Fe 4 Mo 2 Ni 1 ) have been irradiated with 260 MeV 107 Ag and 130 MeV 28 Si ions, respectively at liquid nitrogen temperature. The surfaces have been examined by Scanning Electron Microscopy prior to and after irradiation. It is found that the surfaces have been smoothened after irradiation in both cases. The heights of the ÔhillsÕ have been decreased and the ÔvalleysÕ have been ®lled, without any detectable mass loss. The observed surface smoothing has been explained on the basis of shear¯ow mechanism within the framework of the viscoelastic model. Ó