Muhammad Usman - Academia.edu (original) (raw)

Papers by Muhammad Usman

Cobalt ferrite nanoparticles ͑size: 26Ϯ 4 nm͒ have been synthesized by coprecipitation route. The... more Cobalt ferrite nanoparticles ͑size: 26Ϯ 4 nm͒ have been synthesized by coprecipitation route. The coercivity of nanoparticles follows a simple model of thermal activation of particle moments over the anisotropy barrier in the temperature range of 30-300 K in accordance with Kneller's law; however, at low temperatures ͑ Ͻ 30 K͒, the coercivity shows some deviation from this law. The saturation magnetization follows the modified Bloch's law in the temperature range of 10-300 K. Exchange bias ͑H ex ͒ studies of the samples show that H ex increases with decreasing temperature of the sample. A strong increase in the H ex values is found below 30 K for the low applied field ͑ Ϯ 20 kOe͒, while a smaller increase is found for the high applied field ͑ Ϯ 90 kOe͒. The slow increase in the exchange bias at high applied field has been attributed to the high field effects on the surface ͑shell͒ spins. These shell spins align along the field direction that weakens the core-shell interface interactions leading to the reduction in the exchange bias at lower temperatures.

Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition... more Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition in etched ion-track polycarbonate membranes. Structural characterization of these nanowires with diameter 70, 90, 120 nm and length 30 lm was performed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. The as-prepared wires show uniform diameter along the whole length and X-ray diffraction analysis reveals that [002] texture of these wires become more pronounced as diameter is reduced. Magnetic characterization of the nanowires shows a clear difference of squareness and coercivity between parallel and perpendicular orientations of the wires with respect to the applied field direction. In case of parallel applied field, the coercivity has been found to be decreasing with increasing diameter of the wires while in perpendicular case; the coercivity observes lower values for larger diameter. The results are explained by taking into account the magnetocrystalline and shape anisotropies with respect to the applied field and domain transformation mechanism when single domain limit is surpassed.

Nanoferrites of composition Mn 1−x Ni x Fe 2 O 4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were prepa... more Nanoferrites of composition Mn 1−x Ni x Fe 2 O 4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were prepared by the chemical coprecipitation method. The prepared nanoferrites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological and magnetic changes taking place with varying Ni concentration in the composition of the prepared nanoferrites. IR reveals the presence of both highfrequency and low-frequency bands due to tetrahedral and octahedral sites, respectively. The XRD results indicated the formation of single spinel ferrite with crystalline size in the range of 14-26 nm. The lattice parameters (a) decrease with the increase of the Ni concentration x in the lattice. Further information about the morphology of the nanoferrites was obtained from the AFM and SEM results. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrites. Various magnetic properties such as saturation magnetization (M s ) and remanence (M r ) are calculated from the hysteresis loops and observed to be dependent on the composition. A. Faraz · N.M. Ahmad ( ) · Fazal-ur-Rehman · A. Maqsood ·

Published by the American Institute of Physics. Related Articles Correlation of spin and structur... more Published by the American Institute of Physics. Related Articles Correlation of spin and structure in doped bismuth ferrite nanoparticles J. Appl. Phys. 111, 07D910 (2012) Correlation between magnetic ordering and electric polarization in YMn1−xFexO3 nanocrystalline materials J. Appl. Phys. 111, 07B511 (2012) Temperature effect on dipolar and exchange interactions for SmCo5+Fe65Co35 nanocomposite powders J. Appl. Phys. 111, 07B505 (2012) Structure and magnetotransport properties of epitaxial nanocomposite La0.67Ca0.33MnO3:SrTiO3 thin films grown by a chemical solution approach Appl. Phys. Lett. 100, 082403 (2012) Effect of attrition time on the microwave permeability of magnetic Fe-Si-Al flakes Cu 1Àx Mn x O (0 x 0.08) nanoparticles were synthesized by a coprecipitation method. Powder x ray analysis reveals that samples show a pure CuO phase for x 0.06 and the appearance of a secondary phase CuMn 2 O 4 for x > 0.06. The unit cell volume expands with increasing Mn concentration up to x ¼ 0.06 and remains constant on further increase in Mn concentration. The undoped sample shows the behavior of pure CuO with antiferromagnetic transitions at T N1 ¼ 228 K and T N2 ¼ 214 K. Inclusion of Mn into the Cu sublattice turned antiferromagnetic CuO into a ferromagnet. The origin of ferromagnetism is analyzed on the basis of different possible interactions. It is believed that the indirect coupling between Mn ions mediated by O and Cu ions helps to stabilize the ferromagnetism. V C 2012 American Institute of Physics.

Electrostrictive and relaxor ferroelectric behavior in BiAlO3-modified BaTiO3 lead-free ceramics ... more Electrostrictive and relaxor ferroelectric behavior in BiAlO3-modified BaTiO3 lead-free ceramics J. Appl. Phys. 113, 094102 Abnormal polarization switching of relaxor terpolymer films at low temperatures Appl. Phys. Lett. 102, 072906 Quenching-induced circumvention of integrated aging effect of relaxor lead lanthanum zirconate titanate and (Bi1/2Na1/2)TiO3-BaTiO3 Appl. Phys. Lett. 102, 032901 Relaxor behavior of ferroelectric Ca0.22Sr0.12Ba0.66Nb2O6

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We report the static magnetic properties of Maghemite (γ-Fe2O3) nanoparticles with an average cry... more We report the static magnetic properties of Maghemite (γ-Fe2O3) nanoparticles with an average crystallite size of 14 ± 1.8 nm synthesized via a co-precipitation method. The zero-field-cooled (ZFC) and the field-cooled (FC) magnetization measurements were performed using a physical properties measurements system (PPMS) at temperatures from 5 K to 300 K. The ZFC/FC measurements showed a typical superparamagnetic behavior with a narrow size distribution.

Different biological activities of capped and uncapped ZnO nanoparticles were investigated, and t... more Different biological activities of capped and uncapped ZnO nanoparticles were investigated, and the effects of potential capping agents on these biological activities were studied. ZnO nanoparticles were synthesized and capped by polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) using a simple chemical method of co-precipitation. Characterization by X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR) and UV-vis spectroscopy confirmed the crystallinity, size, functional group, and band gap of synthesized nanoparticles. Reduction in size occurred from 34 nm to 26 nm due to sur-factant. Results of all biological activities indicated significantly higher values in capped as compared to uncapped nanoparticles. Antibacterial activity against Staphylococcus aureus (ATCC 6538), Bacillus sub-tilis (ATCC 6633), Escherichia coli (ATCC15224), and Acetobacter was obtained. This activity was more prominent against Gram-positive bacteria, and ZnO-PVP nanoparticles elucidated highest antibacterial activity (zone of inhibition 17 mm) against Gram-positive, Bacillus subtilis species. Antioxidant activities including total flavonoid content, total phenolic content, total antioxidant capacity, total reducing power and %age inhibition of DPPH, and antidiabetic activity against ␣-amylase enzyme found to be exhibited highest by ZnO-PEG nanoparticles.

Polycrystalline lead-free BaZr 0.15 Ti 0.85 O 3 ceramics doped with ZnO (0 B x B 2 wt%) were prod... more Polycrystalline lead-free BaZr 0.15 Ti 0.85 O 3 ceramics doped with ZnO (0 B x B 2 wt%) were produced via mixed oxide solid-state reaction method. X-ray diffraction confirmed the presence of a single phase having tetragonal symmetry and having space group P4 mm. Scanning electron microscopy confirmed an increase in the density of microstructure and enlargement of grains with increase in ZnO concentration. Complex impedance spectroscopy revealed non-Debye type relaxation phenomenon. It was observed that an increase in the resistance of grain boundaries and decrease in that of grain interior (bulk) occurred with an increase in temperature. Relaxation time decreased with increase in temperature for both grain boundaries and grain interior. Under-standings obtained from this work might be helpful in engineering the microstructure of BZT-based ceramics for useful applications.

Polycrystalline lead-free (1-x)(K 0.5 Na 0.5) (Nb 0.995 Mn 0.005 O 3)-xCuO ceramics where 0 B x B... more Polycrystalline lead-free (1-x)(K 0.5 Na 0.5) (Nb 0.995 Mn 0.005 O 3)-xCuO ceramics where 0 B x B 2% were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis confirmed the presence of single-phase possessing monoclinic symmetry for all the synthesized compositions. Scanning electron microscopy revealed a dense microstructure along with increase in grains size with Cu doping in the KNNMn ceramics. Impedance spectroscopy (IS) showed that Cu doping was found to be helpful in increasing the grain boundary resistance. A temperature-dependent and non-Debye-type relaxation process was also revealed by IS studies. The relaxation time for both bulk and grain boundary decreased with temperature indicating a hopping conduction mechanism. The activation energy was found to be 0.4-0.5 eV, indicating conduction of oxygen vacancies through hopping mechanism. Insights gained from this work could be useful in designing the optimum composition and microstructure of KNN-based ceramics for practical applications.

We present the effects of size and oxygen defects on electrical and optical properties of nano cr... more We present the effects of size and oxygen defects on electrical and optical properties of nano crystalline bismuth ferrite (BiFeO 3) with rhombohedral symmetry synthesized by solution evaporation method. The effects of oxygen vacancies on the behavior of system have been studied by annealing all samples under two different environments, air and oxygen. Single phase crystal structure was confirmed by X-Ray diffraction (XRD). The crystalline size calculated by Scherrer's formula falls in the range of 11-21 nm for air and 20-29 nm in case of oxygen annealing atmosphere. The crystalline size was confirmed by Transmission electron microscope (TEM). Dielectric response reveals that both dielectric constant and dissipation factor (tanδ) decrease with increase of frequency without depicting any peak. Optical studies showed that the system possesses an indirect energy gap whose value increases with increasing particle size. There is an evidence for the presence of intra band states in this system arising from defect states.

This study aims to address the effects of different concentrations (0, 0.1, 1.0, 10, 100 or 1000 ... more This study aims to address the effects of different concentrations (0, 0.1, 1.0, 10, 100 or 1000 mg L À1) of engineered zinc oxide (ZnO) nanoparticles (34 nm in size) on growth parameters, steviol glycosides (rebaudioside A and stevioside) production and antioxidant activities in the tissue culture grown shoots of Stevia rebaudiana Bertoni. The highest percentage of shoot formation (89.6%) at 1 mg L À1 of ZnO nanoparticles concentration suggests a positive influence of ZnO nanoparticles on S. rebaudiana growth as compared to other treatments with or without ZnO nanoparticles. Additionally, HPLC results illustrate a significant enhancement of steviol glycosides (almost doubled as compared to the control) in micro-propagated shoots grown under an oxidative stress of 1 mg L À1 of ZnO nanoparticles. This finding is further affirmed by an increased 2,2-diphenyl-1-picryl hydrazyl (DPPH) scavenging activity, total anti-oxidant capacity, total reducing power, total flavonoid content and total phenolic content, with an ascending oxidative pressure and generation of reactive oxygen species (ROS). However, the antioxidant activities, formation of secondary metabolites and the physiological parameters showed a sudden decline after crossing a threshold of 1 mg L À1 concentration of ZnO nanoparticles and falls to a minimum at 1000 mg L À1 , elucidating maximum phytotoxic effect of ZnO nanoparticles at this concentration. This is the first study evaluating both the favorable and adverse effects of ZnO nanoparticles employed to a highly valuable medicinal plant, S. rebaudiana.

We have investigated structural, magnetic and magnetocaloric properties of CoFe 2-x Mo x O 4 (0.0... more We have investigated structural, magnetic and magnetocaloric properties of CoFe 2-x Mo x O 4 (0.0≤x≤0.3) ferrites. Polycrystalline samples were prepared by the sol gel method and characterized by the powder X-ray diffraction and scanning electron microscopy. X-ray diffraction patterns show that all samples have a cubic spinel structure and the lattice parameter, a, decreases monotonically with increase in Mo concentration. Scanning electron micrographs indicate that most of the particles are in the range of 400-850 nm size. Magnetic measurements, performed by using a cryogen free vibrating sample magnetometer, show that these samples are soft ferromagnets in the measured temperature range. The saturation magnetization, M s , values of Mo-doped samples are larger than the parent compound with a maximum value of~106 emu/g for x=0.2 sample. The magnetic entropy change (−ΔS) increases with increase in applied magnetic field and shows a peak in the vicinity of blocking temperature. A maximum value of 0.56 J kg −1 K −1 at 5 T field has been observed for x=0.2 sample.

Lead free (1-x)Ba(Zr 0.2 Ti 0.8)O 3-x(Ba 0.7 Ca 0.3)TiO 3 (x ¼ 0.3, 0.35, 0.4) ceramics were prep... more Lead free (1-x)Ba(Zr 0.2 Ti 0.8)O 3-x(Ba 0.7 Ca 0.3)TiO 3 (x ¼ 0.3, 0.35, 0.4) ceramics were prepared via conventional two-step solid-state reaction technique. Temperature dependent dielectric measurements, conducted in the frequency range from 1 kHz to 1 MHz, indicate diffused phase transition for all the samples. The diffuseness of the transition has been studied by fitting the data with modified Curie-Weiss law. It is found that the composition with x ¼ 0.3 behaves as a weak relaxor-ferroelectric, superposed by a non-relaxor behavior. Vogel-Fulcher law was used to characterize the relaxor-ferroelectric behavior while the analysis according to the Cole-Cole plots was used to characterize the non-relaxor features.

In this study, we describe an improvement of room temperature ferromag-netism achieved in a PbTi ... more In this study, we describe an improvement of room temperature ferromag-netism achieved in a PbTi 12x Fe x O 3 (0 £ x £ 0.60) system and discuss a correlation between structural, magnetic, dielectric and optical properties. Pure PbTiO 3 , which crystallizes in a tetragonal structure, evolved towards a cubic structure with increases in Fe content. Magnetic measurements showed that all Fe substituted samples are ferromagnetic at room temperature and maximum magnetization at 7 kOe increases with increases in Fe content. The origin and improvement of ferromagnetism is ascribed to the F-center exchange mechanism. The temperature dependence of dielectric behavior showed typical ferroelectric behavior, but ferroelectric transition temperature remained above our maximum measuring temperature. The improvement in dielectric properties of the PbFe x Ti 12x O 3 system may be attributed to increases of resistivity and activation energy. The decrease in band gap with increase in Fe substitution is ascribed to the decrease in c/a ratio, indicating that the optical band gap is affected by the degree of structural disorder in the PbFe x Ti 12x O 3 system.

Transition metal dichalcogenides (TMDs) with a unique sandwich structure have attracted tremendou... more Transition metal dichalcogenides (TMDs) with a unique sandwich structure have attracted tremendous attention in recent years due to their distinctive electrical and optical properties. The performance of TMDs can be tailored by integration with low dimensional nanostructures which possess quantum size effects and large specific surface areas. In this review, we give a brief description of integrated structures, their synthesis methods, and highlight the applications in hydrogen production, lithium batteries, sensors and detectors.

Cobalt ferrite nanoparticles ͑size: 26Ϯ 4 nm͒ have been synthesized by coprecipitation route. The... more Cobalt ferrite nanoparticles ͑size: 26Ϯ 4 nm͒ have been synthesized by coprecipitation route. The coercivity of nanoparticles follows a simple model of thermal activation of particle moments over the anisotropy barrier in the temperature range of 30-300 K in accordance with Kneller's law; however, at low temperatures ͑ Ͻ 30 K͒, the coercivity shows some deviation from this law. The saturation magnetization follows the modified Bloch's law in the temperature range of 10-300 K. Exchange bias ͑H ex ͒ studies of the samples show that H ex increases with decreasing temperature of the sample. A strong increase in the H ex values is found below 30 K for the low applied field ͑ Ϯ 20 kOe͒, while a smaller increase is found for the high applied field ͑ Ϯ 90 kOe͒. The slow increase in the exchange bias at high applied field has been attributed to the high field effects on the surface ͑shell͒ spins. These shell spins align along the field direction that weakens the core-shell interface interactions leading to the reduction in the exchange bias at lower temperatures.

Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition... more Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition in etched ion-track polycarbonate membranes. Structural characterization of these nanowires with diameter 70, 90, 120 nm and length 30 lm was performed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. The as-prepared wires show uniform diameter along the whole length and X-ray diffraction analysis reveals that [002] texture of these wires become more pronounced as diameter is reduced. Magnetic characterization of the nanowires shows a clear difference of squareness and coercivity between parallel and perpendicular orientations of the wires with respect to the applied field direction. In case of parallel applied field, the coercivity has been found to be decreasing with increasing diameter of the wires while in perpendicular case; the coercivity observes lower values for larger diameter. The results are explained by taking into account the magnetocrystalline and shape anisotropies with respect to the applied field and domain transformation mechanism when single domain limit is surpassed.

Nanoferrites of composition Mn 1−x Ni x Fe 2 O 4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were prepa... more Nanoferrites of composition Mn 1−x Ni x Fe 2 O 4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were prepared by the chemical coprecipitation method. The prepared nanoferrites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological and magnetic changes taking place with varying Ni concentration in the composition of the prepared nanoferrites. IR reveals the presence of both highfrequency and low-frequency bands due to tetrahedral and octahedral sites, respectively. The XRD results indicated the formation of single spinel ferrite with crystalline size in the range of 14-26 nm. The lattice parameters (a) decrease with the increase of the Ni concentration x in the lattice. Further information about the morphology of the nanoferrites was obtained from the AFM and SEM results. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrites. Various magnetic properties such as saturation magnetization (M s ) and remanence (M r ) are calculated from the hysteresis loops and observed to be dependent on the composition. A. Faraz · N.M. Ahmad ( ) · Fazal-ur-Rehman · A. Maqsood ·

Published by the American Institute of Physics. Related Articles Correlation of spin and structur... more Published by the American Institute of Physics. Related Articles Correlation of spin and structure in doped bismuth ferrite nanoparticles J. Appl. Phys. 111, 07D910 (2012) Correlation between magnetic ordering and electric polarization in YMn1−xFexO3 nanocrystalline materials J. Appl. Phys. 111, 07B511 (2012) Temperature effect on dipolar and exchange interactions for SmCo5+Fe65Co35 nanocomposite powders J. Appl. Phys. 111, 07B505 (2012) Structure and magnetotransport properties of epitaxial nanocomposite La0.67Ca0.33MnO3:SrTiO3 thin films grown by a chemical solution approach Appl. Phys. Lett. 100, 082403 (2012) Effect of attrition time on the microwave permeability of magnetic Fe-Si-Al flakes Cu 1Àx Mn x O (0 x 0.08) nanoparticles were synthesized by a coprecipitation method. Powder x ray analysis reveals that samples show a pure CuO phase for x 0.06 and the appearance of a secondary phase CuMn 2 O 4 for x > 0.06. The unit cell volume expands with increasing Mn concentration up to x ¼ 0.06 and remains constant on further increase in Mn concentration. The undoped sample shows the behavior of pure CuO with antiferromagnetic transitions at T N1 ¼ 228 K and T N2 ¼ 214 K. Inclusion of Mn into the Cu sublattice turned antiferromagnetic CuO into a ferromagnet. The origin of ferromagnetism is analyzed on the basis of different possible interactions. It is believed that the indirect coupling between Mn ions mediated by O and Cu ions helps to stabilize the ferromagnetism. V C 2012 American Institute of Physics.

Electrostrictive and relaxor ferroelectric behavior in BiAlO3-modified BaTiO3 lead-free ceramics ... more Electrostrictive and relaxor ferroelectric behavior in BiAlO3-modified BaTiO3 lead-free ceramics J. Appl. Phys. 113, 094102 Abnormal polarization switching of relaxor terpolymer films at low temperatures Appl. Phys. Lett. 102, 072906 Quenching-induced circumvention of integrated aging effect of relaxor lead lanthanum zirconate titanate and (Bi1/2Na1/2)TiO3-BaTiO3 Appl. Phys. Lett. 102, 032901 Relaxor behavior of ferroelectric Ca0.22Sr0.12Ba0.66Nb2O6

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We report the static magnetic properties of Maghemite (γ-Fe2O3) nanoparticles with an average cry... more We report the static magnetic properties of Maghemite (γ-Fe2O3) nanoparticles with an average crystallite size of 14 ± 1.8 nm synthesized via a co-precipitation method. The zero-field-cooled (ZFC) and the field-cooled (FC) magnetization measurements were performed using a physical properties measurements system (PPMS) at temperatures from 5 K to 300 K. The ZFC/FC measurements showed a typical superparamagnetic behavior with a narrow size distribution.

Different biological activities of capped and uncapped ZnO nanoparticles were investigated, and t... more Different biological activities of capped and uncapped ZnO nanoparticles were investigated, and the effects of potential capping agents on these biological activities were studied. ZnO nanoparticles were synthesized and capped by polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) using a simple chemical method of co-precipitation. Characterization by X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR) and UV-vis spectroscopy confirmed the crystallinity, size, functional group, and band gap of synthesized nanoparticles. Reduction in size occurred from 34 nm to 26 nm due to sur-factant. Results of all biological activities indicated significantly higher values in capped as compared to uncapped nanoparticles. Antibacterial activity against Staphylococcus aureus (ATCC 6538), Bacillus sub-tilis (ATCC 6633), Escherichia coli (ATCC15224), and Acetobacter was obtained. This activity was more prominent against Gram-positive bacteria, and ZnO-PVP nanoparticles elucidated highest antibacterial activity (zone of inhibition 17 mm) against Gram-positive, Bacillus subtilis species. Antioxidant activities including total flavonoid content, total phenolic content, total antioxidant capacity, total reducing power and %age inhibition of DPPH, and antidiabetic activity against ␣-amylase enzyme found to be exhibited highest by ZnO-PEG nanoparticles.

Polycrystalline lead-free BaZr 0.15 Ti 0.85 O 3 ceramics doped with ZnO (0 B x B 2 wt%) were prod... more Polycrystalline lead-free BaZr 0.15 Ti 0.85 O 3 ceramics doped with ZnO (0 B x B 2 wt%) were produced via mixed oxide solid-state reaction method. X-ray diffraction confirmed the presence of a single phase having tetragonal symmetry and having space group P4 mm. Scanning electron microscopy confirmed an increase in the density of microstructure and enlargement of grains with increase in ZnO concentration. Complex impedance spectroscopy revealed non-Debye type relaxation phenomenon. It was observed that an increase in the resistance of grain boundaries and decrease in that of grain interior (bulk) occurred with an increase in temperature. Relaxation time decreased with increase in temperature for both grain boundaries and grain interior. Under-standings obtained from this work might be helpful in engineering the microstructure of BZT-based ceramics for useful applications.

Polycrystalline lead-free (1-x)(K 0.5 Na 0.5) (Nb 0.995 Mn 0.005 O 3)-xCuO ceramics where 0 B x B... more Polycrystalline lead-free (1-x)(K 0.5 Na 0.5) (Nb 0.995 Mn 0.005 O 3)-xCuO ceramics where 0 B x B 2% were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis confirmed the presence of single-phase possessing monoclinic symmetry for all the synthesized compositions. Scanning electron microscopy revealed a dense microstructure along with increase in grains size with Cu doping in the KNNMn ceramics. Impedance spectroscopy (IS) showed that Cu doping was found to be helpful in increasing the grain boundary resistance. A temperature-dependent and non-Debye-type relaxation process was also revealed by IS studies. The relaxation time for both bulk and grain boundary decreased with temperature indicating a hopping conduction mechanism. The activation energy was found to be 0.4-0.5 eV, indicating conduction of oxygen vacancies through hopping mechanism. Insights gained from this work could be useful in designing the optimum composition and microstructure of KNN-based ceramics for practical applications.

We present the effects of size and oxygen defects on electrical and optical properties of nano cr... more We present the effects of size and oxygen defects on electrical and optical properties of nano crystalline bismuth ferrite (BiFeO 3) with rhombohedral symmetry synthesized by solution evaporation method. The effects of oxygen vacancies on the behavior of system have been studied by annealing all samples under two different environments, air and oxygen. Single phase crystal structure was confirmed by X-Ray diffraction (XRD). The crystalline size calculated by Scherrer's formula falls in the range of 11-21 nm for air and 20-29 nm in case of oxygen annealing atmosphere. The crystalline size was confirmed by Transmission electron microscope (TEM). Dielectric response reveals that both dielectric constant and dissipation factor (tanδ) decrease with increase of frequency without depicting any peak. Optical studies showed that the system possesses an indirect energy gap whose value increases with increasing particle size. There is an evidence for the presence of intra band states in this system arising from defect states.

This study aims to address the effects of different concentrations (0, 0.1, 1.0, 10, 100 or 1000 ... more This study aims to address the effects of different concentrations (0, 0.1, 1.0, 10, 100 or 1000 mg L À1) of engineered zinc oxide (ZnO) nanoparticles (34 nm in size) on growth parameters, steviol glycosides (rebaudioside A and stevioside) production and antioxidant activities in the tissue culture grown shoots of Stevia rebaudiana Bertoni. The highest percentage of shoot formation (89.6%) at 1 mg L À1 of ZnO nanoparticles concentration suggests a positive influence of ZnO nanoparticles on S. rebaudiana growth as compared to other treatments with or without ZnO nanoparticles. Additionally, HPLC results illustrate a significant enhancement of steviol glycosides (almost doubled as compared to the control) in micro-propagated shoots grown under an oxidative stress of 1 mg L À1 of ZnO nanoparticles. This finding is further affirmed by an increased 2,2-diphenyl-1-picryl hydrazyl (DPPH) scavenging activity, total anti-oxidant capacity, total reducing power, total flavonoid content and total phenolic content, with an ascending oxidative pressure and generation of reactive oxygen species (ROS). However, the antioxidant activities, formation of secondary metabolites and the physiological parameters showed a sudden decline after crossing a threshold of 1 mg L À1 concentration of ZnO nanoparticles and falls to a minimum at 1000 mg L À1 , elucidating maximum phytotoxic effect of ZnO nanoparticles at this concentration. This is the first study evaluating both the favorable and adverse effects of ZnO nanoparticles employed to a highly valuable medicinal plant, S. rebaudiana.

We have investigated structural, magnetic and magnetocaloric properties of CoFe 2-x Mo x O 4 (0.0... more We have investigated structural, magnetic and magnetocaloric properties of CoFe 2-x Mo x O 4 (0.0≤x≤0.3) ferrites. Polycrystalline samples were prepared by the sol gel method and characterized by the powder X-ray diffraction and scanning electron microscopy. X-ray diffraction patterns show that all samples have a cubic spinel structure and the lattice parameter, a, decreases monotonically with increase in Mo concentration. Scanning electron micrographs indicate that most of the particles are in the range of 400-850 nm size. Magnetic measurements, performed by using a cryogen free vibrating sample magnetometer, show that these samples are soft ferromagnets in the measured temperature range. The saturation magnetization, M s , values of Mo-doped samples are larger than the parent compound with a maximum value of~106 emu/g for x=0.2 sample. The magnetic entropy change (−ΔS) increases with increase in applied magnetic field and shows a peak in the vicinity of blocking temperature. A maximum value of 0.56 J kg −1 K −1 at 5 T field has been observed for x=0.2 sample.

Lead free (1-x)Ba(Zr 0.2 Ti 0.8)O 3-x(Ba 0.7 Ca 0.3)TiO 3 (x ¼ 0.3, 0.35, 0.4) ceramics were prep... more Lead free (1-x)Ba(Zr 0.2 Ti 0.8)O 3-x(Ba 0.7 Ca 0.3)TiO 3 (x ¼ 0.3, 0.35, 0.4) ceramics were prepared via conventional two-step solid-state reaction technique. Temperature dependent dielectric measurements, conducted in the frequency range from 1 kHz to 1 MHz, indicate diffused phase transition for all the samples. The diffuseness of the transition has been studied by fitting the data with modified Curie-Weiss law. It is found that the composition with x ¼ 0.3 behaves as a weak relaxor-ferroelectric, superposed by a non-relaxor behavior. Vogel-Fulcher law was used to characterize the relaxor-ferroelectric behavior while the analysis according to the Cole-Cole plots was used to characterize the non-relaxor features.

In this study, we describe an improvement of room temperature ferromag-netism achieved in a PbTi ... more In this study, we describe an improvement of room temperature ferromag-netism achieved in a PbTi 12x Fe x O 3 (0 £ x £ 0.60) system and discuss a correlation between structural, magnetic, dielectric and optical properties. Pure PbTiO 3 , which crystallizes in a tetragonal structure, evolved towards a cubic structure with increases in Fe content. Magnetic measurements showed that all Fe substituted samples are ferromagnetic at room temperature and maximum magnetization at 7 kOe increases with increases in Fe content. The origin and improvement of ferromagnetism is ascribed to the F-center exchange mechanism. The temperature dependence of dielectric behavior showed typical ferroelectric behavior, but ferroelectric transition temperature remained above our maximum measuring temperature. The improvement in dielectric properties of the PbFe x Ti 12x O 3 system may be attributed to increases of resistivity and activation energy. The decrease in band gap with increase in Fe substitution is ascribed to the decrease in c/a ratio, indicating that the optical band gap is affected by the degree of structural disorder in the PbFe x Ti 12x O 3 system.

Transition metal dichalcogenides (TMDs) with a unique sandwich structure have attracted tremendou... more Transition metal dichalcogenides (TMDs) with a unique sandwich structure have attracted tremendous attention in recent years due to their distinctive electrical and optical properties. The performance of TMDs can be tailored by integration with low dimensional nanostructures which possess quantum size effects and large specific surface areas. In this review, we give a brief description of integrated structures, their synthesis methods, and highlight the applications in hydrogen production, lithium batteries, sensors and detectors.