M. Husain

Temperature and electric-field dependences of hole mobility in light-emitting diodes based on poly [2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene]

The current-voltage characteristics of poly [2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV)-based hole-only light-emitting diodes are measured as a function of temperature. The hole current is found to be space-charge limited, providing a direct measure of the mobility as a function of temperature and electric field. A thermal activation energy of 0.2eV is obtained for the zero-field mobility, with a room-temperature low-field mobility value for holes of 3.3×10−7cm2∕Vs. The hole mobility exhibits field dependence in accordance with the Poole-Frenkel effect. The combination of space-charge effects and field-dependent mobility thus provides a consistent description of hole transport as a function of temperature and bias voltage in MEH-PPV films.

Structural and magnetic properties of Co1−xFexSr2YCu2O7+δ compounds

Here we study the structural and magnetic properties of the Co1−xFexSr2YCu2O7+δ compound (0≤x≤1). X-ray diffraction patterns and simulated data obtained from Rietveld refinement of the same indicate that the iron ion replacement in Co1−xFexSr2YCu2O7+δ induces a change in crystal structure. The orthorhombic Ima2 space group structure of Co-1212 changes to tetragonal P4/mmm with increasing Fe (x≥0.5) ion. The XPS studies reveal that both Co and Fe ions are in mixed states of 3+/4+ for the former and 2+/3+ in case of later. The magnetization with temperature follows Curie–Weiss behavior, in the range of 150–300 K and short magnetic correlations/spin glasslike features below 150 K. The observed magnetic behavior is due to competition of antiferro/ferromagnetic exchange interaction of Co3+ [intermediate spin (IS)]-O–Co3+ (IS)/Co4+ [low spin (LS)] and Fe3+ [high spin (HS)]-O–Fe2+ (LS)/Fe3+ (HS)/Co3+ (IS)/Co4+ (LS) states. Although none of the studied as synthesized samples in Co1−xFexSr2YCu2O7+δ are superconduc...

Exploring the Superconductors with Scanning Electron Microscopy (SEM)

The characterization of materials supports their development and in particular of superconductors, for their technological applications. Scanning electron microscopy (SEM) is one of these characterization techniques, whose data is used to estimate the properties, determine the shortcomings and hence improve the material. The phenomenon of superconductivity initially develops within the grain and eventually crosses over the grain boundaries, leading to the bulk. Hence SEM can be a useful tool to probe the microstructure of the superconductors and the properties related to it. Along with this the Energydispersive Spectroscopy (EDS) can tell about the chemical composition of compounds. Grain size and its connectivity can be seen through SEM and can be correlated with the corresponding properties. The superconducting materials developed for practical applications are some of the complex materials used today. These materials have large number of potential variables such as their processing conditions, composition, structure etc., whose dependence on the superconducting properties have to be analyzed critically. The characterization techniques are the tools that help to reveal and explore both the macro and microstructure of materials. It is known that the larger grains (reduction in grain boundaries) lead to increased pinning type behavior with enhanced Jc [1]. In contrast Rosko et al. [2] reported that Jc is determined by weak links and grain size has little role on it. Also, Smith et al. [3] interpreted reduction of Jc and activation of weak link type behavior with increasing grain size for YBa2Cu3O7-δ (YBCO) polycrystalline samples in terms of microcracks in large grains. The superconducting parameters are broadly divided into two categories; first, the intrinsic parameters such as penetration depth (┣), which are intrinsic to the material and are not affected by, grain size. On the other hand, values such as shielding/Meissner fraction, the interand intra-grain critical current density and diamagnetic fraction depend upon particle size of bulk superconductors. Thus SEM can be very important to probe and in understanding the superconducting phenomena.

Superconductivity in BiS[sub 2] based Bi[sub 4]O[sub 4]S[sub 3] novel compound

We report here synthesis and basic characterizations of Bi 4 O 4 S 3 superconductor. The sample is crystallized in tetragonal I4/mmm space group with lattice parameters a = 3.969(2) A, c = 41.352(1) A. Both DC magnetization and resistivity measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (Tc ) of 4.4K. Closed loops in isothermal magnetization (MH) measurements are clear signature of flux pinning and irreversible behavior. The lower critical field (Hc1 ) is found to be ∼15 Oe at 2K. The magneto-transport ρ(T, H) measurements showed resistive broadening and decrease in Tc (ρ = 0) with increasing magnetic field. Upper critical field calculated through extrapolation Hc2 (0) is ∼ 31kOe with corresponding Ginzburg-Landau coherence length ∼100 A. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 .

Superconductivity in BiS2based Bi4O4S3novel compound

We report here synthesis and basic characterizations of Bi 4 O 4 S 3 superconductor. The sample is crystallized in tetragonal I4/mmm space group with lattice parameters a = 3.969(2) A, c = 41.352(1) A. Both DC magnetization and resistivity measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (Tc ) of 4.4K. Closed loops in isothermal magnetization (MH) measurements are clear signature of flux pinning and irreversible behavior. The lower critical field (Hc1 ) is found to be ∼15 Oe at 2K. The magneto-transport ρ(T, H) measurements showed resistive broadening and decrease in Tc (ρ = 0) with increasing magnetic field. Upper critical field calculated through extrapolation Hc2 (0) is ∼ 31kOe with corresponding Ginzburg-Landau coherence length ∼100 A. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 .

Superconductivity in BiS2 based Bi4O4S3 novel compound

We report here synthesis and basic characterizations of Bi 4 O 4 S 3 superconductor. The sample is crystallized in tetragonal I4/mmm space group with lattice parameters a = 3.969(2) A, c = 41.352(1) A. Both DC magnetization and resistivity measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (Tc ) of 4.4K. Closed loops in isothermal magnetization (MH) measurements are clear signature of flux pinning and irreversible behavior. The lower critical field (Hc1 ) is found to be ∼15 Oe at 2K. The magneto-transport ρ(T, H) measurements showed resistive broadening and decrease in Tc (ρ = 0) with increasing magnetic field. Upper critical field calculated through extrapolation Hc2 (0) is ∼ 31kOe with corresponding Ginzburg-Landau coherence length ∼100 A. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 .

Superconducting Mechanism Through Direct and Redox Layer Doping in Pnictides

The mechanism of superconductivity in pnictides is discussed through direct doping in superconducting FeAs and also in charge reservoir REO layers of SmFeAsO. The un-doped SmFeAsO is charge neutral Spin Density Wave (SDW) compound with magnetic ordering below 150 K. The Superconducting FeAs layers are doped with Co and Ni at Fe site, whereas REO layers are doped with F at O site. The electron doping in SmFeAsO through Co results in superconductivity with transition temperature (Tc) maximum up to 15 K, whereas F doping results in Tc up to 47 K in SmFeAsO. All these REFe/Co/NiAsO/F compounds are iso-structural to ZrCuSiAs structure. The samples are crystallized in a tetragonal structure with space group P4/nmm. Variation of Tc with different doping routes shows the versatility of the structure and mechanism of occurrence of superconductivity. It seems doping in redox layer is more effective than direct doping in superconducting FeAs layer.