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. The un-doped SmFeAsO is charge neutral SDW (Spin Density Wave) 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 upto 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.Comment: 4 Pages text + Figs: ([email protected]

Role of MgO impurity on the superconducting properties of MgB2

We address the effect of MgO impurity on the superconducting properties of MgB2. The synthesis of MgB2 is very crucial because of sensitivity of Mg to oxidation which may lead to MgO as a secondary phase. Rietveld refinement was performed to determine the quantitative volume fraction of MgO in the samples synthesized by two different techniques. Both the samples were subjected to magnetization measurements under dc and ac applied magnetic fields and the observed results were compared as a function of temperature. Paramagnetic Meissner effect has been observed in a sample of MgB2 having more amount of MgO (with Tc = 37.1K) whereas the pure sample MgB2 having minor quantity of MgO shows diamagnetic Meissner effect with Tc = 38.8K. M-H measurements at 10K reveal a slight difference in irreversibility field which is due to MgO impurity along with wide transition observed from ac magnetic susceptibility measurements. The magnetotransport measurements R(T)H using RN = 90%, 50% and 10% criterion on pure sample of MgB2 has been used to determine the upper critical field whereas the sample having large quantity of MgO does not allow these measurements due to its high resistance.Comment: 15 pages text + Fig

Kemijska svojstva i primjena premaznih materijala na bazi vode i organskih otapala na drvu

Wood finishes are used extensively to improve the aesthetic value and protect wood products from moisture. These organic coatings generally contain volatile organic compounds (VOC) as solvents that evaporate when the coatings cure over the surface. Due to strict legislations against these hazardous VOCs, the buyers across the globe are shifting towards products finished with water borne coats. Two of the most commonly used wood coatings in India are polyurethane and nitrocellulose (NC) lacquer. This paper aims at comparing these two wood coatings with their water borne counterparts. The study was conducted on the wood substrate of Melia dubia. Chemical characterization of the cured coats was attempted through FTIR spectroscopy. Physical appearances in terms of gloss and film thickness were also studied. Bands of urethane, urea and nitric groups were identified, which helped in understanding the changes in chemical structure of the finishes after curing. The thickness of the organic coatings was significantly higher than that of their water-borne counterparts. Gloss of water based coatings was observed to be lesser than that of their organic solvent based counterparts in either coating material. In case of lacquer, the reduction was up-to 33 %. whereas in case of PU, gloss dropped down by about 54 %.Premazni se materijali primjenjuju na drvu kako bi se očuvao njegov estetski izgled i drvni proizvodi zaštitili od vlage. Organski premazni materijali u osnovi sadržavaju hlapljive organske spojeve (HOS) kao otapala koja isparavaju dok premazni materijal otvrdnjava na površini drva. Zbog strogih propisa o tim opasnim hlapljivim organskim spojevima kupci diljem svijeta prelaze na vodene premazne materijale. Dva najčešće upotrebljavana premazna materijala za drvo u Indiji jesu poliuretanski i nitrocelulozni (NC) lak. Cilj rada bio je usporediti ta dva premazna materijala s istim premaznim materijalima na bazi vode. Istraživanje je provedeno na drvu Melia dubia. Kemijska karakterizacija otvrdnutih premaza provedena je primjenom FTIR spektroskopije. Također su proučavani sjaj i debljina filma. Identificirane su skupine uretana, ureje i nitratne skupine koje su pridonijele razumijevanju promjena u kemijskoj strukturi premaza nakon otvrdnjavanja. Debljina premaza na bazi organskih otapala bila je znatno veća od debljine premaza na bazi vode. Uočeno je da je sjaj premaza na bazi vode manji od sjaja premaza na bazi organskih otapala. Za NC lak to je smanjenje bilo do 33 %, a sjaj PU laka smanjio se za oko 54 %

Anomalous Thermoelectric power of over-doped Bi2Sr2CaCu2O8 superconductor

Temperature dependence of thermoelectric power S(T) of three differently processed Bi2Sr2CaCu2O8 (Bi2212) samples, viz. as-processed melt quenched (Bi2212-MQ), 6000C N2-annealed (Bi2212-N2) and 6000C O2-annealed (Bi2212-O2) is reported here. All the samples possess single-phase character and their superconducting transition temperatures (TcR=0) are 85 K, 90 K and 72 K respectively for Bi2212-MQ, Bi2212-N2 and Bi2212-O2. While Bi2212-MQ and Bi2212-N2 samples are in near optimum doping regime, Bi2212-O2 is an over-doped sample. TcS=0 values obtained through S(T) data are also in line with those deduced from the temperature dependence of resistance and DC magnetization. Interestingly, S(T) behaviour of the optimally-doped Bi2212-MQ and Bi2212-N2 samples is seen to be positive in whole temperature range, it is found negative for the over-doped Bi2212-O2 sample above TcS=0. These results have been seen in the light of the recent band structure calculations and the ensuing split Fermi surface as determined by angle-resolved photoelectron spectroscopy (ARPES).Comment: 11 Pages Text + Figs: comments welcome ([email protected]

Structural and Magnetic Properties of Co1-xFexSr2YCu2O7 compounds

Here we study the structural and magnetic properties of the CoFeSr2YCu2O7 compound with x = 0.0 to 1.0. X-ray diffraction patterns and simulated data obtained from Rietveld refinement of the same indicate that the iron ion replacement in CoFeSr2YCu2O7 induces a change in crystal structure. The orthorhombic Ima2 space group structure of Co-1212 changes to tetragonal P4/mmm with increasing Fe ion. The XPS studies reveal that both Co and Fe ions are in mixed states for the former and in case of later.Although none of the studied as synthesized samples in CoFeSr2YCu2O7 are superconducting, the interesting structural changes in terms of their crystallisation space groups and the weak magnetism highlights the rich solid state chemistry of this class of materials.Comment: 20 pages of Text+Figs: comments/suggestions welcome ([email protected]

Structural, electrical, magnetic and thermal studies of Cr-doped La0.7Ca0.3Mn1-xCrxO3 for x = 0.0 to 1.0 manganites

We report detailed structural, electrical, magnetic and specific heat studies on La0.7Ca0.3Mn1-xCrxO3 manganites. Rietveld analysis of fitted and observed XRD patterns exhibited the single-phase nature of all the studied materials, which crystallize in Pbnm space group. Successive substitution of Cr at Mn site in La0.7Ca0.3Mn1-xCrxO3 manganites increases the electrical resistivity and decrease the characteristic insulator-metal transition temperature (TIM) of the parent compound along with a hump like feature for higher Cr-content samples. The hump structure basically signifies the onset of anti-ferromagnetic (AFM) interactions as inferred by both the magnetic and infra-red (IR) spectroscopy studies. The systematic suppression of FM state results in a spin glass (SG) like behavior. IR studies revealed that the vibration mode at 413 cm-1 being associated with internal bending of MnO6 octehedra, becomes softer, indicating an increase in distortion and hence the possible spin glass behavior. The critical exponents alpha, beta and gama are calculated from the heat capacity (CP) data near the TIM/TFM. The same exhibited variations of their values with doping. In particular the value of beta increases from 0.37 to 0.43, clearly indicating the coexistence of both long and short range magnetic orders i.e. tendency towards SG state for Cr doped samples. On the basis of present results, it is suggested that Cr dilutes double-exchange (DE) based FM and rather promotes the AFM based super exchange interactions (SE) via Cr3+/Mn4+ ions. Substitution of Cr systematically destroys both the metallic state and long range ferromagnetic (FM) order.Comment: 24 pages Text + Figs: comments/suggestions([email protected]

Anomalous heat capacity and X-ray photoelectron spectroscopy of Superconducting FeSe1/2Te1/2

The bulk polycrystalline sample FeSe1/2Te1/2 is synthesized by solid state reaction route in an evacuated sealed quartz tube at 750 oC. The presence of superconductivity is confirmed through magnetization/thermoelectric/resistivity studies. It is found that the superconducting transition temperature (Tc) is around 12 K. Heat capacity (Cp) of superconducting FeSe1-xTex exhibited a hump near Tc, instead of well defined Lambda transition. X-ray Photo electron spectroscopy (XPS) studies revealed well defined positions for divalent Fe, Se and Te but with sufficient hybridization of Fe (2p) and Se/Te (3d) core levels. In particular divalent Fe is shifted to higher BE (binding energy) and Se and Te to lower. The situation is similar to that as observed earlier for famous Cu based HTSc (High Tc superconductors), where Cu (3d) orbital hybridizes with O (2p). We also found the satellite peak of Fe at 712.00 eV, which is attributed to charge carrier localization induced by Fe at 2c site.Comment: 12 pages text + Figs contact Author-VPS Awana (www.freewebs.com/vpsawana

Thioridazine: a potential adjuvant in pharmacotherapy of drug resistant tuberculosis Ki

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. Despite advances in control strategies, inadequate treatment and failure to comply with drug regimens have resulted in TB to emerge as one of the most common and deadly infectious diseases worldwide. The emergence of drug-resistant TBhas evolved as a formidable obstacle for comprehensive TB control. Drug-resistant TB can be classified as multi-drug-resistant TB, extensively drug-resistant TB and totally drug resistant TB (TDR-TB). There is a paucity in the development of new drugs against drug-resistant mycobacteria. The focus has shifted to the exploration of anti-mycobacterial properties of drugs approved for other indications. Thioridazine, a drug approved for use in schizophrenia is one such potential agent, which has shown anti-mycobacterial activity. There is evidence of anti-mycobacterial action of Thioridazine in in-vitro and mouse models. There is a compelling need for new anti-mycobacterial drugs that are more effective and have less toxicity. Further clinical trials are advocated favoring the use of thioridazine as an adjuvant in the treatment of TB, especially TDR-TB