Effect of microstructure on properties of MgB 2 synthesized by SHS method

Abstract MgB 2 samples were obtained by self-propagating high-temperature synthesis (SHS). Microstructure, phase and chemical analysis of the samples were studied by XRD and cross-sectional TEM-SAD. MgB 2 samples contained very small uniformly distributed MgO particles. Temperature dependence of the upper critical field and of the critical current densities were determined from ac magnetic susceptibility measurements. Normal metallic state was characterised by measurements of valence band structure by ultraviolet photoelectron spectroscopy (ARUPS). We concluded that MgB 2 is a hard II type superconductor and that SHS method is suitable to fabricate material with strong pinning centers of MgO

Attempt at assessment of Unio tumidus bivalve mollusks suitability for monitoring water iron content

Monitoring of changes in behavioral response of bivalve mollusks can provide a wealth of information on quality of water that could be used in a surveillance system. The aim of this research was to evaluate suitability of Unio tumidus bivalve mollusks as bioindicators of water quality in a surveillance system. The experiment involved a 72-hour observation of the mollusks behavior in tap water containing about 0.04 mgFe/dm3 (almost no iron ions), 0.2 mgFe/dm3 (limit value for drinking water) and 1.7 mgFe/dm3 (average iron ion content for the deep sea). Three behavioral variables considered were: time of activity (time period of water filtering activity), average shell opening degree and its frequency. It was determined that presence of iron ions exceeding the threshold value reduced daily activity time by 5 hours, while the shell opening degree – by over 20%. Variations in frequency of the shell movements were not observed, which might indicate no iron ion impact on the nervous system of the individuals tested. Similarly, lethal states were not demonstrated, even at the relatively high iron concentrations in water. Results of the research conducted demonstrate that the bivalves Unio tumidus may be employed in tap water surveillance system for detection of water contamination with iron compounds.Obserwacja zmian zachowań małży może dostarczyć wielu informacji dotyczących jakości wody, które można wykorzystać w systemie monitoringu. W pracy podjęto próbę oceny możliwości zastosowania małży z gatunku Unio tumidus w monitoringu wody przeznaczonej do spożycia w celu detekcji nadmiernej ilości związków żelaza. Eksperyment polegał na 72-godzinnej obserwacji zachowania małży w wodzie wodociągowej o zawartości jonów żelaza około 0,04 mgFe/dm3 (praktyczny brak jonów żelaza w wodzie) oraz 0,2 mgFe/dm3 (wartość dopuszczalna w wodzie przeznaczonej do spożycia) i 1,7 mgFe/dm3 (średnia zawartość jonów żelaza w wodach głębinowych). Ocenie poddano trzy elementy zachowania małży – czas ich aktywności (czas, w którym małże filtrowały wodę) oraz częstość i średni stopień otwarcia muszli. Stwierdzono, że obecność jonów żelaza w wodzie w ilości przekraczającej wartość dopuszczalną skróciła łączny czas aktywności małż w ciągu doby o 5 godzin i zmniejszyła stopień otwarcia muszli o ponad 20%. Nie zaobserwowano zróżnicowania częstości zmian otwarcia muszli małży, co świadczy o braku oddziaływania jonów żelaza na układ nerwowy badanych osobników. Stwierdzono także brak stanów letalnych u małży, nawet przy stosunkowo dużej ilości żelaza w wodzie. Przeprowadzone badania wykazały, że małże z gatunku Unio tumidus można wykorzystywać w monitoringu wody wodociągowej do detekcji jej zanieczyszczenia związkami żelaza

Effect of Magnetic Field on Resistive Transition of Thin Film Thallium Based Superconductors

The temperature and magnetic field dependences of a.c. resistance of c-axis oriented (Tl$\text{}_{0.5}$Pb$\text{}_{0.5}$)(Sr$\text{}_{0.8}$Ba$\text{}_{0.2}$)$\text{}_{2}$Ca $\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{x}$ and (Tl$\text{}_{0.6}$Pb$\text{}_{0.24}$Bi$\text{}_{0.16}$)(Sr$\text{}_{0.9}$Ba$\text{}_{0.1}$)$\text{}_{2}$Ca$\text{}_{2}$Cu$\text{}_{3}$ O$\text{}_{x}$ thin films as well as of (Tl$\text{}_{0.5}$Pb$\text{}_{0.5}$)(Sr$\text{}_{0.8}$Ba$\text{}_{0.2}$)$\text{}_{2}$Ca$\text{}_{ }$2Cu$\text{}_{3}$O$\text{}_{x}$ bulk sample from 77 K to room temperature and in magnetic fields from zero to 3000 Oe were measured and analyzed. The magnetic field and temperature dependence of the resistive superconducting transition and irreversibility field were discussed both in the flux-creep model and in the superconducting liquid vortex state model. The temperature width of resistive transition was explained taking advantage of the Ambegaokar and Halperin model of the resistance of superconducting Josephson weak links and barrier of vortex motion presented by Tinkham. The irreversibility field was described by an exponential formula

Spin and lattice dynamics of La2/3Ca1/3MnO3 doped with 1% 119Sn

1 at.% 119Sn doped La0.67Ca0.33MnO3 compound was studied by Mössbauer spectroscopy, magnetization, AC susceptibility and resistivity measurements. Huge separation (66 K) of the transition temperatures from the ferromagnetic (FM) to paramagnetic (PM) state (TC) and from metallic to insulating state (TM-I) clearly shows that transition from FM metallic to PM insulator phase goes via FM insulator phase. The Mn lattice dynamics was studied by the relative changes of Lamb-Mössbauer factor f as a function of temperature. In the Debye approximation from the calculated ln(f/f0) values of the characteristic Debye temperatures (čD) were estimated for the FM (368(10) K) and PM (391(6) K) phases. No anomaly of -ln(f/f0) at TM-I and its rather spurious increase around TC was found. The 119Sn isotope as a local diamagnetic probe samples the transferred hyperfine field (Bhf) from its neighbour Mn magnetic moments and witnesses the dynamics of the Mn moments. Theoretical curve based on the molecular field theory was fitted to the experimental values of Bm hf ax and the value of the ordering temperature (TC * H 280 K) of Mn moments inside the large FM domains was estimated. It is much higher than the TC (172 K) obtained from magnetization measurement. The coexistence of FM and PM phases, which is evident from the shape of our 119Sn Mössbauer spectra, was confirmed for temperatures T e 150 K and indicates the inhomogeneous character of the magnetic transition

Structural, Thermal, Magnetic, and Transport Properties of (La2/3\text{}_{2}\text{}_{/}\text{}_{3} Ca1/3\text{}_{1}\text{}_{/}\text{}_{3} )(Mn1−x\text{}_{1-x}Snx\text{}_{x})O3−δ\text{}_{3-δ} Compounds

The structural, magnetic, and electrical transport properties of Sn-doped manganite La$\text{}_{0.67}$Ca$\text{}_{0.33}$Mn$\text{}_{1-x}$ Sn$\text{}_{x}$O$\text{}_{3-δ}$ (x=0, 0.01, 0.03, andδ≈0.06) compounds were studied using X-ray powder diffraction, scanning electron microscopy, AC susceptometer and vibrating sample magnetometer measurements as well as four-probe resistance measurements. The specific heat was measured by the heat-pulse method. The Curie temperature T$\text{}_{C}$ and the metal-insulator transition temperature T$\text{}_{M-I}$ decreased nonlinearly with increasing Sn content. The T$\text{}_{C}$ and T$\text{}_{M-I}$ values, for the x=0, 0.01, and 0.03 compounds were separated by 18.2 K, 66.3 K, and 10 K, respectively. The resistivity above T$\text{}_{C}$ for all of these compounds followed the Mott variable-range-hopping model. This allowed the estimation of the localization lengths of 2.2Å (x = 0), 1.33Å (x=0.01) and 1.26Å (x=0.03). The x=0 and x=0.01 compounds exhibited anomalies of R(T) at corresponding T$\text{}_{C}$ and allowed the separation of the magnitude of the purely magnetic contribution to the resistance which for x=0 was≈5 .7Ω and for x=0.01,≈22 .4Ω. The specific heat of the Sn-free sample exhibited a sharp peak at T$\text{}_{C}$. With increasing Sn content the peak at T$\text{}_{C}$ broadened and the area under the peak decreased. For x= 0.03 the peak was hardly detectable. Our results on La$\text{}_{0.67}$Ca$\text{}_{0.33}$ Mn$\text{}_{1-x}$Sn$\text{}_{x}$O$\text{}_{3}$ reveal that a small substitution of Sn$\text{}^{4+}$ for Mn$\text{}^{4+}$ suppresses double exchange interactions and strongly affects the magnetic, thermal, and transport properties of the parent compound

Electronic Properties of High-Temperature Superconductor DyBa2\text{}_{2}Cu3\text{}_{3}O7\text{}_{7} from Critical Fields and Specific Heat Studies

The lower and upper critical fields, as well as the specific heat were measured as a function of temperature for good quality DyBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ high-temperature superconductor in the vicinity of superconducting transition temperature T$\text{}_{c}$ = 91.2 K. The number of superconducting and normal state electronic quantities were determined basing on the Ginzburg-Landau-Abrikosov-Gorkov theory. It is argued that on the basis of this BCS-like theory one can describe the superconducting properties and, in combination with some information on the electronic structure, also the magnetic properties of high-temperature superconductors