The RuSr 2 Gd 1.5 Ce 0.5 Cu 2 O 10-δ (Ru-1222) compounds, with varying oxygen content, crystallize in a tetragonal crystal structure (space group I4/mmm).Resistance (R) versus temperature (T) measurements show that the air -annealed samples exhibit superconductivity with superconducting transition temperature (T c ) onset at around 32 K and R=0 at 3.5 K. On the other hand , the N 2 -annealed sample is semiconducting down to 2 K. Magneto-transport measurements on airannealed sample in applied magnetic fields of 3 and 6 Tesla show a decrease in both T c onset and T R=0 . Magnetoresistance of up to 20% is observed in N 2annealed sample at 2 K and 3 T applied field. The DC magnetization data (M vs. T ) reveal magnetic transitions (T mag. ) at 100 K and 106 K, respectively, for both air-and N 2 -annealed samples. Ferromagnetic components in the magnetization 2 are observed for both samples at 5K and 20 K. The superconducting transition temperature (T c ) seems to compete with the magnetic transition temperature (T mag. ). Our results suggest that the magnetic ordering temperature (T mag. ) of Ru moments in RuO 6 octahedra may have direct influence/connection with the appearance of superconductivity in Cu-O 2 planes of Ru-1222 compounds.

Measurements have been performed of the resistivity of the samples of MgB 2 , AlB 2 and AgB 2 . The samples show presence of impurities. Analyzing the data in terms of the impurity scattering, electron-phonon scattering, and weak localization it has been found that the AlB 2 (AgB 2 ) sample involves maximum (minimum) effect of the impurity, electron-phonon interaction and weak localization.

Lesotho Southern AfricaWe report optimization of the synthesis parameters viz. heating temperature (T H ), and hold time (t hold ) for vacuum (10 -5 torr) annealed and LN 2 (liquid nitrogen) quenched MgB 2 compound.These are single-phase compounds crystallizing in the hexagonal structure (space group P 6 /mmm) at room temperature. Our XRD results indicated that for phase-pure MgB 2 , the T H for 10 -5 torr annealed and LN 2 quenched samples is 750 0 C. The right stoichiometry i.e., MgB 2 of the compound corresponding to 10 -5 Torr and T H of 750 0 C is found for the hold time (t hold ) of 2.30 hours. With varying t hold from 1-4 hours at fixed T H (750 0 C) and vacuum (10 -5 torr), the c-lattice parameter decreases first and later increases with t hold (hours) before a near saturation, while the alattice parameter first increase and later decreases beyond t hold of 2.30 hours. c/a ratio versus t hold plot showed an inverted bell shape curve, touching the lowest value of 1.141 which is reported value for perfect stoichiometry of MgB 2 . The optimized stoichimetric MgB 2 compound exhibited superconductivity at 39.2 K with transition width of 0.6 K. In conclusion, the synthesis parameters for phase pure stoichimetric vacuum annealed MgB 2 compound are optimized and are compared with widely reported Ta tube encapsulated samples.

Results of thermo-electric power (S) and electrical resistivity (ρ) measurements are reported on Na x CoO 2 compounds with x = 1.0, 0.7 and 0.6. These are single-phase compounds crystallizing in the hexagonal structure (space group P6 3 /mmc) at room temperature. Thermo-electric power values at 300K (S 300K ) are, ≅ 80µV/K, 39µV/K and 37µV/K for x = 1.0, 0.7 and 0.6 samples, respectively. The samples with x=0.7 and 1.0 are metallic down to 5 K, while the x = 0.6 sample is semiconducting. The value of ρ 300K for x = 1.0 sample is ~0.895 mΩ-cm and the power factor (S 2 /ρ) is ~ 7.04 x 10 -3 W/mK 2 which qualifies it as a good thermo-electric material. In x =1.0 sample, S(T) is positive throughout 300−5K 2 temperature range and decreases monotonically to zero as temperature T→ 0. In contrast, S(T) of x = 0.7 and 0.6 samples changes sign and shows negative values between 90 K and 16 K before approaching zero as T → 0. Anomalous S(T) behavior of x = 0.6 and 0.7 samples, which are coincidentally the precursor materials to the reported superconductivity in this class of materials, indicates a dramatic change in the electronic structure of these compounds on lowering the Na content.

Results of phase formation, resistivity (ρ), and thermo-electric power (S), are reported on Y 1-x Ca x Ba 2 Cu 2.7 Co 0.3 O 7 compounds with x = 0.1 and 0.2. Pristine compound i.e. without Co or Ca substitution crystallizes in orthorhombic structure with space group P/mmm. Cu-site Co substituted compound i.e. YBa 2 Cu 2.7 Co 0.3 O 7 is tetragonal. With simultaneous doping of Ca at Y site in Co substituted compound i.e. Y 1-x Ca x Ba 2 Cu 2.7 Co 0.3 O 7 the tetragonal nature still remains. ρ(T) measurements showed superconducting transition temperature (T c ) to decrease from 90K (YBa 2 Cu 3 O 7 ) to 33 K for YBa 2 Cu 2.7 Co 0.3 O 7 which with further Ca substitution increases from 33K to 53K (Y 0.9 Ca 0.1 Ba 2 Cu 2.7 Co 0.3 O 7 ) and 67 K for Y 0.8 Ca 0.2 Ba 2 Cu 2.7 Co 0.3 O 7 . T c decreases first with Cu-site Co substitution by hole-filling and later recovers by simultaneous hole creation by Y site Ca substitution. Room temperature thermoelectric power S(300 K), which is an indirect measure of mobile carriers shows the decrease of carriers with Co doping and creation by Ca substitution. Our results demonstrate the hole filling by Co substitution is compensated by simultaneous Ca substitution.