Y. S. Reddy

Crystal structure, electrical conductivity and thermal expansion of Nd1–xCaxCoO3–δ (0≤x≤0·5)

Abstract The synthesis, crystal structure, thermal expansion and electrical conductivity of the ceramic oxide materials (Nd1–xCax)CoO3 (0≤x≤0·5) were investigated. These powders with perovskites structure were synthesized using the sol–gel method. Compositions have a pure orthorhombic structure up to 0·3 Ca doping. The lattice parameters were determined at room temperature (RT) by powder X-ray diffraction. Thermal expansion measurements on the sintered samples were carried out from RT to 900°C. The average linear thermal expansion coefficient range was found to decrease with increasing Ca doping up to x=0·4 and thereafter it increased. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. Electrical DC conductivity measurements were taken from RT to 600°C. The conductivity of the samples increased with Ca concentration up to 0·3.

EFFECT OF Ba SUBSTITUTION ON ELECTRICAL TRANSPORT AND MAGNETORESISTANCE OF La1.2Sr1.8Mn2O7

Polycrystalline samples of double layered (DL) manganite system La1.2(Sr1-xBax)1.8Mn2O7(0.0≤×≤0.4) were prepared by the sol-gel method. The anisotropic lattice expansion is observed with the substitution of Ba2+ into Sr2+ sites. The electrical resistivity and magnetoresistance (MR) measurements were carried out over the temperature range 4.2 K–300 K. The substitution of Ba results in the suppression of TIM, insulator-to-metal transition temperature. A low temperature upturn of resistivity is seen in all the samples of the system, which is attributed to the spin-glass-like transition. The conduction mechanism above TIM is explained by Mott variable range hopping (VRH) mechanism. The variation of MR with temperature and applied magnetic field is discussed. From the temperature dependent MR curves, it is observed that the large MR values are present over a wide temperature range and the maximum MR values occur at . The x=0.4 sample exhibits ~31% of MR with the application of a mere 0.4 T field at 5 K, which accounts for ~35% enhancement of MR of parent compound (~23% of MR% at 0.4 T at 5 K). The MR — H data is fitted to the power law ρ = ρ0-αHn, and it is found that the low temperature MR varies as square root of the applied magnetic field, as expected in conventional metals.

The effect of Pr co-dopant in samarium doped ceria

The compositions of Ce0.8−xSm0.2PrxO2−δ (x=0, 0.02, 0.04, 0.06) were prepared through the sol-gel route. The effect of Pr addition on the crystal structure, densification and thermal expansion of Ce0.8Sm0.2O2−δ was studied. The powder X-ray diffraction (XRD) analysis showed that all the samples exhibit a fluorite structure. The lattice parameters and volume of the unit cell increase with Pr doping. Density of all the samples is more than 90% of theoretical density. The thermal expansion was measured using dilatometric technique in the temperature range 30-1000°C and it was observed that the thermal expansion increased linearly with increasing temperature for all the samples.

CRYSTAL STRUCTURE, ELECTRICAL CONDUCTIVITY AND THERMAL EXPANSION OF Pr1-xSrxFeO3-δ(0 ≤ x ≤ 0.6)

The crystal structure at room temperature (RT), thermal expansion from RT to 1000°C and electrical conductivity, from RT to 600°C, of the perovskite-type oxides in the system Pr1-xSrxFeO3(x = 0, 0.2, 0.4, 0.6) were studied. All the compounds have the orthorhombic perovskite GdFeO3-type structure with space group Pbnm. The lattice parameters were determined by X-ray powder diffraction. The Pseudo cubic lattice parameter decreases with an increase in x, while the coefficient of linear thermal expansion increases. The thermal expansion is almost linear for x = 0 and 0.2. The electrical conductivity increases with increasing x while the activation energy decreases. The electrical conductivity can be described by the small polaron hopping conductivity model.

Structural, Electrical And Magnetic Properties Of La1.2Sr1.8−xAxMn2O7 (A = Ca, Ba)

The structural, electrical and magnetic properties of the double layered manganite La1.2Sr1.8−xAxMn2O7 (A = Ca, Ba) were investigated and were compared with that of the parent compound La1.2Sr1.8Mn2O7 (LS0). Ca/Ba substituted samples exhibit reduced conductivity and the magnetic moments decrease (increase) with increase of Ca (Ba) content. The conduction mechanism was found to be of Mott variable range hopping (VRH)‐type.