Abstract: The significance of substituting concentrations of Pr and Nd at La-sites, in La0.67Ba0.33MnO3 perovskite compounds, for the structural and electrical properties have been studied. Polycrystalline samples (La1-x Prx)0.67Ba0.33MnO3 and (La1-x Ndx)0.67Ba0.33MnO3 with x = 0.00, 0.167, 0.333, 0.5, 0.667, 0.833 and 1.0 were synthesized via conventional solid-state reaction in the bulk. All of the samples were calcined at 900oC for 12 hours, pelletized and sintered at 1300oC for 24 hours and investigated. In this paper the structural patterns and microstructural properties of bulk samples have been investigated via x-ray diffractometry (XRD) and scanning electron microscopy (SEM). XRD patterns show that these systems are single-phase, with orthorhombic distorted perovskite structures. The electrical property, Tp, was determined by using standard four-point probe resistivity measurements in the temperature range of 20 K to 300 K. The result shows that Pr and Nd dopants shift the value of TP to a lower temperature. When the temperature is above Tp, T > Tp, the variation of the electrical resistance was found to follow the an Arhenius-type law, ρ = ρo exp (-Ea/KBT). It was used to calculate the activation energy of every sample. The resistivity curves show semiconducting behavior of all samples above their Tp.
Abstract: 9Cr-1Mo ferritic steel samples containing 0.2 and 0.5 wt % silicon in 40 % cold rolled state were recrystallize-annealed at 1100, 1200 and 1300 K. The grain growth and mechanical properties after recrystallization-annealing for 20 hr to 100 hr were investigated. No significant grain growth was observed even after 100 hr annealing at 1100 and 1200 K. The recrystallization-annealing at 1200 K resulted grains smaller in size than those at 1100 K. Annealing at 1300 K exhibited the enhanced grain growth with decorative microstructures. Initial annealing after cold rolling at 1100 K exhibited low hardness which further increased with annealing temperature. Annealing at 1100 K for 20 hrs exhibited low yield strength and ultimate tensile strength compared to those of as received samples. However, for 100 hrs annealing these properties remained nearly constant for 0.2 Si composition and increased marginally for 0.5 Si composition. Recrystallization-annealing exhibited improved ductility for both the compositions.
Abstract: In this article, the liquid-solid interface solidification stability of dilute binary alloy systems during unidirectional (z) solidification was investigated. A new quantitative approach is proposed with (z-δ) as a variable to solve the equation of solute diffusion in the liquid, where δ is the real diffusion layer thickness.
Abstract: The spin Hamiltonian parameters (zero-field splitting D and the g factors) for NiX2 and CdX2:Ni2+ (X=Cl, Br) are quantitatively investigated from the perturbation formulas of these parameters for a 3d8 ion in trigonally distorted octahedra based on the cluster approach. In the calculations, the trigonal field parameters and ′ are determined from the superposition model and the local structures of Ni2+ in the halides. The theoretical g factors show reasonable agreement with the observed values, and the experimental D for CdX2:Ni2+ are also interpreted by considering suitable lattice distortions (angular decreases) in the impurity-ligand bond angles related to the C3 axis due to the size mismatching substitution. The contributions from the ligand orbital and spin-orbit coupling interactions are important and should be taken into account.