Alloying Behavior of Ni3Nb, Ni3V and Ni3Ti Compounds

The site preference of ternary additions in Ni3X-type GCP compounds was determined from the direction of solubility lobe of the GCP phase on the experimentally reported ternary phase diagrams. In Ni3Nb (D0a), Co and Cu preferred the substitution for Ni-site, Ti, V and W the substitution for Nb-site, and Fe the substitution for both sites. In Ni3V (D022), Co preferred the substitution for Ni-site, Cr the substitution for both sites, and Ti the substitution for V-site. In Ni3Ti (D024), Fe, Co, Cu, and Si preferred the substitution for Ni-site, Nb, Mo and V the substitution for Ti-site. The thermodynamic model, which was based on the change in total bonding energy of the host compound by a small addition of ternary solute, was applied to predict the site preference of ternary additions. The bond energy of each nearest neighbor pair used in the thermodynamic calculation was derived from the heat of compound formation by Miedema’s formula. The agreement between the thermodynamic model and the result of the literature search was excellent. Both transition and B-subgroup elements have two possibilities, i.e., the case of substitution for Ni-site or the case for X-site, depending on the relative value of two interaction energies.

LEVEL CROSSING AND QUANTUM PHASE TRANSITION OF THE XY RING

The ground state of a spin-1/2 ring in the Heisenberg XY model is investigated. The spatial correlation and concurrence between an arbitrary nearest-neighbor pair of spins are calculated with different coupling strength, anisotropic parameter and magnitude of the transverse field. Abrupt changes of the correlation and concurrence due to the competition between coupling and alignment are observed. The transition is found to be the direct result of the level crossing of a finite size spin system.