Doctor of Philosophy (PhD)
The structural and physical characterization of several early and latter rare earth Ln-Ni-Ga systems, which include Ln2NiGa12 (Ln = Pr, Nd, Sm), alpha-LnNiGa4 (Ln = Y, Gd – Yb) and beta-LnNiGa4 (Ln = Tb – Ho) will be presented in this work. These systems are thermodynamically located within a copious, robust phase space and provide a rich understanding of how slight modifications to synthetic preparations can yield the adoption of different structure types in a Ga-rich regime. Each of these phases is made up of well-studied substructures which lend an additional angle of apperception as to how their structure and properties are related. Ln2MGa12 (Ln = Pr, Nd, Sm; M = Ni, Cu) were studied to determine the evolution structure and properties as a function of rare earth and transition metal. These compounds are composed of alternating slabs of Ln surrounded by 14 Ga atoms and [NiGa/CuGa] rectangular prisms along the c-axis. Based on X-ray diffraction studies it was determined that the Ln2CuGa12 analogues were Cu-deficient, with 90%, 78% and 77% Cu in Pr2CuGa12, Nd2CuGa12, and Sm2CuGa12, respectively. Phases of alpha-LnNiGa4 (Ln = Y, Gd – Yb) and beta-LnNiGa4 (Ln = Tb – Ho) were studied to determine how the crystal chemistry and properties change as a function of latter rare earth usage. Alpha-LnNiGa4 (Ln = Y, Gd – Yb) is comprised of partial AlB2 and distorted alpha-Fe substructures. Anisotropic magnetism is observed in these phases where a stronger coupling of the magnetic rare earth ions is present in the ab-plane. The variation of Curie-Weiss temperature as a function of Ln-Ln distance indicates RKKY-type magnetic interactions. Beta-LnNiGa4 (Ln = Tb – Ho), a polymorph of alpha-LnNiGa4, is composed of an inhomogeneous linear intergrowth of BaAl4- and CaF2-structure types. These phases are a disordered derivative of Ce2NiGa10 and, based on previous work, are believed to be a modulated system within the Ni-Ga nets.
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Thomas, Kandace R., "Synthesis and Characterization of Rare Earth-Nickel-Gallium Ternary Intermetallics" (2010). LSU Doctoral Dissertations. 3656.