Identifier

etd-11182010-180558

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

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.

Date

2010

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Julia Chan

DOI

10.31390/gradschool_dissertations.3656

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