Degree Type

Dissertation

Date of Award

2014

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Gordon J. Miller

Abstract

Combining experiments and electronic structure theory provides the framework to design and discover new families of complex intermetallic phases and to understand factors that stabilize both new and known phases. Using solid state synthesis and multiple structural determinations, ferromagnetic β-Mn type Co8+xZn12-x was analyzed for their crystal and electronic structures. Inspection of the atomic arrangements of Co8+xZn12-x reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna Ab-initio Simulation Package (VASP) and starting from the undistorted, defect Laves phase structure achieved energy minimization at the observed β-Mn structure type, a result which offers greater insights into the &beta-Mn structure type and establishes a closer relationship with the corresponding α-Mn structure (cI58). Continuously, our research moved on Zn-rich γ-brasses Co-Zn system which has a homogeneity range Co2+xZn11-yVacanciesy-x including a small concentration of vacancies as the Co content increased as well as clear site preference of Co atoms in the structure. Inspired by the electronic structure calculated for Co2Zn11, substituting Pd atoms for Zn or Co atoms in the Co-Zn system leads to the discovery of a ferromagnetic (ferrimagnetic) Co2.5Pd2.5Zn8 γ-brass compound. To extend the research on Hume-Rothery phases, &gamma-brasses Fe-Pd-Zn system was also investigate to study the site preference of transition metals in Hume-Rothery phases.

Additionally, establishing structure-property relationships for complex metal-rich materials, e.g., thermoelectric, magnetic and superconductors is related to both practical as well as fundamental issues. Cr22Sn24Zn72 and V23.3(1)Sn23.6(1)Zn68.4(1) crystallize in space group Fm3 ̅c, Z = 8, Pearson symbol cF944, with unit cell parameters, respectively, a = 25.184(4) Ã? and 25.080(3) Ã?. Their structures can be described as a cubic NaZn13-type packing of two distinct, yet condensed intermetallic clusters, or a simple cubic packing of I13 clusters condensed via extreme Zn sites with rhombic dodecahedra in the voids. Instead of using transition metals Cr/V, rare earth element, Ce, was also used to react with Zn and Sn. The new cerium-based ternary intermetallic phase, Ce(Sn1-xZnx)6 (0.45(1) < x < 0.49(1)) adopted to CeCu6-type structure. It exhibits a structural transition from orthorhombic to monoclinic around 150 K. Moreover, the magnetic properties of a sample analyzed as CeSn3.33(6)Zn2.67 shows it to be Langegin paramagnetic above 2K.

DOI

https://doi.org/10.31274/etd-180810-2759

Copyright Owner

Weiwei Xie

Language

en

File Format

application/pdf

File Size

215 pages

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