Degree Type

Dissertation

Date of Award

2018

Degree Name

Doctor of Philosophy

Department

Chemistry

Major

Inorganic Chemistry

First Advisor

Gerd H. Meyer

Second Advisor

Gordon J. Miller

Abstract

Our research efforts have focused on the investigation of novel intermetallic compounds containing transition metals with rare earth elements, specifically cobalt and platinum with praseodymium. The Co/Pr and Pt/Pr phase diagrams have been well explored. However, recent work has shown the existence of new binaries within these systems that are not present within the known phase diagrams. The binary Pt3Pr4 crystallizes in a new monoclinic structure type with six crystallographically independent Pt positions. Within the Co/Pr system, Co7Pr17 (cubic) was characterized to crystallize in another new structure type consisting of eight and nine coordinated Co atoms. Most recently our investigation of the binary systems, including Pt1.99Pr3 as well as the ternary Pt/Pr/Sn and Co/Pr/Sn systems have yielded several new compounds including new structure types.

Through exploration of the binary Pt/Pr system using NaCl flux, single crystals of Pt1.99Pr3 were obtained. Pt1.99Pr3 adopts the Ga2Gd3 structure type where Pt atoms are coordinated by Pr atoms in chains of alternating cubes and square antiprism chains along the c axis. The remaining Pr positions form trigonal prisms and distorted tetrahedra around Pt atoms in 1:2 chains. The reported structure found for Pt2Pr3 is that of hexagonal Ni2Ho3. Subsequent loading of Pt2Pr3 in a Sn flux yielded two new ternaries in the Pt/Pr/Sn system: Single crystal analysis identified Pr4Pt12Sn25 and Pr3Pt4Sn6. The first is isostructural to Gd3Ni8Sn16 while the latter is a new ternary in the RE3T4E6 family (R = rare earth; T = Pt, Pd; E = Ge, Al, Sn, Si) where Pt and Sn form hexagonal and pentagonal nets.

Further investigation into the R3T4E6 family led to the characterization of four new compounds within the family for T = Pt and R = La, Ce, Pr, and Nd. The neodymium compound forms a new high-temperature modification of the parent R3T4E6 structure type (Pr3Pt4Ge6) where Pt atoms are seven coordinate in polyhedra that share edges and vertices. This new R3Pt4Sn6 structure type is also orthorhombic with a slightly smaller volume, approximately 3%. Interestingly, Pr3Pt4Sn6 forms both modifications as well, while La and Ce do not exhibit the high temperature modification.

Single crystal X-ray diffraction analysis of Co/Pr samples containing Sn as a flux revealed CoSn3Pr1-x (x = 0.04) and Co2–xSn7Pr3 (x = 0.78), adding two new ternaries to the Co-Sn-Pr system. In the first, trigonal prisms of Sn around the Co atoms form vertex-sharing networks. The latter structure contains Co atoms surrounded by square prisms of Sn connected to {PrSn12} cuboctahedra to form slabs.

Copyright Owner

Melissa Rhodehouse

Language

en

File Format

application/pdf

File Size

105 pages

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