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Metal flux synthesis was used to discover new Zintl phase materials and to grow crystals of superconducting phases. Reactions of barium and the pnictide elements Pn = P or As in indium melts produced new Zintl phases Ba2In5Pn5. This structure features indium arsenide slabs separated by barium cations. The connectivity of the indium and the arsenide leads to charge balancing according to the Zintl-Klemm concept ((Ba2+)2[(4b-In−)5(4b-Pn+)(3b-Pn0)4]4−). Band structure calculations indicate that these phases should be semiconducting, but resistivity and NMR studies show them to be metals. This may be due to very small amounts of excess indium doping onto Pn sites. Reactions of barium, iron, and arsenic in tin flux yield the phase BaFe2As2. This can be converted into a superconductor by doping with potassium. The difficulty in handling the volatile and reactive potassium metal was solved by using a Zintl phase, K4Sn4, as a potassium source. Varying amounts of this compound were combined with barium, iron, and arsenic in tin flux reactions, producing a series of KxBa1-xFe2As2 crystalline products. The superconducting transition temperature varied with x as expected, but the use of tin flux added the complication of incorporating small amounts of tin; this also affected the Tc. Lead flux was used to synthesize ANi2Sb2 phases. (A = Sr, Eu) which crystallized in either the ThCr2Si2 and CaBe2Ge2 structure types. Products forming with the ThCr2Si2 type consistently showed vacancies on the nickel site (ANi2-xSb2, x < 0.3) whereas the CaBe2Ge2 type products did not show these defects. Another ternary phase was also isolated, Eu2Ni7Sb5, with a new structure that is a stuffed variant of the La2NiGa10 structure type. EuNi2-xSb2 exhibits metallic behavior as given from resistivity data, and exhibits an antiferromagnetic transition at 5.8 K, which can be partially suppressed by applying an external magnetic field perpendicular to the c-axis. No suppression of the antiferromagnetic transition was found by applying an external magnetic field parallel to the c-axis up to 5 T.
A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Bibliography Note
Includes bibliographical references.
Advisory Committee
Susan Latturner, Professor Directing Dissertation; Eric Hellstrom, University Representative; Naresh Dalal, Committee Member; Oliver Steinbock, Committee Member.
Publisher
Florida State University
Identifier
FSU_migr_etd-8595
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