Identifier

etd-11102008-130405

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

This dissertation focuses on the investigation of new ternary intermetallic gallides, which may exhibit exotic physical properties such as heavy-fermion behavior, large magnetoresistance, and even superconductivity. In particular, the Ln-Cu-Ga (Ln = lanthanides) system has been systematically investigated by changing a reaction ratio and/or using a different temperature profile to optimize desired phases. Single crystals of Ln2MGa12 (Ln = La, Ce; M = Ni, Cu) have been synthesized using Ga flux and compared to their Pd analogues. Interestingly, Ce2MGa12 (M = Ni, Cu) show enhanced Sommerfeld coefficient of ¡Ö 191 mJmol-1K-2 and ¡Ö 69 mJmol-1K-2 for Ni and Cu compounds, respectively. Three different structure types such as Ln(Cu,Ga)13 (Ln = La¨CNd, Eu), SmCu4Ga8, and Ln(Cu,Ga)12 (Ln = Y, Gd¨CEr, Yb) have been synthesized by increasing Cu concentration. A large positive magnetoresistance up to 154 % at a field of 9 T is observed for Pr(Cu,Ga)13. Most interestingly, Pr(Cu,Ga)13 shows T2 temperature-dependent resistivity and satisfies Kadowaki-Woods relation, which is indicative of heavy-fermion behavior. The ordered SmCu4Ga8 grown by flux method has been compared to its isostructural disordered analogue, SmCu4.1Ga6.9. Ln(Cu,Ga)12 (Ln = Gd¨CEr) compounds order antiferromagnetically at 12.5 K, 13.5 K, 6.7 K, and 3.4 K for Gd-, Tb-, Dy-, and Er-analogues, respectively. Ln4MGa12 (Ln = Dy¨CEr; M = Pd, Pt) have been grown from Ga flux. Magnetic measurements show that Dy4PdGa12 and Er4PdGa12 are antiferromagnetic with transitions at TN = 10 K and 5.2 K, respectively, while Ho4PdGa12 does not show any magnetic ordering down to 2 K. Ln4PtGa12 (Ln = Dy¨CEr) order antiferromagnetically at TN = 9.8 K, 3.6 K and 5.1 K for Dy-, Ho-, and Er-analogues, respectively. The electrical resistivity data show metallic behavior. Large positive magnetoresistance is shown up to 900 % at 3 K and 9 T for the Ho4PtGa12 analogue. Single crystals of LnAgyX4-y (Ln = La, Ce; X = Al, Ga; y ¡Ö 0.72) have been synthesized by aluminum or gallium flux. These compounds show an occupational disorder for Ag sites. CeAg0.72Al3.28 and CeAg0.67Ga3.33 are metallic, and magnetic measurements indicate that both order ferromagnetically near 3 K.

Date

2008

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 Y. Chan

DOI

10.31390/gradschool_dissertations.1802

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