Identifier

etd-08272012-123825

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

The focus of the research presented herein was to grow single crystals of Ln-M-X (Ln = lanthanide; M = Ti-Cr, Cu, Mo, Pd; X = Al, Ga) intermetallic compounds and to characterize their crystal structures and physical properties. Overall, the flux growth technique facilitated a detailed analysis of previously known structure-types (LnM2Al20 (Ln = La, Ce, Pr, Yb; M = Ti, V, Cr), Ln6M4Al43 (Ln = Gd, Yb; M = Cr, Mo), and Yb2Pd3Ga9), as well as the synthesis and characterization of new compounds (LnCrxGa3 (Ln = Ho, Er; x ~ 0.13), YbCr2Al20-xFex (x ~ 0.2), Ln(Cu,Al,Ga)13-x, and Ln2PdGa12 (Ln = Pr, Nd, Sm)). LnCrxGa3 (Ln = Ho, Er) adopt a stuffed variant of the AuCu3 structure-type rather than the related Y4PdGa12 structure-type which is adopted by the latter transition metals. Like the related Ln4MGa12 compounds, both analogues exhibit positive magnetoresistance, with ErCrxGa3 reaching ~25% at H = 9 T. After characterizing a number of LnM2Al20 (Ln = La, Ce, Pr, Yb; M = Ti, V, Cr) compounds, Fe was introduced to determine if it would influence the physical properties and to better understand the stability of the CeCr2Al20 structure-type. Mössbauer spectroscopy results for YbCr2FexAl20-x indicate that Fe atoms occupy two crystallographic sites, and X ray diffraction refinements suggest that the Fe atoms occupy the Al1 and Al2 sites rather than the Cr site. These results are consistent with LnM2Al20 compounds only forming for early transition metals. Single crystals of Yb6M4Al43 are non-magnetic consistent with divalent Yb, which contrasts with previously reports. Gd6M4Al43 (M = Ce, Mo, W) appear to order antiferromagnetically below 20 K with positive Weiss temperatures, suggesting that the magnetic structures of these materials are complex. Single crystals of Ln2PdGa12 order antiferromagnetically at 18, 7.5, and 7.5 K, respectively, and heat capacity measurements indicate that Pr2PdGa12 may be a new Pr containing heavy fermion compound. Single crystal neutron diffraction experiments were successfully carried out on NaZn13 type Ln(Cu,Al,Ga)13-x, including Eu(Cu,Al,Ga)13-x, to understand the site occupancies and disorder, and it was found that Cu partially occupies the 8b site while the 96i site is populated with Al, Cu, and Ga.

Date

2012

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

Chan, Julia Y

Included in

Chemistry Commons

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