Doctor of Philosophy (PhD)
The focal point of this dissertation is the investigation of substitution and disorder effects in ternary intermetallics. The crystal growth, crystal structure, and physical properties are reported on single crystals of Ln6W4-xAl43-yTx+y (Ln = Gd, Yb; T= Mn, Fe), LnCr2FexAl20-x (Ln = Yb, Gd), Sm1.33Pd3Ga8, and CeCo2-xMxAl8 (M = Mn, Fe, Ni; 0 ≤ x < 1). The reported compounds were grown via the flux growth method with the strategic synthetic parameters described. Correlations between the structural and physical properties in relation to substitution and disorder of Ln6W4-xAl43-yTx+y (Ln = Gd, Yb; T= Mn, Fe), LnCr2FexAl20-x (Ln = Yb, Gd), Sm1.33Pd3Ga8, and CeCo2-xMxAl8 (M = Mn, Fe, Ni; 0 ≤ x < 1) are discussed. The synthesis and characterization of Mn- and Fe- substituted Ln6W4Al43 (Ln = Gd, Yb) are reported. The compounds adopt the Ho6Mo4Al43 structure type with lattice parameters of a ~ 11 Å and c ~ 17.8 Å with structural site preferences for Mn and Fe. The magnetization of Yb6W4Al43 is sensitive to Mn and Fe doping, which is evident by an increase in the field dependent magnetization. Gd6W4Al43, Gd6W4Al42.31(11)Mn0.69(11), and Gd6W4Al41.69(12)Fe1.30(12) order antiferromagnetically in the ab- and c-direction at 15, 14, and 13 K, respectively, with positive Weiss constants, suggesting the presence of ferromagnetic exchange interactions. Anisotropic magnetization data of Gd6W4Al43-yTy (T= Mn, Fe) analogs are discussed. Crystal growth, structure determination, and magnetic properties of LnCr2Al20-xFex (Ln = La, Gd, Yb) adopting the CeCr2Al20 structure type with space group Fd3¯ m, a ~ 14.5 Å, type are reported. Single crystal X-ray diffraction and Mössbauer spectroscopy are employed to fully characterize the crystal structure of LnCr2Al20-xFex (Ln = La, Gd, Yb). LnCr2Al20-xFex (Ln = La, Gd, Yb) are the first pseudo-ternaries adopting the CeCr2Al20 structure type with a transition metal occupying the main group site. The Yb analogues are Pauli paramagnets with the Yb ion adopting an electronic configuration close to Yb2+, while the Gd analogues show paramagnetic behavior with no magnetic order down to 3 K. The synthesis and characterization of Sm1.33Pd3Ga8 is reported. Sm1.33Pd3Ga8 adopts a disordered variant of the Er4Pt9Al24-structure type with lattice parameters of a = 4.353(5) and c = 38.98(4) Å and V = 639.70(12) Å3. The structure of Sm1.33Pd3Ga8 is composed of three distinct building blocks: Pd2Ga4, PdGa2, and Sm0.67Ga. The Sm0.67Ga slab does not magnetically order, which directly affect the structure. Sm1.33Pd3Ga8 is a temperature independent paramagnet. Field dependent magnetization of Sm1.33Pd3Ga8 displays anisotropic behavior. Single crystals of CeCo2-xMxAl8 (M = Mn, Fe, Ni; 0 ≤ x < 1) were grown and crystallize in the CaCo2Al8 structure type with space group Pbam. Single crystal X-ray diffraction data suggest that the Ce 4f-state is valence fluctuating as Fe concentration increases, whereas the Ni-doped analogues do not exhibit valence fluctuating. The results suggest that hole doping leads to an admixture of Ce3+/Ce4+.
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Treadwell, LaRico Juan, "Substitution and Disorder Effects in Ternary Intermetallics" (2014). LSU Doctoral Dissertations. 1380.
Stanley, George G.