Doctor of Philosophy (PhD)
This dissertation describes the crystal growth, chemical structures, and efforts made towards the understanding of the physical properties of novel ternary rare-earth intermetallics, which may display signature behavior such as superconductivity, heavy fermion behavior, intermediate valence, and/or large magnetoresistance. To address the problem of correlating these characteristics with structural features, several ternary antimony- and tin-containing phases, Ln-T-X (Ln = lanthanide; T = Co, Ni, Pd; X = Sn, Sb), have been synthesized in single crystalline form by metallic flux-growth methods and characterized by X-ray diffraction. The antimonide compounds LnNi1-xSb2 (Ln = Y, Gd-Tb, Er, Yb), alpha, beta-LnNiSb3 (Ln = La, Ce, Pr, Nd, Sm), and LnPdSb3 (Ln = La, Ce) are structurally similar containing Ln-capped Sb nets, and adopt three different structure types. The contributing effects on the physical properties (large magnetic anisotropy and/or large positive magnetoresistance) due to the low-dimensionality and layering are discussed. The high symmetry of the stannides Ln3Co4Sn13 (Ln = La, Ce) leads to interesting magnetic and transport behavior. Transport measurements for the tetragonal (P4/nmm, No. 129) HfCuSi2-type LnNi1-xSb2 (Ln = Y, Gd-Er; x ~ 0.4) compounds indicate metallic behavior and, most interestingly, positive magnetoresistance for each compound, with giant positive magnetoresistance [MR(%) = (rhoH - rho0)/rho0 x 100] above 100% for the Y-, Dy-, and Ho-analogues at 3 K and 9 T. Magnetization data for the orthorhombic (Pbcm, No. 57) CeNiSb3-type PrNiSb3, NdNiSb3 and SmNiSb3 compounds show antiferromagnetic behavior with TN = 4.5 K (PrNiSb3), 4.6 K (NdNiSb3), and 2.9 K (SmNiSb3). Resistivity data indicate metallic behavior. CePdSb3 and beta-CeNiSb3, have been grown from an Sb flux and adopt a new structure type (Pbcm, No. 57), with Z = 8, and a ~ 12 Å, b ~ 6 Å, c ~ 12 Å, and V ~ 1000 Å3. These compounds are compared to CeCrSb3 and CeNiSb3. Cubic (Pm3n, No. 223) Ln3Co4Sn13 (Ln = La, Ce) adopt the Yb3Rh4Sn13-type structure. The La compound shows a corresponding sharp superconducting transition at Tc ~ 2.8 K, while a largely enhanced specific heat coefficient at low T with a low magnetic transition temperature suggests a heavy-fermionic character for the Ce compound.
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Thomas, Evan Lyle, "Crystal growth and the search for highly correlated ternary intermetallic antimonides and stannides" (2006). LSU Doctoral Dissertations. 1788.
Julia Y Chan