Crystal growth and the search for highly correlated ternary intermetallic antimonides and stannides

Abstract

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.