Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Physics and Astronomy


Many high superconducting transition temperature (T(,c)) super-^conductors have been discovered in rare earth transition metal^borides, such as some compounds in the primitive tetragonal^RERh(,4)B(,4), body-centered tetragonal RERu(,4)B(,4) or orthorhombic^RERuB(,2) systems. The high transition temperatures present in many^of those compounds as well as the regular sublattice of rare earth^atoms provide an opportunity for studying the interaction of superconductivity and long range magnetic order. The close correlation between superconductivity, magnetic order and structural features is demonstrated with the study of the pseudoternary systems Er(Rh(,1-x)Ru(,x))(,4)B(,4), Y(Rh(,1-x)Ru(,x))(,4)B(,4) and (Lu(,1-x)Er(,x))RuB(,2). The systematic investigation of the role of each atom in the particular ternary boride structure is addressed by low temperature measurements of electronic, transport and magnetic properties as well as by metallurgical methods;An abrupt depression of T(,c) versus transition metal concentration occurs at x (DBLTURN) 0.50 after a plateau with T(,c) (DBLTURN) 7.7K in the Er(Rh(,1-x)Ru(,x))(,4)B(,4) pseudoternary system. Superconductivity and long range magentic order both occur, but are exclusive of each other in this Er-based system;The superconducting-normal state boundary in the low temperature phase diagram is determined for the isostructural, nonmagnetic system Y(Rh(,1-x)Ru(,x))(,4)B(,4). From single crystal x-ray diffraction data, the size of the transition metal clusters and intercluster distances are related to the occurrence of superconductivity;Particular emphasis is placed on the orthorhombic (Lu(,1-x)Er(,x))RuB(,2) system which exhibits reentrant superconductivity. Two distinct magnetic transitions are observed for samples in the concentration range, 0.5 (LESSTHEQ) x (LESSTHEQ) 1. Heat capacity, upper critical field and resistivity data for samples in this system are measured in order to study the competition between superconductivity and magnetic order. A high Debye temperature (487K), modified Debye model and BCS theory provide an excellent description of the superconducting (T(,c) = 10K)LuRuB(,2);Finally, metallurgical methods are applied in studying the relation between the structure type and superconductivity. The presence of boron pairs was found to be an important structure factor for the occurrence of superconductivity in these ternary boride systems;*DOE Report IS-T-1039. This work was performed under ContractNo. W-7405-Eng-82 with the U.S. Department of Energy.



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Herng-Er Horng



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104 pages