Effect of Antimony Doping in Iron Chalcogenides

Abstract

This thesis is organized in to six chapters. The contents of each chapter are briefly summarized in the following sections. Chapter 1 introduces different Fe-based superconductors. Within a very short span of their discovery, they quickly expanded to include six different crystal structures. The crystal structure of these systems and their Tc’s are discussed in this chapter. In particular, the properties of Fe1+yTe are described with specific reference to isovalent doping and nonisovalent doping using different elements that affect the superconducting transition in this material. In chapter 2, the basic principles of growth and characterization techniques are explained. These are: 1. Modified Bridgman technique, 2. X-ray diffraction technique, 3. Electron Probe Micro Analyzer to determine chemical composition, 4. SQuID – For magnetization measurements, 5. Closed cycle refrigerator and He Cryostat – for resistivity measurements. The fabrication of high temperature furnace for Bridgman setup is also discussed. Crystal growth and characterization of parent Fe1+yTe and Sb doped Fe1+yTe system are discussed in chapter 3 and chapter 4 respectively. Details of crystal growth by modified Bridgman technique are described here. The characterization includes analysis of crystalline phase, structure and composition. Detailed structural information is extracted from Rietveld refinement of X-ray powder diffraction and the composition analyzed using EPMA. Temperature dependence of magnetization and transport behavior are also discussed. The ideal doping range of Sb in Fe1+yTe is defined in this chapter. In chapter 5, the effect of Sb doping of Fe1.05Te0.50Se0.50 is investigated. The crystal growth and characterization of the new superconductor, Fe1.05Te0.50Se0.48Sb0.02 are deliberated. The superconducting transition observed in transport measurements at zero field and the magnetic field dependence of transition temperatures are discussed. Estimation of upper critical Page|vi|Preface field using Ginzburg-Landau theory as well as the field dependence of magnetization of this crystal is explained in this chapter. The thesis concludes with a chapter on summary and outlook on all investigations. Finally, the scope of future work is outlined in the last section.