Materials Synthesis from Atoms to Systems
Understanding Novel Materials through Single CrystalsMarch 01, 2013
: single crystals of iron-based superconductors
The materials of central importance in our research include superconductors, transparent conductors, and thermoelectrics, for which there is a need to understand and control transport (electrons, holes, phonon) properties. Designing and producing crystalline materials with properties that allow these uses is critical for understanding the fundamental nature of the materials’ physics, and if these materials are to fulfill their promise in energy-related applications, such as wires in powerful and compact superconducting generators; highly-efficient transparent conducting electrodes in solar cells; and effective bulk thermoelectric materials in generators. Within the Physical Sciences Directorate (PSD) and over the past several years, techniques for synthesizing such crystalline materials have advanced considerably, allowing easier crystal growth from solution, vapor, liquid, or solid phases using a variety of techniques such as flux growth, chemical-vapor transport, Bridgman, Czochralski, float zone, and spark plasma sintering. This wide range of synthesis capabilities and expertise has attracted international attention for its novel and high-quality crystals based on a wide range of chemical elements, including pnictides and chalcogenides (oxides). The research on such advanced crystals has led to the investigation of intrinsic materials performance and extensive international and national scientific collaborations. In addition, the research has fostered robust materials and neutron scattering research programs, particularly on the superconductors, taking advantage of deep expertise and capabilities of neutron sciences at ORNL. Designs for promising energy-related crystals are showcased on this poster, as well as how investigation into their growth may yield breakthrough advances for performance materials. The development of superconducting crystals with certain structural characteristics and chemical compositions (e.g., Co- and Pr-doped BaFe2As2, Ba1-dFe2Se2) has already permitted anisotropic studies of the crystals’ thermodynamic and transport properties. Along with theoretical and neutron research efforts, these developments have led to improvements in material superconductivity parameters. In addition, the development of quality single crystals of transparent conducting oxides (e.g., In2O3, SnO2, and ZnO) has enabled extensive, thorough studies of surface properties using atomically resolved scanning-tunneling microscopy, low-energy ion-scattering spectroscopy, and polarized infrared light investigations. Moreover, large single-crystal preparations of thermoelectric materials have led to studies of inelastic neutron scattering that will further our understanding of the very-low thermal conductivity (e.g., in AgSbTe2), which might in turn, lead to improved thermoelectric efficiency.