Glassy, Nanostructured, Crystalline Solids. Mechanical, Thermoelectronic, Magnetic properties

Transcription

1 Glassy, Nanostructured, Crystalline Solids Research Area = Materials Physics/Condensed matter physics Methods = Experiment coupled with theory/computation Research Goals New Materials Discovery Physics of materials Superior Properties Mechanical, Thermoelectronic, Magnetic properties

2 X-ray diffraction Some of the Tools Atomic force microscopy Low energy electron microscope Materials synthesis Ultrasound measurement Electrical transport measurement Resistivity (mω-cm) Ti 0.9 Zr 0.1 NiSn 0.99 Sb 0.01 Ti 0.9 Hf 0.1 NiSn 0.99 Sb 0 Ti 0.5 Zr 0.25 Hf 0.25 NiSn 0.99 Sb Ti 0.25 Zr 0.25 Hf 0.5 NiSn 0.99 Sb 0.01 Magnetic measurement Temperature (K) Temperature (K) MPMS VSM

3 Physics of States of Matter Amorphous/Glassy Metals Glasses are ubiquitous in nature, e.g. optoelectronic, window, copy machine, biological systems. Glasses are highly frustrated systems with strong particle-particle correlations. Potential energy Crystal 1 Ideal glass Crystal 2 Glassy state can be described by multi- dimensional energy landscape, and shares much of the physics of spin glass, neural network and protein folding. Coordinates More Why some systems are trapped in the glassy state? What are the properties? How to improve glass formability?

4 Superior Properties High strength per unit mass, Soft magnetism, Superior surface properties (GPa) Stress Ceramic Steel Ti Amorphous Steel UVa Polymer Application Areas Transportation systems Space vehicle/structure Micro-machines/actuators /sensors Transformers Electric engines Surface coating Catalysis Elastic Strain (%)

5 Physics of Glassy Metals Multi-component systems Complexity science Atomistic scale design Atomistic scale structure Density Functional Theory (DFT) Molecular Dynamics (MD)

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7 Half-Heuslers Th3P4 Skutterudites ZrCoSb La 2 Te 3 Clathrates Chevrel Phases LaCo 4 Sb 12 Ba 8 Ga 16 Ge 30 Cu 4 Mo 6 Se 8

8 Metallic crystals exhibit unusual electronic structure Example of unusual electronic structures interplay of orbitals and crystal structure Tobola et al, 1998

9 Scientific issues of interest Bandgap material - interesting thermoelectronic properties Magnetic state with gapless spin-up band and gapped spin-down band (spinpolarized state) ordinary metal Thermopower T (K) Energy (ev)

10 Harvesting Energy using Thermoelectrics: Cooling and Power Generation Thermoelectric materials are used in electronic refrigeration and power generation. The materials are environmentally green. The devices are compact and involve no moving parts. Cooling of computer chips (CPU), low noise amplifiers, IR detectors. Power generation using waste heat - Space (NASA) and Naval applications.

11 NASA Applications Radioisotope TE Generator (RTG) 250W Pu 238 O 2 Heat Source Safe - α decay 88 year half life Voyager & Pioneer > 25 years SiGe TE elements 250 W for 50 kg Necessary for outer planet missions low solar flux, (Cassini, Galileo) Next Generation (MMRTG) PbTe/TAGS TE elements Fission reactor Power (100 kw) High Temperature: 1000 C hot, 500 C cold TE or Brayton Engine for energy conversion Weight, Size, Reliability are issues shielding, heat rejection panels, ion propulsion, science package, $B Missions Jupiter Icy Moons Orbiter Mars/Lunar Missions

12 Thermoelectric Performance is defined by a dimensionless figure-of-merit = ZT, Z = S 2 ρκ or 2 S σ κ S=Seebeck thermopower ρ=resistivity κ=thermal conductivity State-of-the-art ZT 1 ZT >>1 needed to Carnot efficiency? ZT ~2-3 great!

13 ZT of our new compounds matches SiGe New electronic materials can lead to high S 2 σ 20 Atomic- and nanoscale structural design can lead to low κ TiNiSn 0.95 Sb 0.05 TiNiSn TiNiSn 0.95 Sb 0.05 (BMSC) TiNiSn(BMSC) Temperature (K)

14 Why study Nanostructured and Glassy Solids? 1. Can form a broader range of materials (non-equilibrium methods involve short length and time scales) resulting in new magnetic, structural, thermoelectronic materials 2. Investigate non-crystalline properties 3. Investigate size dependence of properties Nanocrystalline State Crystal size confines electronic and vibrational states, modifies spectra, dislocation structure and scattering. 3D 2D 1D 0D

15 Nanolayers Nanocrystallites Magnetic Behavior of Nanostructure

16 NM (Fe0.8Co0.2)78Mo3B7C5P7 mass = g Moment (emu) Applied Field (Oe) NM (Fe0.8Co0.2)78Mo3B7C5P7 mass = g Moment (emu) Applied Field (Oe)

17 Nanostructured Magnetic Materials Electric Power Systems High density power High speed machines Materials breakthroughs Spin manipulation Transformer cores Hard disk drive Casette recording heads Ultrahigh density media