Research Area= Materials Physics/Condensed matter physics
Methods= Experiment coupled with theory/computation
Research Goals
Glassy, Nanostructured, Crystalline Solids
Research Goals•••• New Materials Discovery
•••• Physics of materials
•••• Superior Properties
Mechanical, Thermoelectronic, Magnetic properties
X-ray diffraction Atomic force microscopyLow energy electron microscope
Materials synthesisUltrasound measurement
Some of the Tools
Electrical transportmeasurement
Magnetic measurement
Temperature (K)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 100 200 300 400 500 600 700
Ti0.9Zr 0.1NiSn0.99Sb0.01Ti0.9Hf 0.1NiSn0.99Sb0
.01Ti0.5Zr 0.25 Hf 0.25NiSn0.99Sb0.01Ti0.25Zr 0.25 Hf 0.5NiSn0.99Sb0.01
Res
istiv
ity (
mΩΩ ΩΩ
-cm
)
Temperature (K)
MPMS
VSM
Physics of States of MatterAmorphous/Glassy MetalsGlasses are ubiquitous in nature, e.g.optoelectronic, window, copy machine, biological systems.
Glasses are highly frustrated systems with strong particle-particle correlations.
Glassy state can be described by multi-dimensional energy landscape, and
Pot
entia
l ene
rgy
Coordinates
Ideal glass
Crystal 2Crystal 1
dimensional energy landscape, and shares much of the physics of spin glass, neural network and protein folding.
More ……
Why some systems are trapped in the glassy state? What are the properties?How to improve glass formability?
3
4
Str
ess
(G
Pa)
5
Cer
amic
Application AreasTransportation systems Space vehicle/structureMicro-machines/actuators/sensors Transformers
Superior Properties
High strength per unit mass, Soft magnetism, Superior surface properties
Amorphous Steel discovered @ UVa
1
2
3
Elastic Strain (%)
Str
ess
(G
Pa)
1 2 3
Steel
Ti
0
Polymer
TransformersElectric enginesSurface coatingCatalysis
Multi-component systems→→→→ Complexity scienceAtomistic scale designAtomistic scale structure
Molecular Dynamics(MD)Density Functional Theory(DFT)
Physics of Glassy Metals
Molecular Dynamics(MD)Density Functional Theory(DFT)
Skutterudites
Clathrates Chevrel Phases
Th3P4Half-Heuslers
La2Te3ZrCoSb
LaCo4Sb12
Clathrates
Ba8Ga16Ge30
Chevrel Phases
Cu4Mo6Se8
Metallic crystals exhibit unusual electronic structure
Example of unusual electronic structures –interplay of orbitals and crystal structure
Tobola et al, 1998
Scientific issues of interest Bandgap material -
interesting thermoelectronic properties
Magnetic state with gapless spin-up band and gapped spin-down band (spin-
polarized state)
T (K)
ordinarymetal
Thermopower
Energy (eV)
Harvesting Energy using Thermoelectrics: Cooling and Power GenerationHarvesting Energy using Thermoelectrics: Cooling and Power GenerationHarvesting Energy using Thermoelectrics: Cooling and Power GenerationHarvesting 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.
Radioisotope TE Generator
(RTG) 250W
Fission reactor Power (100 kW)
High Temperature: 1000 C hot, 500 C coldTE 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
NASA Applications
• Pu238O2 Heat Source
– “Safe” -α decay88 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
Jupiter Icy Moons Orbiter
Mars/Lunar Missions
State-of-the-art ZT ≈≈≈≈ 1
dimensionless figure-of-merit = ZT, ρκ
2SZ =
κσ2S
orS=Seebeck thermopowerρ=resistivityκ=thermal conductivity
??
Thermoelectric Performanceis defined by a
ZT >>1 needed to→→→→ Carnot efficiency
ZT ~2-3 great!??
ZT ~2-3 great!
• New electronic materialscan lead to high S2σ
ZT of our new compounds matches SiGe
0
5
10
15
20
0 50 100 150 200 250 300 350
Temperature (K)
TiNiSn0.95
Sb0.05
TiNiSn
TiNiSn0.95
Sb0.05
(BMSC)
TiNiSn(BMSC)
• Atomic- and nano-scale structural designcan lead to low κ
Why study Nanostructured and Glassy Solids ?
1. Can form a Can form a Can form a Can form a broader rangebroader rangebroader rangebroader range of materialsof materialsof materialsof materials(non-equilibrium methods involve short length and time scales)
resulting in resulting in resulting in resulting in newnewnewnew magnetic, structural, thermoelectronic materialsmagnetic, structural, thermoelectronic materialsmagnetic, structural, thermoelectronic materialsmagnetic, structural, thermoelectronic materials
2. Investigate Investigate Investigate Investigate nonnonnonnon----crystallinecrystallinecrystallinecrystalline propertiespropertiespropertiesproperties
3. Investigate Investigate Investigate Investigate size dependencesize dependencesize dependencesize dependence of propertiesof propertiesof propertiesof properties
Nanocrystalline StateCrystal size confines electronic and vibrational states, modifies spectra,dislocation structure and scattering.
3D 2D 1D 0D
Nanolayers Nanocrystallites
Magnetic Behavior of Nanostructure
NM07-019 (Fe0.8Co0.2)78Mo3B7C5P7 mass = 0.00477g
NM07-019 (Fe0.8Co0.2)78Mo3B7C5P7 mass = 0.00477g
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-1000 -800 -600 -400 -200 0 200 400 600 800 1000
Applied Field (Oe)
Mom
ent
(em
u)
mass = 0.00477g
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Applied Field (Oe)
Mo
men
t (e
mu
)
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
