electronic properties of glassy metals mse 410 rochan mehta
DESCRIPTION
Conduction in Regular metals Band structure arises from Brillouin zones Overlap of the first and second band leads to easy transfer from valence to conduction bandTRANSCRIPT
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Electronic Properties of Glassy Metals
MSE 410Rochan Mehta
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Overview Basics of conduction in regular metals Basics of metallic glasses Conduction of metallic glasses Comparisons of resistances
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Conduction in Regular metals Band structure arises
from Brillouin zones Overlap of the first and
second band leads to easy transfer from valence to conduction band
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Metallic Glasses Historically produced
by two methods Spin casting with heat
transfer rates at over 1e6 degrees/sec
Vapor deposition without nucleation site
Cannot create band structure with traditional method
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X-ray diffraction X-ray diffraction shows
one big peak, with broad overlays
This is opposed to a peak with periodic smaller peaks as seen with crystalline solids
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Structure of Metallic Glass Metallic glasses have
no long range order Short range has some
order within the first and second degree
Each one of the nearest neighbors produces the noted peaks
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Band Structure Need to use slightly
different model to create the band structure
Splitting of bands Lowest unoccupied
molecular orbital Highest occupied molecular
orbital Can be used to
approximate a band structure
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Photoelectron Spectroscopy Experiments have been done to measure the valence
band Seems to be an overlay of the other two materials
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Sources of Resistance Defects
Impurities Grain Boundaries
Non-existent in Glassy Metals
Scattering Based on lattice
vibrations Ewald sphere
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Scattering in Glassy Metals due to Phonons
Exist, although are not extended waves Specific heat measurements have shown that
they are more anharmonious than crystalline materials
Causes scattering of the electrons, increasing overall resistance
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Temperature Effects of Phonons At low T, below the Debye Temp, there is a
T2 dependance of scattering For pure crystalline alkali metals the value is
exp(-c/T) At high temp, it becomes proportional to the
absolute temp
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Resistance as a Function of Level of Crystallinity As you can see, overall
increases in resistance in the glassy phases
In line with extrapolation of liquid phase However, unlike liquid
which has mobility of atoms, mostly only the electrons are conductors
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Conclusion Band structure only approximations, due to
first and second nearest neighbors Glassy metals have interesting
dependences of Temp and over all resistance
Extrapolate liquid curve to approximate glassy metals
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Questions?