Electronic Properties of Glassy Metals MSE 410 Rochan Mehta

Electronic Properties of Glassy Metals

MSE 410Rochan Mehta

Overview Basics of conduction in regular metals Basics of metallic glasses Conduction of metallic glasses Comparisons of resistances

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

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

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

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

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

Photoelectron Spectroscopy Experiments have been done to measure the valence

band Seems to be an overlay of the other two materials

Sources of Resistance Defects

Impurities Grain Boundaries

Non-existent in Glassy Metals

Scattering Based on lattice

vibrations Ewald sphere

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

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

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

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

Questions?