Electronic Properties of Glassy Metals MSE 410 Rochan 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 T 2 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?