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Matse 400 Final Exam (New Material) With Complete Solutions
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Matse 400 Final Exam (New Material) With Complete Solutions
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Solution 2024/2025Pepper
Matse 400 Final Exam (New Material) With
Complete Solutions
4 types of defects in crystals ANS✔✔ point
line
area
volume
2 types of line defects ANS✔✔ edge
screw
edge dislocation ANS✔✔ -insertion of extra half plane of atoms
- bergers vector perpendicular to dislocation
- tensile stress below dislocation
- compressive stress above dislocation
screw dislocation ANS✔✔ - bergers vector parallel to dislocation
Stoichiometric defects ANS✔✔ Schottky
Frenkel
- stoichiometric defects change things like diffusion coefficients and ionic conductivity
Schottky defect ANS✔✔ - missing cations and anions in the ratio of the chemical formula
- example: MgO
- as concentration of point defects inc. temp. inc.
, Solution 2024/2025
Pepper
Frenkel defect ANS✔✔ - vacancy and interstitial pair
- example CaF2: large interstice in center of unit cell fits F
- defect concentration. inc. as temp. inc.
- easier to make frenkel defects on cation sites bc smaller cations easily fit into interstices than larger ions
non-stoichiometric defects ANS✔✔ - example: oxygen vacancies in MgO
conservation laws for defect chemistry ANS✔✔ - conserve mass: don't create/destroy atoms
- conserve charge; don't create/destroy charge
- conserve crystal structure: on either side of the reaction, need to have sites in same ratio as chemical formula
Thermal expansion ANS✔✔ - as you change temp of solid, typically changes shape
- higher t melt, lower therm. exp.
- as bond strenght inc., therm. exp. dec.
- anisotropy in layered structures
Thermal expansion behaviors ANS✔✔ 1. distance from origin to surface is proportional to them. exp. in that direction.
- isotropic when therm. exp. is indep. of direction (equal in all directions)
- amorphous and cubic systems
2. uniaxial: 1 high symm. direction (equal in 2 directions)
- trigonal, tetragonal, hexagonal systems
3. biaxial: not equal in any direction
- orthorhombic, monoclinic, triclinic systems
4. Open structures: hard to predict therm. exp.
- can get small therm. exp. due to internal vibration room
- can get large therm. exp. due to cooperative rotation of polyhedra
- example: silicate 6 ring, cristobalite
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