CME-260: Chapter 4

Solid Solution

An atomic-scale mixture of two or more elements forming a single crystalline phase.

Solvent

The major component in a solid solution (host material)

Solute

The minor component that dissolves into the solvent

Substitutional Solid Solution

A solid solution in which solute atoms replace solvent atoms at normal lattice sites

Interstitial Solid Solution

A solid solution in which small solute atoms occupy interstitial (void) spaces between solvent atoms

Random Solid Solution

A solid solution where solute atoms are randomly distributed among lattice sites

Ordered Solid Solution

A solid solution in which solute atoms occupy specific lattice positions in a repeating pattern

Hume-Rothery Rules

Conditions favoring substitutional solid solution formation:

1. <15% atomic radius difference

2. Same crystal structure

3. Similar electronegativity

4. Same valence

Nonstoichiometric Compound

A compound in which variations in ionic charge cause deviations from ideal chemical ratios

Point Defect

Zero-dimensional imperfection at a single lattice point

Vacancy

A missing atom at a lattice site

Interstitialcy

An atom located at an interstitial site (between normal lattice positions)

Frenkel Defect

A vacancy-interstitial pair where an ion leaves its normal site and occupies an interstitial site

Schottky Defect

A pair of oppositely charged ion vacancies in an ionic crystal to maintain charge

Linear Defect

One-dimensional lattice imperfection along a line of atoms

Dislocation

A linear defect responsible for plastic deformation in crystalline materials

Edge Dislocation

A dislocation formed by an extra half-plane of atoms

Burgers vector is perpendicular to the dislocation line

Screw Dislocation

A dislocation characterized by a spiral stacking of crystal planes.

Burgers vector is parallel to the dislocation line.

Mixed Dislocation

A dislocation that has both edge and screw character.

Burgers Vector

The displacement vector needed to close a stepwise loop around a dislocation.

Planar Defect

Two-dimensional disorder in crystal structure.

Grain

A single crystal region within a polycrystalline material.

Grain Boundary

The interface between two adjacent grains of different orientations.

Twin Boundary

A special grain boundary where the crystal structures on either side are mirror images

Tilt Boundary

A low-angle grain boundary formed by a periodic array of edge dislocations.

Grain-Boundary Dislocation (GBD)

Dislocations that exist along high-angle grain boundaries.

Grain-Size Number (G)

A measure of grain size defined by:

where N is number of grains per square inch at 100x magnification

Hirth-Pound Model

A model describing crystal surfaces as containing atomic ledges and kinks rather than smooth planes

Noncrystalline Solid

A solid lacking long-range atomic order (amorphous)

Amorphous Metal

A metallic glass formed by rapid cooling that prevents crystallization.

Amorphous Semiconductor

A semiconductor material lacking long-range order

Short-Range Order

Local atomic arrangement resembling crystalline bonding.

Medium-Range Order

Atomic ordering extending beyond nearest neighbors but not fully periodic.

Long-Range Order

Regular, repeating atomic pattern throughout the material (crystallinity)

Random Network Theory

Theory describing amorphous solids as continuous random atomic networks

Zachariasen Model

Model of oxide glass structure describing a random network of connected polyhedra.

Bernal Model

Model of amorphous metals representing atoms as irregularly connected polyhedra