Structures of Metals and Ceramics (ENGR1722) — VOCABULARY Flashcards

Vocabulary flashcards covering key concepts from the lecture notes on metallic and ceramic crystal structures.

Interatomic bonding

Bonding that arises from the electron structures of atoms and determines the type (metallic, ionic, covalent) and properties of a material.

Crystalline material

A material in which atoms are arranged in a periodic, three-dimensional lattice.

Amorphous (non-crystalline)

A material lacking long-range periodic order; often formed by rapid cooling (e.g., amorphous SiO2).

Unit cell

The smallest repeating unit of a crystal that, when stacked, reproduces the entire crystal structure.

Lattice parameters

The six parameters a, b, c, α, β, γ that define the geometry of a unit cell.

Crystal systems

Classifications of crystal structures based on lattice parameters; seven systems, including cubic, tetragonal, and hexagonal.

Simple Cubic (SC)

A cubic crystal system with atoms at corners only; CN = 6; 1 atom per unit cell; APF ≈ 0.52.

Body-Centered Cubic (BCC)

A cubic system with an atom at each corner and one in the center; CN = 8; 2 atoms per unit cell; APF ≈ 0.68.

Face-Centered Cubic (FCC)

A cubic system with atoms at corners and face centers; CN = 12; 4 atoms per unit cell; APF ≈ 0.74; close-packed along face diagonals.

Hexagonal Close-Packed (HCP)

A hexagonal close-packed structure with ABAB stacking; CN = 12; 6 atoms per unit cell; APF ≈ 0.74; c/a ≈ 1.633.

Atomic Packing Factor (APF)

The fraction of space occupied by atoms in a unit cell; APF = (volume of atoms in cell)/(volume of unit cell).

Coordination Number (CN)

The number of nearest-neighbor atoms surrounding a given atom in a crystal structure.

Polonium (Po) simple cubic structure

A rare metal with a simple cubic structure; atoms touch along cube edges; CN = 6.

Rock Salt structure (NaCl-type, AX)

AX crystal structure where cations occupy octahedral sites around anions; CN = 6; examples include NaCl, MgO, MnS.

Radius ratio rule

Rule that predicts stable coordination and crystal structure from the ratio rcation/ranion; defines preferred CN and geometries (linear, triangular, tetrahedral, octahedral, cubic).

Fluorite structure (CaF2)

AX2 crystal structure; Ca2+ occupies cubic sites and F− occupies other positions; common example includes CaF2; typically 4 formula units per unit cell.

Perovskite structure (ABX3)

Crystal structure with formula ABX3; A-site cation, B-site cation, X anion; example BaTiO3.

Theoretical density (ρ)

Calculated density using ρ = (nA)/(Vc NA), where n is the number of atoms per unit cell, A is atomic weight, Vc is unit cell volume, and NA is Avogadro’s number.

Density trends by material class

Generally, metals have higher density than ceramics, which are higher than polymers.

Atoms per unit cell (SC/BCC/FCC)

SC has 1 atom per cell; BCC has 2 atoms per cell; FCC has 4 atoms per cell, which affects properties like density and APF.