Chapter 12 Structures and properties of ceramics Flashcards
atomic bonds in ceramics
can be ___ and ___
ionic character _____ with difference in electronegativity of atoms
Ceramic Crystal Structures Oxide structures
- oxygen anions ____ than metal cations
- ______ oxygen in a lattice (usually FCC)
- cations fit into ______ among oxygen ions
Ceramic Crystal Structures Oxide structures
- oxygen anions larger than metal cations
- close-packed oxygen in a lattice (usually FCC)
- cations fit into interstitial sites among oxygen ions
2 factors that determine crystal structure
1) relative sizes of ions
2) maintenance of charge neutrality
coordination number
number of ions that basically touch each other in a solid body diagram
ionic radii
ionic radii is the distance between the nucleus and the electron in the outermost shell of an ion.
coordination number and ionic radii together
computation of minimum cation-anion radius ratio
bond hybridization
concept of mixing atomic orbitals to form new hybrid orbitals suitable for describing bonding properties.
Example Problem: Predicting the Crystal
Structure of FeO
• On the basis of ionic radii, what crystal structure
would you predict for FeO?
rock salt structure
Rock salt (NaCl) is an ionic compound that occurs naturally as white crystals. It is extracted from the mineral form halite or evaporation of seawater. The structure of NaCl is formed by repeating the face-centered cubic unit cell.
*quick reference *
MgO and Feo MgO and Feo also have the NaCl structure
cesium chloride
can be thought of as two interpenetrating simple cubic arrays where the corner of one cell sits at the body center of the other.
fluorite structure
the fluorite structure refers to a common motif for compounds with the formula MX₂.
perovskite structure
ABX3
A perovskite is any material with a crystal structure similar to the mineral called perovskite, which consists of calcium titanium oxide.
density computations for ceramics
formula explained
what 2 materials make up silicates
Silicates are materials composed generally of silicon and oxygen. It is the first technical ceramics developed to support early electrical technologies.
* quick reference *
glass structure
2 polymorphic forms of carbon
diamond and graphite represent two different allotropes of carbon, which also makes them different polymorphs of carbon
point defects in ceramics
1) vacancies
2) interstitials
point defects in ceramics
1) vacancies - is a type of point defect in a crystal where an atom is missing from one of the lattice site
2) interstitials - is a type of point crystallographic defect where an atom of the same or of a different type, occupies a normally unoccupied site in the crystal structure.
point defects in ceramics
3) Frenkel defect
4) Schottky defect
3) Frenkel defect - A Frenkel defect is a type of point defect in crystalline solids, The defect forms when an atom or smaller ion (usual cation) leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location.
4) Schottky defect - is an excitation of the site occupations in a crystal lattice leading to point defects. it refers to simple lattice vacancies, also called valency defects.
imperfections in ceramics
SUMMARY
- Interatomic bonding in ceramics is ionic and/or covalent.
- Ceramic crystal structures are based on:
- Imperfections
- Room-temperature mechanical behavior
