LECTURE 17 Crystalline compounds

LECTURE 17 Crystalline compounds - SUMMARY FROM LAST CLASS...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Dr. P. Lucas U of A MSE 110 Crystalline solids Packing density: Simple cubic: 52% Body Centered Cubic (BCC): 68% Faced Center Cubic (FCC) and Hexagonal Close Packed (HCP) : 74% Stacking dense layers generate octahedral and tetrahedral interstitial sites. Close packed structures have two tetrahedral site and one octahedral site for each atom: FCC : 4 atoms per unit cell, 8 tetra sites and 4 octa sites per cell. HCP : 6 atoms per unit cell, 12 tetra sites and 6 octa sites per cell Cubic sites are not present in close packed structure. The larger the number of atoms generating an interstitial site, the larger the volume of the site: Cubic>Octa>Tetra An interstitial atom must be at least as large as the site it occupies. SUMMARY FROM LAST CLASS
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Dr. P. Lucas U of A MSE 110 FCC Crystal structure based on close packed lattices: The crystalline structure of many compounds can be described as a lattice of atoms with its interstitial sites filled with one or several different atoms. CRYSTALLINE STRUCTURE FCC These arrangements (CaF 2 , ZnS, NaCl…) define some structure types that can be adopted by many other compounds of different compositions.
Background image of page 2
U of A MSE 110 The NaCl structure can then be seen as two intertwined FCC lattices shifted by ½ cell parameter. CRYSTALLINE STRUCTURE The structure of sodium chloride is referred to as the rocksalt structure. It is a very important structure type adopted by many other compounds. The Na or Cl can sit as the unit cell corner atom equivalently as both atoms form an equivalent FCC lattice. Crystal structure based on FCC: NaCl It is based on a FCC lattice with all four octahedral site filled with another atom. Since there are four atoms in the FCC unit cell, the resulting composition is one to
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 14

LECTURE 17 Crystalline compounds - SUMMARY FROM LAST CLASS...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online