lec-26-Chap11-3_4-1

# lec-26-Chap11-3_4-1 - Crystalline Solids 2d unit cell...

This preview shows pages 1–2. Sign up to view the full content.

1 48 Crystalline Solids 2 d unit cell unit cell example: • The unit cell is a square. • Each corner contributes ¼ of a circle to the unit cell. • Net of 1 circle/unit cell. • The entire lattice can be formed by adding unit cells to each face 49 Cubic Unit Cells Crystals have 3 d unit cells. There are 7 types . The simplest are the cubic cells with 3 subtypes: – simple (or primitive) cubic (sc). – body-centered cubic (bcc). – face-centered cubic (fcc). Faces meet at 90° with equal-length sides. 50 Cubic Unit Cells Primitive (simple) cubic Primitive (simple) cubic (sc) • Atoms sit at the corners of squares. • Layers stack atom-on-atom. • One atom/cell (8 x 1/8). • Atoms occupy 52 % of the total V . 1 3 2 4 5 6 at rear Each atom has 6 equivalent neighbors: 51 Cubic Unit Cells Body Body -centered cubic centered cubic (bcc) (bcc) • An extra (unshared) atom sits in the center • (8 x 1/8 ) + 1 = 2 atoms/cell 68 % of the space is occupied. 52 Cubic Unit Cells Face Face -centered cubic centered cubic (fcc fcc ) 1 atom at the center of each face. Face atoms are shared by 2 cells. (corner atoms are shared by 4 cells) (6 x ½ + 8 x 1/8 ) = 4 atoms/cell. 74 % of the space is filled by atoms 53 Closest Packing of Spheres Metal crystals have equal-sized atoms (spheres).

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

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 5

lec-26-Chap11-3_4-1 - Crystalline Solids 2d unit cell...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online