Crystal Structures EMA3050

cubic crystal structure

tetragonal crystal structure

orthorhomic crystal structure

hexagonal crystal structure

Monoclinic crystal structure

Triclinic crystal structure

How to find crystallographic planes (for cubic)

1. Identify instersections → If it passes through the origin move the origin

2. Take reciprocals of intercepts

3. Clear fractions

4. Enclose in parenthesis

Find HCP vector

1. Find direction using a₁ , a₂ , and c

2. Find head point 

3. Find tail point

4. take head - tail

5. Put in [h k i l] form where k = -(h+k)

Fnd planes in hexgonal HCP

1. Use a₁ , a₂ , and c to find intercepts

2. Take reciprocal of intercept

3. Convert to 4 index (h k i l)

What is the coord number

number of nearest nieghbor atoms

APF of FCC and HCP

74%

What can the ratio of atomic radii of cations to anions tell you about binary structures

It can tell you the CN and thus the structure 

(probably not on exam)

[NaCl]

[FCC] + octahedral (edge sharing)

[diamond] & [zincblend]

[FCC] + ½ tetrahedral (corner sharing)

Note: for diamond r = asqr(3)/4

[flourite] , [antifluorite]  

[FCC] + tetrahedral (edge sharing) 

[nickel arsenide]

[HCP] + ½ octahedral sites (corner sharing)

[wurtzite]

[HCP] + ½ tetrahedral (corner sharing)

[rutile]

[HCP] + ½ octehedral sites (edge sharing)

[corundum]

[HCP] + ²/₃ octahedral sites (face sharing) 

What are Pauling’s Rules