| 2q | I (obs) |
|---|---|
| 7.5 | 67 |
| 8.07 | 7727 |
| 10.25 | 3634 |
| 11.77 | 104 |
| 14.82 | 1731 |
| 15.05 | 557 |
| 16.09 | 199 |
| 16.64 | 108 |
| 16.9 | 448 |
| 17.15 | 1861 |
| 18.07 | 740 |
| 18.27 | 185 |
| 18.81 | 2587 |
| 19.36 | 1031 |
| 20.63 | 680 |
| 20.84 | 65 |
| 22.67 | 228 |
| 23.45 | 626 |
| 24.27 | 1793 |
| 24.41 | 135 |
a = 23.742 Å, b = 6.176 Å, c =
11.035 Å
a = 90°, b = 97.88°, g = 90°
Crystal system is monoclinic as a¹b¹c and a=g = 90°, b¹90°
Excellent
5 Marks
2. Bravais lattice type will be mP because the crystal system is monoclinic and the lattice type is type is primitive.
Correct, but a much fuller justification is
required here.
2 Marks
3. From hkl program space group is P2/m which does not have screw axes or glide planes therefore there are no reflection conditions.
Comment:
You have to compare the output for P2/m with what
you observe in the data. In particular you need to check h0l and 0k0
reflections.
0 Marks
4. Space group is P2/m.
Comment:
See model answer.
0 Marks
5.
| 2q | h | k | l | 2q | h | k | l | 2q | h | k | l | ||
| 7.50 | 2 | 0 | 0 | 14.82 | 1 | 1 | 0 | 16.90 | -2 | 0 | 2 | ||
| 8.07 | 0 | 0 | 1 | 15.05 | 4 | 0 | 0 | 17.15 | 1 | 1 | 1 | ||
| 10.25 | -2 | 0 | 1 | 16.09 | -4 | 0 | 1 | 18.07 | 4 | 0 | 1 | ||
| 11.77 | 2 | 0 | 1 | 16.64 | -1 | 1 | 1 | 18.27 | 3 | 1 | 0 |
| a (Å) | b (Å) | c (Å) | a (°) | b (°) | g (°) | |
| Value | 23.72951 | 6.17132 | 11.03174 | 89.9869 | 97.9013 | 90.0200 |
| ESD | 0.00928 | 0.00333 | 0.00518 | 0.0461 | 0.0176 | 0.0350 |
Comment: When the symmetry is monoclinic, you must refine as such, i.e. you must make sure that the 90° angles are fixed. In addition, you should give an appropriate number of decimal places (that depend on the magnitude of the esd value).
2qzero = -0.0135 ± 0.0053
You need to comment on the value here.
The peaks are very weak in the high angle region so cannot include the high
angle data and greater error is caused at high angles by the the diffractometer
as collecting data.
Comment:
See model answer for second reason.
4 Marks