 Solution

ID: past-exam-of-the-condensed-matter-physics-course-of-the-university-of-oxford/2012/1/d/solution

(100)

reflection:

a_{P} = \frac{0.154 nm}{2 s i n 14.8 5 ^{\circ}} = 0.30044 nm .

Conserve the number of NaCl formula units. The low-pressure conventional unit cell contains four, whereas the high-pressure cell contains one. The volume per formula unit changes from

a_{0}^{3} /4

a_{P}^{3}

, so

\frac{V _{P}}{V _{0}} = 4 (\frac{a _{P}}{a _{0}})^{3} ≃ 0.605.

The sample contracts by about

39.5%

. Comparing

a_{P}^{3}

directly with

a_{0}^{3}

would compare different amounts of material.

 New to topics? Read the docs here!