- #1

unscientific

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## Homework Statement

[/B]

(a) Show Compression of FCC leads to BCC.

(b) State rules for X-rays reflection in FCC.

(c) What are the new Miller Indices after compression?

## Homework Equations

## The Attempt at a Solution

__Part(a)__[/B]

I'm quite confused as to what they mean by 'principal axes'.

For an FCC lattice, the basis is given by ##[0,0,0]## and ##[\frac{1}{2},\frac{1}{2},0]## and ##[\frac{1}{2},0,\frac{1}{2}]## and ##[0,\frac{1}{2},\frac{1}{2}]##..

The primitive lattice vectors are ##\left( \frac{1}{2} \hat x + \frac{1}{2}\hat y + 0 \hat z \right)## and ##\left( \frac{1}{2} \hat x + 0 \hat y + \frac{1}{2} \hat z \right)## and ##\left( 0 \hat x + \frac{1}{2} \hat y + \frac{1}{2} \hat z \right)##.

Are the principal axes the ##x,y,z## axes?

I'm not sure how the Bain compression changes FCC to BCC:

__Part(b)__Structure Factor for FCC is ##S_{(hkl)} = f_{fcc} \left[1 + (-1)^{h+k} + (-1)^{h+l} + (-1)^{k+l} \right]##. For reflection to occur, rule is (hkl) must be

**or**

__all even__**.**

__all odd__Structure Factor for BCC is ##S_{(hkl)} = f_{bcc} \left[1 + (-1)^{h+k+l} \right]##. For reflection to occur, rule is (h+k+l) must be

**.**

__even__

__Part(c)__How does compression change the miller indices?