# Homework Help: A problem from crystallography

1. Aug 24, 2011

### vrinda mukund

1. The problem statement, all variables and given/known data

In a tetragonal lattice a=b=0.25 nm and c= 0.18nm, deduce the spacing between (1,1,1) planes.

2. Relevant equations

the basic equation in this case is

$$d=\frac{a}{\sqrt{h^2+k^2+l^2}}$$
3. The attempt at a solution

here in the question we are provided with the h,k,l value. my doubt is how to find lattice constant a. for a tetragonal crystal we are having diffrent values for c and a,b. so the lattice constant will not be the same through out the crystal, rite? how to solve this?

Last edited: Aug 24, 2011
2. Sep 2, 2011

### nickjer

Use:
$$d = \frac{2\pi}{\left|\vec{G}\right|}$$
Where $\vec{G}$ is just the shortest reciprocal lattice vector orthogonal to that plane.

I suggest first finding the three reciprocal primitive vectors. And then construct the shortest reciprocal lattice vector orthogonal to the (1,1,1) planes from those.