Question

Name the parameters that characterise a unit cell.

Answer 1

Unit cell

Unit cell is a portion of crystal lattice which on repetition leads to crystal structure. It has all the characteristics of crystal lattice. The unit cell is characterized by three distances along the three edges of the lattice and the angles between them.

Parameters that characterise a unit cell

The parameters that characterize a unit cell are

• Axial distances or edge lengths along the three edges $a,b\text{and}c$. These edges may or may not be equal and mutually perpendicular.
• Axial angles between the edges, $\alpha$ (between $b\text{and}c),\beta$ (between $a\text{and}c$), $\gamma$ (between $a\text{and}b$).

Thus, a unit cell is characterised by six parameters i.e., $a,b,c,\alpha ,\beta \text{and}\gamma$.

Final answer: Edge lengths of unit cell ($a,b,c$) and angles between edges ($\alpha ,\beta ,\gamma$).