Question

Effect of temperature and pressure on crystal structure

Answer 1

Keep 2 things in mind, while dealing with crystal structure.
Temperature increases, atoms or molecules gain energy, they vibrate, they mive far apart, and finally becomes fluid( melts).
Increase pressure, atoms come closer, they cannot move, and they become more rigid.

Cordination number of an atom/molecule is the number of atoms or molecules touching or in contact with the atom.

There coordination number changes on heating ....coordination number decreases , as atoms move far apart, and change in lattice takes place on heating the solid , as atoms go far away. The lattice structure may change.
Reverse is true for an increasing pressure ..Atoms come close, cordination number increases. further heating of crystalline solid it undergoes melting at its melting point and on sudden cooling i.e on quenching it becomes amorphous solid.