X-ray and neutron diffraction are the most powerful experimental methods for determining a crystal structure, and the bonds between atoms can only be elucidated by using them.
Polymorphism is the phenomenon in which different kinds of crystals of a solid-state compound are obtained in which the atomic arrangements are not the same .
Changes between different polymorphous phases with variations in temperature and/or pressure, or phase transitions, are an interesting and important problem in solid-state chemistry or physics.