AAndré Guinier and his followers have introduced, using original techniques involving small-angle X-ray scattering and large-angle X-ray diffuse scattering, methods for a fine analysis of organisation and local order in various states of matter. The general philosophy consisted in giving the utmost attention to the departures from perfect crystalline order. In a first stage the studies, frequently issued from metallurgy, concerned small deviations around crystalline perfection (Guinier-Preston zones, solid solutions, etc.) but also concerned examples for which only local order persists (metallic amorphous materials).
The experimental study of defects in solids, in particular created by irradiation, gradually evolved towards the study of structural instabilities and phase transitions in insulators (for instance, ferroelectricity in perovskites), one-dimensional conductors (charge density waves and Peierls transition), quasi-periodic structures (incommensurate modulated phases, quasi-crystals) and ill-organised matter (soft matter and biological objects). Researches have more and more benefited from the use of techniques connected to great instruments (neutron scattering, synchrotron radiation).