A 1985 Hewlett-Packard Europhysics Prize Winner Continuous phase transitions and the associated critical phenomena have been one of the most active areas of research in condensed matter physics for several decades. This short review can only be one cut through this huge subject and we have chosen to emphasize dif fraction studies as a basic experimental method and illustrate how diffraction experiments have revealed the role of dimensionality in the general classification of phase transitions.

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... n Elementary Example : β-Brass Beta-brass Is an alloy of Cu and Zn In almost equal amounts. The crystalline structure is body centred cubic and at room temperature, Cu atoms (open circles in Fig. 1B ) occupy the cube cor ners, whereas Zn atoms (hatched) oc cupy cube centres. In the elementary argument for scattering of X-rays from a crystalline structure one considers the interference between a ray scattered from the top layer of atoms with that scattered from the next layer, and so on.