Synchrotron x-ray diffraction has been used to study the surface reconstruction of W(001) through its phase transition at around 230 K. We find that, although the superlattice peak intensity decreases a thousand fold over the range studied, the integrated intensity, and hence the structure factor, is nearly constant. This indicates that the surface undergoes an order-disorder transition with little change in the magnitude of the atomic displacements. The critical behavior is compared with predictions of the 2D XY and Ising models.

• Received 23 August 1988

DOI:https://doi.org/10.1103/PhysRevLett.62.1294