The terminology "Peierls distortion ͑PD͒" has been widely accepted in disordered systems ever since the discovery of PD in liquid As ͓R. Bellissent et al., Phys. Rev. Lett. 59, 661 ͑1987͔͒. It has not been clarified, however, to what extent the PD in liquids mirrors the PD in crystals. Here we report the observation on the pressure-induced suppression of PD in liquid As and liquid GeX ͑X =S,Se,Te͒, by which we clarified the qualitative differences as well as similarities between the PD of liquid and crystalline systems. By the appearance of prepeak that accompanies PD, we show that the intermediate-range order is related to the "Peierls distortion" in liquids, just as the Peierls distortion doubles the periodicity in one-dimensional lattice model.

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X-ray diffraction of liquid CuI, CuBr and CuCl has been measured up to 19 GPa using synchrotron radiations. Static structure factor S(Q) and pair distribution function g(r) were obtained. For liquid CuI, CuBr and CuCl, S(Q) and g(r) change their shapes continuously with increasing pressure, indicating anisotropic compression of the local structures. The pressure dependence of the peak position ratio r(2)/r(1) of g(r) shows that Cu atoms are located in a tetrahedral site at low pressures and then in an octahedral site at high pressures in these liquid copper halides. At higher pressures, the local structure of liquid CuCl is similar to the intermediate structure between NaCl and CsCl structures. These results are compared with the pressure-induced structural transformation in the crystalline phase.