FORMATION OF LONG–RANGE ORDER NEAR THE SECOND–ORDER PHASE TRANSITION TEMPERATURE IN (NbSe4)3I

Abstract

The static critical behavior near the second-order displacive phase transition temperature Tc =274 K in (NbSe4)3I was investigated by means of the X-ray diffraction technique. The diffuse scattering from the soft-phonon modes, especially B mode above Tc, were measured along the a* direction around (0 3 6) point. The obtained critical exponents are β=0.36±0.01, γ=0.56±0.04 and v=0.61±0.05. The temperature dependence of the full width of the half maximum of the thermal diffuse scattering clarified the formation of the long-range order near Tc.