Formation of long-range order near the second-order phase transition temperature in (NbSe 4) 3I

Abstract

The static critical behavior near the second-order displacive phase transition temperature T c =274 K in (NbSe 4) 3I was investigated by means of the X-ray diffraction technique. The diffuse scattering from the soft-phonon modes, especially B 1u mode above T c, were measured along the a ∗ direction around (0 3 6) point. The obtained critical exponents are beta;=0.36±0.01, γ=0.56±0.04 and υ=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 T c.