Incommensurate phase transition in sodium nitrite: A study of the dynamics by neutron spin echo technique

Abstract

NaNO2 is a model system for crystals undergoing an incommensurate order-disorder phase transition. In this case, the incommensurate phase transition is charaterized by a relaxational mode which exhibits critical slowing-down. We have performed neutron experiments to study the pretransitional fluctuations and the dynamics in the modulated phase. The order of magnitude of relaxation times being 109 s, we used a high resolution technique: neutron spin-echo. Surprisingly, it has been found that the relaxation process contains a fast and a "central peak"-type slow component. It appears that previous macroscopic measurements, interpreted in terms of a single relaxation time model, produced intermediate effective relaxation rates.