Effects of defects on the incommensurate phase of sodium nitrite crystals.

Abstract

Specific-heat measurements on virgin and \ensuremath{\gamma}-ray\char21{}irradiated single crystals of ${\mathrm{NaNO}}_{2}$ have been carried out to study the effects of defects on the incommensurate phase. Observation of a small specific-heat anomaly at a temperature just above the commensurate-incommensurate (CI) phase-transition point is reported for the first time. It is suggested that this new anomaly may be evidence for a defect-induced intermediate state between the commensurate and incommensurate phases. We discuss qualitatively the observed new anomaly and thermal hysteresis in the CI phase transition.