INCOMMENSURATE PHASE IN BARIUM SODIUM NIOBATE - THERMAL-ANALYSIS STUDY

Differential-scanning-calorimetry measurements have been performed on single-crystalline barium sodium niobate from 400 to 900 K. Special attention was paid LO measurements in the temperature range 500-650 K. Three thermal peaks were detected; one was at 850 K near the ferroelectric transition temperature, the two others were at 532 K and 549 K, respectively, and their latent heat was estimated. A specific-heat-capacity anomaly was also observed at 590 K within experimental accuracy. These thermal anomalies are discussed in the framework of the available structure-transition and incommensurate-phase models.