Low-temperature transition in barium sodium nioba

In order to examine a low-temperature transition in barium sodium niobate (Formula presented)(Formula presented)(Formula presented) (BSN), an in situ observation was made in the temperature range between room temperature and 25 K by a transmission electron microscope. It was revealed that satellite reflection spots characterizing the incommensurate structure, which appear around 573 K, do not disappear even around 25 K. On the other hand, it was found that microdomains elongating along the [010] direction with a width of about 10 nm appear around 200 K, together with the appearance of both new satellite spots at the (h, k, l+1/2) points with h, k, l integers and new faint diffuse streaks through the (h, k+1/2, l+1/2) points along the [100] direction. It is concluded that the low-temperature transition in BSN is a transition from the 1q quasicommensurate state to the 2q one in which two modulated waves arise along the [100] and [010] directions.