EFFECT OF GADOLINIUM CONTENT ON THE THERMAL VOLUME CHANGE OF BA4NA2NB10O30-BA3NAGDNB10O30 SOLID-SOLUTIONS AT FERROELECTRIC PHASE-TRANSITION TEMPERATURE

For sintered samples of Ba3+x Na1+xGd1-xNb10O30 (1 ≥x ≥ 0), the effect of the addition of gadolinium to barium sodium niobate (BNN, x = 1, tungsten bronze type) was examined by differential scanning calorimetry (DSC) and X-ray powder diffractometry. The volume change (i.e. especially the change of c-axis length) at the ferroelectric phase transition temperature (Tc< 590 dg C) decreased with the increasing gadolinium content. This result suggests that the addition of gadolinium or other lanthanide elements to BNN is possibly effective to obtain an uncracked single crystal with the Czochralski technique. The DSC indicator method is useful to determine the relative magnitude of volume change at Tc for the same type of sample series, a method which is much easier than the dilatometer method. The relation between the DSC peak area and the volume change of unit cell at Tc is discussed from the thermodynamic viewpoint. © 1990 Chapman and Hall Ltd.