Abstract
The phase relations of the system Na(Nb1−xTax)O3 in the solid state are studied by means of the dielectric constant measurements, x-ray diffraction studies and optical observations.
The transition point vs. composition curve of this system exhibits a discontinuity in 0.55>x>0.54. The solid solutions with the composition range x≤0.54 show two transition temperatures, one of which was determined by the dielectric measurements and the other by the optical means. These two transition temperatures increase with increasing value of x showing a maximum near x=0.1, and then decrease monotonically. The room temperature phase is antiferroelectric in this range.
On the other hand, in the range x≥0.55 the dielectric anomaly corresponding to the ferroelectric Curie point exists below room temperature and it decreases monotonically with increasing value of x. Any dielectric anomaly, however, is not found in NaTaO3, and it may not be ferroelectric down to liquid helium temperature. Other three transitions at higher temperatures are observed only by optical means.
