ALKALI STRONTIUM-BARIUM-LEAD NIOBATE SYSTEMS WITH A TUNGSTEN BRONZE STRUCTURE - CRYSTALLOGRAPHIC PROPERTIES AND CURIE POINTS

Crystallographic parameters, Curie points, and freezing temperatures are presented for a series of A+A22+Nb5O15 compositions with tungsten bronze‐related structures, where A+=Na, K, or Rb, and A2+=Sr or Ba. Results are also reported for bronze solid solutions in the systems KNbO3‐PbNb2O6, K(Sr‐Ba)2Nb5O15, K(Ba‐Pb)2Nb5O15, K(Sr‐Pb)2Nb5O15, and (KSr2‐K2La)Nb5O15. On the basis of these data, an empirical relation is shown between the ferroelectric transition temperature, Tc, and axial ratio °10 co/a0. The Tc vs °10 c0/a0 curve for compositions with polar axes perpendicular to [00l] has a negative slope, whereas that for compositions with polar axes parallel to [00l] has a positive slope of about the same magnitude. These results are compared with measurements of the temperature dependence of c0/a0 for KSrPbNb5O15, and KBa2Nb5O15; the latter is discussed in terms of the Devonshire free energy theory. Copyright © 1969, Wiley Blackwell. All rights reserved