Effects of A1/A2-Sites Occupancy upon Ferroelectric Transition in ( Sr x Ba1 −x) Nb2 O6 Tungsten Bronze Ceramics.

The dielectric and ferroelectric characteristics of ( Sr x Ba1− x) Nb2 O6 unfilled tungsten bronze ceramics have been investigated together with the structure. The dielectric and ferroelectric characteristics of the present ceramics vary significantly with x, and the A1/A2-sites occupancy has been determined as the primary parameter governing this variation tendency. Ba ions tend to occupy A2-sites, Sr ions tend to occupy A1-sites, and one A1-site is empty. When the ratio of Sr/ Ba is close to 1:4 (where four A2-sites are just occupied by Ba ions, and one A1-site is occupied by Sr ion while another A1-site is empty), the normal ferroelectric transition is observed with one anomaly in the tanδ- T curve ( x = 0.25). When the ratio of Sr/ Ba is far away from 1:4, the typical relaxor behavior is indicated together with three anomalies in the tanδ- T curve ( x = 0.75). The incommensurate oxygen octahedral tilting and A-site random distribution are considered to be the structure origins for the relaxor ferroelectricity and low temperature dielectric relaxations. [ABSTRACT FROM AUTHOR]