Dielectric and ferroelectric properties of tetragonal tungsten bronze Sr2-xCaxNaNb5O15 (x=0.05-0.35) ceramics

This letter reports the dielectric and ferroelectric properties of tungsten bronze Sr2-xCaxNaNb5O15 (SCNN, x=0.05-0.35) ceramics. Two dielectric anomalies and a diffuse ferroelectric transition behavior were appreciably observed in the compositions of x=0.05-0.25. The incorporation of smaller calcium cations into the crystal structure resulted in an increase in the Curie temperature, from 279 (x=0.05) to 297 (x=0.35), and a decrease in the permittivity, from 1353 to 543, at their respective Curie temperatures. Ferroelectricity was observed in the compositions with x=0.05-0.25, but absent in the compositions with x=0.30 and 0.35 at room temperature. The maximum spontaneous polarization P-s of 9.1 muC/cm(2) and remanent polarization P-r of 3.0 muC/cm(2) were achieved in the composition of x=0.15. (C) 2002 American Institute of Physics.