Relaxor nature in lead-free Sr5LaTi3Nb7O30 tetragonal tungsten bronze ceramics

Abstract

Lead-free tetragonal tungsten bronze Sr5LaTi3Nb7O30 ceramics were prepared and the correlation of the relaxor nature and crystal structure was studied using dielectric spectroscopy and powder X-ray diffraction. Three dielectric relaxations were observed below the deviation temperature T-D similar to 330 K. Relaxation I and II followed the Vogel-Fulcher law with the freezing temperatures of 189 K and similar to 90 K. Low temperature relaxation III, which was first observed in filled tungsten bronze, followed well the Arrhenius law. Dielectric response becomes static below 50 K. Polarization-field (P-E) hysteresis loops were evaluated from 183 K to 298 K. P-r value of 0.41 mu C/cm(2) was observed at 183 K. Deviation of lattice parameter c from the linear contraction and increasing of tetragonality (c/a ratio) were observed below T-D, reflecting the structure change during the formation of polar nanoregions and the following freezing process. Opposite tendency was observed below 100 K for all the lattice parameters, corresponding to relaxation III. Generally, the main dielectric relaxation I and II were attributed to flipping and breathing of polar nanoregions along c axis, while the concerted rotations of the oxygen octahedra in the ab plane were suggested as the origin of relaxation III. (C) 2013 AIP Publishing LLC.