The structure and dielectric properties of a new family of tetragonal tungsten bronze structured ceramics with the general formula, Ba2ReNb3Ti2O15 (BReNTO15,Re=Bi3+,La3+,Nd3+,Sm3+,Gd3+) have been investigated. BLNTO15 Tmax ~ -100 C) and BBNTO15 (Tmax ~ -80 C) exhibited relaxor-like dielectric behaviour with the maximum dielectric constants observed at Tm~-100 C and Tm~-80 C, respectively. In contrast, BNNTO15 (Curie temperature, Tc ~ 165 C), BSNTO15 (Tc ~ 250 C), and BGNTO15 (Tc ~ 320 C) were ordinary ferroelectrics. The Tm/Tc ratio increased with decreasing radius of the Re ion. Room-temperature X-ray powder diffraction patterns of all the compounds could be indexed according to a prototype P4/mbm (or P4bm) space group with lattice parameters a~12.4 A and c~4 A. However electron diffraction revealed that both BLNTO15 and BBNTO15 phases exhibit an incommensurate modulation, whereas BNNTO15, BSNTO15 and BGNTO15 feature an orthorhombic superstructure with lattice parameters a~b~aTTB 2 and c~2cTTB.
Citation: Journal of Applied Physics
Pub Type: Journals
ferroelectrics, relaxors, tetragonal tungsten bronzes