abstract
The dielectric and relaxor properties of Ba5SmFe1.5Nb8.5O30 tungsten bronze ceramics were investigated together with the crystal structure. Tetragonal filled tungsten bronze structure was in space group P4bm with lattice parameters of a=b=12.527(6) angstrom, c=3.955(2) angstrom. Three dielectric relaxations were observed in the temperature range from 128 to 623 K. A temperature stable dielectric constant plateau (similar to 2.5x10(3)) was observed between the middle and high temperature relaxations. The low temperature dielectric relaxation (similar to 250 K) illustrated a typical relaxor ferroelectric behaviour. The middle temperature dielectric relaxation (dispersing from similar to 150 to 450 K) and the high temperature dielectric relaxation (>500 K) were Debye type thermal active processes. The middle temperature relaxation had an active energy with a magnitude of 10(-1) eV, and a relaxation frequency of similar to 10(8) Hz was attributed to the inhomogeneous structure. The high temperature relaxation with an active energy similar to 1.4 eV and a relaxation frequency similar to 10(16) Hz was attributed to the electrode polarisation. Introduction of Fe ions generates large and temperature stable dielectric constant between the middle temperature and high temperature relaxations, disturbs the polarisation ordering and depresses the ferroelectric relaxation temperature.
keywords
SYSTEM; PERMITTIVITY
subject category
Materials Science
authors
Zhu, XL; Bai, Y; Liu, XQ; Chen, XM
our authors
Xiaoli Zhu
Post-doc FellowshipGroups
acknowledgements
This work was partially supported by National Science Foundation of China under grant nos. 50832005, 51102210 and 90922024. X.L. Zhu acknowledges FCT for financial support (grant no. SFRH/BPD/82534/2011).