Bulk (Na0.5 Bi0.5)1-x BaxTiO3 (NBT-BT) materials have been prepared in the composition range between pure NBT and the morphotropic phase boundary included, 0 <=x<=0.08. The materials are obtained by the conventional solid state reaction of the starting oxides. Reliability and reproducibility are still issues for these complex systems and careful control of every processing parameters from raw materials purity and granulometry to intermediate steps of mixing and homogenisation must be assessed. The main issues affecting the dielectric and ferroelectric properties are cation ordering, stoichiometry and related defects providing ionized electronic charges. The more critical parameter is the Bi or Na loss that can be affected by the sintering conditions, especially by the surrounding atmosphere. The dynamic Young's modulus of ceramic NBT has been measured between 100 and 920 K and anelastic spectra of samples of NBT prepared in different ways are presented and discussed. This perovskite ferroelectric has disorder in the Na+/Bi3+ sublattice and two phase transitions: i) from rhombohedral ferroelectric (R-FE) to tetragonal antiferroelectric (T-AFE) with a broad coexistence region between 530 and 670 K and ii) to cubic (C) at TT-C = 820 K. The rhombohedral and tetragonal phases involve rotations of the octahedra about their pseudocubic [111] and [001] axes, respectively. On the other hand, the dielectric susceptibility is known to display: i) a ferroelectric transition only during heating from the poled state, generally below 500 K; ii) a broad peak in correspondence with the coexistence of R-FE with T-AFE, iii) no anomaly at the transition to cubic. In spite of ample evidence of disorder and structural heterogeneity, the R-T transition remains sharp up to x=0.06, whereas the T-C transition merges into the diffuse and relaxor like transition associated with broad maxima of the dielectric and elastic susceptibilities. Powder processing steps will be focused and examples of the effects on the electromechanical properties will be discussed
Processing features and structural transformations in the ferroelectric perovskite Na0.5Bi0.5TiO3-BaTiO3
Galassi Carmen;Cordero Francesco;Craciun Floriana;Capiani Claudio;Baldisserri Carlo
2011
Abstract
Bulk (Na0.5 Bi0.5)1-x BaxTiO3 (NBT-BT) materials have been prepared in the composition range between pure NBT and the morphotropic phase boundary included, 0 <=x<=0.08. The materials are obtained by the conventional solid state reaction of the starting oxides. Reliability and reproducibility are still issues for these complex systems and careful control of every processing parameters from raw materials purity and granulometry to intermediate steps of mixing and homogenisation must be assessed. The main issues affecting the dielectric and ferroelectric properties are cation ordering, stoichiometry and related defects providing ionized electronic charges. The more critical parameter is the Bi or Na loss that can be affected by the sintering conditions, especially by the surrounding atmosphere. The dynamic Young's modulus of ceramic NBT has been measured between 100 and 920 K and anelastic spectra of samples of NBT prepared in different ways are presented and discussed. This perovskite ferroelectric has disorder in the Na+/Bi3+ sublattice and two phase transitions: i) from rhombohedral ferroelectric (R-FE) to tetragonal antiferroelectric (T-AFE) with a broad coexistence region between 530 and 670 K and ii) to cubic (C) at TT-C = 820 K. The rhombohedral and tetragonal phases involve rotations of the octahedra about their pseudocubic [111] and [001] axes, respectively. On the other hand, the dielectric susceptibility is known to display: i) a ferroelectric transition only during heating from the poled state, generally below 500 K; ii) a broad peak in correspondence with the coexistence of R-FE with T-AFE, iii) no anomaly at the transition to cubic. In spite of ample evidence of disorder and structural heterogeneity, the R-T transition remains sharp up to x=0.06, whereas the T-C transition merges into the diffuse and relaxor like transition associated with broad maxima of the dielectric and elastic susceptibilities. Powder processing steps will be focused and examples of the effects on the electromechanical properties will be discussedI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
