Synthesis and sintering improvement of Aurivillius type structure ferroelectric ceramics by mechanochemical activation
1999; Royal Society of Chemistry; Volume: 9; Issue: 6 Linguagem: Inglês
10.1039/a902492a
ISSN1364-5501
AutoresA. Castro, P. Millán, L. Pardo, Basílio Jiménez,
Tópico(s)Liquid Crystal Research Advancements
ResumoAn oxide mixture of composition 3Bi 2 O 3 :Nb 2 O 5 :2TiO 2 has been mechanochemically activated in a laboratory mill for different times from 3 to 336 h. The as-milled powder and an unmilled mixture of identical composition were annealed at different temperatures up to the formation of the Aurivillius-type oxide Bi 3 NbTiO 9 , and examined by X-ray diffraction (XRD) and differential thermal analysis (DTA). The sample milled for 336 h shows complete amorphization. Its DTA curve exhibits two exothermic process at 370 and 560 °C, corresponding to the formation of a metastable fluorite phase and the Aurivillius-type oxide, respectively. The crystallization temperature of this Aurivillius phase from the unmilled oxide mixture is reported to be 1050 °C, whereas from the amorphous powder obtained by 336 h of mechanochemical activation this temperature becomes as low as 600 °C. Ceramics of this composition must be prepared by hot-pressing in order to obtain low porosities, owing to the lamellar morphology of the conventionally crystallized powder, which gives rise to textured anisotropic materials. Non-textured ceramics were obtained both from the conventionally crystallized and the amorphous powder by natural sintering at 1100 °C. Ceramics obtained from amorphous powder show lower porosity and higher electromechanical coupling factors.
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