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PIRAMID Résumé de rapport

Project ID: G5RD-CT-2001-00456
Financé au titre de: FP5-GROWTH
Pays: Denmark

Bi containing powder composition (low lead)

A new piezoelectric composition has been developed. Rather than the well-known PZT (i.e., Pb(Zr,Ti)O3) system, this composition belongs to a new system of the general form BiMe - PT (i.e., solid solution between BiMeO3 and PbTiO3, where Me signifies a metal ion or combination of metal ions with an effective valence of +3). In this system, a large part of the toxic heavy metal Pb is substituted by Bi, so these compositions have a lower environmental impact than PZT. With a proper choice of Me ion, this system furthermore shows very interesting properties, e.g. a high Curie point compared to the PZT system.

A number of Me ions are accommodated by the general formula, but within PIRAMID an important criterion has been the cost of precursors, in order to avoid that the price itself should prevent the exploitation of the composition. Therefore, such exotic Me ions as Sc3+ (previously reported in the literature) have been avoided and a combination of the form (Me1(II)_1/2,Me2(IV)_1/2) has been chosen on the basis of a similar average ionic radius. A very high Curie point of approximately 600ºC has been obtained for the most promising composition, but a phase transition close to 375ºC (probably ferroelectric-ferroelectric) seems to limit the operating temperature of this one (depolarisation occurs at 300ºC). Other relevant properties of this new composition include piezoelectric coefficients d33 and d31 of 100pC/N and -25 pC/N, respectively, free relative permittivity epsilon_r3{sigma)? 830 and thickness coupling factor k_t 0.3.

Although the BiMe?PT composition developed in PIRAMID is an example of an interesting new type of piezoceramic systems, the future exploitation will be limited by the competition on one side from the well-established doped PZT compositions and on the other side from Aurivillius compounds (Bi layer oxides). Since the piezoelectric properties of doped PZT are significantly higher (d_33 higher by a factor of 3 to 6, k_t higher by a factor of 1.5), the justification of the BiMe - PT composition (presently d_33 ?100 pC/N; k_t 0.3) should be an extended temperature range of operation compared to PZT, combined with enhanced properties in comparison with the Aurivillius compounds (d_33 < 20 pC/N, k_t = 0.2). As described above, however, the low-temperature phase transition at present makes it impossible to take advantage of the high Curie point. On the other hand, future work with dopants may make it possible to shift the former transition temperature to below room temperature. Such future development should be driven by a market demand for a new material filling in the gap between PZT and the Aurivillius compounds, and when this demand is sufficiently important, the experience gathered within PIRAMID will be very useful.


Erling RINGGAARD, (R&D Manager)
Tél.: +45-49127100
Fax: +45-49138188