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Multilayer actuators for high temperature piezoelectric applications
Keywords: multilayer, actuator, high TC
Pb(Zr,Ti)O3 has been the dominant base of piezoelectric ceramics for the fabrication of monolithic and multilayer actuators since the 196o’s. It is incredibly versatile and its properties can be tailored to suit a wide variety of applications by the use of suitable dopants. However, it is fundamentally limited to an upper operating temperature of ~ 250-300 oC due to issues of depoling under high drive fields as the ferroelectric phase transition temperature (TC) is approached. In undoped compositions, TC = 380 oC but the piezoelectric coefficient (d33) is low (<<200 pC/N) All dopants which enhance d33 also reduce TC. Thus, no commercial PZT based ceramics are sold with a TC significantly higher than ~350 oC. In 2001, Eitel, Randall, Shrout and co-workers published the first data on a new family of high TC piezoelectrics based on BiScO3 – PbTiO3 (TC = 450 oC, d33 = 450 pC/N). To date however, there has been zero commercial uptake of this composition due to the excessive cost of Sc2O3. At Sheffield, as at other institutes, there has been a protracted effort to eliminate Sc2O3 from compositions but no Sc2O3 free, high TC candidate has yet emerged. Recent work however, by Sebastian et al (2010) has revealed a compromise solution in which the Sc2O3 content is reduced to half that in the original Eitel compositions for an acceptable deterioration in performance. Compositions based on the pseudo-quaternary system, 0.5(0.3BiFeO3 – 0.35BiMg1/2Ti1/2O3 – 0.35BiScO3) – 0.5PbTiO3 show great promise with d33 = 380 pC/N and TC = 450 oC. Moreover, the phase assemblage of these compounds may be reproducibly controlled with little or no second phase observed even for rhombohedral compositions. Compositions within this solid solution have also been used to form multilayer actuators using initially Pt internal electrodes with excellent performance at room and high temperature. The presentation assesses the merits of various candidate materials for high TC piezoelectric applications and describes the key issues surrounding their scale-up for the fabrication of multilayer actuators.
Ian M Reaney, Professor
University of Sheffield
Sheffield, south yorkshire
UK


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