title: Lead-free piezoelectric ceramic transducer in the donor-doped K1/2Na1/2NbO3 solid solution system.
abstract: Lead-based piezoelectric ceramics are suitable materials for noninvasive applications of ultrasound in medicine. However, the embedded therapeutic and diagnostic procedures require the use of lead-free piezoelectric materials as active elements in transducers. With this goal in mind, we investigated the substitution of Ba(2+) cations in a lead-free piezoelectric system of K(1/2)Na(1/2)NbO(3)-LiTaO(3)-LiSbO(3) (KNN-LT-LS) with perovskite structure. The Ba(2+) was added to the system as an A-site dopant in the range of 0-2 mol% in increments of 0.5 mol%. The addition of Ba(2+) improved the piezoelectric charge coefficient, d(33), and longitudinal coupling coefficient, k(33). The composition with 1 mol% Ba2+ had 36% and 58% higher d(33) and k(33), respectively, than the undoped composition. It appeared that the addition of Ba(2+) induced "soft" characteristics in this lead-free piezoelectric system. This was verified by the increase of remnant polarization along with the decline of coercive field. The Ba(2+) behaved as a grain growth inhibitor and caused a drastic reduction in polarization level (approximately 60%) when the grain size became smaller than approximately 1.5 microm. Incorporation of Ba(2+) up to 1.5 mol% increased the bulk resistivity of the KNN-LT-LS system and then reduced it drastically at higher dopant concentrations. The electron-hole compensation model fit well with the results obtained in this study and verified the A-site substitution of donor-doped barium. KNN-LT-LS ceramics with 0 mol% and 1 mol% Ba(2+) were used to fabricate single-element ultrasonic transducers resonating at 5.5 MHz. The -6 dB fractional bandwidth and -20 dB pulse length of the probe made of doped ceramic were 50% and 1.68 micros, respectively. This indicated that this system could be considered as a candidate for invasive and/or embedded medical ultrasound applications.
authors.affiliation: Department of Materials Science and Engineering, Rutgers, State Univ. of New Jersey, Piscataway, NJ 08854-8065, USA. nmhagh@rci.rutgers.edu
authors.forename: Nader Marandian
authors.initials: NM
authors.lastname: Hagh
authors.forename: Bahram
authors.initials: B
authors.lastname: Jadidian
authors.forename: Eric
authors.initials: E
authors.lastname: Ashbahian
authors.forename: Ahmad
authors.initials: A
authors.lastname: Safari
mesh_terms: D002516:Ceramics / Q000737:chemistry* / Q000528:radiation effects*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007854:Lead; D008422:Materials Testing; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012996:Solutions; D014159:Transducers; D014463:Ultrasonography / Q000295:instrumentation*
chemical_list: D012996:Solutions; D007854:Lead