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.

Novel electroactive nanostructured silver molybdenum oxyfluoride (SMOF) perovskites Ag1+ 3Mo6+(O3F3) have been successfully synthesized by a mechanochemical reaction. The formation of this perovskite was investigated throughout the Ag−Mo composition range with the use of either Ag1+ or Ag2+ in the form of AgF and AgF2 as the reactant, respectively. The compositional study combined with X-ray diffraction and extensive Raman investigation was utilized to determine structure and cation distribution and infer oxidation state. Finally, preliminary electrochemical characterization of the perovskites vs lithium was investigated.

There has been a significant driving force to eliminate the utilization, recycling, and disposal of ferroelectric ceramics with high content of toxic element (Pb). Recently, the ternary system of KNN-LT-LS has proven to be an outstanding lead-free piezoceramic with properties almost comparable to their lead-based counterpart, PZT. This study reports the effect of various processing conditions on the electromechanical properties of (K 0.44 Na 0.52 Li 0.04 )(Nb 0.84 Ta 0.10 Sb 0.06 )O 3 system. This includes powder processing, humidity, and exposure to oxygen rich environment during sintering. The Perovskite and Mixed-Oxide methods are used to prepare the stoichiometric powders. It will be shown that both processing methods are notably sensitive to the moisture of as received raw materials and the humidity of environment. Optimum results are obtained when the raw materials undergo a pre-heat treatment followed by formulating the desired composition in an inert atmosphere. The highest electromechanical properties are achieved when the ceramics are completely exposed to oxygen with a high flow rate. Sintered at 1150°C for 1 h with an oxygen flow rate of 180 cm 3 /min, the KNN-LT-LS ceramics prepared by Perovskite and Mixed-Oxide routes have d 33 ≥300 pC/N, " T 33 ¼ 1865, tan δ=0.02, k 33 =0.65.

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