We report the growth of single-phase (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated ⟨001⟩ oriented SrTiO3 substrates by using pulsed laser deposition. Films grown at 600°C under low laser fluence exhibit a ⟨001⟩ textured columnar grained nanostructure, which coalesce with increasing deposition temperature, leading to a uniform fully epitaxial highly stoichiometric film at 750°C. However, films deposited at lower temperatures exhibit compositional fluctuations as verified by Rutherford backscattering spectroscopy. The epitaxial films of 400–600nm thickness have a room temperature relative permittivity of ∼750 and a loss tangent of ∼6% at 1kHz. The room temperature remnant polarization of the films is 4μC∕cm2, while the saturation polarization is 7.1μC∕cm2 at 24kV∕cm and the coercive field is ∼7.3kV∕cm. The results indicate that approximately 50% of the bulk permittivity and 20% of bulk spontaneous polarization can be retained in submicron epitaxial KNN-LT-LS thin film, respectively. The conductivity of the films remains to be a challenge as evidenced by the high loss tangent, leakage currents, and broad hysteresis loops.

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.

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNNLT- LS(K(0.44)Na(0.52)Li(0.04))(Nb(0.84)Ta(0.10)S(0.06)b)O(3) powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and k(t) of 0.50, the KNN-LT-LS composition may be a good candidate for high frequency transducer applications. PZT fibers with 25 microm diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged k(t) = 0.64 and d(33) = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The -6 dB bandwidth and insertion loss were 70% and -21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 ohm and higher thickness coupling coefficient of the ceramic transducer.

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