Bong-Yeon Lee

Piezoelectric properties of high Curie temperature barium titanate-bismuth perovskite-type oxide system ceramics

Barium titanate (BaTiO3, BT)—bismuth magnesium titanium oxide [Bi(Mg0.5Ti0.5)O3, BMT] system ceramics were prepared in an ambient atmosphere in order to increase the Curie temperature (Tc) of BT above 132 °C. A single perovskite phase was observed for BT–BMT ceramics with BMT compositions less than 50 mol %, and their relative densities were greater than 94%. Synchrotron measured x-ray diffraction patterns revealed that all the cations in the ceramics were homogeneously distributed. The temperature dependence of the dielectric properties revealed that the BT–BMT system ceramics exhibited relaxorlike characteristics with a dielectric maximum temperature as high as 360 °C for the 0.5BT–0.5BMT ceramic. The apparent piezoelectric constant (d∗) was 60 pC/N for the 0.4BT–0.6BMT ceramic. Based upon these results, the BT–BMT system shows potential as a new type of lead-free material for high Tc piezoelectric applications.

Improvement in Ferroelectric Properties of Chemically Synthesized Lead-Free Piezoelectric (K,Na)(Nb,Ta)O3 Thin Films by Mn Doping

Lead-free piezoelectric (K,Na)(Nb,Ta)O3 thin films were prepared by chemical solution deposition. Perovskite single-phase (K0.5Na0.5)(Nb0.8Ta0.2)O3 and Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films were successfully fabricated at 600 °C on Pt/TiOx/SiO2/Si substrates by controlling the excess amounts of K and Na, and Mn by doping. The (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films showed poor ferroelectric polarizations due to the insufficient insulating resistance at room temperature. The leakage current density of the (K0.5Na0.5)(Nb0.8Ta0.2)O3 films, especially in the high-applied-field region, was markedly reduced by doping with a small amount of Mn. Also, the ferroelectric properties of the (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films were markedly improved by Mn doping. 0.5 and 1.0 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films exhibited well-shaped ferroelectric polarization–electric field (P–E) hysteresis loops at room temperature. The remanent polarization (Pr) and coercive field (Ec) values of the 0.5 and 1.0 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films at 1 kHz were approximately 14 and 21 µC/cm2, and 111 and 86 kV/cm, respectively. Furthermore, these films showed a typical field-induced butterfly loop, and the estimated effective d33 values were 58 pm/V for the 0.5 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films and 41 pm/V for the 1.0 mol % Mn-doped (K0.5Na0.5)(Nb0.8Ta0.2)O3 thin films.

Electrical Properties of Lead-Free Ferroelectric Mn-Doped K0.5Na0.5NbO3?CaZrO3 Thin Films Prepared by Chemical Solution Deposition

Lead-free ferroelectric K0.5Na0.5NbO3–CaZrO3 thin films were prepared by chemical solution deposition. Chemically optimized K0.5Na0.5NbO3–CaZrO3 precursor thin films crystallized in the perovskite single phase on Pt/TiOx/SiO2/Si substrates at 650 °C. The K0.5Na0.5NbO3–CaZrO3 thin films showed poor ferroelectric polarizations due to the insufficient insulating resistance. The leakage current of the K0.5Na0.5NbO3–CaZrO3 films, especially in the high-applied-field region, was markedly reduced by 1 mol % Mn doping for the Nb site. Also, the ferroelectric properties of the K0.5Na0.5NbO3–CaZrO3 thin films depended on CaZrO3 concentration. 1 mol % Mn-doped K0.5Na0.5NbO3–CaZrO3 thin films exhibited slim and small ferroelectric polarization–electric field (P–E) hysteresis loops at room temperature with an increase in CaZrO3 amount. Furthermore, these films showed a typical field-induced displacement curve with a small hysteresis, and the estimated effective d33 values were 32 pm/V for the 1 mol % Mn-doped 0.95K0.5Na0.5NbO3–0.05CaZrO3 thin films and 21 pm/V for the 1 mol % Mn-doped 0.9K0.5Na0.5NbO3–0.1CaZrO3 thin films.