Key Engineering Materials Vol. 566

Abstract: Fatigue tests on lead zirconate titanate (PZT) were performed by using single-edge-V-notched specimens under cyclic mechanical loading with or without superposition of a DC electric field. Fatigue life was prolonged by applying a DC electric field to the PZT ceramics. To estimate the domain contribution, fatigue tests on barium strontium titanate (BST) ceramics in both ferroelectric and paraelectric phase were carried out. The fatigue life of the ferroelectric phase was much shorter than that of the paraelectric phase. Comparing the fatigue lives of two PZT ceramics with different values of coercive electric field (E_c) revealed that the fatigue life of the PZT with higher E_c is about one order of magnitude longer than that with lower E_c when the stress-intensity factor of fatigue test is low. It is therefore concluded that non-180°domain switching probably deteriorates the fatigue life of ferroelectric ceramics.

Abstract: Time-dependent dielectric breakdown (TDDB) of lead titanate zirconate (PZT) thin-film capacitors derived by a sol-gel deposition process has been studied. Without any change in heat treatment conditions such as temperature, ramping rate, and keeping time, the films grain size was varied by adding a small amount of organic additive to PZT sol-gel solution for a control of nucleation to form PZT oxide. The reliability was remarkably improved by fabricating interfaces with multi-annealing process, parallel to film surface when the grain size is greater than film thickness, which seems to suppress conductivity of oxygen vacancies.

Abstract: Pure Barium titanate (BaTiO₃) ceramics with grain sizes of 0.6, 1.5, and 18 μm on average were prepared by using a two-step sintering method. The wideband dielectric spectra in the range from kHz to THz were measured at 25 and 150 °C to understand the polarization mechanism of fine-grained BaTiO₃ ceramics. It was revealed that the dipole and ionic polarizations decreased with decreasing grain size at 25 and 150 °C when the grain size was smaller than 1 μm. These mechanisms were interpreted as a grain boundary effect.

Abstract: The electric field distributions in loaded dielectric layers of multilayer ceramic capacitors were investigated at several stages of insulation degradation for the load, using Kelvin probe force microscopy. The electric field distribution was found to be different at each stage of loaded time. Initially, the electric field was concentrated near the cathode, indicating that the insulation resistance near the anode decreased. Then, following the homogeneous distribution shown for an intermediate stage, the electric field eventually concentrated near the anode. This change indicates how insulation degradation occurs locally; this change can plausibly be explained by a hole density increase.

Abstract: The relation between the dielectric tunability and the electro-optic (EO) effect of barium strontium titanate (Ba_0.5Sr_0.5TiO₃) thin film was discussed. The tunability of dielectric permittivity calculated from the complex admittance with planer electrodes reached to 53.1%, and the tunability of birefringence by EO effect was 0.6%. The birefringence change from EO effect was much lower than the tunability of dielectric permittivity. The materials with high tunability do not always exhibit high EO effect. This is concluded to arise due to the ionic mass in the EO materials.

Abstract: A single crystal of ferroelectric 0.88(Bi,Na)TiO₃0.12BaTiO₃ (BNTBT) solid solution with tetragonal P4mm structure was grown by the top-seeded solution growth (TSSG) method at a high oxygen pressure (PO₂) of 0.9 MPa. The crystals grown by the high-PO₂ TSSG method exhibited a large remanent polarization (P_r) of 54 μC/cm², which leads to a spontaneous polarization of 54 μC/cm². The large P_r compared with that of crystals grown at PO₂ = 0.1 MPa is suggested to originate from a low oxygen vacancy concentration for the crystals grown at a higher PO₂. The high-PO₂ TSSG method was demonstrated to be effective for obtaining BNTBT crystals with superior polarization and piezoelectric properties.

Abstract: Top-seeded solution growth method under high-oxygen-pressure atmosphere has been developed for obtaining high-performance and large-sized single crystals of ferroelectric (Bi_0.5Na_0.5)TiO₃ (BNT). Crystals grown at 1000 °C at a Po₂ of 0.9 MPa exhibited a well-saturated hysteresis with a remanent polarization of 34 μC/cm² and a coercive field of 22 kV/cm along <100>_cubic. The spontaneous polarization of BNT along <111>_cubic is estimated to be 59 μC/cm² from the measured polarization properties along <100>_cubic of the crystals obtained. Domain observations using piezoresponse force microscopy revealed that the degraded performance of BNT crystals grown at a low Po₂ is attributed to unswitched 71° domains remaining even after applying a high electric field to the crystals .

Abstract: In this study, 0.8 KNbO₃ (KN) -0.2 BaTiO₃ (BT) ceramics were prepared using KN powder with the diameter of 100 nm and BT powders with the diameter of 100, 300, or 500 nm. The relative densities were more than 96 % of the theoretical densities of the samples. The dielectric constant of the samples was temperature-stable at temperatures between-50 and 300 °C and it was found that the dielectric constant of the 0.8KN-0.2BT ceramics increased as the BT diameter increased.

Abstract: Barium titanate (BaTiO₃) porous ceramics were prepared by conventional sintering method, and their dielectric and piezoelectric properties were measured using 31-resonators. With decreasing sintering temperature, dielectric constant showed a maximum of 5500 at 1300 °C, while piezoelectric constant and elastic compliance increased. These resonators were developed to unimorph-type vibrators and their instantaneous electric powers were measured. As the results, the maximum electric power of 129 μW was measured for the BaTiO₃ porous ceramics sintered at 1200 °C, and this value was 20 times greater than that for dense BaTiO₃ ceramics.