Revealing of Core Shell Effect on Frequency-Dependent Properties of Bi-based Relaxor/Ferroelectric Ceramic Composites

Enhanced Ferroelectric and Dielectric Properties of Niobium-Doped Lead-Free Piezoceramics

Lead-free ceramics are promising candidates for replacing lead-based piezoelectric materials such as lead-zirconate-titanate (PZT) if they can compete in dielectric and ferroelectric characteristics. In this work, for lead-free piezoelectric ceramic, 0.74(Bi_0.5Na_0.5TiO₃)-0.26(SrTiO₃) (BNT-ST26) and niobium-substituted (Nb-BNT-ST26) ceramics were synthesized by solid-state reactions. The evolution of niobium substitution to the perovskite phase structure of BNT-ST26 ceramics was confirmed by X-ray diffraction (XRD) analysis and Raman spectra. Electromechanical properties of Nb-BNT-ST26 ceramics initially increased with the addition of niobium up to 0.5% and decreased with a further increase in Nb content. Temperature-dependent dielectric curves showed that the depolarization temperature (T_d) decreased below room temperature because of Nb substitution. The composition with 0.5% Nb yielded a maximum bipolar strain (S_max) of 0.265% and normalized strain of d₃₃* ~ 576 pm/V under an electric field of 4.6 kV/mm at room temperature. At this critical concentration of 0.5% Nb, maximum saturation polarization of 26 μC/cm² was achieved. The dielectric constant with temperature peaks became more diffused and the depolarization temperature decreased with the increasing Nb content. The study concludes that Nb-doped BNT-ST26 is an excellent material for high-temperature, stable, frequency-dependent, lead-free piezoelectric devices.

Revealing the Effects of Microarc Oxidation on the Mechanical and Degradation Properties of Mg-Based Biodegradable Composites

To overcome the inherent weakness of polylactic acid (PLA), used as scaffolding materials, multiple samples of Mg/PLA alloy composite materials was made by plastic injection molding. To enhance the interfacial interaction with PLA, magnesium alloy was treated with microarc oxidation (MAO) at four different frequencies, resulting in an improvement in mechanical strength and toughness. The microarc oxidation films consisted mainly of a porous MgO ceramic layer on the Mg rod. Based on the phenomenon of micro-anchoring and electrostatic interaction, a change in frequency during MAO showed considerable improvements in the ductility of the composite materials. The presence of the ceramic layer enriched the interfacial bonding between the Mg rod and outer PLA cladding, resulting in the PLA-clad Mg rod showing a higher tensile strength. In vitro degradation test was carried out in Hank's solution for different time periods. Surface-treated Mg alloy-based composite samples displayed a lower degradation rate as compared to untreated Mg alloy samples. The surface-treated sample at a 800 Hz pulse frequency showed the best degradation resistance and mechanical properties after being immersed in Hank's solution as compared to other samples. Mg-reinforced PLA composite rods are promising candidates for orthopedic implants.

Enhanced Mechanical Properties of Surface Treated AZ31 Reinforced Polymer Composites

To enhance the potential application of naturally biodegradable polylactic acid (PLA)-based composites reinforced with magnesium alloy, anodized coatings between Mg and PLA were fabricated on AZ31 magnesium alloy rods. After anodizing (AO) at four different treatment times, the surface demonstrated a typical porous MgO ceramics morphology, which greatly improved the mechanical properties of composite rods compared to untreated pure Mg. This was attributed to the micro-anchoring effect, which increases interfacial binding forces significantly between the Mg rod and PLA. Additionally, the AO layer can also substantially improve the degradability of composite rods in Hank’s solution, due to good corrosion resistance and stronger bonding between PLA and Mg. With a prolonged immersion time of up to 30 days, the porous MgO coating was eventually found to be degraded, evolving to a comparatively smooth surface resulting in a decline in mechanical properties due to a decrease in interfacial bonding strength. According to the current findings, the PLA-clad surface treated Mg composite rod may hold promise for use as a bioresorbable implant material for orthopedic inner fixation.

Improved Multilayered (Bi,Sc)O3-(Pb,Ti)O3 Piezoelectric Energy Harvesters Based on Impedance Matching Technique

As a piezoelectric material, (Bi,Sc)O₃-(Pb,Ti)O₃ ceramics have been tested and analyzed for sensors and energy harvester applications owing to their relatively high Curie temperature and high piezoelectric coefficient. In this work, we prepared optimized (Bi,Sc)O₃-(Pb,Ti)O₃ piezoelectric materials through the conventional ceramic process. To increase the output energy, a multilayered structure was proposed and designed, and to obtain the maximum output energy, impedance matching techniques were considered and tested. By varying and measuring the energy harvesting system, we confirmed that the output energies were optimized by varying the load resistance. As the load resistance increased, the output voltage became saturated. Then, we calculated the optimized output power using the electric energy formula. Consequently, we identified the highest output energy of 5.93 µW/cm² at 3 MΩ for the quadruple-layer harvester and load resistor using the impedance matching system. We characterized and improved the electrical properties of the piezoelectric energy harvesters by introducing impedance matching and performing the modeling of the energy harvesting component. Modeling was conducted for the piezoelectric generator component by introducing the mechanical force dependent voltage sources and load resistors and piezoelectric capacitor connected in parallel. Moreover, the generated output voltages were simulated by introducing an impedance matching technique. This work is designed to explain the modeling of piezoelectric energy harvesters. In this model, the relationship between applied mechanical force and output energy was discussed by employing experimental results and simulation.

Relaxation-Related Piezoelectric and Dielectric Behavior of Bi(Mg,Ti)O3⁻PbTiO3 Ceramic

Piezoelectric and dielectric materials have attracted much attention for their functional device applications. Despite its excellent piezoelectric properties, the content of lead in piezoelectric materials should be restricted to prevent future environmental problems. Therefore, reduced lead content in piezoelectric materials with similar piezoelectric properties is favorable. In our research, piezoelectric materials with decreased lead content will be studied and discussed. Even though the lead content is decreased in Bi(Mg_0.5Ti_0.5)O₃-PbTiO₃ ceramics, they show piezoelectric properties similar to that of lead zirconate titanate (PZT)-based materials. We believe this high piezoelectric behavior is related to the relaxation behavior of Bi(Mg_0.5Ti_0.5)O₃-PbTiO₃ (BMT-PT) ceramics. In this study, 0.62Bi(Mg_0.5Ti_0.5)O₃-0.38PbTiO₃ ceramics were prepared by the conventional sintering process. These piezoelectric ceramics were sintered at varying temperatures of 975-1100 °C. Crystallinity and structural properties were analyzed and discussed. X-ray diffraction pattern analysis demonstrated that the optimal sintering temperature was around 1075 °C. A very high Curie temperature of 447 °C was recorded for 0.62BMT-0.38PT ceramics sintered at 1075 °C. For the first time, we found that the origin of the high Curie temperature, d₃₃, and the dielectric constant is the relaxation behavior of different dipoles in 0.62BMT-0.38PT ceramics.