Wangfeng Bai

Piezoelectric grain-size effects of BaTiO3 ceramics under different sintering atmospheres

Two groups of barium titanate (BaTiO3) ceramics with high piezoelectric coefficient (d33) have been successfully fabricated by the conventional solid-state reaction technique under different sintering atmospheres. The influences of sintering atmosphere on piezoelectric grain-size effects were systematically investigated. It was found that d33 first increases then decreases with the increase of grain size (g) for both two groups of ceramics. However, the d33 value reaches the maxima (501pC/N) at gu2009=u20091.13xa0µm for the samples sintered under the air sintering atmosphere (BaTiO3–Air). The samples sintered under the oxygen atmosphere (BaTiO3–O2) exhibit a large d33 (>450pC/N) plateau at g from 0.98 to 7.30xa0µm. The experimental results indicated that the piezoelectric grain-size effects of BaTiO3 ceramics were strongly affected by the sintering atmosphere. Related mechanisms may be attributed to the variations of the domain configuration under different sintering atmospheres.

Low electric field-driven giant strain response in 〈001〉 textured BNT-based lead-free piezoelectric materials

The applied electric field to drive intended large strain response in Bi0.5Na0.5TiO3-based piezoelectric ceramics is usually high (mostly with Exa0≥xa060xa0kV/cm) and remains a long-standing drawback for actual actuator applications. In this work, we report 〈001〉 oriented (1−x) (0.83Bi0.5Na0.5TiO3–0.17Bi0.5K0.5TiO3)–xBaTiO3 (BNT–BKT–BT) lead-free piezoelectric ceramics using BT as the template particles to tailor the strain behavior under a low driving field. The strain response exhibited an increasing trend with the increasing grain orientation, and remarkably giant Smax/Emax of 800xa0pm/V was acquired under a relatively low electric field of 45xa0kV/cm in the optimized microstructure for textured BNT-BKT–1BT ceramics compared with the reported lead-free Bi-based perovskite ceramics. Furthermore, the achieved textured ceramics showed prominent electric field- and temperature-dependent strain characteristic featured by both a high room-temperature Smax/Emax of 621xa0pm/V under a very low driving field of 35xa0kV/cm and an achievable large Smax/Emax of 531xa0pm/V with almost vanished hysteretic behavior at high temperature. Our work may be helpful for designing BNT-based lead-free materials with promising strain response and thus provides a new approach to resolve this drawback of BNT-based lead-free piezoelectric ceramics.

Nd3+/Yb3+ cascade-sensitized single-band red upconversion emission in active-core/active-shell nanocrystals

Lanthanide-doped upconversion nanomaterials (UCNMs) have promoted extensive interest for its biological research and biomedical applications, benefiting from low autofluorescence background, deep light penetration depth, and minimal photo-damage to biological tissues. However, owing to the 980 nm laser-induced overheating issue and the attenuation effect associated with conventional multi-peak emissions, the usage of UCNMs as fluorescent bioprobes is still limited. To address these issues, an effective strategy has been proposed to tune both the excitation and emission peaks of UCNMs into the first biological window (650xa0∼xa0900 nm), where the light absorption by water and hemoglobin in biological tissues is minimal. Based on the Nd3+/Yb3+ cascade-sensitized upconversion process and efficient exchange-energy transfer between Mn2+ and Er3+ in conjunction with the active-core@active-shell nanostructured design, we have developed a new class of upconversion nanoparticles (UCNPs) that exhibit strong single-band red emission upon excitation of an 808 nm near-infrared laser. Hopefully, the well-designed KMnF3:Yb/Er/Nd@ KMnF3:Yb/Nd core-shell nanocrystals will be considered a promising alternative to conventionally used UCNPs for biolabeling applications without the concern of the overheating issue and the attenuation constraints.