Yafei Hou

Defect dipole induced large recoverable strain and high energy-storage density in lead-free Na0.5Bi0.5TiO3-based systems

In this letter, we propose an effective route to obtain large recoverable strain, purely electrostrictive effects and high energy-storage density by inducing defect dipoles into Na0.5Bi0.5TiO3 (NBT)-based relaxor ferroelectrics. It has been found that pinched and double polarization hysteresis loops with high maximum polarization (Pmax) and negligible remanent polarization (Pr) can be observed due to the presence of acceptor-induced defect dipoles. A large recoverable strain of 0.24% with very little hysteresis and high electrostriction coefficient of 0.022 m4 C2 with purely electrostrictive characteristics were acquired when 11 mol. ‰ Mn-doped. Meanwhile, a high recoverable energy density of 1.06 J/cm3 with excellent temperature stability was obtained at the same composition owing to the enlarged value of Pmax-Pr (36.8 μC/cm2) and relatively high electric field (95 kV/cm). Our achievement can open up the exciting opportunities for ferroelectric materials in high-precision positioning devices and high ele...

pH-Responsive drug release and NIR-triggered singlet oxygen generation based on a multifunctional core–shell–shell structure

A multifunctional platform with pH-responsive drug release and near-infrared (NIR) light-triggered photodynamic therapy (PDT) was designed and prepared using the novel core-shell-shell structure. The multifunctional platform consists of an upconversion nanoparticle (UCNP) emission core, a photosensitizer methylene blue (MB) embedded dense silica sandwich shell, and a polyethyleneimine conjugated folic acid (PEI-FA) gated mesoporous silica (MS) outmost shell with doxorubicin hydrochloride (DOX) loaded inside. The simulated drug release experiments revealed that DOX will release from the nanoparticles because of the distortion in the PEI-FA layer under acidic conditions. Moreover, under 980 nm NIR irradiation, a 660 nm red light emission was excited, activating MB to generate a singlet oxygen (1O2), which acts as the PDT drug. The multifunctional platform integrated pH-responsive drug release and UCNP-based PDT drug together show promising potential in nanomedicine for future chemotherapy and NIR-triggered PDT.

Positive/negative electrocaloric effect induced by defect dipoles in PZT ferroelectric bilayer thin films

Double hysteresis loops induced by defect dipoles are obtained in PbZr0.52Ti0.48O3/PbZr0.8Ti0.2O3 ferroelectric bilayer thin films prepared by a sol–gel method. The migration of the defect dipoles related to the temperature and applied electric field is investigated in detail, which has a deep influence on the polarization due to the effect of the domain pinning caused by defect dipoles. Meanwhile, the electrocaloric effect based on double hysteresis loops induced by defect dipoles has been studied. The coexistence of a negative electrocaloric effect and positive electrocaloric effect has been achieved in PbZr0.52Ti0.48O3/PbZr0.8Ti0.2O3 bilayer films, ΔT = −8.4 K at 155 °C, and ΔT = 4.4 K at 45 °C. The amplifying effect of the applied electric field in the PZr0.8Ti0.2O3 layer films plays an important role in the excellent negative electrocaloric values. More interestingly, the coexistence of the negative electrocaloric and positive electrocaloric effect can be obtained by regulating the applied electric field, which is beneficial to enhancing the cooling efficiency during the cycling of the applied electric field.

Negative Capacitance in BaTiO3/BiFeO3 Bilayer Capacitors

Negative capacitances provide an approach to reduce heat generations in field-effect transistors during the switch processes, which contributes to further miniaturization of the conventional integrated circuits. Although there are many studies about negative capacitances using ferroelectric materials, the direct observation of stable ferroelectric negative capacitances has rarely been reported. Here, we put forward a dc bias assistant model in bilayer capacitors, where one ferroelectric layer with large dielectric constant and the other ferroelectric layer with small dielectric constant are needed. Negative capacitances can be obtained when external dc bias electric fields are larger than a critical value. Based on the model, BaTiO3/BiFeO3 bilayer capacitors are chosen as study objects, and negative capacitances are observed directly. Additionally, the upward self-polarization effect in the ferroelectric layer reduces the critical electric field, which may provide a method for realizing zero and/or small dc bias assistant negative capacitances.