Impact of Ba2+ on Structure and Piezoelectric Properties of PMN–PZN–PNN–PT Ceramics Near the Morphotropic Phase Boundary

The effect of using Ba²⁺ to modify the structure and dielectric and piezoelectric properties of Pb_(1?x)Ba_x(Mg_1/3Nb_2/3)_m(Zn_1/3Nb_2/3)_y(Ni_1/3Nb_2/3)_nTi_zO₃(x = 0–0.15) ceramics near the morphotropic phase boundary has been investigated. It is found that increasing the content of Ba²⁺ leads to a sequence of structural transformations from heterophase state (tetragonal and pseudocubic phases) to a cubic state via an intermediate pseudocubic phase. The evolution of the dielectric and piezoelectric properties (sequences of transformations: normal ferroelectric →relaxor ferroelectric → paraelectric) is shown. It is stated that ceramics with x = 0.025–0.050 possess the optimal combination of functional parameters for use in low‐frequency receivers and actuators. They are characterized by high values of small‐signal and large‐signal piezoelectric coefficients d₃₃ of 621 pC/N and ~1500 m/V (at E = 5 kV/cm), respectively, and also by increased values of dielectric permittivity ε/ε₀ and tunability coefficient (К = [(ε/ε₀(E = 0) ? ε/ε₀(E≠0))/ε/ε₀(E = 0)]·100%), equal to ~7000 and ~80%, respectively (at E = 20 kV/cm). It is shown that for the creation of high‐power piezoelectric transducers it is necessary to use ceramics with x = 0.125, which differs with high values of the mechanical quality factor Q_m and ε/ε₀ (1406 and 10 890, respectively).     

Responsive Spiral Photonic Structures for Visible Vapor Sensing,Pattern Transformation and Encryption

Two photon polymerisation using direct laser writing is a burgeoning field of research, with recent focus being placed on bringing added value to microstructures, by incorporating soft, responsive polymers. Moving to the micron-scale can have a profound impact on such stimuli-responsive materials, whose speed of actuation can be increased many-fold compared to their mm-scale counterparts. Here, the fabrication of submicron 2D photonic structures, based on a vapor-responsive photoresist with a refractive index <1.55, in the visible wavelength range. The fabricated concentric spiral arrays are evaluated for their feasibility as vapor sensors by testing spectral and structural color reproducibility and reversibility under water, ethanol, isopropanol, and acetone vapors. This approach allows for the realization of predictable uniform color displays that can be modulated upon stimuli response. The transmitted colour in the dry and hydrated states can be accurately modelled. This knowledge is used to design and demonstrate structures for cloaking and image transformation. Such capability can be used for encryption and anti-counterfeiting applications.     

Two-Photon Polymerization of Sugar Responsive 4D Microstructures

Stimuli-responsive hydrogels have attracted much attention owing to the versatility of their programmed response in offering intelligent solutions for biomimicry applications, such as soft robotics, tissue engineering, and drug delivery. To achieve the complexity of biomimetic structures, two photon polymerization (2PP) has provided a means of fabricating intricate 3D structures from stimuli-responsive hydrogels. Rapid swelling hydrogel microstructures are advantageous for osmotically driven stimuli-response, where actuation speed, that is reliant on the diffusion of analytes or bioanalytes, can be optimized. Herein, the flexibility of 2PP is exploited to showcase a novel sugar-responsive, phenylboronic acid-based photoresist. This offers a remarkable solution for achieving fast response hydrogel systems that have been often hindered by the volume-dependent diffusion times of analytes to receptor sites. A phenylboronic acid-based photoresist compatible with 2PP is presented to fabricate stimuli-responsive microstructures with accelerated response times. Moreover, microstructures with programmable actuation (i.e., bending and opening) are fabricated using the same photoresist within a one-step fabrication process. By combining the flexibility of 2PP with an easily adaptable photoresist, an accessible fabrication method is showcased for sophisticated and chemo-responsive 3D hydrogel actuators.