Search Results (5)

Uninterrupted breakthroughs in the room temperature piezoelectric properties of KNN-based piezoceramics have been witnessed over the past two decades; however, poor temperature stability presents a major challenge for KNN-based piezoelectric ceramics in their effort to replace their lead-based counterparts. Herein, to enhance temperature stability in KNN-based ceramics while preserving the high piezoelectric response, multilayer composite ceramics were fabricated using textured thick films with distinct polymorphic phase transition temperatures. The results demonstrated that the composite ceramics exhibited both outstanding piezoelectric performance (d₃₃~467 ± 16 pC/N; S~0.17% at 40 kV/cm) and excellent temperature stability with d₃₃ and strain variations of 9.1% and 2.9%, respectively, over a broad temperature range of 25–180 °C. This superior piezoelectric temperature stability is attributed to the inter-inhibitive piezoelectric fluctuations between the component layers, the diffused phase transition, and the stable phase structure with a rising temperature, as well as the permanent contribution of crystal orientation to piezoelectric performance over the studied temperature range. This novel strategy, which addresses the piezoelectric and strain temperature sensitivity while maintaining high performance, is well-positioned to advance the commercial application of KNN-based lead-free piezoelectric ceramics. Full article

(K_0.5Na_0.5)NbO₃ (KNN)-based ceramics have been extensively investigated as replacements for Pb(Zr, Ti)O₃-based ceramics. KNN-based ceramics exhibit an orthorhombic structure at room temperature and a rhombohedral–orthorhombic (R–O) phase transition temperature (T_R–O), orthorhombic–tetragonal (O–T) phase transition temperature (T_O–T), and Curie temperature of −110, 190, and 420 °C, respectively. Forming KNN-based ceramics with a multistructure that can assist in domain rotation is one technique for enhancing their piezoelectric properties. This review investigates and introduces KNN-based ceramics with various multistructures. A reactive-templated grain growth method that aligns the grains of piezoceramics in a specific orientation is another approach for improving the piezoelectric properties of KNN-modified ceramics. The piezoelectric properties of the [001]-textured KNN-based ceramics are improved because their microstructures are similar to those of the [001]-oriented single crystals. The improvement in the piezoelectric properties after [001] texturing is largely influenced by the crystal structure of the textured ceramics. In this review, [001]-textured KNN-based ceramics with different crystal structures are investigated and systematically summarized. Full article

In this work, to systematically investigate the evolution characteristics of electrical properties in polymorphic piezoceramics, the Ba(Ti_0.92Zr_0.08)O₃ ceramics are selected as a paradigm that possesses all the general phase structures above room temperature. It is found that the evolution of electrical properties with temperature change can be divided into three stages based on phase structure transforming: high ferroelectric and stable strain properties at R and R-O, high ferroelectric and enhanced strain/converse piezoelectric properties at O, O-T, and T phase, and the rapidly decreased ferroelectric and strain properties in T-C and C phase. However, the ferroelectric and strain properties all increase with rising electric field and their evolution can be divided into two parts based on phase structures. The high property and slow increase rate are present at R, R-O, O, and O-T, while the poor property but a high increase rate is present around T-C. Similar results can be found in the evolution of electrostrictive property. Finally, the highest d₃₃* of ~1240 pm/V and Q₃₃ of ~0.053 m⁴/C² are obtained at O-T due to the high ferroelectricity but easy domain switching. This work affords important guidance for the property optimization of polymorphic piezoceramics. Full article

We report the investigation of various experimental conditions and their influence on polymorphism of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, commonly known as ROY. These conditions include an in-house-developed microfluidic chip with controlled mixing of parallel flows. We observed that different ROY concentrations and different solvent to antisolvent ratios naturally favored different polymorphs. Nonetheless, identical samples prepared with different mixing methods, such as rotation and magnetic stirring, consistently led to the formation of different polymorphs. A fourth parameter, namely the confinement of the sample, was also considered. Untangling all those parameters and their influences on polymorphism called for an experimental setup allowing all four to be controlled accurately. To that end, we developed a novel customized microfluidic setup allowing reproducible and controlled mixing conditions. Two parallel flows of antisolvent and ROY dissolved in solvent were infused into a transparent microchannel. Next, slow and progressive mixing could be obtained by molecular diffusion. Additionally, the microfluidic chip was equipped with a piezoceramic element, allowing the implementation of various mixing rates by acoustic mixing. With this device, we demonstrated the importance of parameters other than concentration on the polymorphism of ROY. Full article

In this work, we report the investigation of various experimental conditions and their influence on the polymorphism of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophen carbonitrile, commonly known as ROY. These conditions include an in-house-developed microfluidic chip with controlled mixing of parallel flows. ROY is known for its ability to form a large variety of polymorphs, including at least ten forming under standard conditions. Nucleation is triggered by adding water as an antisolvent to ROY dissolved in acetone. We observe that different ROY concentrations and different solvent-to-antisolvent ratios naturally favor different polymorphs. Nevertheless, identical samples prepared with different mixing methods, such as shaking and magnetic stirring, consistently lead to the formation of different polymorphs. In addition, different mixing rates that can be linked to shear stress strongly influence the crystallization. A fourth parameter, namely confinement of the sample, is also found to be critical. Untangling all of these parameters and their influences on polymorphism calls for an experimental setup allowing all four to be controlled accurately. To that end, we developed a novel customized microfluidic setup allowing reproducible and controlled mixing conditions. Two parallel flows of antisolvent and ROY dissolved in solvent are injected into a transparent microchannel. Next, slow and progressive mixing can be achieved through molecular diffusion. Additionally, the microfluidic chip is equipped with a piezoceramic element, allowing the implementation of various mixing rates through acoustic mixing. With this device, we demonstrate the importance of parameters other than concentration that are involved in the polymorphism of ROY. Full article