We fabricated TiO 2 nanoparticles modified by a thin salt solution layer. The suspensions, formed by the nanoparticles in silicone oil, serve as model systems for exploring very general theories about interactions between colloidal particles with arbitrary ions confined on surfaces in the presence of an applied electric field. The system showed a static-yield-stress peak, not found before. The peak can be manipulated by tuning the amount of cations and anions confined in the salt solution layer. Excellent agreement between our experiment and theory reveals the mechanism concerning the competition between ions' polarized trapped state and conductively transmitted state. This work makes it possible to manipulate colloidal interactions by confining exogenous ions appropriately, and it is expected to have applications in colloidal science, materials engineering, and biotechnology.
Demand for replacing the current lead-based piezoelectric materials with some lead-free ones becomes increasingly strong from environmental concerns. In this article, we report the piezoelectric performance, the phase transitions, and the domain configurations of highly dense 0.96(K0.48Na0.52)(Nb0.96Sb0.04)O3−0.04(Bi0.50Na0.50)ZrO3 ceramics prepared by two step-sintering through solid-state reaction. This material has outstanding piezoelectric properties of piezoelectric coefficient d33 = 512 pC/N and electromechanical coupling coefficient kp ≈ 0.56 at room temperature. While d33 exhibits a broad peak and is greater than 430 pC/N between −30 °C and 70 °C, kp depends weakly on temperature below 50 °C but decreases considerably with further increasing the temperature. In terms of thermal aging, both d33 and kp remain stable from −50 °C to 240 °C. The degradation of kp quickly stabilizes in the first thermal cycle between −50 °C and 150 °C. Furthermore, the measurement of relative dielectric permittivity ε′ upon heating indicates that rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transitions occur at TR-O ≈ −40 °C, TO-T ≈ 54 °C, and TC ≈ 265 °C, respectively. The X-ray diffraction analysis shows that the crystalline structure at room temperature is of orthorhombic-tetragonal phase coexistence. We also investigate the domain structure with an acid etching technique. The unpoled ceramic exhibits a complicated domain pattern consisting of irregularly shaped domains of long parallel stripes separated by 180° domain boundaries from neighboring domains. In contrast, upon poling, the domain pattern becomes simpler and takes the form of long parallel stripes of diverse widths, with a hierarchical nanodomain structure appearing inside some of the broader stripes. We consider that the superior piezoelectric properties and reasonable temperature stability are closely related to the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions and to the characteristic domain structure.
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