RESUMEN
Dielectric ceramics with ultrahigh polarization and energy density are the core components used in next-generation pulse power generators based on explosive energy conversion. However, the low polarization of ferroelectric materials and high depolarized pressure hinder their development toward miniaturization, light weight, and integration, while antiferroelectric materials possessing larger nonlinear saturated polarization and rich phase structure are neglected in pulse power energy conversion. Here, an effective strategy of constructing antiferroelectric-to-ferroelectric overlap zone is achieved in binary system (1 - x)(Pb,La)(Zr,Ti)O3-xBa(Al1/2Nb1/2)O3 antiferroelectric ceramics to realize an excellent polarization of 41 µC/cm2 and a large depolarization efficiency of >99% under 150 MPa as well as a record high energy harvesting density of 2.5 J/cm3 under 400 MPa. The excellent comprehensive energy conversion and energy harvesting performance is mainly attributed to the strategy of antiferroelectric-to-ferroelectric overlap zone and improved microdomain density, at which orthorhombic-to-rhombohedral structure evolution is confirmed by transmission electron microscopy, piezo-response force microscopy, and Raman spectrum, resulting in substantially enhanced remanent polarization compared to ferroelectric ceramics. Besides, excellent temperature stability (â¼180 °C) and optimized depolarization pressure also support that this binary system is a candidate for energy conversion and energy harvesting application. This work demonstrates that antiferroelectric-to-ferroelectric overlap based on antiferroelectric materials is an excellent strategy to develop dielectric materials with excellent depolarized polarization and energy harvesting density for energy conversion and harvesting.
RESUMEN
Lead-free piezoceramics with large controllable deformations are highly desirable for numerous energy converter applications ranging from consumer electronics to medical microrobots. Although several new classes of high-performance ferroelectrics have been discovered, a universal strategy to enable various piezoceramics to realize large electromechanical deformations is still lacking. Herein, by gradually reducing the thickness from 0.5 mm to 0.1 mm, we discover that a large nominal electrostrain of â¼11.49% can be achieved in thin 0.937(Bi0.5Na0.5)TiO3-0.063BaTiO3 (BNT-BT) ceramics with highly asymmetric strain-electric field curves. Further analyses of the polarization switching process reveal that the boosted strain curves originate from the bending deformation driven by asymmetric ferroelastic switching in the surface layers. Based on this, one monolayer BNT-BT was designed to realize digital displacement actuation and a scanning mirror application with a maximum mirror deflection angle of 44.38°. Moreover, the surface effect-induced bending deformation can be extended to other piezoceramics, accompanied by derived shape retention effects. These discoveries raise the possibility of utilizing thickness engineering to design large-displacement actuators and may accelerate the development of high-performance lead-free piezoceramics.
RESUMEN
Exploring the structural evolution of clusters with similar sizes and atom numbers induced by the removal or addition of a few atoms contributes to a deep understanding of structure-property relationships. Herein, three well-characterized copper-hydride nanoclusters that provide insight into the surface-vacancy-defect to non-defect structural evolution were reported. A surface-defective copper hydride nanocluster [Cu28(S-c-C6H11)18(PPh2Py)3H8]2+ (Cu28-PPh2Py for short) with only one C 1 symmetry axis was synthesized using a one-pot method under mild conditions, and its structure was determined. Through ligand regulation, a 29th copper atom was inserted into the surface vacancy site to give two non-defective copper hydride nanoclusters, namely [Cu29(SAdm)15Cl3(P(Ph-Cl)3)4H10]+ (Cu29-P(Ph-Cl)3 for short) with one C 3 symmetry axis and (Cu29(S-c-C6H11)18(P(Ph-pMe)3)4H10)+ (Cu29-P(Ph-Me)3 for short) with four C 3 symmetry axes. The optimized structures show that the 10 hydrides cap four triangular and all six square-planar structures of the cuboctahedral Cu13 core of Cu29-P(Ph-Me)3, while the 10 hydrides cap four triangular and six square-planar structures of the anti-cuboctahedral Cu13 core of Cu29-P(Ph-Cl)3, with the eight hydrides in Cu28-PPh2Py capping four triangular and four square planar-structures of its anti-cuboctahedral Cu13 core. Cluster stability was found to increase sequentially from Cu28-PPh2Py to Cu29-P(Ph-Cl)3 and then to Cu29-P(Ph-Me)3, which indicates that stability is affected by the overall structure of the cluster. Structural adjustments to the metal core, shell, and core-shell bonding model, in moving from Cu28-PPh2Py to Cu29-P(Ph-Cl)3 and then to Cu29-P(Ph-Me)3, enable the structural evolution and mechanism responsible for their physicochemical properties to be understood and provide valuable insight into the structures of surface vacancies in copper nanoclusters and structure-property relationships.
RESUMEN
Thermal conductivity k dominates in a heat transfer medium, and a field modulated k would facilitate delicate control in thermal management technology, yet it is hardly realized in a single solid material unless with changing temperature. Herein, in BaTiO3 ceramic, a modulated k was discovered by adjusting ferroelectric polarization P, which was a conventional strategy in ferroelectric functional materials. Four different states (P1, P2, P3, P4) were obtained by controlling poling time and field strength, showing that k leaped from 2.704 ± 0.054 to 3.201 ± 0.070 W (m K)-1 with increased P. Moreover, the strong correlation between P and k was also verified by the thermal depolarization measurement from room temperature to Curie temperature. The underlying origin of P modulated k was attributed to the internal bias field, which is born in the oriented ferroelectric domains, tightening special phonon modes in BaTiO3 ceramics. Raman spectrum, P-E loops, first-order reversible curve, XRD analysis, and PFM measurement were then employed to clarify how ferroelectric polarization structurally influences phonon transport and subsequent thermal conductivity. This work will pave a brand-new research route for conventional ferroelectric ceramic, also potentiating the idea of the electric field-controlled k component and active solid heat-transport device in the future.
RESUMEN
An intermediate-sized atomically precise metalloid silver nanocluster [Ag71(SR)31(Dppm)](SbF6)2 (Dppm = bis (diphenylphosphino)methane, SR = S-tBu) is reported, which comprises one building block Ag64, six SR5 pentagons, one sole SR ligand, a DppmAg2 handle, and an Ag5 lid. Structurally, a decahedron Ag23 kernel is observed in the metalloid silver nanocluster. Moreover, the Ag64 unit provides insights into the growth of large clusters such as Ag136(SR)64Cl3 and Ag141(SR)40Br12via assembly. The observed decahedron Ag23 provides a deeper understanding on Marks decahedron in larger nanoclusters, and the [Ag71(S-tBu)31(Dppm)](SbF6)2 uses Ag64 as a building block to predict the structure of larger metalloid nanoclusters.
RESUMEN
Herein, we report the synthesis and total structure of a Cu-rich alloy nanocluster protected by twelve adamantanethiolate ligands, i.e., [Ag13Cu10(SAdm)12]X3 (-SAdm = SC10H15, X = counterion), which was confirmed by single-crystal X-ray structure determination and electrospray ionization mass spectrometry (ESI-MS). X-ray crystallographic analysis indicated that [Ag13Cu10(SAdm)12]X3 consisted of an icosahedral Ag13 core, covered by a cage-like shell of Cu10(SAdm)12. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the geometric and electronic structures and KS orbitals and UV-vis spectroscopy were performed on the model [Ag13Cu10(SMe)12]3+ and its monometallic analog [Ag23(SMe)12]3+. This work will deepen the understanding of core-shell Ag-Cu alloy nanoclusters.
RESUMEN
The phase boundaries of dielectric materials have constantly been valuable for instructing the design of phase structures, revealing correlations between compositions and structures, and attaining the desired functional properties for piezoelectric, pyroelectric, electrostriction, electrocaloric, energy storage and energy harvesting applications. We here observe a new type of phase boundary in a solid solution of xPbTiO3·(1 - x)Pb(Yb1/2Nb1/2)O3 (x = 0.00-0.20), which is between an antiferroelectric (AFE) phase and a relaxor ferroelectric (RFE) phase. x = 0.10 is confirmed as the phase boundary. XRD, TEM, PFM and Raman spectroscopy analysis reveal two fundamental traits of the phase structure: (1) the polar state changes from AFE to FE order; and (2) the domain range evolves from micrometer-sized to nanometer-sized, both of which are normally separated but coexist around the phase boundary. The intriguing phase structure contributes to the distinctive dielectric properties: (1) a broad compositional zone (x < 0.10 and x ≥ 0.14) features low remnant polarization, low hysteresis and highly reversible domain wall motion, and is expected to be utilized for dielectric energy storage and electrostriction applications; and (2) a narrow nonergodic RFE zone (0.10 ≤ x < 0.14) demonstrates remnant and maximum polarization, co-dominated by composition and temperature, and has potential for pyroelectric and electrocaloric applications.
