[Show abstract][Hide abstract] ABSTRACT: Regelation, i.e., ice melts under compression and freezes again when the pressure is relieved, remains puzzling since its discovery in 1850's by Faraday. Here we show that hydrogen bond (O:H-O) cooperativity and its extraordinary recoverability resolve this anomaly. The H-O bond and the O:H nonbond possesses each a specific heat ηx(T/ΘDx) whose Debye temperature ΘDx is proportional to its characteristic phonon frequency ωx according to Einstein's relationship. A superposition of the ηx(T/ΘDx) curves for the H-O bond (x = H, ωH ~ 3200 cm(-1)) and the O:H nonbond (x = L, ωL ~ 200 cm(-1), ΘDL = 198 K) yields two intersecting temperatures that define the liquid/quasisolid/solid phase boundaries. Compression shortens the O:H nonbond and stiffens its phonon but does the opposite to the H-O bond through O-O Coulomb repulsion, which closes up the intersection temperatures and hence depress the melting temperature of quasisolid ice. Reproduction of the Tm(P) profile clarifies that the H-O bond energy EH determines the Tm with derivative of EH = 3.97 eV for bulk water and ice. Oxygen atom always finds bonding partners to retain its sp(3)-orbital hybridization once the O:H breaks, which ensures O:H-O bond recoverability to its original state once the pressure is relieved.
[Show abstract][Hide abstract] ABSTRACT: The electrical and domain switching properties of Bi3.15Nd0.85Ti3O12 (BNT) thin films have been studied, which were prepared by pulse laser deposition (PLD) on exact and miscut (2°) Si substrates. The films have a bismuth-layered perovskite structure, and the leakage current of BNT film on miscut substrate is smaller than that on exact one. The domain structure, domain switching and hysteresis loops of BNT film on miscut substrate were studied, multidirectional domain structure, complete domain switching and strong piezoresponse are found in it. The phase-voltage hysteresis and butterfly loops were very saturated with a coercive voltage (Vc) about 3.75 V. The film also exhibited excellent piezoelectric property with a high piezoelectric coefficient d33~20 pm/V.
[Show abstract][Hide abstract] ABSTRACT: The polarization switching of the incommensurate (INC) phases induced by flexocoupling in perovskite ferroelectric thin films is investigated with a multi-field coupling theoretical framework combining the flexoelectric effect. The dominant factors of the formation of INC phases that show antiferroelectric-like double hysteresis loops are examined. The simulations show that mechanical boundary conditions have little influence on the polarization responses of INC phases. The polarization switching behaviors of INC phases are governed by the flexocoupling types described by different flexocoupling coefficients. Only the transverse flexocoupling coefficient related INC phases show antiferroelectric-like double hysteresis loop. The longitudinal flexocoupling coefficient related and shear flexocoupling coefficient related INC phases show imprint-like hysteresis loops and hysteresis loops similar to those of the ferroelectric phase, respectively. The observed different polarization switching behaviors are rationalized by free energy density curves of the INC phases.
[Show abstract][Hide abstract] ABSTRACT: The influence of local stress on the polarization switching of a two-dimensional ferroelectric thin film is investigated by a multi-field coupling model of flexoelectric effect. The evolution law of domain in a ferroelectric film under a local mechanical force is obtained. That is: under increasing mechanical stress, domain evolution in ferroelectric film will experience six stages “small angle of rotation → emergence of 90° domain switching → expansion of 90° domain → emergence of 180° domain switching → expansion of 180° domain → steady state”. f1111 related flexocoupling type and f1122 related flexocoupling type both play crucial roles in the whole switching process. 90° switching arises from the combined effect of the gradient of transverse strain in the thickness and horizontal direction as well as the gradient of out-of-plane strain in the horizontal direction, while 180° switching is attributed to the combined effect of the gradient of transverse strain and out-of-plane strain in the thickness direction.
[Show abstract][Hide abstract] ABSTRACT: An extended tetrahedron unifies the length scale, geometry, and density of water ice.•O:H–O bond cooperative relaxation stems anomalies of water and ice.•Water prefers 4-coordinated mono-phase with a supersolid skin unless at nanoscale.•An elastic, hydrophobic and less dense skin slipperizes ice and toughens water skin.•H-bond memory and skin supersolidity resolve Mpemba effect - hot water freezes faster.
[Show abstract][Hide abstract] ABSTRACT: Epitaxial PbZr0.52Ti0.48O3 (PZT) films with perfectly c-axis oriented tetragonal phase were deposited on SrTiO3 (STO) substrates using a SrRuO3 (SRO) buffer layer by pulsed laser deposition (PLD) method. Ferroelectric behavior of PZT on STO substrates along with an improved remnant polarization (2Pr) of 118 μC/cm2 and a low coercive field (Ec) of 193 kV/cm at 15 V were observed at room temperature indicating that the SRO/STO substrates with small lattice misfit can make some contributions to enhance PZT film's ferroelectric properties. Moreover, the capacitance characteristics of the PZT thin films were detected, a large dielectric constant of 1476, the charging and discharging characteristics determine the large dielectric strength of the PZT thin film capacitors.
[Show abstract][Hide abstract] ABSTRACT: Thin films of ferroelectric Pb0.82La0.08Sr0.1Ti0.98O3 (PLST) thin films were fabricated on LaNiO3 buffered Pt/Ti/SiO2/Si substrates via the sol–gel deposition method. The dielectric and tunable properties were investigated as a function of DC bias and frequency to exhibit effect of LNO buffer layer on the tunable dielectric thin film. It shows that PLST thin film deposited on LNO/Pt/Ti/SiO2/Si substrates possesses higher dielectric constant and lower dielectric loss compared with the one directly deposited on Pt/Ti/SiO2/Si substrates. Furthermore, the tunability of the LNO-buffered PLST thin film is 68% at the DC bias of 20 V, which is higher than 60% of the pure PLST thin film. The results suggest the addition of LNO buffer layer could effectively improve the dielectric and tunable properties of PLST thin film and make it suitable for high quality dielectric tunable devices.
[Show abstract][Hide abstract] ABSTRACT: We present the effects of an amorphous ZrO2 layer on the TiO2-based bipolar resistive switching memory device where the ZrO2 layer plays an important role as a supplementary reservoir of oxygen vacancies. Compared with Pt/TiO2/Pt monolayer device, a remarkably improved uniformity of switching parameters such as switching voltages and resistances in high/low states is demonstrated in the Pt/ZrO2/TiO2/Pt system. The resistive switching mechanism of memory devices incorporating the ZrO2/TiO2 bilayer structure can be attributed to multiple conducting filaments through the occurrence of redox reactions at the ZrO2/TiO2 surface.
[Show abstract][Hide abstract] ABSTRACT: Mpemba paradox, that is, hotter water freezes faster than colder water does, has baffled thinkers like Francis Bacon, René Descartes, and Aristotle since B.C. 350. However, a commonly accepted understanding or theoretical reproduction of this effect remains challenging. Numerical reproduction of observations, shown herewith, confirms that water skin supersolidity [Zhang et al., PCCP, in press] enhances the local thermal diffusivity favoring heat flowing outwardly in the liquid path. Analysis of experimental database reveals that hydrogen bond (O:H-O) possesses memory to emit energy at a rate depending on its initial storage. Unlike other usual materials that lengthen and soften all bonds when they are absorbing thermal energy, water performs abnormally at heating to lengthen the O:H nonbond and shorten the H-O covalent bond through inter-oxygen Coulomb coupling [Sun, et al., J. Phys. Chem. Lett., 2013. 4: 3238]. Cooling does oppositely to release energy, like releasing a coupled pair of bungees, at a rate of history dependence. Being sensitive to the source volume, skin radiation, and the drain temperature, Mpemba effect proceeds only in the strictly non-adiabatic ‘source-path-drain’ cycling system for the heat “emission-conduction-dissipation” dynamics with a relaxation time that drops exponentially with the rise of the initial temperature of the liquid source.
[Show abstract][Hide abstract] ABSTRACT: The magneto-mechanical coupling effect of amorphous Co40Fe40B20 (CoFeB) films (10-200 nm) on flexible polyethylene terephthalate substrates were investigated in detail. The normalized remanent magnetization (Mr/Ms) of CoFeB films changes significantly (up to 62%) under small tensile or compressive strain. Moreover, the thickness dependence of the magneto-mechanical coupling effect for the flexible CoFeB films was demonstrated. These results provide important information for the development of CoFeB-based magnetic tunnel junction used in flexible spintronic devices.
[Show abstract][Hide abstract] ABSTRACT: Consistency in experimental observations, numerical calculations, and theoretical predictions revealed that skins of water and ice share the same attribute of supersolidity that is characterized by the identical H-O vibration frequency of 3450 cm-1 in comparison to the values of 3200/3150 cm-1 for bulk water/ice. Molecular undercoordination and inter-electron-pair repulsion relax the hydrogen bond (O:H-O) asymmetrically and cooperatively in length and energy associated with a dual process of nonbonding electron polarization. This relaxation-polarization process enhances the dipole moment, elasticity, viscosity, thermal stability of these skins with 25% density loss, which is responsible for the hydrophobicity and toughness of water skin and for the slippery of ice.
[Show abstract][Hide abstract] ABSTRACT: Iron fluoride cathodes have been attracting considerable interest due to their high electromotive force value of 2.7 V and their high theoretical capacity of 237 mA h g(-1) (1 e(-) transfer). In this study, uniform iron fluoride hollow porous microspheres have been synthesized for the first time by using a facile and scalable solution-phase route. These uniform porous and hollow microspheres show a high specific capacity of 210 mA h g(-1) at 0.1 C, and excellent rate capability (100 mA h g(-1) at 1 C) between 1.7 and 4.5 V versus Li/Li(+) . When in the range of 1.3 to 4.5 V, stable capacity was achieved at 350 mA h g(-1) at a current of 50 mA g(-1) .
Chemistry - A European Journal 05/2014; 20(19). DOI:10.1002/chem.201304713 · 5.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multilayered thin films consisting of both 0.88BaTiO3–0.12Bi(Mg0.5,Ti0.5)O3 ferroelectric layers and PbZrO3 antiferroelectric layers were prepared by sol–gel method, exhibiting high dielectric permittivity, large polarization, high recoverable energy storage density and high energy storage efficiency. A maximum polarization of 93 μC/cm2, recoverable energy storage density of 24.7 J/cm3 and energy storage efficiency of ~60% have been achieved at an electric field of 1050 kV/cm. Furthermore, the energy storage performance of the multilayered thin films was improved by modified layer-by-layer annealing process, where larger polarization (115 μC/cm2), higher recoverable energy storage density (33 J/cm3) and higher energy storage efficiency (~70%) were obtained.
Ceramics International 05/2014; 40(4):5327–5332. DOI:10.1016/j.ceramint.2013.10.110 · 2.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An in situ carbon-encapsulating solution route for the synthesis of Li4Ti5O12@C composite hollow microspheres has been developed. The finally obtained Li4Ti5O12@C hollow microspheres possess a microsized spherical shape, embedded Li4Ti5O12 nanocrystals, and fully encapsulating conductive carbon shells, which endow this Li4Ti5O12 anode material with high specific capacity, rate capability, and cycle stability. Owing to their unique microstructure characteristics, these hollow Li4Ti5O12@C microsphere composites are promising anode materials for highly efficient Li-ion batteries with an excellent rate capability (discharge capacity of 169, 152, 130, 116, 93, and 76 mA h g–1 at 0.2, 1, 2, 5, 30 and 60C, respectively) and a significantly enhanced cycling performance.
European Journal of Inorganic Chemistry 04/2014; 2014(12). DOI:10.1002/ejic.201301558 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Novel hierarchical Bi4Ti3O12 (BIT) micro-cross spheres were prepared by a solvothermal process with surfactant assistance. Experimental results show that the hierarchical BIT micro-cross spheres exhibit a mono-dispersed morphology with a diameter of about 5 μm. And they consist of nano-sheets which assemble into a cross intercalated structure. Moreover, the morphological evolution process indicates that the type and concentration of surfactant play important roles in the shape controlled synthesis and cetyltrimethylammonium bromide is important in determining the self-assembling process of BIT micro-cross spheres. In addition, UV/vis absorption spectra show that the as-synthesized BIT samples have a slightly red-shift behavior and exhibit different band gaps with different morphologies.
[Show abstract][Hide abstract] ABSTRACT: V-doped SrTiO3 (V:STO) thin films on Si and Pt/Ti/SiO2/Si substrates are synthesized by sol–gel method to form metal–insulator–metal (MIM) structures. Bipolar resistive switching (RS) characteristics were investigated in Pt/V:STO/Si and Pt/V:STO/Pt structures respectively. The enhancement of resistive switching behavior in Pt/V:STO/Pt/Ti/SiO2/Si structures were demonstrated in terms of the maximum operation voltage reduced from 20 to 2 V and the improved ROFF/RON ratio increased from 102 to 103. The electrochemical migration of oxygen vacancies resulted from the metal–oxide interfaces was applied to explain the resistive switching behaviors. On the basis of current–voltage characteristics, the switching mechanisms for the low resistance state (LRS) and high resistance state (HRS) currents of V:STO films are considered as Ohmic and trap-controlled space charge-limited current (SCLC) behavior, respectively.
Japanese Journal of Applied Physics 02/2014; 53(3):035503. DOI:10.7567/JJAP.53.035503 · 1.13 Impact Factor