We studied the crystallization kinetics in a diblock copolymer system exhibiting different mesophase structures in the melt. A symmetric poly(ethylene oxide)-block-poly(1,4-butadiene) (PEO-b-PB) was blended with a low molecular weight PB homopolymer to yield the block copolymer blends containing lamellar, cylindrical, and spherical PEO microdomains. The crystallization kinetics of PEO blocks in these nanoscaled microdomains was then studied by monitoring the development of crystallinity in the course of isothermal crystallization. In the lamellar melt, crystallization could occur at the normal undercooling, and its kinetics closely followed the classical Avrami model found in the spherulitic crystallization of homopolymers. Crystallinity developments in the cylindrical and spherical morphology obeyed a simple exponential function prescribed by the first-order kinetics. This first-order kinetic behavior along with the exceedingly large undercooling verified the homogeneous nucleation controlled kinetics in these two types of mesophases. Crystallization in the lamellar melt transformed the melt structure into a highly interconnected lamellar morphology due to the ability of the crystal growth fronts to repeatedly thrust into the microdomains yet to be crystallized. For the crystallization condition chosen (i.e., cooling at −5 °C/min from the melt), the melt structures associated with the cylindrical and spherical morphology were not totally disrupted and transformed into one-dimensionally stacked lamellae upon crystallization. The melt mesophases were not fully preserved either, suggesting that some intermediate structures may have been formed through the crystallization.

The influence of La doping on the crystal structure and multiferroic properties of BiFeO3 (BFO) thin films was investigated. BFO-based films of pure perovskite phase were deposited on BaPbO3∕Pt∕TiOx∕SiO2∕Si substrates by rf-magnetron sputtering. The increased dielectric constant and remanent polarization of the La-doped BFO films were due to the increased lattice parameters and an improved crystallinity. The polarization switching and the fatigue behavior of the BFO films were significantly enhanced by the La doping. The in-plane magnetization-field curves revealed that the room-temperature saturated magnetization of the BFO films increased with La doping.

The growth of colloidal metal nanocrystals typically involves an autocatalytic process, in which the salt precursor adsorbs onto the surface of a growing nanocrystal, followed by chemical reduction to atoms for their incorporation into the nanocrystal. Despite its universal role in the synthesis of colloidal nanocrystals, it is still poorly understood and controlled in terms of kinetics. Through the use of well-defined nanocrystals as seeds, including those with different types of facets, sizes, and internal twin structure, here we quantitatively analyze the kinetics of autocatalytic surface reduction in an effort to control the evolution of nanocrystals into predictable shapes. Our kinetic measurements demonstrate that the activation energy barrier to autocatalytic surface reduction is highly dependent on both the type of facet and the presence of twin boundary, corresponding to distinctive growth patterns and products. Interestingly, the autocatalytic process is effective not only in eliminating homogeneous nucleation but also in activating and sustaining the growth of octahedral nanocrystals. This work represents a major step forward toward achieving a quantitative understanding and control of the autocatalytic process involved in the synthesis of colloidal metal nanocrystals.

BiFeO 3 (BFO) thin films of pure perovskite phase were deposited on LaNiO3-buffered Pt∕TiOx∕SiO2∕Si (LNO) and Pt∕TiOx∕SiO2∕Si (Pt) substrates by RF magnetron sputtering. Highly (100)-oriented BFO film was coherently grown on LNO at a temperature as low as 300 °C. The crystal structure and the film/electrode interface of BFO films were characterized using x-ray diffraction and scanning transmission electron microscope high-angle annular dark-field imaging. The conventional problem of the leakage current was greatly reduced with remarkable improvement in the film/electrode interface, chemical homogeneity, crystallinity, and surface roughness of the BFO film.

Articles you may be interested inReduced leakage current in BiFeO 3 -BiCrO 3 nanocomposite films formed by chemical solution deposition J. Appl. Phys. 108, 054102 (2010); 10.1063/1.3467965 Structural, ferroelectric, dielectric, and magnetic properties of BiFeO 3 / Bi 3.15 Nd 0.85 Ti 3 O 12 multilayer films derived by chemical solution deposition

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By changing the electrode combination of Pt and LaNiO3 (LNO), four capacitor types of Pt/PZT/Pt/Si, Pt/LNO/PZT/Pt/Si, Pt/LNO/PZT/LNO/Pt/Si, and Pt/PZT/LNO/Pt/Si, were prepared to investigate the fatigue and hysteresis characteristics of the sol-gel-derived Pb(Zr0.53Ti0.47)O3 (PZT) ferroelectric thin films. Among them, the (100)- and (001)-oriented PZT films were grown on the (100)-textured LNO electrode, but randomly oriented films were obtained on the Pt electrode. It was found that the use of LNO bottom electrode would improve the fatigue property quite significantly, but only the capacitor with LNO as both top and bottom electrodes is shown to be fatigue-free up to 1011 cycles, and the shapes of the hysteresis loop almost unchanged after the fatigue test.

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