Nanoscale potassium niobate crystal structure and phase transition

Nanoscale potassium niobate (KNbO3) powders of orthorhombic structure were synthesized using the sol-gel method. The heat-treatment temperature of the gels had a pronounced effect on KNbO3 particle size and morphology. Field emission scanning electron microscopy and transmission electron microscopy were used to determine particle size and morphology. The average KNbO3 grain size was estimated to be less than 100 nm, and transmission electron microscopy images indicated that KNbO3 particles had a brick-like morphology. Synchrotron X-ray diffraction was used to identify the room-temperature structures using Rietveld refinement. The ferroelectric orthorhombic phase was retained even for particles smaller than 50 nm. The orthorhombic to tetragonal and tetragonal to cubic phase transitions of nanocrystalline KNbO3 were investigated using temperature-dependent powder X-ray diffraction. Differential scanning calorimetry was used to examine the temperature dependence of KNbO3 phase transition. The Curie temperature and phase transition were independent of particle size, and Rietveld analyses showed increasing distortions with decreasing particle size

Substrate-borne vibrations disrupt the mating behaviors of the neotropical brown stink bug, Euschistus heros: implications for pest management.

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Brillouin scattering in SA and SB phases of butyloxy-benzilidene octylaniline

The anisotropy of the quasilongitudinal sound waves in the SA and SB phases of n-butyloxy-benzilidene n-octylaniline was measured. From the data, three elastic constants were determined. A propagating shear wave was not observed in spite of a relatively large value of the relevant elastic constant.Nous avons mesuré l'anisotropie des ondes sonores quasilongitudinales dans les phases SA et SB de n-butyloxy-benzilidène n-octylaniline. Les données expérimentales permettent de déterminer les grandeurs des trois constantes d'élasticité. Bien que la valeur de la constante d'élasticité correspondante aux ondes de cisaillement soit relativement très élevée, la propagation d'une telle onde n'a pas été observée

Microscopic ordering in smectic phases of liquid crystals

Orientational order in smectic phases of a ferroelectric liquid-crystalline material 4'-(2S, 3S)-2"-chloro-3"-methylpentanoyloxyphenyl-4-decyloxy thiobenzoate, abbreviated 10.S.C1Iso-leu, was examined by IR absorption spectroscopy. Oriented samples were prepared in both bookshelf and homeotropic alignment geometry. Several stronger IR vibrations were selected characterizing different parts and orientations of the molecules. Results show that the molecular tilt of the core parts of the molecules changes very little from the SA to the S* C phase implying that the core parts of the molecules are already tilted in the SA phase. Axes of the core parts, that are disordered on a cone in the SA phase, start to align with each other but remain on this cone on lowering the temperature into the S*C phase. The model agrees with some previous results.On a étudié par spectroscopie d'absorption infrarouge l'ordre orientationel dans les phases smectiques d'un matériau cristal liquide ferroélectri que, le décyloxy-4-thiobenzoate de [(2S, 3S)-chloro-2-méthyl-3-pentanoyloxy]-4'-phényle, en abrégé 10.S.C1Isoleu. Deux types d'échantillons orientés, l'un homéotrope, l'autre en configuration Clark-Lagerwall, ont été préparés et plusieurs bandes intenses en infrarouge, caractéristiques des différentes parties et orientations des molécules, ont été choisies. Les résultats montrent que l'inclinaison des parties centrales (cœurs) des molécules varie très peu de la phase SA à la phase S*C, ce qui implique que les cœurs des molécules sont déjà inclinés dans la phase SA. Leurs axes, qui sont désordonnés sur un cône dans la phase SA, s'alignent mais restent sur ce cône quand on passe en phase S*Cen abaissant la température. Ce modèle est en accord avec quelques résultats antérieurs