Showing papers on "Single crystal published in 1984"
TL;DR: In this paper, a number of interesting results on the physical properties of poly-3-hydroxybutyrate (PHB) were presented on crystallization kinetics, morphology of melt-and solution-crystallized PHB, the variation of lamellar thickness with crystallization temperature, and the assessment of some thermodynamic quantities.
Abstract: This paper presents a number of interesting results on the physical properties of poly-3-hydroxybutyrate (PHB). Data are presented on crystallization kinetics, morphology of melt- and solution-crystallized PHB, the variation of lamellar thickness with crystallization temperature, and the assessment of some thermodynamic quantities. These properties include surface free energies, heat of fusion and melting, and glass transition temperatures. It is shown that the special properties of PHB such as the large spherulite size, which is probably due to its exceptional purity, make it an ideal material for model studies of polymer crystallization and morphology. For example, we show that the variation of growth rate with crystallization temperature is consistent with the very latest theories; and that the single crystal morphology has important implications for the understanding of crystal growth in other polymer systems.
913 citations
TL;DR: In this article, the Schottky-barrier heights of NiSi2layers grown under ultrahigh-vacuum conditions on n-type Si(111) are found to be 0.65 and 0.79 eV for type-A and type-Bepitaxial systems, respectively.
Abstract: Electrical behaviors at two single-crystal metal-semiconductor interfaces are studied. Schottky-barrier heights of NiSi2layers grown under ultrahigh-vacuum conditions on n- type Si(111) are found to be 0.65 and 0.79 eV for type-Aand type-Bepitaxial systems, respectively. These results are compared with the proposed theoretical models of Schottky barriers.
364 citations
TL;DR: In this paper, the photoelectrochemical behavior of an n-TiO2 (rutile) single crystal under different treatments (mechanical polishing and chemical and photo electrochemical etching) is analyzed and the conditions under which Gartner's model can be applied are determined.
Abstract: The photoelectrochemical behavior of an n‐TiO2 (rutile) single crystal under different treatments (mechanical polishing and chemical and photoelectrochemical etching) is analyzed and the conditions under which Gartner’s model can be applied are determined. The hole diffusion length Lp obtained from the photoelectrochemical data is about 10−6 cm for the etched single crystal and seems to be governed by electron‐hole recombination at centers associated to impurities introduced in the lattice during the manufacturing process. This value of the hole diffusion length determines the minimum value of the donor concentration Nd for an efficient separation of carriers within the semiconductor depletion layer. This explains the existence of a maximum of the quantum efficiency for Nd∼6×1018 cm−3, which has been found to be a value common to n‐TiO2 single crystals of different origin. Lattice deffects introduced near the crystal surface by mechanical polishing behave as recombination centers which reduce Lp to values...
208 citations
TL;DR: In this article, a geometrical sodalite model is developed, which, when calibrated with the parameters from the refined structure, enables: (1) the accurate prediction of the atomic coordinates of all members of the Sodalite-group minerals at both room and elevated temperatures; (2) the chemical limits of structural stability of all such materials; (3) thermalexpansion data and substitution of interframework ions to be rationalized and predicted in terms of the rotation of the (A1, Si)O4 tetrahedra.
Abstract: Sodalite, Nas(A16Si6024)CI2, is cubic, P43n, M, = 969-2, F(000) = 476, a = 8.882(1)~, Dx = 2 . 3 0 M g m -3, Z = I , R = 0 . 0 1 7 for 157 unique observed reflections measured on an automated fourcircle X-ray diffractometer using Mo Ka radiation. The 1:1 aluminosilicate framework is completely ordered. A geometrical sodalite model has been developed, which, when calibrated with the parameters from the refined structure, enables: (1) the accurate prediction of the atomic coordinates of all members of the sodalite-group minerals at both room and elevated temperatures; (2) the prediction of the chemical limits of structural stability of all such materials; (3) thermal-expansion data and substitution of interframework ions to be rationalized and predicted in terms of the rotation of the (A1, Si)O4 tetrahedra.
193 citations
TL;DR: Mesures de l'electrodiffusion en mode stationnaire et de la diffusion anisotrope de 63 Ni dans l'etain β monocristallin par une technique de section de traceur.
Abstract: Mesures de l'electrodiffusion en mode stationnaire et de la diffusion anisotrope de 63 Ni dans l'etain β monocristallin par une technique de section de traceur
159 citations
TL;DR: In this paper, the conductivity of polycrystalline Y2O3-ZrO2 samples has been studied by complex impedance and four-probe direct current techniques.
Abstract: The conductivity of several single crystal and polycrystalline Y2O3-ZrO2 samples has been studied by complex impedance and four-probe direct current techniques. For single crystals only one arc, due to lattice conductivity, was observed in the complex impedance representation. Polycrystalline materials showed a second arc, due to grain boundary resistance, the extent of which decreased as the impurity concentration was reduced and as the electrolyte microstructure improved. The activation energies for the volume and total conductivity of the purest polycrystalline samples were similar and agreed with those for the single crystals. These values, however, decreased by 20 to 25 kJ mol−1 on going from low ( 850° C) temperatures. The change in the activation energy with temperature is thought to be due to a gradual transition between an association region, where vacancies are bound to dopant cations, and a dissociation region where vacancies are free and mobile.
147 citations
TL;DR: In this article, the origin of the shoulder structure in the X-ray absorption spectra of a single crystal of (creatinium)2CuCl4 was found to be exclusively polarized in the direction normal to the molecular plane of the CuCl42− ion.
143 citations
TL;DR: In this article, the nature of the buffer layers needed for the single crystal deposition of cubic SiC on Si substrates was studied and it was concluded that the buffer layer is a stressed monocrystalline layer of cubic siC.
Abstract: The nature of the buffer layers needed for the single crystal deposition of cubic SiC on Si substrates was studied. It is concluded that the buffer layer is a stressed monocrystalline layer of cubic SiC.
138 citations
Abstract: Sintered pellets of CeO2 and UO2, as well as PuO2 powder, have been irradiated with alpha particles emitted from an effectively semi-infinite 238PuO2 source. The lattice parameters of all three materials increased with dose, Dα, according to the expression δa/a0 = A[1—exp(—BDα)], in agreement with a previously developed model. The recovery behavior of the lattice defects has been studied by isochronal annealing. Two recovery stages were observed in the temperature range between 50 and 1000°C for each material, and the activation energies were estimated based on previous single crystal studies. Comparisons with self-damage from alpha decay are made, and the behavior of the lattice defects is discussed.
137 citations
TL;DR: In this article, the diffusivity of Ti into LiNbO3 has been measured as a function of crystal orientation and Li/Nb ratio in the temperature range 980-1112 C.
Abstract: The diffusivity of Ti into LiNbO3 has been measured as a function of crystal orientation and Li/Nb ratio in the temperature range 980–1112 °C. The Li/Nb ratios of single crystal samples were adjusted by vapor phase equilibration with fixed Li2O activities. No anisotropy of diffusivity with crystal orientation could be detected. The diffusion constants for Ti in LiNbO3 decrease with increasing Li2O content. At 1050 °C, the values decrease from 2.60×10−12 cm2/s at the Li2O‐deficient phase boundary (48.1 mol % Li2O) to 1.06×10−12 cm2/s at the congruently melting composition at (48.6 mol % Li2O) to 0.4×10−12 cm2/s at the Li2O‐rich phase boundary (50.0 mol % Li2O). It is suggested that enhanced lateral diffusion observed for stripe geometry Ti sources results from increased diffusivity in a surface layer formed by Li2O outdiffusion.
136 citations
TL;DR: In this paper, the microstructural state just beneath the surface of the sheet before cold rolling is shown to be an important factor in the successful development of Goss texture during simulated processing.
Abstract: A number of experiments involving cold rolling and annealing have been carried out on polycrystalline and single crystal silicon iron. It is shown that the microstructural state just beneath the surface of the sheet before cold rolling is an important factor in the successful development of Goss texture during simulated processing. A coarse grained surface zone encourages formation of shear bands during rolling and these become preferential sites for nucleation during primary recrystallization. Nucleation of secondary grains, which also occurs just beneath the sheet surface, appears to be dependent on the prior existence of the shear band structure. Single crystals with the orientation (111)[112] are prone to shear banding during cold rolling especially when strain aging conditions are established. During subsequent annealing the shear bands recrystallize first, producing new grains which have the Goss orientation. The texture after complete recrystallization is the same as that of the shear band ...
TL;DR: In this article, self-diffusion in an α-zirconium single crystal was investigated over the temperature range 779 to 1128 K. Gaussian penetration curves were observed.
TL;DR: In this article, the authors showed that the light-induced erasure rate of a refractive index grating depends on the optical intensity of the grating and showed that higher optical intensity is required to achieve high-speed operation of BaTiO3 devices than previously thought.
Abstract: We present data on the speed of light‐induced refractive index changes in a BaTiO3 single crystal. The light‐induced erasure rate of a refractive index grating is shown to depend on optical intensity as I x where x<1. The exponent x depends weakly on temperature and increases from 0.62±0.02 to 0.71±0.02 when the temperature is varied between 12 and 40 °C. The sublinear dependence of rate on intensity implies that higher optical intensity is required to achieve high‐speed operation of BaTiO3 devices than previously thought. The dark erasure rate has an anomolously strong temperature dependence; it increases by a factor of 50 over the same temperature range. We have also determined that the number density of photorefractive charge carriers is 6×1016 cm−3 in this crystal.
TL;DR: In this paper, a new conceptual model for interstratified clays is proposed, based on complementary use of the transmission electron microscope (TEM) and X-ray diffraction (XRD).
Abstract: A new conceptual model for interstratified clays is proposed, based on complementary use of the transmission electron microscope (TEM) and X-ray diffraction (XRD). Clays yielding interstratified XRD patterns are shown to be composed of aggregates of fundamental particles (here defined as an individual or free particle which yields a single crystal pattern by electron diffraction) whose interfaces are capable of adsorbing water and organic molecules. In these circumstances, the interstratified XRD character results from an interparticle diffraction phenomenon. Smectites are shown to be primarily composed of particles 10 A thick corresponding to elementary 2:1 silicate layers. Nearest-neighbour regularly interstratified illitesmectite (K-rectorite) is composed of particles of elementary ‘illite’ 20 A. thick, corresponding to two silicate layers coordinated by a single plane of potassium ions. Regularly interstratified chlorite-smectite (corrensite) consists of particles 24 A thick corresponding to two silicate layers coordinated by a single brucitic sheet. The layer sequence examined by XRD is determined by the types and proportions of particles present within the clay material. Thus a sedimented aggregate of 20 A elementary ‘illite’ particles appears to be a regularly alternating sequence of illite and smectite layers by XRD. Randomly interstratified itlite-smectite and chlorite-smectite can be synthesised by making mixed suspensions of the 50 A thick. This conceptual model has implications for the chemistry, behaviour and genesis of interstratified clays which are common constituents of soils and sediments.
TL;DR: In this paper, the adsorption of Ni on W (110) and W (211) single crystal faces is studied in the coverage range up to several monolayers from 300 to 1200 K by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), work function change (Δφ) measurements and thermal desorption spectrograms.
TL;DR: In this paper, the crystal structure of barium hexaaluminate phase I (Ba 0.79 Al 10.9 O 17.14 ) was determined by single crystal X-ray reflection data.
TL;DR: In this paper, it was shown that strong local strains existing at the interface between the porous layer and the substrate can be virtually eliminated by choosing a proper composition of the electrolyte.
TL;DR: In this article, it was shown that at temperatures below 160 K, crystalline NaN is transformed into an extremely long-living metastable state, and the new state decays exponentially with red light.
Abstract: Below 160 K, crystalline ${\mathrm{Na}}_{2}$[Fe${(\mathrm{CN})}_{5}$NO] \ifmmode\cdot\else\textperiodcentered\fi{} 2${\mathrm{H}}_{2}$O is transformed into an extremely longliving metastable state ($\ensuremath{\tau}g{10}^{7}$ sec) by irradiation with 400-540-nm light. At $Tg160$ K and by irradiation with red light the new state decays exponentially. During population the transmission of the crystal shows characteristic time behavior with wavelength-dependent saturation. Raman spectra show the coexistence of the ground and metastable states. New infrared and visible absorption bands are interpreted in terms of an energy scheme of the metastable state.
TL;DR: In this paper, the role of electron-electron correlations and highly charge correlated electron excited states in the second and third order nonlinear optical responses of organic and polymer structures has been investigated.
Abstract: Physical studies of nonlinear optical properties of organic and polymer structures have demonstrated exceptionally large second and third order nonlinear optical responses that are important to the fields of nonlinear optics and optical device technologies. These unusual responses have been exhibited by a large number of structures, phases, and states that include organic solids and films, single crystal polymers, Langmuir-Blodgett films, liquid crystals, and liquid crystal polymers. Experimental and theoretical studies of such systems have achieved significant advances in the understanding of these exceptional macroscopic nonlinear optical responses based on theoretically calculated microscopic electronic mechanisms, especially the role of electron-electron correlations and highly charge correlated electron excited states. Combined theory and experiment has led to the recent discovery of liquid crystal polymerization of divinyldiacetylene monomers to form highly conjugated liquid crystal polymer...
TL;DR: In this paper, the electrical resistivity of monocrystalline and polycrystalline TiB/sub 2/ was measured under an inert atmosphere by a four-point ac impedance technique over the range 298 to 1373 K.
Abstract: The electrical resistivity of monocrystalline and polycrystalline TiB/sub 2/ was measured under an inert atmosphere by a four-point ac impedance technique over the range 298 to 1373 K. The results are expressed in the form /rho/ - /rho//sub 298/ = m(T - 298). The following values of /rho//sub 298/ (..mu cap omega..Xcm) and m(/eta/..cap omega..XcmXK/sup -1/) were determined: for polycrystalline TiB/sub 2/ (69% dense) 18.2 and 95; for polycrystalline TiB/sub 2/ (99% dense) 7.4 and 42; and for monocrystalline TiB/sub 2/ 6.6 and 34.9.
TL;DR: In this paper, the reduction of H+ from 1 M FICiO, and 1 IV NaCIO, solurions at polycrystalline and single crystal faces of very pure gold electrode, was studied by determining the forward rate constant kr as a funcrion of porential and of H' concentration.
TL;DR: In this paper, the first growth of high-quality, single crystal thin films of Cd1−xMnxTe was reported, and the films are deposited by molecular beam epitaxy.
Abstract: In this letter we report the first growth of high‐quality, single crystal thin films of Cd1−xMnxTe; the films are deposited by molecular beam epitaxy. Cd1−xMnxTe is one of a newly developed class of magneto‐optic materials called diluted magnetic semiconductors. Films with mole fractions of up to 50% Mn have been grown with no indication of any MnTe phases. A sputtered Auger electron spectroscopy depth profile shows that the Mn is uniformly incorporated throughout the film.
TL;DR: A photoluminescence band with unusual spectral properties has been observed in MBE grown CdTe, particularly prominent in single crystal layers containing large concentrations of extended defects generated either by metallurgical imperfections or contamination at the substrate-layer interface.
Abstract: A photoluminescence band with unusual spectral properties has been observed in MBE grown CdTe. It is particularly prominent in single crystal layers containing large concentrations of extended defects generated either by metallurgical imperfections or contamination at the substrate-layer interface. It is suggested that this luminescence results from electron-hole recombination at these extended defects. The weak LO phonon coupling may result from the delocalisation of the electronic binding potential between several nearly equivalent sites, while the spectral breadth of the no-phonon component may result from the influence of small environmental differences between these sites. Similar bands have been observed in ZnSe.
TL;DR: In this article, resistivity measurements on a series of uranium-platinum compounds were carried out in the range 1.3 up to 300 K and pressures up to 5 kbar.
TL;DR: In this paper, the I(E) profiles obtained display at least two oxidation peaks which can be attributed to the oxidation of different adsorbed CO species, and the results at the solid-gas interface and calculation of the quantity of electricity involved for each peak suggest that these two kinds of CO may be linearly bonded CO and bridge or multibonded CO.
TL;DR: In this article, the effects of underpotential lead and bismuth adsorbates on the cathodic reduction of O2 and H2O2 in perchloric acid solution obtained on rotating disc Au and Ag single crystal surfaces of (111), (100) and (110) crystallographic orientation are discussed.
TL;DR: The least square refinement of lanthanum hexaaluminate (La0.827Al11.9O19.09) was performed using single crystal X-ray diffraction data.
TL;DR: In this paper, a laterally uniform layer of CoSi2 was formed by annealing at temperatures between 405° and 500°C from CoSi with evaporated Si films.
Abstract: 2 MeV4He+ backscattering spectrometry and CuK
α x-ray diffraction were used to study CoSi2 formed by annealing at temperatures between 405° and 500 °C from CoSi with evaporated Si films. A laterally uniform layer of CoSi2 forms, in contrast to the laterally nonuniform CoSi2 layer that is obtained on single crystal Si substrates. The thickness of the CoSi2 film formed is proportional to the square root of time at a fixed temperature. The activation energy of this reaction is about 2.3 eV.
TL;DR: In this paper, a SiC/graphite composite, tested only at 680K, suffered almost complete delamination as a result of swelling of the SiC and densification of the graphite.
TL;DR: In this article, the ionic conductivity of single crystals of tysonite-type solid solutions La 1− x Ba x F 3− x (0⩽ x ⩽0.095) has been studied parallel and perpendicular to the crystallographic c axis in the temperature range 293-1300 K.