Showing papers on "Single crystal published in 1972"
TL;DR: In this paper, the authors reviewed the literature concerning the decomposition of Zr and Ti alloys with particular emphasis on the b.c. phase transformation and the structure of the b-c.c structure relative to a 2 3 longitudinal displacement wave.
Abstract: The literature concerning the decomposition of Zr and Ti alloys is reviewed with particular emphasis on the b.c.c. ( β )→athermal omega ( ω ) transformation and the structure of Zr and Ti b.c.c. solid solutions. Illustrative examples are taken principally from the ZrNb and TiNb systems. High resolution dark-field electron microscopy, diffraction, and ultrasonic techniques have been used to follow the β → ω phase transformation in Zr and Ti alloys. The ω morphology was shown to consist of 10–15 A diameter particles arranged in 〈111〉 rows. As well, clusters of rows were presented in low solute content alloys and the cluster size decreased with increasing solute content. The observed morphology can explain the presence of {111} planes of diffuse intensity in reciprocal space and the change in appearance of the ω reflections with increasing solute content. The mechanism of the transformation is discussed in terms of instability or metastability of the b.c.c. structure relative to a 2 3 〈111〉 longitudinal displacement wave. This mechanism can be thought of as involving the 〈111〉 displacement of 2 neighboring close-packed rows of atoms relative to each other. Single crystal elastic constant measurements on ZrNb alloys show that C 44 decreases in the vicinity of the β → ω transformation. This is attributed to a softening of the b.c.c. structure which is a precursor to the actual transformation. Alloys that are known to be well above the M s temperature for the β → ω transformation, and hence must be single phase b.c.c. solid solutions, exhibit diffuse ω reflections. It is suggested that the diffuse intensity is due to the presence of a 〈111〉 linear fault (or disorder) in the b.c.c. phase. The atom movements associated with this fault are similar to the displacements required for the β → ω transformation.
157 citations
TL;DR: In this paper, the interaction of O 2 with a single crystal W(100) surface at 300K has been examined using a combination of techniques, where a precision gas dosing system was used to deposit O 2 onto the crystal; the absolute accuracy in the average flux F (molecules cm −2 s −1 ) is ± 6 %.
155 citations
TL;DR: In this article, the diffusion coefficient of hydrogen in zirconium, Zircaloy-2 and Zirca-4 was determined in the temperature range, 275 °C to 700 °C.
152 citations
TL;DR: In this article, coherent averaging techniques were used to examine the 19F shielding tensors of the trifluoromethyl group in single crystals of silver trflluoroacetate.
Abstract: Coherent averaging techniques are used to examine the 19F shielding tensors of the trifluoromethyl group in single crystals of silver trifluoroacetate. At room temperature, where the CF3 groups are rotating rapidly, the spectrum consists of a single line whose orientation dependence allows a determination of the orientation of the CF3 groups in the unit cell. The rigid lattice (40°K) spectra exhibit the six lines expected on the basis of the x‐ray crystal structure, also determined in this work, and allow a determination of all six independent elements of each of the three incongruent chemical shift tensors.
148 citations
147 citations
TL;DR: In this paper, the authors observed on a NiO single crystal two superlattice X ray diffraction peaks, which disappear above the Neel point, and their intensities, 4 × 10 -8 smaller than normal ones, agree with those evaluated from photon-electron spin interaction.
133 citations
TL;DR: In this article, the authors describe the preparation of the following complex oxide crystals which have not previously been grown by the flux method: FeNbO4, MnWO4 and CoWO 4.
Abstract: This paper describes the preparation of the following complex oxide crystals which have not previously been grown by the flux method: FeNbO4, MnWO4, CoWO4, NiWO4, RMn2O5 (R = Er to Sm, and Y), RMnO3 (R = Er to Gd), LaOCl, La2Ti2O71, Bi2Sn2O7, and PbTiP2O8. Single crystal X-ray diffraction data are reported for the latter material, the preparation of which has not previously been reported, and for La2Ti2O7 and Bi2Sn2O71, for which only powder data were previously available. Improved methods for the growth of Mn3O4, LaCoO3, RPO4 (R = Yb to Gd), RCrO3 (R = Lu, Yb), ErOF and NaNbO3 are also reported.
126 citations
TL;DR: In this article, the authors report light-wave propagation experiments in singlecrystal epitaxially grown garnet films, and discuss refractive index and lattice constant considerations for various garnets, and also the use of iron and gallium garnet substrates as magneto-optical waveguides useful in integrated optics.
Abstract: We report light‐wave propagation experiments in single‐crystal epitaxially grown garnet films. The discussion includes refractive index and lattice constant considerations for various garnets, and also the use of iron garnet films on gallium garnet substrates as magneto‐optical waveguides useful in integrated optics.
124 citations
TL;DR: In this paper, the catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and o2 and various temperatures.
Abstract: The catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and O2 and various temperatures. The surface cleanliness of the Pt crystal is monitored by Auger electron spectroscopy. The results of the reaction study are generally in agreement with previous studies for polycrystalline Pt catalysts. The temperature dependence of the formation rate of CO2 exhibits a maximum whose position depends on the composition of the gas phase. At T=215°C two different rate laws are valid. For PO2>PCO the rate of CO2 formation is proportional to PO21.1PCO−0.6, while for PO2>PCO it is proportional to PO20.25 PCO0.75. These observations support the idea that the reaction obeys an Eley-Rideal mechanism in the pressure and temperature range investigated, and the results are evaluated accordingly. The influence of segregated Si on the CO oxidation reaction is investigated and found to be small.
120 citations
TL;DR: In this paper, the authors present a review of the state-of-the-art work in the field of thermal Neutron Diffraction, focusing on the use of the Aeta Cryst.
Abstract: ABRAHAMS, S. C. 8~ PRINCE, E. (1962). J. Chem. Phys. 36, 50. BACON, G. E. (1969). Acta Cryst. A25, 391. BINAS, H. (1966). Z. anorg, allg. Chem. 347, 133. BUSING, W. R. & LEVY, H. A. (1964). Acta Cryst. 17, 142. CALLERI, M. t~ FERRARIS, G. (1967). Per. Mineral, 36, 1. CASSIEN, M., HERPIN, P. & PERMINGEAT, F. (1966). Bull. Soc. franc. Min~r. Crist. 89, 18. CHIDAMBARAM, P., SEQUEIRA, A. • SIKKA, S. K. (1964). J. Chem. Phys. 41, 3616. COOPER, M. J. (1969). Acta Cryst. A25, 488. COPPENS, P. (1970). Chap. 6 in Thermal Neutron Diffraction. Edited by B. T. M. WILLIS. Oxford Univ. Press. COULSON, C. A. (1970). Chap. 5 in Thermal Neutron Diffraction. Edited by B. T. M. Wn.Lm. Oxford Univ. Press. CURRY, N. A., DENNE, W. A. & JONES, D. W. (1968). Bull. Soc. Chim. France, p. 1748. DENNE, W. A. & JONES, D. W. (1969). Aeta Cryst. A25, S 125. FERRARIS, G., JONES, D. W. & YERKESS, J. (1971a). Acta Cryst. B27, 349. FERRARIS, G., JONES, D. W. 8¢. YERKESS, J. (1971b). Acta Cryst. B27, 354. FISCHER, E. (1960). Chem. der Erde, 20, 162. GUI~RIN, H. (1941). Ann. Chim. 16, 101. MARTIN, C., DURIF, A. & AVERBUCH-POUCHOT, M.-T. (1970). Bull. Soc. fi'anf. MinOr. Crist. 93, 397.
116 citations
TL;DR: In this paper, the elemental composition of a surface can be derived from the energy spectrum of singly reflected noble gas ions, and it is shown that it is also possible to obtain information about certain structural features on the surface from energy spectra of multiply reflected ions.
TL;DR: Pd2Si contacts to single crystal silicon have been made by depositing Pd at room temperature and annealing at a succession of elevated temperatures as discussed by the authors, which leads to an appreciation of the excellent electrical characteristics of these contacts which are shown to be superior to alloyed aluminum.
Abstract: Pd2Si contacts to single crystal silicon have been made by depositing Pd at room temperature and annealing at a succession of elevated temperatures. The silicide initially formed is a single crystal, even at room temperature. Its crystal structure is uniquely related to that of the underlying silicon with the basal plane of Pd2Si making an excellent match, with respect to silicon atom positions, with the (111) plane of silicon. Understanding this epitaxy leads to an appreciation of the excellent electrical characteristics of these contacts which are shown to be superior to alloyed aluminum. For comparison, barrier height measurements reproduce earlier results of Kircher on Pd2Si formed during a high temperature (200°C) deposition of Pd.
TL;DR: In this paper, the authors investigated the sorption of oxygen on the (110) face of a nickel single crystal and obtained the spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom.
Abstract: In an experiment which combines low energy noble gas ion backscattering with LEED the sorption of oxygen on the (110) face of a nickel single crystal is investigated. The energy of the backscattered He+ ions is governed by binary collisions whereas the intensity of the spectrum is given by the cross sections, the concentration of surface atoms, the neutralization probabilities and the geometry. The spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom. From a shadow effect observed at small angles of incidence it can be estimated that the adsorbed oxygen protrudes beyond the plane of the Ni atoms by about 0.4–0.8 A.
TL;DR: In this paper, the angular dependence of the linewidths of a spin probe in the mesophase of a smectic liquid crystal has been studied and a theory for its angular dependence has been developed.
Abstract: A spin probe dissolved in the mesophase of a nematic or smectic liquid crystal behaves, in many ways, as if it were encorporated in a uniaxial single crystal. For example the positions of the lines in the electron resonance spectrum of the probe depend on the orientation of the liquid crystal with respect to the magnetic field. In addition the widths of the spectral lines might also be expected to be angular dependent. The form of this angular dependence is readily calculated provided the dominant spin relaxation process results from molecular reorientation with respect to the director in the mesophase. In this paper we develop a theory for the angular dependence of the linewidths and show how it could be used, with some advantage, to investigate molecular reorientation in a macroscopically anisotropic system. The observed angular dependence of the linewidths for a nitroxide spin probe dissolved in the mesophase of a smectic A liquid crystal confirms certain aspects of the theory.
TL;DR: In this paper, the energy spectra of atoms sputtered from a gold target have been measured as a function of ion energy and species for target temperatures in the range 100 to 1200°K.
Abstract: The energy spectra of atoms sputtered from a gold target have been measured as a function of ion energy and species for target temperatures in the range 100 to 1200°K. Both single crystal and polycrystal targets have been used, with surface topography monitored by a scanning electron microscope. The effect of raising the target temperature towards 1200°K is always to produce a low energy peak in the energy spectrum near 0.1 eV. This is found to have behaviour consistent with a thermal spike model, and at high temperature accounts for a large fraction of the total sputtering yield. The time-of-flight spectra show two peaks, one at about 10 eV the other at about 500 eV. The former was always present and when a crystal target was used with ejection along a axis it took on a kinked shape consistent with a contribution from focused collisions. The effect of increasing the temperature was to reduce this effect, presumably by thermal scattering of focused collisions. The 500 eV peak was also affec...
TL;DR: In this article, large diamond crystals up to 6 mm in average diameter were grown at high pressures (55-60 kbar) and temperatures (1400-1500 °C) by causing diamond to dissolve in a molten catalyst metal (Fe, Ni, Co, etc.) in a hot region and deposit upon a seed crystal in a slightly cooler region.
Abstract: Large diamond crystals up to 6 mm in average diameter may be grown at high pressures (55–60 kbar) and temperatures (1400–1500 °C) by causing diamond to dissolve in a molten catalyst metal (Fe, Ni, Co, etc.) in a hot region and deposit upon a seed crystal in a slightly cooler region. Several days are required to produce a high quality single crystal. The process can be controlled to produce different kinds of diamonds whose properties have been studied.
TL;DR: The epitaxial growth of GaN by vapor phase reaction between GaCl and NH 3 in a He carrier gas was described in this paper, where single crystal layers 100-200 ωm thick and ∼ 1 cm 2 in area were obtained on (0001) oriented sapphire substrates at deposition temperatures near 1050 °C.
TL;DR: In this paper, the authors studied the diffusion of hydrogen in a single crystal of palladium (Pd${\mathrm{H}}_{0.03}$) by quasielastic neutron scattering.
Abstract: The diffusion of hydrogen in a single crystal of palladium (Pd${\mathrm{H}}_{0.03}$) has been studied by quasielastic neutron scattering. The results provide the best evidence yet obtained for the applicability of a simple jump model of hydrogen diffusion in a metal and confirm the predominant occupation of octahedral sites in the Pd crystal, with a mean residence time at 623 K of 2.8 psec between jumps.
TL;DR: The magnetic structures of metallic samarium have been determined from neutron-diffraction data on a single crystal of $^{154}\mathrm{Sm}$ as discussed by the authors, where anomalies in a number of physical properties of this metal at 106 and 13.8\ifmmode^\circ\else\textdegree\fi{}K are associated with ordering of the moments on the hexagonal and cubic sites, respectively.
Abstract: The magnetic structures of metallic samarium have been determined from neutron-diffraction data on a single crystal of $^{154}\mathrm{Sm}$. Anomalies in a number of physical properties of this metal at 106 and 13.8\ifmmode^\circ\else\textdegree\fi{}K are associated with ordering of the moments on the hexagonal and cubic sites, respectively. The unusual form factor expected for a $4{f}^{5}$ configuration has been observed. Striking evidence for important conduction-electron polarization effects has been found.
TL;DR: The crystal structure of the mineral analcime, NaAISi206, known from x-ray analysis to approximate closely to the cubic space-group symmetry Ia3d, has been examined by neutron diffraction.
Abstract: The crystal structure of the mineral analcime, NaAISi206 . H20, known from x-ray analysis to approximate closely to the cubic space-group symmetry Ia3d, has been examined by neutron diffraction. Intensity data from a single crystal were collected for one octant so as to be representative of cubic and some lower symmetries. In general, the systematic absences were consistent with the space group Ia3d; within experimental error, the six reflections equivalent for Laue group m 3 m were equal in intensity. From Fourier difference syntheses and least-squares refinements, it is concluded that the neutron data, like the x-ray data, are consistent with an averaged Ia3d structure. Full-matrix
TL;DR: In this article, the exact atomic arrangement of SnP3 is described as a layer structure related to the As-type structure (A7) and the identical layers consist of puckered P6 rings connected by Sn atoms.
01 Jun 1972
TL;DR: In this article, the elastic and plastic properties of textured polycrystalline metals are calculated using the crystallite orientation distribution function derived from X-ray texture data together with data which describe the single crystal behavior.
Abstract: Methods are described for the calculation of the elastic and plastic properties of textured polycrystalline metals. The calculations involve the crystallite orientation distribution function derived from X-ray texture data together with data which describe the single crystal behavior. Subsequently, it is shown how a knowledge of the elastic properties can be used to make an analytical prediction of the plastic properties. In making this prediction use is made of the fact that for cubic metals both the elastic and plastic properties are influenced predominantly through the zeroth and fourth order coefficients of the crystallite distribution function. The methods are illustrated by application to the analysis of the data of Stickels and Mould. The statistical correlation they observed is shown to have a justifiable analytical basis.
TL;DR: The crystal structure of trisacetylacetonato (1,10-phenanthroline) europium(III), Eu(C 6 H 7 O 2 ) 3 (C 12 H 8 N 2 ), has been determined by single crystal X-ray diffraction techniques.
TL;DR: In this article, single crystal epitaxial layers of Gaxln1−xP alloys have been grown by the steady-state liquid phase (LPS) epitaxia growth technique on (111)B GaAs substrates.
Abstract: Single crystal epitaxial layers of Gaxln1−xP alloys have been grown by the steady-state liquid phase epitaxial growth technique on (111)B GaAs substrates. The crystal growth process has been studied in detail and the resultant epitaxial layers have been characterized with respect to their structural, electrical and optical properties. Epitaxial layers of good structural quality could be grown only in the composition range x = 0.48 to 0.53, where the lattice parameter is close to that of the GaAs substrate. The band gap of these crystals was in the range 1.86 – 1.92 eV as determined by optical absorption and photoluminescence measurements.
TL;DR: In this article, the authors measured the oxygen partial pressure and temperature dependence of the departure from stoichiometry, electrical conductivity and Seebeck coefficient of CoO single crystal and polycrystalline specimens.
01 Jan 1972
TL;DR: The importance of the atomic structure of solid surfaces and of adsorbed molecules in heterogeneous catalysis has been advocated by many scientists throughout the years as mentioned in this paper, however, the difficulties of determining the atomic structures of catalyst surfaces proved to be almost insurmountable, mostly because of the configuration of the catalyst systems.
Abstract: The importance of the atomic structure of solid surfaces and of adsorbed molecules in heterogeneous catalysis has been advocated by many scientists throughout the years. Early studies by Balandin [l], for example, have suggested the presence of close-packed structures of adsorbed molecules that are intermediates in catalytic reactions. In his view both the atomic structure of the substrate metal surface and the structure of the adsorbed molecules were of primary importance in carrying out certain types of catalytic reactions. In the past, however, the difficulties of determining the atomic structure of catalyst surfaces proved to be almost insurmountable, mostly because of the configuration of the catalyst systems. In the case of metal catalysts most commercial catalyst systems consist of finely dispersed metal particles that are deposited on a high surface area support, most frequently silica or alumina. Even at present the atomic structure of such polydispersed systems cannot be ascertained una...