摘要:

Primary normal alkylammonium halides crystallize in a preferred crystallographic orientation, forming single or twinned layers. The basal spacings are related to the number of carbon atoms within the homologous series, and are doubled in the twin layers. The orientation of the hydrocarbon chains between the ionic heads is discussed.

ISSN:1600-5767    

DOI:10.1107/S0021889871006423

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

Pure samples of the three most common hexagonal SiC polytypes have been examined in transmission electron diffraction. The diffraction patterns from the most densely populated planes in reciprocal space, the (h0l)* planes, differ considerably from the calculated patterns. The difference can be attributed to ubiquitous multiple diffraction. Calculated intensity distributions for 100 kV electrons are given for 4H, 6H, and 15RSiC. SiC whiskers have also been examined, and the unusual diffraction effects seen can, in general, be explained as a combination of (a) extreme disorder, (b) distorted lattices and (c) multiple diffractio

ISSN:1600-5767    

DOI:10.1107/S0021889871006435

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

At the stoichiometric 1 : 1 ratio of atoms, the cubic NaCl‐type monoxides TiO, VO and NbO have a large number of vacant sites on both the metal and oxygen sublattices. X‐ray determinations of the thermal expansions of these materials show quite distinct differences. At 298 °K, the coefficients of linear expansion defined as α = (1/a)(da/dT) are as follows: (TiO)0.856()0.144, α = 6.6 (7) x 10−6; (VO)0.848()0.152, α = 9.3 (6) x 10−6; (NbO)0.750()0.250, α = 4.8 (0) x 10−6. Progressive filling of the vacancies in titanium monoxide merely shifts the expansion curves parallel to each other in the direction of hig

ISSN:1600-5767    

DOI:10.1107/S0021889871006447

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

The compressibilities of titanium, vanadium and niobium monoxide have been determined using an X‐ray tetrahedral anvil press with NaCl as an internal standard. An extrapolation technique involving the plotting of (da/a)NaClversus(da/a)oxidewas developed for eliminating the errors in lattice parameter determination resulting from sample movement within the pressure cell. The Grüneisen constants of the monoxides were evaluated using published specific heat data and our own determinations of thermal expansi

ISSN:1600-5767    

DOI:10.1107/S0021889871006459

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

In the field of polymer physics, X‐ray diffraction line profile analysis methods have yet to acquire the significance which they possess in the analysis of the fine structure of metals and alloys. The present paper attempts to put these methods on a solid theoretical basis and to introduce new concepts in the analysis of polymeric X‐ray diffraction profiles. The theory of paracrystals has been used to calculate the expressions for integral line breadth and variance–range function of 0k0 diffraction profiles. The methodology is illustrated by an application of the integral breadth and variance methods to a polynosic viscose fibre, Tufcel, whose axial structure has been shown to be `paracrystalline'. Special emphasis is laid on the elimination of diffuse background scatter, the correction of profiles for angular variation factors, the problem of overlapping reflexionsetc. and the superiority of the variance method over the integral breadth method in the analysis of polymeric X‐ray diffraction profiles is esta

ISSN:1600-5767    

DOI:10.1107/S0021889871006460

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

An expression has been developed for the fourth moment–range function of an X‐ray diffraction profile in terms of the effects of finite crystal size and type II lattice distortions. A methodology has also been developed for its determination, which would be valuable in the analysis of the first order peaks from fibrous polymers. A computer program written in Fortran II for an IBM 1620 Computer, is described for this purp

ISSN:1600-5767    

DOI:10.1107/S0021889871006472

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

The theory of the X‐ray double‐crystal spectrometer is outlined. For a vertical rotation axis, crystal planes should be vertical and the X‐ray beam horizontal. Geometrical errors are introduced by crystal tilts (departure from vertical) and misalignment (departure of central ray from horizontal). Even with perfect alignment a vertical divergence correction is required. A typographical error in Schwarzschild's analysis of these geometrical effects led to erroneous results by Schnopper, later corrected in an erratum. The physical significance of this revision is considered here. The resulting expression for relative wavelength error indicates that, for zero tilt, misalignment produces no significant errors inrelativewavelengths. Geometrical errors are shown to be negligible in recent measurements of Bearden and very small in earlier work of Bearden&Shaw. The Williams vertical divergence correction, used by Bearden, is proven valid; the Parratt form, preferred by Schnopper, is incorrect. An alignment procedure which can reduce geometrical errors below 1 part per million is described. It employs a precision engineer's level (with autocollimating telescope) and a simple technique for grinding crystal faces parallel to atomic p

ISSN:1600-5767    

DOI:10.1107/S0021889871006484

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

For X‐ray investigations of structural changes in solids (including extremely air sensitive substances, frozen liquids or condensed gases) as a function of temperature a moving film camera has been developed on the basis of a modified Guinier technique. Temperatures can be maintained to within ±0.05°C from −1190° to 400 °C. The phase transitions occurring in solid hydrogen bromide have been investigated with the new camera. HBr is shown to crystallize in two orthorhombic low temperature and two face‐centered cubic high tempera

ISSN:1600-5767    

DOI:10.1107/S0021889871006496

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

Several applications of X‐ray topography with Ru‐filtered AgKα2radiation are described. Two of these are variations of the Lang method combined with a Ru filter. The first one is to improve the Lang traverse pattern from a specimen crystal including locally highly distorted regions such as inclusions, as demonstrated for a pure iron crystal. The second is to obtain a traverse pattern from the whole area on the same topograph for a specimen including appreciably misoriented parts, by making the first slit wider than usual. This example has been shown for a Ge crystal. Another application is concerned with taking a topograph of an area as wide as of the order of the length of a line focus, in a shorter exposure time, with high resolution. Examples have been shown for Ge and Si crys

ISSN:1600-5767    

DOI:10.1107/S0021889871006502

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY

摘要:

An attachment to a horizontal goniometer for X‐ray powder diffraction at temperatures up to about 2,000°C in a vacuum in the 10−9torr range is described. Specimen heating is by direct contact to a resistance strip heater with provision for electron beam heating. Temperature measurement is by thermocouple or optical pyrometer. High‐temperature parameter measurements on vanadium are presented as one of the examples of the capability of the app

ISSN:1600-5767    

DOI:10.1107/S0021889871006514

出版商:International Union of Crystallography    

年代:1971

数据来源: WILEY