摘要:

A method is described for the least‐squares refinement of lattice constants from powder diffraction data. This method differs from the other analogous methods mainly because it takes into account, for the indexing of the observed peaks, also the structure factors of the reflexionshkl. The refinement is carried out on the weighted observed peaks where the weightwOdepends on (1) an individual standard error which takes into account the peculiarities of the peak, and (2) a parabolic function of the θOvalue. The description of a computer program based on this method is giv

ISSN:1600-5767    

DOI:10.1107/S0021889876011643

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The Burgers vectors of dislocations in a Czochralski‐grown LiNbO3crystal have been determined by using Lang X‐ray diffraction topography. Dislocations with Burgers vectors of both ⅙〈201〉 and ⅓〈101〉 types (in hexagonal indices) are observed. The direction of the two Burgers vectors is thus identified to be along the line from one Nb (or Li) to the nearest Nb (or Li), and along the line from one Nb (or Li) to the second neighbou

ISSN:1600-5767    

DOI:10.1107/S0021889876011655

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A simple cryostat made of glass for X‐ray diffraction at low temperatures is described. The windows for the X‐rays are made from Mylar films fixed to slots cut in the base of a glass helium reservoir. This glass cryostat weighs only 6 kg and specimens can be easily handled in the cryostat. A specimen chamber has also been designed so thatin‐situpulse annealing can be easily carried out. Some examples of measurements with this cryostat are de

ISSN:1600-5767    

DOI:10.1107/S0021889876011667

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A Fourier transform method is proposed for the analysis of halo profiles from amorphous materials, which is analogous to the Fourier method for the analysis of Debye–Scherrer line profiles as originally expounded by Warren&Averbach [J. Appl. Phys. (1950),21, 595]. Applied to the first haloes of amorphous alloys, it gives radial distribution functions in which only those atom pairs are represented whose separations are atomic diameters or integral multiples thereof. The method is applied to the first haloes of amorphous Pt–C and Ni–P, which correspond to the nearest neighbour distances of metallic atoms. The result from amorphous Pt20C80confirms the microcrystalline model with diameter 2 × 2.27 Å. The analysis of amorphous Ni83P17gives a result less simple to understand. The correlation between neighbouring atoms extends as far as 5 × 2.2 Å, which explains the sharpness of the first halo observed. Directly neighbouring pair separations are found to be increased by 0.2~0.4 Å. The definition of amorphous scattering is discussed in relation to that in very broad Debye–Sc

ISSN:1600-5767    

DOI:10.1107/S0021889876011679

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

Twinning has been studied in Ti4O7crystals. It has been found that they are twinned by reticular pseudomerohedry. The sublattice controlling the twinning has an orthorhombic pseudosymmetry and is obtained from the triclinic cell (a= 5.593,b= 7.125,c= 12.456 Å, α = 95.02, β = 95.21, γ = 108.83°) by means of the transformation (a/b/c)* (½½½/½02/½2) (a/b/c)* triclinic. The effect of the twinning on the electron paramagnetic resonance spectra is al

ISSN:1600-5767    

DOI:10.1107/S0021889876011680

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

An experimental method of measuring absolute structure factors in imperfect single crystals by means of Bragg diffraction of 0.03 Åγ‐radiation is presented. It is shown that in principle atomic scattering factors can be deduced with an accuracy of about ±0.5% from rocking curves measured by means of γ‐ray diffractometry. Due to the uncertainties in the correction for thermal motion of the atoms, however, the values of the atomic scattering factors of copper at the 220, 22 and 333 reflexions could be derived only with an accuracy of ±1%. The measurements were made at room t

ISSN:1600-5767    

DOI:10.1107/S0021889876011692

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The hexagonal cell dimensionsaandcof 2H‐MoS2, 2H‐MoSe2and 2H‐WSe2have been measured over the temperature range 20 to 800 °C. In all three compoundsaandcincreased non‐linearly with temperature, the linear thermal expansion coefficient ofcbeing greater than that ofa. Above 500°C the compounds begin to decompose

ISSN:1600-5767    

DOI:10.1107/S0021889876011709

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A study has been made of the dislocations found in molybdenum ditelluride. Three different types were observed: undissociated dislocations, widely dissociated ribbons, and ribbons of an intermediate width. The γ/λ ratio was determined for each type of dislocation and found to lie in the range 10−11to 6.2 × 10−12 cm. In addition an estimation was made of both the growth fault and deformation fault proba

ISSN:1600-5767    

DOI:10.1107/S0021889876011710

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

Crystals of phosphorus oxynitride are tetragonal witha= 4.621 (2),c= 7.007 (4) Å,Z= 4, space group

ISSN:1600-5767    

DOI:10.1107/S0021889876011722

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

Ammonium phosphoberyllate, Be2P3O10NH4, is monoclinic with a unit cella= 12.200 (8),b= 8.645 (3),c= 8.937 (3) Å, β = 117.40 (5)° andZ= 4. Possible space groups areCcorC2/c. The chemical preparation and crystal data are given for this

ISSN:1600-5767    

DOI:10.1107/S0021889876011734

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY