摘要:

The Bond method for accurate lattice‐parameter measurements has been applied to spheroidal crystals smaller in diameter than the incident beam. By measuring bothhand to reduce the effects of mis‐centering and using a circle accurate to ±0.001°, a precision of a few parts per million can be attained. The accuracy of the method has been tested by measuring the lattice parameter of vacuum float‐zone refined silicon by the conventional Bond method (using large, flat specimens) and by the modified method (using spheroidal specimens 0.25 mm in diameter). The results indicate that in addition to the usual corrections for refraction, emission‐line asymmetry, and vertical divergence, a correction is required for changes in the asymmetric diffraction profile caused by the combined effects of horizontal divergence and absorption in the sphere. The correction is approximately 15 p.p.m. or 0.000079 Å in the case of the Si spheres and an instrument having a horizontal divergence of ±0.0013 rad. The corrected lattice parameter agrees within 4 p.p.m. with results obtained by the conventional method. These results demonstrate the feasibility of making precise and accurate measurements on many materials that are not available in the form of larg

ISSN:1600-5767    

DOI:10.1107/S002188987601039X

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The method of determining the ratio between lattice parameter and electron wavelength from Kikuchi‐line intersections with an accuracy about 0.1% which was described by Høier [Acta Cryst. (1969). A25, 516–518] for cubic crystals, is extended to crystals with any lower symmetry. A computer program using a least‐squares refinement has been developed and applied to the determination of unknown lattice parameters in an orthorhombic olivine and a triclinic feldspar crystal. A combination of energy‐dispersive X‐ray analysis and Kikuchi‐line intersection measurements can in many cases be utilized to increase the accuracy in the determination of the lattice parameters. For the feldspars such a combination of measurements can be used to determine the distribution of the Al and Si atoms in the tetrahedral positions of t

ISSN:1600-5767    

DOI:10.1107/S0021889876010406

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A detailed description of an automatic low‐temperature apparatus to be used in single‐crystal diffractometry is given. The crystal is cooled by a stream of nitrogen gas. Prevention of ice formation on the crystal is achieved by heating the outer parts of the gas stream by a conical metal device. The unit‐cell dimensions of α‐quartz have been determined in the temperature range 86–298 K with this apparatus on a four‐circle diffractometer

ISSN:1600-5767    

DOI:10.1107/S0021889876010418

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

Pellets of the ferrimagnetic material Ba3Co2Fe24O41were sintered at temperatures between 1220°C and 1310°C in (1) a non‐oriented state, (2) with a fibre texture generated by a rotating magnetic field during pressing and (3) with a fan texture due to a static magnetic field. During sintering up to 24 h. the changes in texture sharpness and density were studied. Textured samples attained a higher ultimate density than non‐oriented ones and those with fibre texture became densest. To determine the sharpnesses of the texture the maximum standardized intensities of the reflexions 0′0′0′14, 1′0′′16, 1′1′′10 and 110 were calculated from the experimental intensities. The mutual relations of the maximum standardized intensities of the four reflexions were given by representing the intensities of these reflexions for both textures as polynomials. The dependence of sharpness of texture on position in the pellet has been determined. It followed that this sharpness had to be averaged over the height of the pellet, to get a representative value for the whole pellet. Both kinds of texture were found to sharpen during normal grain growth, but during exaggerated grain growth in the last stage of sintering the sharpness of the fibre texture decreased, whereas that of the fan texture still increased. A possible explanation of this phenomenon is given on the basis of the different characters of these textures. A linear relationship is found between sharpness of texture and area porosity during normal grain growth. The compound starts decomposing at a lower temperature than

ISSN:1600-5767    

DOI:10.1107/S002188987601042X

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A fast computer program written in Fortran is presented. It calculates with a trial‐and‐error method the unit‐cell dimensions from thedvalues obtained from powder patterns. The special techniques used in this program to keep the computation time short are described. The program itself is designed primarily for triclinic and orthorhombic lattices. Monoclinic lattices are treated like triclinic ones: for tetragonal, hexagonal and rhombohedral structures orthorhombic cells can be calcu

ISSN:1600-5767    

DOI:10.1107/S0021889876010431

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

X‐ray reflection topographs were taken of a zinc surface oriented about 1° from a basal plane. Basal dislocations are revealed in the topographs, and their apparent depth was determined using stereo pairs of topographs. The apparent depths observed in a complimentary pair of topographs using 103 and 013 reflections were significantly greater than those observed in an asymmetric pair of topographs in which the same 103 reflection was used. This difference is attributed to shifts of the image with respect to the dislocation position. Quantitative estimates of the image shifts and the actual depths of the observed dislocations are obtained from the measurement of apparent depths. Dislocations are visible over the range of depths from 1.7 to 4.5

ISSN:1600-5767    

DOI:10.1107/S0021889876010443

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The dislocation structure in olivine crystals has been studied by means of X‐ray topography. The dislocations have Burgers vector [100] or [001], the majority of the dislocations lying in the (100) or the (001) plane and being of the edge, screw or mixed type. Some dislocation tangles are apparently closely connected to Ca‐rich inclusions. The observed dislocation structure and its possible origins are discussed in relation to previous electron diffraction studies and slip line observations on olivine crystals deformed naturally or experimentally at various temperatu

ISSN:1600-5767    

DOI:10.1107/S0021889876010455

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The absolute polarity of single crystals of α‐Cu(IO3)2and Nd(IO3)3.H2O, determined by anomalous X‐ray scattering techniques, has been related to the sense of the piezoelectricd22and pyroelectricp2coefficients in these monoclinic crystals. The absolute sense ofd22in both cases is predictable from a consideration of the behavior of the spontaneous polarizationPsunder stress.Pswas calculated on the basis of a simple point‐charge and dipole model. The positive sense ofp2in α‐Cu(IO3)2and Nd(IO3)3.H2O (each with magnitudes of about 2 x 10−5Cm−2deg−1: the secondary pyroelectric coefficients are probably nearly an order of magnitude smaller) allows the inference that |Ps| increases with increasing temperature. The absolute sense ofd33in hexagonal LiIO3, determined by Morosin [Private communication (1972) quoted as Ref. 25 of Bergman, J. G.&Crane, G. R. (1974).J. Chem. Phys.60, 2470–2474] is similarly predictable from the calculatedPs. Turner's [J. Appl. Cryst. (1976).9, 52] measurement ofp3in LiIO3combined withPsalso leads to the inference of increasing |Ps|

ISSN:1600-5767    

DOI:10.1107/S0021889876010467

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

Single crystals of Bi–Sb alloys were etched in transverse magnetic fields ranging from 1000 to 4000 gauss. It has been shown from the study of the etch pattern on the oppositely matched cleavage faces and from successive etching that the dislocations move in the magnetic fi

ISSN:1600-5767    

DOI:10.1107/S0021889876010479

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A difference method for precise determination of lattice constants on Weissenberg counter diffractometers is described. For a monoclinic cell the reciprocal constantsa* andc* are determined directly and β* is calculated from them.b* is determined from a second setting

ISSN:1600-5767    

DOI:10.1107/S0021889876010480

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY