摘要:

A study has been made of the molecular and crystallographic structures of Langmuir–Blodgett multilayer films of lead stearate. Electron microscopy and diffraction were used in the examination of such a film which had separated from the glass slide on which it had been formed. The films consist of a large number of three‐dimensionally ordered lead stearate crystals arranged in near‐perfect alignment, with the longest axes of their unit cell projecting from the plane of the supporting substrate. The unit cell of the lead stearate crystal is either monoclinic with the space groupP21/aor orthorhombic with the space groupP21212. The former is considered to be rather the more likely. The major lattice spacings are 4.96 Å (100), 7.38 Å (010) and 47 Å (001). The β angle of the monoclinic unit cell is not known but is probably within a few degrees of 90°. The lead atoms are in special positions in the basal plane, regardless of which is the correct unit cell, and the hydrocarbon chains make an angle of 62±5 ° with the basal plane. Any free stearic acid in the films occurs a

ISSN:1600-5767    

DOI:10.1107/S002188986900639X

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

The use of a BECM‐4 computer is described for interpreting X‐ray powder patterns of polycrystals belonging to the tetragonal, hexagonal or rhombohedral systems after Neskuchaev's technique. A program is proposed for direct indexing and the determination of crystal lattice parameters from the X‐ray powder pattern diffraction data of polycrystals belonging to these crystalline systems. The program is designed to make optimal use of the machine time. A block‐diagram shows the complete procedure for the computations. The program has been tested by application to the X‐ray powder diffraction pattern of calcium tungstate (scheelite), CaWO4, lead phosphate hydroxide, Pb5(PO4)3OH, and nickel fluorosilicate hexahydrate, NiSiF6.6H2O. Twenty or thirty experimental values are used for the computations. The average period between the experimental data input and the results output corresponds to ten minutes of machine time. Computations by the programming technique suggested are neither complicated nor

ISSN:1600-5767    

DOI:10.1107/S0021889869006406

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

The use of a BECM‐4 computer for interpreting X‐ray powder patterns of polycrystals belonging to the orthorhombic system is described. By modifying the program for the intermediate crystalline systems the proper program is obtained for the direct indexing of X‐ray powder patterns in the orthorhombic system after Neskuchaev's method, and the unit‐cell dimensions are computed. The program has been tested and has been used for the calculation of the powder pattern of lead oxide (yellow massicot), PbO. A block diagram showing the complete procedure for the computations i

ISSN:1600-5767    

DOI:10.1107/S0021889869006418

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

The usual method of specimen preparation for electron‐probe microanalysis can introduce errors of up to about ±3% in the estimates of the amount of an element present. It is believed that these errors are caused by the formation of `flowed' layers on the surfaces of polished samples. Two methods of reducing the errors are describ

ISSN:1600-5767    

DOI:10.1107/S002188986900642X

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

A method is presented for analyzing satellite reflections in X‐ray diffraction patterns in terms of two‐ or three‐dimensional atomic ordering arrangements. The ordered arrangement of Nd atoms in Nd2(MoO4)3has been successfully determined by this method. The derived model is consistent with the observed location and intensity distribution of the satellite reflections, as confirmed by structure factor calculation and by optical diffra

ISSN:1600-5767    

DOI:10.1107/S0021889869006431

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

The lattice constants and the atomic position parameter,z, of a high purity, low strain, single‐crystal of arsenic have been determined. Low extinction reflections of filtered MoKα and AgKα radiation were used for the determination ofz. The Bond precision technique with MoKα radiation was used for the determination of the unit‐cell dimensionsaandc. Average values foraandcin Å, and forzare: 4.2°Kz= 0.22764a= 3.7597c= 10.4412; 78°Kz= 0.22754a= 3.7595c= 10.4573; 299±3°Kz= 0.22707a= 3.7598c= 10.5475. The estimated standard deviation ofzis ±0.00004 at 4.2°K, ±0.00002 at 78°K and ±0.00005 at 299°K. The precision of a is estimated to be ±0–0001 Å and that forcto be ±0.0002 Å. The results for As are compared with those

ISSN:1600-5767    

DOI:10.1107/S0021889869006443

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

A simple design is suggested for a triple‐axis neutron spectrometer. Although the instrument does not have the flexibility of sophisticated machines, it is capable of the measurements required by most phonon problems. As it has only one working configuration it should be very simple to use. The basic design problem of these instruments is the control of a heavily shielded counter at the extremity of three variable arms. In the suggested instrument the counter is free only to rotate about the vertical. Support and control of the heavy shielding is, therefore, much simplified. The geometry is altered by varying the lengths of two of the arms, which is possible to high accurac

ISSN:1600-5767    

DOI:10.1107/S0021889869006455

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

X‐ray diffraction topography can be used to describe ultrasonic vibrational modes in resonating crystals. Dependence of intensity enhancement on Bragg reflection and on the vibrational displacement parallel to the diffraction vector allows the determination of the polarization direction and positional details of the standing waves to be made with four or five topographs in simple cases. In an SL‐cut quartz resonator designed to operate at 455 kHz the principal mode is thereby shown to be third‐order fac

ISSN:1600-5767    

DOI:10.1107/S0021889869006467

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

ISSN:1600-5767    

DOI:10.1107/S0021889869006479

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

ISSN:1600-5767    

DOI:10.1107/S0021889869006492

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY