[en] The Harwell TAILS computer program is a versatile program for crystal structure refinement through the analysis of neutron or X-ray diffraction data from single crystals or powders. The main features of the program are described and details are given of the data input and output specifications. (author)

[en] A new computer program (SCRAP) for the analysis of powder diffraction patterns is described. A least-squares fitting of the observed and calculated intensities for individual points on the diffraction profile is used to determine values for the integrated intensities of the peaks, as well as any specified profile parameters. Conventional least-squares analysis of the integrated intensities can then be used to refine the values of the structural parameters. Use of this program therefore overcomes the limitations of the Rietveld profile refinement program (Rietveld. Acta Cryst.; 22: 151 (1967) and J. Appl. Cryst.; 2: 65 (1969)), in particular the unreliability of the estimated standard deviation values given by the latter. (author)

[en] A computer program is described which determines the multiplicity factors for a given set of X-ray or neutron powder diffraction reflections. The value of the multiplicity for each reflection is determined from a look-up table which is indexed by the symmetry type and the reflection type. The symmetry type is determined directly from the Space Group number and the reflection type from the Miller indices. There are no restrictions on the choice of indices which are used to specify the reflections. (author)

No abstract available

[en] A computer program has been written which determines the multiplicity factors for a given set of X-ray or neutron powder diffraction reflexions for crystals of any space group. The value of the multiplicity for each reflexion is determined from a look-up table which is indexed by the symmetry type, determined directly from the space-group number, and the reflexion type, determined from the Miller indices. There are no restrictions on the choice of indices which are used to specify the reflexions. (Auth.)

[en] The previously published result for the anisotropic fourth-order anharmonic vibrations in KCl, determined from neutron diffraction measurements, contained an error in sign. The parameter deltasub(Cl) which characterizes the appropriate term in the effective one-particle potential should be negative, indicating the predominance of Coulombic attractive forces between the ions in determining this contribution. (Auth.)

No abstract available

[en] The measurements of nuclear neutron diffraction intensities for a single crystal of UO₂ by Faber and Lander [Phys. Rev. B (1976), 14, 1151-1164] have been re-analysed using both the Cooper-Rouse and Becker-Coppens extinction formalisms. The results indicate that this crystal is type I in nature, not type II as was suggested by Faber and Lander, and this conclusion is essentially the same as that obtained for a different single crystal of UO₂ used in an earlier study of the wavelength dependence of extinction in this material [Sakata, Cooper, Rouse and Willis (1978). Acta Cryst. A34, 336-341]. The analysis of the Faber and Lander data gave a value for the scattering-length ratio bsub(U)/bsub(O) = 1.448 (2). (Auth.)

No abstract available

[en] A neutron diffraction study of cubic CsPbX₃ (X = Cl or Br) has been carried out over the temperature ranges 325-623 K for CsPbCl₃ and 408-673 K for CsPbBr₃. The temperature factors for the perovskite structure were derived following the method of Matsubara [Prog. Theor. Phys. (1975), 53, 1210-1211] which includes the use of cumulant coefficients to characterize anharmonic components for an Einstein model. The potential parameters were then obtained using a numerical integration method to analyse the temperature dependence of the temperature factors. It was found that the anharmonic components in the potential were very large for the Cs and X atoms which undergo displacements on passing through the phase transitions at lower temperatures (321 K for CsPbCl₃ and 403 K for CsPbBr₃). On the other hand, a harmonic potential is quite adequate to describe the thermal vibration of the Pb atoms, which are not displaced at the phase transitions. Thus the existence of the anharmonicity in the cubic phase seems to be anticipating the atomic displacement through the successive phase transitions for these substances. In addition to this anharmonicity, the temperature factors of the X atoms parallel to the (100) plane show an anomalous behaviour near the cubic to tetragonal phase-transition temperature, which should be connected with the softening of phonon mode at this phase transition. (Auth.)