No abstract available

[en] Using traditional approximations, the correction for thermal diffuse scattering in the neutron time-of-flight diffraction on monocrystals is calculated. This scattering measured by the time-of-flight method from that measured by the angular dispersive diffraction method and this can be explained with the aid of the scattering surface. In time-of-flight the scattering surface has different geometries in three regions of the ratio between the sound velocity in crystal and the neutron velocity; in the angular dispersive method are only two such regions. The difference between the two methods disappears if the flight path after sample is very small comparatively with the total flight path

[en] Elastic residual and inhomogeneous defect-related strains are very important parameters when considering thin-film and microelectronics device properties and operation. In regard to the residual strain/stress modeling, we describe a novel approach to model diffraction line shifts caused by elastic residual or applied stresses in textured polycrystals. The model yields the complete texture-weighted strain and stress tensors as a function of crystallite orientations, the so-called weighted strain orientation distribution function. In the second part, we present an extension to the phenomenological thermodynamic theory for ferroelectrics. It includes the contribution of both residual-elastic lattice-misfit strain and inhomogeneous strain caused by lattice defects. The model yields correction terms for dielectric and ferroelectric quantities in terms of both elastic misfit strain and defect-related strain that was successfully applied to the pristine, W and Mn 1% doped Ba_0.6Sr_0.4TiO₃ epitaxial thin films grown on the LaAlO₃ substrate

No abstract available

[en] This article re-analyses the extinction problem in diffraction. It has been proved that Hamilton's equations are valid only for mosaic crystals, type I. The solution of these equations has been found for any shape of crystal using general initial conditions. (Auth.)

[en] The theoretical treatment of one-phonon thermal diffuse scattering (TDS) in single-crystal neutron diffraction at fixed incident wavelength is reanalysed in the light of the analysis given by Popa and Willis [Acta Cryst. (1994), (1997)] for the time-of-flight method. Isotropic propagation of sound with different velocities for the longitudinal and transverse modes is assumed. As in time-of-flight diffraction, there exists, for certain scanning variables, a forbidden range in the one-phonon TDS of slower-than-sound neutrons, and this permits the determination of the sound velocity in the crystal. A fast algorithm is given for the TDS correction of neutron diffraction data collected at a fixed wavelength: this algorithm is similar to that reported earlier for the time-of-flight case. (orig.)

[en] A new concept of high-resolution focusing configuration begins to be accepted as an alternative solution to the existing conventional configurations. Among the earliest work performed in this direction is that performed at the Institute for Nuclear Research, Pitesti. These results are presented below. The experimentally determined resolution properties for two focusing configurations obtained at TRIGA reactor Pitesti and at VVRS reactor Bucharest are given in order to be compared with those obtained for the conventional ones. The principles to get focusing in crystal neutron diffractometry are presented. The main characteristics for a focusing instrument are given. (author)

[en] Complete text of publication follows. Recently [1] were proposed the principle and the construction of a high-resolution powder diffractometer with pneumatically bent monochromator crystal and flat thin sample. Working on a focusing principle the peak profile and position are sensitive to a lot of instrumental aberrations. The instrumental profile is calculated by Monte Carlo procedure taking account of the real shape of the pneumatically bent monochromator and the misalignment parameters of the instrument. These calculations will be important in a further effort to find instrumental corrections mainly for the reliable crystallite size and the strain of first and second kind determinations. (author) [1] I. Ionita, A.D. Stoica, M. Popovici, N.C. Popa, Design for a Focusing High-Resolution Neutron Crystal Diffractometer, accepted for publication in Nuclear Instruments and Methods A

[en] The scatterina law of the heavy water is determined as a function of temperature. The experimental values corresponding to 295degK, 365degK, 453degK and 533degK are reported. (authors)

[en] The phase transitions and symmetries in LiKSO₄ are studied by the neutron time-of-flight diffraction. Four from the five transitions given in literature are found in the temperature range of 15 to 960 K. One of the transitions having no ferroelastic nature, is not observed. In three phases the splitting of the diffraction peaks takes place due to domain occurence, confirming thus their ferroelastic nature. The geometry of the splitting gives the symmetry mm2 for the phase appearing for T < 189 K. At the transition into this phase the unit cell deformation consists in a dilation upon orthorhombic axes Δa/a = -Δb/b = 0.018 accompanied by a rotation around the c axis with an angle of 15'. (author)