Characteristic features of the TOF (time of flight) neutron diffraction are summarized. In this method, i) all the reciproal points on the rod passing through the origin in the reciprocal space can be scanned by each burst of white neutrons, ii) it is easy to measure high index reflections at the large scattering angle, iii) each reflection is not affected by the higher-order harmonics, and iv) it is easy to measure the physical properties depending on the neutron wavelength. The pulse neutron generator as well as the data acquisition system in the Laboratory of Naclear Science of Tohoku University is described. The TOF method seems to be very powerful if it is applied to the accurate structure analysis. The data correction methods are discussed. The TOF method is prospective to the study of transient phenomena. In this method one can apply to the crystalline sample an external field pulsed with the same frequency as the neutrons. By using this method, the transient state of the polarization reversal of the ferroelectric NaNO2 has been observed. The magnetically pulsed neutron TOF spectrometer is briefly introduced after a review of the choper history.
Emphasis has been placed to the phenomena which seem to clearly show the nature of the one-dimensional array of TCNQ and to the X-ray analyses of two types of the superlattice structures of a molecular complex and an anion radical salt of TCNQ. The subjects outlined are as follows: (1) the possibility of a neutral↔ionic transition of the ground state charge distribution in the mixed-stacking columns of charge transfer complexes, (2) the relation between electrical conductivities and columnar structures of TCNQ anion radical salts, (3) Peierls instability of one-dimensional metal, (4) charge distribution and localization of excess electrons in TCNQ columns, (5) the evidence for monomer-dimer transition of alkali metal-TCNQ from X-ray diffraction patterns of these salts, (6) observation of X-ray satellite reflexion and the analysis of the sinusoidal structure of PTZ-TCNQ, (7) X-ray analysis of the anti-phase domain structure and stacking disorder of NH4-TCNQ.
The formalism of higher order elasticity theory, which is used to describe the finite deformation of crystals, is at first presented. The importance of the higher order elastic constants, which are defined as the higher-order finite-strain derivatives of crystal energy, is emphasized. Experimental methods for determining the higher order elastic constants of crystals and also theoretical aspects of calculating the higher order elastic constants of various kinds of materials are explained. Two examples of application of the higher order elasticity theory for treating anharmonic properties of crystals ae shown, namely, the thermal expansion of crystals and the scattering of phonons by static strain fields in crystals.