[en] The ultrasonic second- and third-order coupling parameters, K₂ and K₃, determined by ultrasonic second-harmonic generation, are evaluated in terms of the second- and third-order elastic moduli, for a number of crystalline systems. It is shown that K₂ and K₃ turn out simply to be the values of the elastic moduli C₁₁ and C₁₁₁, transformed into the direction of propagation. The possibility of evaluating the complete set of third-order elastic moduli from measurements of second-harmonic generation and hydrostatic pressure dependence of the sound velocity for pure mode propagation is discussed. Symmetries considered: cubic, hexagonal, rhombohedral, tetragonal, and orthorhombic

[en] A computer oriented numerical method is developed to calculate the various parameters associated with elastic wave propagation in the case of the most general crystalline system with 24 elastic constants. The method involves the evaluation of various wave surfaces (phase velocity, inverse velocity and energy surfaces), deviation of energy vector from wave vector, phonon magnification etc. starting from the basic Christoffel's equation in a general direction. Calculations have been carried out for various crystal systems such as cubic (A-15 compounds), tetragonal (ADP, KDP, TeO₂, BaTiO₃, Rutile, Indium), Orthorhombic (Iodic acid, Rochelle salt, Barium Sodium Niobate) and trigonal (Quartz, Sapphire) systems. This study of the phonon focusing is expected to find a very important role in various phenomena in crystals such as lattice conductivity, mode-mode coupling, etc. as these phenomena can be modulated by phonon focusing. (K.B.)

[en] Taking time reversal into account there are 122 crystallographic Shubnikov point groups and 21 limiting Shubnikov point groups containing ∞-fold rotation axes. The restrictions on the form of the tensor describing the piezomagnetoelectric effect are given for all these groups and compared with results of other authors. Antiferromagnetic materials with non-centrosymmetric point groups containing space-time inversion are suitable candidates for measuring the piezomagnetoelectric effect. (orig.)

No abstract available

[en] A phenomenological model of lattice dynamics of hcp metals has been developed by assuming the ions to have a spheroidal shape with the axis of revolution parallel to the c axis. Overlap of spheroidal ions causes a noncentral interaction between the first neighbors (as in beryllium). The model is derived from a force system consisting of this noncentral overlap interaction, as six-neighbor central pair potential, and an electron-ion interaction term. Application of this model to zinc and beryllium shows that the force parameters coupling neighbors beyond the second are rather small as compared with the parameters for the first two neighbors. The dispersion curves derived from the model present a good agreement with the experimental curves

[en] Lattice-vibrations of bcc transition metals have been discussed on the basis of a seven parameter model. Four parameters are associated with the central ion-ion interactions extending upto fourth neighbours. Two parameters describe the angular forces operating between first and second neighbouring ions. Ions-electron-ion interactions assumed to be non central are discussed in terms of the remaining parameter. The phonon-frequencies for Vanadium and Tantalum have been computed on the basis of the model. Experimental data on the phonon-frequencies of these metals are found to be in good agreement with the computed ones. (author)

[en] A convenient method for the description of orientation data for cubic, hexagonal, tetragonal and orthorhombic crystals is given. The method can also be used for the representation of disorientation data, where disorientations between any two crystals of the specified symmetry lattices are considered. It is based on the quaternion formalism introduced into the discussion of orientations and disorientations by Grimmer, Frank and others. Since orientations and disorientations can be interpreted as rotations which in turn can be represented by only three parameters a vector description is used. These vectors span a rotation space corresponding to the usual space of Eulerian angles. It is called Rodrigues vector space. The direction of a Rodrigues vector is parallel to the rotation axis and its length is tan (Θ/2), where Θ describes the rotation angle. A method for selecting a unique representative out of the numerous symmetrically equivalent Rodrigues vectors is given. Since these selection rules depend on the symmetry of the crystal lattices considered they yield compact domains in the Rodrigues vector space which are typical for each type of lattice or lattice pair. These domains are always bounded by planes. Frank (1987) called them fundamental zones and described them for the orientations of cubic, hexagonal and orthorhombic crystals. (orig.)

[en] Existence of two crystalline modifications of zirconium tetraiodide (α-rhombic and β-tetragonal ones) is established. Parameters of crystal lattices are determined and supposition on the direction of iodine atoms layer interchange is made. Convergence of roentgenograms of both modifications and cubic zirconium tetraiodide is accounted for. The density of cubic modification is the lowest of all modifications

No abstract available

[en] High temperature C-ray diffraction is used to investigate calcium uranate of theoretical formulation 'CaUO₃' which is obtained either by interaction of uranium dioxide and lime under vacuum or by 'CaUO₆' oxide reduction. This new phase of monoclinic symmetry between 20 and 1,500 deg. C becomes orthorhombic above 1,500 deg. C, and shows a linear expansion and a constant composition between 800 and 1,500 deg. C (U/O + Ca ≅ 1.5). The pseudo-cubic cell displays at 20 deg. C a 0.6 % linear increase with regard to the isomorphic compound 'Ca₃UO₆' which is related to U^VI -> U^IV substitution between the two distorted perovskites. (authors)