Improvement of cubic silicon carbide crystals grown from solution

Cubic-silicon carbide crystals have been grown from carbon-rich silicon solutions using the travelling-zone method. To improve the growth process, we investigated the effect of controlling more tightly some of the growth parameters. Using such improved growth conditions, our best sample is a 12 mm diameter and 3 mm long 3C–SiC crystal. It is grown on a (0001) 2 off, 6H–SiC seed and has 111-orientation. The low amount of silicon inclusions results in a reduced internal stress, which is demonstrated by the consideration of μ-Raman spectra collected at room temperature on a large number of samples.     

Debye temperature of cubic crystals

An algorithm for determination of the Debye temperature is presented, which enables the easy computation of the Debye temperature for arbitrary stable cubic crystal.     

Damage studies in cubic ZnSe single crystals grown from melt

A microscopy study of the morphology of the damage produced by TEA-CO₂ laser pulses in cubic ZnSe single crystals grown from melt is presented. The observed bulk filamentary damage consists of relatively uniformly distributed elementary damaged zones, located at specific sites where absorbing inclusions could exist. Transmission electron microscopy and laser ion mass spectroscopy investigations revealed the absorbing inclusions to be thin graphite foils, originating from the crucible used for crystal growth.     

Optical birefringence in cubic ZnSe crystals

Optical birefringence of the spatial dispersion type has been observed in cubic ZnSe crystals.     

Sound velocity anisotropy in cubic crystals

Simple analytical expressions may be derived for sound velocities in cubic crystals by using lattice harmonics or functions which are invariant under the crystal symmetry operations. These expressions are in good agreement with the exact results for typical crystals such as metallic iron and potassium fluoride.     

Scissors Modes in crystals with cubic symmetry

We recently suggested that the Scissors Mode (a collective excitation in which one system rotates with respect another one conserving its shape) can occur in crystals with axially symmetric atoms as a precession of these atoms around the anisotropy axis of their cells, giving rise to a form of dichroism. In the present paper we investigate how the Scissors Mode can be realized in crystals with cubic symmetry and evaluate its photo-absorption cross-section. This turns out to be of the same order of magnitude as that for crystals with axially symmetric atoms, but does not exhibit any correlation between the direction of the photon and the axes of the cell.     

Anisotropic surface melting in lyotropic cubic crystals

From experiments with ice or metal crystals, in the vicinity of their crystal/liquid/vapor triple points, it is known that melting of crystals starts on their surfaces and is anisotropic. It is shown here by direct observations under an optical microscope that this anisotropic surface melting phenomenon occurs also in lyotropic systems. In the case of C12EO2/water mixture, it takes place in the vicinity of the peritectic Pn3m/L3/L1 triple point. Above the peritectic triple point, where the Pn3m and L1 phases coexist in the bulk, the surface of a Pn3m-in-L1 crystal is composed of (111)-type facets surrounded by rough surfaces. The angular junction suggests that rough surfaces are wet by a L3-like layer while facets stay “dry”. This is analogous to the pre-melting at rough surfaces in solid crystals. Upon cooling below the peritectic triple point, where L3 and L1 phases coexist in the bulk, a thick layer of the L3 phase grows from the pre-melted, rough Pn3m/L1 interface. Simultaneously, facets stay dry and their radius decreases. In this tri-phasic configuration, stable in a narrow temperature range, the L3/L1 and L3/Pn3m interfaces have shapes of constant mean curvature surfaces having common borders: edges of facets.     

Anisotropic surface melting in lyotropic cubic crystals

From experiments with metal crystals, in the vicinity of their crystal/liquid/vapor triple points, it is known that melting of crystals starts on their surfaces and is anisotropic. Recently, we have shown that anisotropic surface melting occurs also in lyotropic systems. In our previous paper (Eur. Phys. J. E 19, 223 (2006)), we have focused on the case of poor faceting at the Pn3m/L1 interface in C12EO2/water binary mixtures. There anisotropic melting occurs in the vicinity of a Pn3m/L3/L1 triple point. In the present paper, we focus on the opposite case of a rich devil's-staircase-type faceting at Ia3d/vapor interfaces in monoolein/water and phytantriol/water mixtures. We show that anisotropic surface melting takes place in these systems in a narrow humidity range close to the Ia3d-L2 transition. As whole (hkl) sets of facets disappear one after another when the transition is approached, surface melting occurs in a facet-by-facet type.     

Bulk and surface ordering in cubic crystals

The order-disorder transition of face and body centred cubic crystals is studied by a Monte Carlo simulation of a two-component lattice gas with nearest neighbour interactions, and of different compositions. It is shown that the degree of surface order may both be higher and lower than that of the bulk. General guide lines are drawn from the results to predict such behaviour in experimental situations.     

Magnetic dipole energies in tetragonally-distorted cubic crystals

Dipole energies in tetragonally-distorted cubic crystals have been calculated by the Ewald-Kornfeld method for the case in which the dipoles are parallel to the c-axis. The results are accurate to at least 1 part in 10⁵, sufficient to provide accurate values of the strain-dependence and hence the dipolar magnetostriction constant h₁ within the range 0.98 ?c/a?1.02. Calculations are presented for bcc, fcc and diamond lattices.     

Precise lattice constants determination of cubic crystals from x-ray powder diffractometric measurements

An analytical method for precise determination of lattice constants of cubic crystals, from x-ray diffractometric measurements, was formulated. The method minimizes both systematic and random errors and enables the estimation of the uncertainties in the constants. For higher precision, a weighting factor may also be used.The method was applied to diffractometric data from a Si powder standard reference material and was considered to be highly reliable for precise measurements.     

Phase changes in cubic rare earth crystals

An explanation is offered of the structural transitions and magnetic orderings in the cubic rare earth compounds LnX with particular emphasis on the anomalous spin arrangements observed in HoP, DyP and DyAs and in ErSb and ErP.     

Polarization-independent modulation of light in gyrotropic cubic crystals

Polarization-independent modulation of light in gyrotropic cubic crystals is investigated in the Bragg and intermediate diffraction regimes. It is found that, for crystals with considerable specific rotation, the photoelastic anisotropy is suppressed by the circular anisotropy and the observed diffraction efficiency depends weakly on the polarization azimuth of the incident light. Good agreement is obtained between modulation parameters calculated theoretically on the basis of the coupled wave theory and experimental results for a bismuth silicate crystal in the intermediate diffraction regime.     

Generation of terahertz radiation in cubic non-centrosymmetric crystals

The conditions of parametric radiation generation on polaritons in cubic noncentrosymmetric crystals are studied. The possibility of such generation is theoretically justified. The polariton radiation frequencies are calculated for GaP, ZnSe, ZnTe, and GaAs crystals. The obtained generation frequencies are compared to the experimental results on Raman scattering on polaritons. The block diagram of the terahertz radiation generator operation using a GaP crystal and a pulsed laser with high peak power at low energy of laser pump pulses is presented. The lasing frequency shift is analyzed depending on the scattering geometry. The coefficient of exciting radiation conversion to the terahertz range is determined.     

Scattering matrix for Raman effect in cubic crystals

The scattering matrix for Raman effect in cubic crystals for any general orientation of the crystal and any angle of scattering is given. The averages of the matrix over all possible orientations is also given and checks with the well known value of 6/7 for the depolarisation of degenerate lines for transverse scattering. The scattering matrix for backward scattering in terms of polar angles and for some special cases are also given.     

Anisotropy and twinning in cubic zinc sulfide crystals

The structure of zinc sulfide single crystals grown from the vapor has been studied by a unique combination of X-ray crystallography and thermal conductivity measurements. Weissenberg patterns reveal the face centered cubic structure with rotational twinning in the [111] direction, which could be ascribed to two overlapping lattices. These could be explained by normal stacking faults or by inverted twins. A strong anisotropy in thermal conductivity was measured and interpreted as favoring the inverted twin model.