Thick gallium nitride films 250–350 µm in thickness were grown on 2-inch-diameter (0001) sapphire wafers by hydride vapor phase epitaxy. The size of the free-standing GaN substrates without cracks separated from the sapphire substrates by laser processing was equal to that of the initial sapphire substrates. The origin of bowing and the broad photoluminescence (PL) spectra of GaN films was considered the difference in the residual strain between the front and bottom surfaces caused by threading dislocations.

The domain structure of ferroelastic BiVO4 crystals was investigated by X-ray diffraction, nuclear magnetic resonance, optical polarizing microscopy, transmission electron microscope, and electron diffraction techniques. From these results, it is found that the BiVO4 crystals have only prominent W walls and no non-prominent W' domain walls. A model of the twin structure is suggested, and all experimental results are explained in terms of this model. However, the prominent W wall obtained from our experimental results should not occur in the ferroelastic species 4/mF2/m previously reported. From the acoustic symmetry character of the elastic behaviour, it has been established that there exist two possible W and W' walls for permissible planar walls that are consistent with all experimental observations. Thus, it can be concluded that the BiVO4 crystals having only the W walls found by our group and W' walls obtained by other groups are consistent with the ferroelastic species 4/mmmF2/m rather than 4/mF2/m.

The electron paramagnetic resonance of an Fe 3ϩ ͑Sϭ5/2͒ impurity in the ferroelastic phase of a BiVO 4 single crystal has been investigated. The rotation patterns of the resonance fields measured on the crystallographic planes are analyzed with the monoclinic spin Hamiltonian. The determined parameters are g xx ϭ1.976, g xz ϭ0.0033, g yy ϭ1.995, g zz ϭ1.994, and B 2 0 ϭ467.3, B 2 2 ϭ2339, B 2 1 ϭ1693, B 4 0 ϭ0.12, B 4 1 ϭ Ϫ2.3, B 4 2 ϭϪ0.8, B 4 3 ϭ4, and B 4 4 ϭϪ0.3 in units of the 10 Ϫ4 cm Ϫ1 . The principal X, Y and Z axes of the D tensor are found to be along the crystallographic c*ϩ30.5°, aϩ30.5°in the c*a plane, and b axis, respectively. The zero-field splitting ͑ZFS͒ parameters D and E are calculated both within the point-charge electrostatic model and the superposition model. Comparison of experimental data with calculated second-order axial and rhombic ZFS parameters suggests that the Fe 3ϩ impurity substitutes for the V 5ϩ ion in BiVO 4 .

The water molecules in acid and salt forms of perfluorinated sulfocation membranes (MF-4SK) have been investigated by employing nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC) techniques. The mobility parameters, correlation time and activation energy of water molecules were estimated from the results of the temperature dependence of ~H relaxation times and compared with water self-diffusion coefficients obtained with pulsed field gradient NMR. The NMR data showed no frozen unbound water in membranes at low water content with an amount of water molecules per sulfonate group n being comparable to the cationic bydration number h0, whereas DSC thermograms showed peaks which are usually interpreted asa water fusion phenomenon in the membranes. The diffusion mechanism of water molecules below 260 K is different from that above 300 K due to additional hydrogen bonds in water clusters at the low-temperature region.

EPR spenra of Fe3+ ions in single crystals of KliOPOr (KTP), synthesized by the Eux method, have been investigated at mom temperature by employing a Bruker Q-band spectrometer. From the angular dependence of the EPR spectm two Fe3+ centres denoted as C1 and C2 have been identified, in agreement with the previous analysis by other investigators. In this study, for the first time we have fully identified two groups of four magnetically inequivalent Fe3+ sites each belonging to the centres C1 and C2. Two sets of triclinic spin-Hamiltonian parameters, which simultaneously fiited EPR data for the four sites belonging to the centres C1 and Q, were determined. The direction cosines of the principal axes of the g-tensor as well as the second-order zero-field splitting (ZFS) tensor are found to be given by the relations: Imn, imn, lrirn, and i%n for each four F$+ sites of C1 as well as C2, respectively, consistent with the crystallographic point group mm2 of KTP.