No abstract available

No abstract available

No abstract available

[en] The inelastic neutron scattering spectra were measured for several Sr concentrations of polycrystalline La_2-xSr_xNiO₄. The authors find that the generalized phonon density-of-states is identical for x = 0 and x = 1/8. For x = 1/3 and x = 1/2, the band of phonons corresponding to the in-plane oxygen vibrations (> 65 meV) splits into two subbands centered at 75 meV and 85 meV. The lower frequency band increases in amplitude for the x = 1/2 sample, indicating that it is directly related to the hole concentration. These changes are associated with the coupling of oxygen vibrations to doped holes which reside in the NiO₂ planes and are a signature of strong electron-lattice coupling. Comparison of La_1.9Sr_0.1CuO₄ and La_1.875Sr_0.125NiO₄ demonstrates that much stronger electron-lattice coupling occurs for particular modes in the cuprate for modest doping and is likely related to the metallic nature of the cuprate

[en] We present results of the inelastic neutron scattering and the heat capacity measurements in PrBa₂Cu₃O₆/O₇ compounds. It is shown that these data correspond to the crystal-field splitting predicted theoretically for trivalent Pr. Our data for oxygen-deficient compound at low temperatures indicate the lowering of the symmetry at the Pr site, possibly of the Jahn-Teller origin

[en] Using X_α discrete variation a quantum-chemical calculation of clusters simulating superconducting and nonsuperconducting yttrium ceramics is carried out. Analysis of electron density distribution has shown that the electrostatic field of Ba ions increases the strength of oxygen chemical bonds in chains and the defects in Ba initiate oxygen volatility from the chains

[en] TiN coatings were deposited onto steel substrates and grey cast iron by means of an r.f. sputtering unit by varying systematically the deposition parameters bias voltage and deposition time. The fundamental properties such as adhesion, hardness and structure were determined and correlated with results of investigations of the wear and fatigue properties of the coated samples. It was shown that the coatings with high hardness combined with good adhesion to the substrate have the best wear properties. The fatigue resistance increased by about 10% as a result of the coating process and was only negligibly influenced by variations in the deposition parameters. (orig.)

[en] Gd₂O₃-doped Bi₂O₃ polycrystalline ceramics containing between 2 and 7 mol% Gd₂O₃ were fabricated by pressureless sintering powder compacts. The as-sintered samples were tetragonal at room temperature. High-temperature X-ray diffraction (XRD) traces showed that the samples were cubic at elevated temperatures and transformed into the tetragonal polymorph during cooling. On the basis of conductivity measurements as a function of temperature and differential scanning calorimetry (DSC), the cubic → tetragonal as well as tetragonal → cubic transition temperatures were determined as a function of Gd₂O₃ concentration. The cubic → tetragonal transformation appears to be a displacive transformation. It was observed that additions of ZrO₂ as a dopant, which is known to suppress cation interdiffusion in rare-earth oxide-Bi₂O₃ systems, did not suppress the transition, consistent with it being a displacive transition. Annealing of samples at temperatures ≤ 660 C for several hundred hours led to decomposition into a mixture of monoclinic and rhombohedral phases. This shows that the tetragonal polymorph is a metastable phase

[en] It has been shown that the use of thin titanium interlayers improves the coating-substrate adhesion of physical vapour deposition (PVD) titanium nitride thin films on a stainless steel substrate. This improvement arises from a combination of chemical gettering and mechanical compliance effects. The improved adhesion of plasma-assisted chemical vapour deposition TiN coatings with increasing interlayer thickness has been shown to be largely attributable to the compliance effect. The development of practical methods to improve adhesion is hampered by the difficulties involved in quantitative measurements of the effect. To avoid the influence of the intrinsic and extrinsic parameters involved in scratch test and microhardness measurements, efforts have been made to apply fracture mechanical testing methods to the determination of the adhesion strength of the film on the substrate (S. Berg, S. W. Kim, V. Grajewski and E. Fromm, Mater. Sci. Eng. A, 139 (1991) 345). In our study the influence of Ti interlayers on the adhesion of PVD TiN coatings on oxidized stainless steel substrates was investigated using a pull-off test for adhesion measurements and scanning tunnelling microscopy and secondary ion mass spectrometry for analysis of the fractured surfaces. It was shown that the thickness of the Ti layer must be chosen according to the thickness of the oxide layer. An excess of Ti leads to lower adhesion values due to failure in the Ti layer, while a shortage of Ti leads to unreacted oxide and minimum adhesion due to brittle fracture in the oxide layer, which was shown to be amorphous. (orig.)

[en] The major features of microstructure formation of thick films of HTSC with YBa₂Cu₃O_7-x composition were investigated. The availability of aggregates of particles in initial powder affects on crystallite growth in film as well as the main factor inhibiting this event is scorching of powder particles on the substrate. It is established that using protective silver sublayer with responsible low temperature and partial pressure of oxygen in gas phase during sintering allows not only avoid interaction of film but intensify sintering in the film