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Electron paramagnetic resonance studies of the impurity Fe$^{3+}$ and Mn$^{4+}$ centers indicate that the symmetry of the crystal structure of millimeter-scale strontium titanate plates above 105 K lowers in the bulk from cubic to tetragonal, different from that of the conventional low-temperature antiferrodistortive phase. It is shown that the effect does not originate from the residual stress; its magnitude (observed tetragonal distortion) and particular manifestations depend on plate orientation, surface quality and the geometry of a sample. Peculiarities of the observed phenomenon are presented and possible scenario of its realization is discussed., 14 pages, 4 figures

We have analyzed the phase transitions in a square lattice of vortices using the thermodynamic approach. For a square array of the artificially created pin centers in Nb superconducting film we have calculated the phase diagram, which reveals the re-entrant melting features. We explain this effect by the nonmonotonic temperature dependence of the vortex-vortex interaction potential.

We report the results of an electron spin resonance study of Ti3+ centres in SrTiO3 single crystals. The Ti3+ centres are created in perturbed regular Ti4+ sites by trapping a photoelectron from the conduction band after ultraviolet irradiation of the sample at low temperature (T Tc (Tc ≈ 105 K corresponds to the temperature of the cubic–tetragonal phase transition), the Ti3+ centre exhibits an orthorhombic symmetry of the g-tensor with its principal axes oriented exactly along 001 and 110 crystal directions: g[110] = 1.9920, g[10] = 1.9375, g[001] = 1.8843. At T < Tc, due to a structural phase transition, two of the Ti3+ principal axes are tilted relative to the 110 directions by up to ±8o in the (001) crystal plane. The spectroscopic data are explained assuming Jahn–Teller orthorhombic distortions of the oxygen octahedron with non-linear T2g × (eg + t2g) vibronic coupling.

Electron paramagnetic resonance (EPR) of exchange-coupled pairs of C2+ ions was observed in KTaO3:Cu, K1−xLixTaO3:Cu and K1−xLixTa1−yNbyO3:Cu single crystals. The spectra are typical of centres with S = 1 and tetragonal symmetry with the pair axis parallel to the [100], [010] or [001] directions. The angular and temperature dependences of the signals have been studied. The experimental results are explained in terms of a pair centre model, which consists of a chain of two equivalent copper ions and three oxygen vacancies. The two copper ions occupy neighbouring tantalum sites and one of the oxygen vacancies lies between them, the chain running in the 100 direction. Ferromagnetic exchange coupling takes place between the copper ions, as confirmed by the thermal behaviour of the corresponding EPR spectra.

The description and investigation of a new atmospheric plasma source for the treatment and coatings of surfaces are presented in this paper. This new system is a modification of a well-known atmospheric torch discharge stabilized by a flowing channel of the working gas through an RF powered nozzle. The new version of this source prevents the transition to the regime with hot electrodes. This modification is suitable for surface and coatings applications of such substrates sensitive to overheating causing undesirable phase transition or melting. The new source called in our paper as an RF barrier-torch atmospheric discharge employs dielectrically coated nozzles instead of bare metallic ones. In that case, the plasma jet has quite different properties, as it is clear from presented experiments. The new version allowed excitation of the atmospheric plasma channel interacting with the substrate independently on the conductivity of the substrate. Simultaneously it is possible to hold the substrate temperature under atmospheric jet interaction below the limit point of aluminium melting or below an even lower limit of 80°C in a pulse-modulated mode. Extension to the multi-nozzle barrier-torch system was attained with the application of nine quartz nozzles. This multi-plasma jet excitation and its interaction was demonstrated with the substrate made of either quartz or aluminium plate, both possibly with non-flat shape. Emission spectroscopy and RF voltage and current amplitude measurements were employed in order to characterize the RF barrier-torch discharge.

The temperature-frequency behaviour of the complex dielectric permittivity of K0.957Li0.043TaO3 (KLT) was studied in detail. Below 250 K a pronounced relaxation-type dielectric dispersion occurs with two wide temperature maxima shifted to lower temperatures increasing in magnitude as the alternating-current monitoring frequency decreases. The results obtained are analysed by using a theory proposed considering the coupling of the TO1 soft mode (TO standing for transverse optical) to two Li relaxation modes known in moderately concentrated KLT as π- and (π/2)-relaxations.

Time evolution of stress in diamond-like films with small quantities (10-20 at%) of titanium (Ti-C:H) was investigated together with their structure, electrical resistivity, optical constants, Raman spectra, and composition. The compressive stresses for all films were found to increase, regardless of their structure (either amorphous or a-C:H with TiC nanocrystalline inclusions) and composition (10-20 at% Ti) over a period of several months. The conductivity and optical constants (n and k) decreased with time, and Raman spectra indicated no change of the film structure. The observations can be explained by a migration of interstitial atoms (probably hydrogen) resulting in a saturation of dangling bonds and, consequently, leading to a reduction in the number of free carriers. Vacancy clustering and effects of hydrogen atoms on stress increase are discussed.

Raman scattering observations were performed on samples of K1-xLixTa1-yNbyO3, with x in the range 0.6-1.0 mol% and y in the range 0.2-0.3 mol%. Concentrations of Li and Nb, determined by analytical methods, were below the known thresholds at which these substituents can separately induce a ferroelectric transition in the quantum paraelectric KTaO3. The temperature evolution of TO1 and TO4 spectra was monitored. The results show a critical behaviour below 50 K, characterized by an abrupt increase of first-order scattering strengths and by spontaneous splitting of the non-softening TO1 mode. From our data, we infer the occurrence of a ferroelectric phase transition of order-disorder character. This proves that small additions of Nb enhance the tendency of the Li subsystem towards cooperative ordering in the KTaO3 matrix.

Photoluminescence and optical absorption in Cr-doped were observed for the first time and studied within the 300-800 nm spectral region and over a 7-300 K temperature range. `Nominally pure' crystals, with Cr impurities detected by means of EPR, and intentionally Cr-doped crystals grown by the top-seeded solution method were studied. Cr doping results in additional absorption over the whole visible region, increasing towards the band-edge area (at ), and wide absorption bands centred at about 470 nm, 575 nm, and 610 nm. At 74 K, exposure to optical excitation with results in luminescence in the near-infra-red region consisting of four sharp lines, (781.65 nm, ), (776.4 nm, ), (768.8 nm, ), (766.8 nm, ), and several additional weak emission lines. The luminescence excitation spectrum for each A line consists of two complex bands centred at 630 nm and at 400 nm for T = 74 K. With decreasing temperature, all of the sharp lines, such as the zero-phonon lines of in , shift to lower energies, which is opposite to the behaviour of such lines for ionic crystals. The thermal shift for the line is the largest, . Taking into consideration EPR data, temperature transformations, and the lifetime of the sharp emission lines ( at 70 K), we argue that the and lines are lines, i.e. originating from zero-phonon transitions of single ions replacing ions. The nature of the emission lines is not quite clear, but can be considered to originate from ions exchange coupled with other, unknown defects (including exchange-coupled pairs) or with -type transitions of centres perturbed by nearest-site hole polarons, or .

The ESR spectra of impurity in single crystals are studied in the 4.2 - 300 K temperature range. It is shown that substitutes for with a charge compensation in distant spheres. The axial-symmetry crystal-field parameter is negative and exhibits unusual (for a deep tetragonal phase) temperature behaviour: increases linearly as the temperature is reduced to = 170 - 180 K and then for its value strongly decreases. It is shown that the reason for this decreasing is the displacement of from the central position in the oxygen cage which is occupied by for . A possible connection of this phenomenon with a small lattice distortion at T = 170 - 180 K, which was observed earlier, is discussed.

Recently, very intriguing dipole-ordering phenomena near the critical temperature and down into the low temperature phase were reported for K{sub 1-x}Li{sub x}Ta{sub 1-y}Nb{sub y}O{sub 3}. The understanding of these processes is a crucial aspect of basic research and applications. In the present work, we report on Raman experiments in K{sub 1-x}Li{sub x}Ta{sub 1-y}Nb{sub y}O{sub 3} crystals with x -0.004 and y -0.031. Systematic analysis of TO{sub 1} and TO{sub 4} spectra within the temperature range of 17-150 K was performed. All the measurements were performed after both zero-field and field cooling. The results enable us to gain new evidence of the competition between long-range order and the Li-related dipole glasslike subsystem.

Recently we reported on an reentrant dipole glass-like phase formation in K0.9986Li0.0014Ta0.976Nb0.024O3 (V. Trepakov et al.: Phys. Rev. B 63 (2001) 172203). Here we present the detailed low-frequency dielectric permittivity and Raman scattering data for nearly the same composition but without Li admixture, namely for KTa0.982Nb0.018O3 (KTN 1.8). We found that upon cool down, KTN 1.8 exhibits soft-mode-driven long-range displacive dynamics with phase transition at TC = 27 K. Below TC the randomness of the Nb distribution leads to a pronounced crossover to the order-disorder polar microregion dynamics which is also accompanied, nevertheless, by TO1 mode stiffness upon cooling. The application of a dc-bias returns the long-range displacive behavior to the system.

In this work, we present our study of the phase transitions and the temperature dependence of the optical properties of the PbZr0.235Ti0.765O3 films prepared by multi-target reactive sputtering and sol-gel methods. Optical measurements were performed with the J. A. Woollam spectral ellipsometer operating in rotating analyzer mode. The main ellipsometric angles Ψ and Δ were measured in the spectral range from 300 to 1200 nm. High-temperature measurements were performed in a specially designed thermostat system. The samples were heated to 500°C to reach the paraelectric phase. The temperature dependences of the refractive index and the absorption coefficient at fixed wavelengths, and the optical gap Eg obtained from isoabsorption curves at a=1000 cm-1 were obtained from ellipsometric experiment.

The theoretically predicted appearance of the temperature difference between the opposite sides of charging or discharging capacitors was observed for the first time. The capacitor of ferroelectric PbMg1/3Nb2/3O3 crystal with Ni electrodes was charged applying the field to E = 106 V/m with the time constant ≈ 10−5 s. The temperature difference at 300 K reached ≈ 10−4 K. The theoretical analysis of a "generalized Peltier effect" at the boundary of two arbitrary materials is done and it is shown that the experimental result can be considered as a "dieletric Peltier effect".

Experiments on K0.957Li0.043TaO3 samples indicate two different relaxation processes (π and π/2). First-principles computations clarify the natures of these relaxations, and yield good agreement with experiment.

The optical functions of strontium titanate (SrTiO3) (STO) single crystals were determined with spectroscopic ellipsometry in the 1-6eV spectral region and the 4.2-300K temperature region. On approaching the band gap edge, the optical absorption shows Urbach tail behavior followed by the onset of indirect optical transitions starting at 3.2eV and extending up to 3.68eV; then direct transitions are very well seen. The refractive index and its temperature and spectral dependences were obtained. In the visible region, the refractive index rises on cooling (negative thermooptic effect) down to 50K, saturating at lower temperatures. The energy of indirect interband optical transitions increases on cooling up to 3.23eV at 100K. The observed magnitude @E/@T = 1.7◊ 10 4 eVK 1 is typical of ionic crystals. Surprisingly, the absorption edge in the region of the lowest direct interband optical transitions 3.7-4eV shifts to lower energies on cooling. It is concluded that the presence of this 'soft electronic band' together with the rise in absorption intensity at 4.8eV is responsible for the increase of refractive index on cooling, elucidating the origin of the negative proper thermooptics in STO.

The crystal structure, optical absorption, and photoluminescence of chromium impurity centers were studied in nanocrystalline SrTiO(3):Cr (0.1 mol%) powders with average particle size within the range 13-100 nm prepared by the Pechini-type polymeric sol-gel method. Only the presence of a cubic perovskite phase of O(h)(1) symmetry was proved for the powders at room temperature, by means of x-ray diffraction. The lattice constant a = 3.910 Å, larger than that of bulk SrTiO(3) crystals (a = 3.905 Å), was found for nanoparticles with the size about 20 nm. The optical absorption edge and the zero-phonon R-line ([Formula: see text]) of luminescence of the octahedral Cr(3+) centers shifted to higher energies with decreasing nanoparticle size. These size effects were regarded as intrinsic to SrTiO(3). An unusual and large temperature shift of the R-line position very similar to the 'dielectric related' one of the bulk crystals was observed for all powders, evidencing their quantum paraelectric behavior. However, the powders with the average particle size about 13 and 20 nm did not reveal completely reproducible behavior of the R-line position at low temperatures. This instability was considered a possible manifestation of a low-temperature phase transition in small enough SrTiO(3) nanoparticles.

Eighty years have passed since Langmuir's first use of the word 'plasma' for describing ionized media. On this occasion we would like to present selected recent results on the application of Langmuir probes to diagnose plasma jet systems. To demonstrate the versatility of the Langmuir probe method we give examples of measurements of the spatial distribution of the plasma parameters as well as their temporal dependence in cases when the plasma jet system operates in a pulsed regime. A part of this paper is devoted to introducing the Langmuir probe technique, especially with regard to its application under conditions when collisions between the charged and neutral particles in the probe sheath cannot be neglected and when the electron energy distribution function in plasma cannot be approximated by a Maxwellian one. In the experimental part we present Langmuir probe measurement of low-pressure and atmospheric-pressure plasma jet systems that are currently used for experiments with deposition of materials with special properties.Most of the experimental results presented in this paper are original data. However, in order to fill in the picture we have used in the case of a barrier-torch discharge three figures that have already been published.

We investigate diffusion of particles adsorbed on a heterogeneous honeycomb lattice with two kinds of non-equivalent sites. General analytical expressions for the chemical and jump diffusion coefficients have been derived in the case of strong inhomogeneity. It is shown that the character of the particle migration depends crucially on the relative jump frequencies of particles occupying deep and shallow sites. In the case of widely differing jump frequencies, particles perform pairs of strongly correlated jumps. We have calculated coverage dependencies of the diffusion coefficients and some thermodynamic quantities for attractive and repulsive lateral pairwise interactions and compared them with the results of the kinetic Monte Carlo simulations of the particle diffusion. Almost perfect agreement between the respective results has been found.

The dielectric permittivity (100 Hz–1 MHz) and IR reflectivity of SrTiO3:Mn(0.1 at.%) crystals and SrTiO3:Mn(0.1–3 at.%) ceramics prepared maintaining the ratio (Sr+Mn)/ Ti = 1 or (Ti+Mn)/Sr = 1 (A- and B-type ceramics, respectively) were studied. Surprisingly, the magnitude and e'(T) dependence for the crystals and B-type ceramics with 0.1 at.% of Mn appeared to be nearly the same; the magnitudes rise on cooling and reach ~3000 at T = 7 K. At the same time, IR spectra of SrTiO3:Mn(0.1 at.%) crystals reveal that TO (transverse optical) phonons yield a magnitude of low frequency permittivity of ~4000 at T = 5 K, evidencing crystal inhomogeneity. Both crystals, like B-type SrTiO3:Mn(0.1 at.%) ceramics, reveal faint low temperature relaxations with the Arrhenius activation energies ~37–40 meV and ~120–130 meV (P- and T-relaxations). These relaxations emerge in losses only and were tentatively attributed to reorientation of defects associated with MnTi2+–O−-type polaronic centres and Oh1–D4h18 phase transition related effects, respectively. In reduced crystals P-relaxation strongly enhances, becoming distinctly seen in the real part of the permittivity. More heavily Mn doped A- and B-type ceramics reveal strongly pronounced Arrhenius-type dielectric relaxation with activation energy ~59–68 meV depending on the Mn concentration.

Laser absorption spectroscopy of aluminium atoms in pulsed magnetron discharge with pure argon, argon/oxygen, and argon/methane gas mixtures is reported. Time-averaged densities and temperatures of sputtered aluminium atoms were extracted from the absorption signal. The measured Al density depended almost linearly on the pulse current and showed a small dependence on pressure. Al atom temperature increased with discharge current and vice versa with pressure. A drastic decrease of the Al atom density was observed in the Ar/O2 mixture. The Al density dropped to a value close to zero once a critical oxygen gas flow rate was reached. This critical oxygen gas flow was significantly higher in pulsed mode than in DC mode.

Holographic interferometry of atmospheric RF barrier-torch discharge burning in argon and helium is reported. Holographic interferometer of Mach–Zehnder type with He–Ne laser was used for temperature measurement of neutral particles of working gas. Interference pattern was registered by a high-speed charge-coupled devices (CCD) camera. Resulting temperature ranged from 330 to 450 K. A slight difference between temperatures measured close to the glass nozzle outlet and close to the substrate was observed.