The influence of the lanthanide cation type and calcination temperature on the crystal, local, and electronic structures of both individual and high-entropy (HE) Ln chromates/chromites (Ln = La - Yb, and Y) prepared by a coprecipitation is studied by using synchrotron X-ray diffraction, X-ray absorption fine structure spectroscopy, Raman and Fourier transform infrared spectroscopies, scanning electron microscopy with energy-dispersive Xray spectroscopy, simultaneous thermal analysis, and inductively coupled plasma atomic emission spectroscopy. Calcination of X-ray amorphous precursors at 550 degrees C resulted in the formation of individual LnCrO4 chromates with monoclinic (sp. gr. P21/n for Ln = La) or tetragonal (sp. gr. I41/amd for Ln = Sm - Yb, Y) structure. The PrCrO4 and NdCrO4 samples were a mixture of monoclinic and tetragonal phases. The HE LnCrO4 chromates were characterized by tetragonal structure regardless of the Ln3+ cation type involved. A further increase in temperature >= 650 degrees C led to the formation of Ln chromites having the orthorhombic symmetry (sp. gr. Pnma for LaCrO3, sp. gr. Pbnm for individual Ln = Pr - Yb, Y, and HE chromites). For all synthesized LnCrO3 samples, the lattice parameters, unit cell volumes, Cr-O-Cr bond angles, average Ln-O distances diminish with decreasing the Ln3+ cation radius. On the contrary, the octahedral distortions within CrO6 units increase with decreasing the Ln3+ cation radius. An analysis of the electronic structure showed the presence of an oxidation state (3+) for both Ln and Cr cations in all synthesized precursors and Ln chromites, and Cr5+ for Ln chromates. The local environment of the Ln3+ and Cr3+ cations in HE Ln chromites is close to that of similar ions in individual compounds. The local environment of the La3+ cation in La-containing compounds differs significantly from that of Ln3+ cations in other Ln chromites (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Yb, Y).

In this paper, a study of the influence of laser processing parameters with pulsed nanosecond laser radiation on the degree of metallization and the quality of the metallized surface of aluminum nitride ceramics is presented. Experiments were carried out to create conductive structures with the lowest resistance using direct laser metallization. The dependences of resistance on duration, pulse overlap, and laser fluence were obtained and analyzed, and changes in surface roughness were considered. In addition, the composition of the surface of laser-metallized ceramics was studied using energy-dispersive x-ray spectroscopy. As a result, it was shown that the resistance is inversely proportional to the square root of the pulse duration, the thermal diffusion length was estimated as lT = 8.2 mu m for 200 ns and lT = 1.2 mu m for 4 ns, and the presence of optimal values of pulse overlap Oy (scanning direction) equal to 50% and pulse overlap Ox (step direction) equal to 96% and 99.7% for pulse durations of 200 and 4 ns, respectively, was determined. The choice of optimal pulse overlaps with the highest laser fluence allowed us to obtain the minimum resistance value with maximum performance.

The synthesis and detailed study of six series of high-entropy complex oxides containing lanthanides (Ln) and transition metals with the general formula Ln(2)M(2)O(7) (Ln = La-Yb, and Y; M = Ti, Zr, and Ce) with the number of different Ln cations not less than six in each case are reported. The influence of synthesis conditions (types of the Ln(3+) and M4+ cations, calcination temperature) used in the synthesis via either coprecipitation or sol-gel method on the crystal and local structures of target materials is comprehensively surveyed. The studies were carried out using a combination of long- (s-XRD), medium- (Raman, FT-IR, SEM-EDS) and short-range (XAFS) sensitive techniques, as well as AES-ICP and STA. It was established that the ratio of the cation radii gamma = (r) over bar (3+)(Ln)/(r) over bar (4+)(M) is the main factor that determines the type of initially formed crystal structure. In the boundary region (gamma similar to 1.42-1.47), the average radius of lanthanide cation ((r) over bar (3+)(Ln)), along with the (r) over bar (3+)(Ln)/(r) over bar (4+)(M) ratio, also plays a significant role in the type of the resulting crystal structure of the high-entropy lanthanide complex oxides. The presence of inhomogeneity in the distribution of elements in precursors significantly affects the phase composition of the resulting high-entropy oxides. An increase in the calcination temperature promotes not only the occurrence of subsequent phase transitions, but also an increase in the single-phase nature of the resulting high-entropy complex rare-earth oxides. At the same time, the cations included in the composition retain some independence, despite the fact that they occupy one crystallographic position in the resulting crystal structure.

The influence of Yb3+ cations substitution for Pr3+ on the structure and catalytic activity of (Pr1−xYbx)2Zr2O7 powders synthesized via coprecipitation followed by calcination is studied using a combination of long- (s-XRD), medium- (Raman, FT-IR, and SEM-EDS) and short-range (XAFS) sensitive methods, as well as adsorption and catalytic techniques. It is established that chemical composition and calcination temperature are the two major factors that govern the phase composition, crystallographic, and local-structure parameters of these polycrystalline materials. The crystallographic and local-structure parameters of (Pr1−xYbx)2Zr2O7 samples prepared at 1400 °C/3 h demonstrate a tight correlation with their catalytic activity towards propane cracking. The progressive replacement of Pr3+ with Yb3+ cations gives rise to an increase in the catalytic activity. A mechanism of the catalytic cracking of propane is proposed, which considers the geometrical match between the metal–oxygen (Pr–O, Yb–O, and Zr–O) bond lengths within the active sites and the size of adsorbed propane molecule to be the decisive factor governing the reaction route.

Possibility of nitriding of internal cylindrical surfaces in plasma of abnormal glow discharge with hollow cathode in the pulse-periodic mode in N-2+H-2 was investigated. Tubes with internal diameters of 6, 8, and 9 mm and with the aspect ratio from 12 to 50 were made a low carbon steel were used. Regimes of the discharge were investigated. Nitrided layers in different parts of the tubes were analyzed.

The lanthanide titanates Ln(2)Ti(2)O(7) (Ln = lanthanide) demonstrate a very broad range of structural, chemical and physical properties. We have studied the whole process of the crystallization and local atomic structure rearrangement in Ln(2)Ti(2)O(7) (Ln = Gd, Tb, Dy) samples synthesized by combination of sol-gel and coprecipitation methods with the subsequent calcination of Ln-Ti precursors. X-ray absorption spectroscopy (XAFS), X-ray powder diffraction, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and simultaneous thermal analysis were used for the complex analysis of the structural properties. It was shown that crystallization of amorphous precursors directly resulted in the formation of nanocrystalline powders with the pyrochlore structure which is formed in process of ordering of both cationic and anionic sublattices. We have demonstrated that both XAFS and Raman spectroscopy ensure the particularly sensitive markers of changes in local electronic and crystal structure of Ln(2)Ti(2)O(7) depending on the type of Ln element and the preparation procedure. It was established that splitting of the first Ln-O shell in the FT modulus of L-3-Ln EXAFS spectra appears to be the reliable indicator of the ordered pyrochlore structure formation, while the changes in the pre-edge region of the K-Ti XANES spectra reflect the process of the Ln(2)Ti(2)O(7) electronic structure formation. (c) 2018 Elsevier B.V. All rights reserved.

Parameters of inductively coupled plasma (ICP) discharges in a mixture of gases N2, H2, and Ar at a total pressure of 1.5 × 10–3 mbar and a partial pressure ratio N2: H2: Ar = 2: 12: 1 are discussed. The plasma properties are analyzed using Langmuir probes and optical emission spectroscopy. The ICP discharge is used for the nitriding of specimens made of Russian grade 30ChGSA structural steel. The nitriding experiments are performed at different bias voltages V b in the range of–200 V to +100 V with respect to the walls of the discharge chamber. The surface hardness of the treated specimens depends substantially on the bias voltage, being much higher than the initial value in all cases. The obtained results demonstrate the possibility of increasing the surface hardness up to 1000 HV (4–5 times the initial values) at the bias voltage equal to the floating potential.