Specific Features of the Structure and the Dielectric Properties of Sodium–Bismuth Titanate-Based Ceramics

The phase formation, specific features, and the dielectric properties of the ceramics of compositions from the region of morphotropic interface in the (Na_0.5Bi_0.5)TiO₃–BaTiO₃ system modified by Bi(Mg_0.5Ti_0.5)O₃ and also low-melting additions KCl, NaCl–LiF, CuO, and MnO₂ that favor the control of the stoichiometry and the properties of the ceramics have been studied. The ceramics are characterized by ferroelectric phase transitions that are observed as jumps at temperatures near 400 K and maxima at T_m ~ 600 K in the temperature dependences of the dielectric permittivity. The phase transitions at ~400 K demonstrate the relaxor behavior indicating the existence of polar domains in the nonpolar matrix. An increase in the content of Bi(Mg_0.5Ti_0.5)O₃ favor a decrease in the electrical conductivity and dielectric losses of the samples, and the relative dielectric permittivity at room temperature ε_rt is retained quite high, achieving the highest values ε_rt = 1080–1350 in the ceramics modified with KCl.     

Specific Features of the Properties of Co–Cu Granular Media Caused by the Structure of the Material

A comparative analysis of rapidly quenched strips and thin films prepared from Co–Cu alloys with giant reluctance is performed. It is established that their microstructure and phase composition differ strongly. Precipitates of Co-enriched phase of two types that differ in their origin and sizes are present in strips. Large particles (100 nm) having the fcc structure determine the magnetic properties, and small particles ( 5 nm) determine the reluctance. In films, Co particles of only one type are detected. They have hexagonal close-packed lattice, can be in superparamagnetic and ferromagnetic states, and yield the corresponding contributions to the giant reluctance. The above-indicated specific features in the microstructure lead to different magnetic and reluctance properties of strips and films.     

Structure and Mechanical Properties of the CaO–ZrO2–Al2O3 Ceramic Composites at Low Corundum Concentrations

Technical Physics - We have studied the effect of the ratio between concentrations of zirconium dioxide (stabilized by CaO) and corundum on phase composition and mechanical properties of...     

Infrared photoluminescence and Raman spectra in the Y2O3–ZrO2 system

In this work we present laser-excited infrared photoluminescence and Raman spectra of zirconia with different yttria content (2%–9.5% Y ₂O₃) in order to investigate the effect of dopant on their optical properties. All the Raman spectra were taken over the range 100–800 cm^?1, and the Ar⁺ laser-excited luminescence over the range 16,000–19,000 cm^?1 (absolute frequency). The results are discussed on the basis of defects related to anion vacancies and changes in the disorder degree induced mainly by yttria content in the samples.     

Study of the Defect Structure and Crystal-Field Parameters of α-Al2O3:Yb3+

The methods currently used for studying the defect structure of laser host crystals doped with transition metal or rare-earth ions have several drawbacks or limitations. This study proposes an alternative approach for obtaining optimized impurity structures using molecular dynamics calculation in conjunction with the superposition model. This new approach is specifically applied to a system named α-Al₂O₃:Yb³⁺, in which the simulated defect structure is used to fit the superposition model parameters directly onto the observed energy levels. Such an approach provides predicted values of crystal-field parameters, Zeeman splitting g-factor, and hyperfine structure constants. Moreover, the C_3v site symmetry is found to be a good approximation for the actual C₃ site of Yb³⁺, as doped in an α-Al₂O₃ crystal.     

Spectroscopic Properties of Er3+/Yb3+-codoped PbO–Bi2O3–Ga2O3–GeO2 Glasses

We investigate the spectroscopic properties of the 1.5-μm emission from the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ions in PbO–Bi₂O₃–Ga₂O₃–GeO₂ glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width at half-maximum of ∼45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 × 10⁻²⁰ cm² and a large product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-μm emission with a commercially available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the ²H_11/2 of Er³⁺. The results indicate the possibility towards the development of lead–bismuth–gallate–germanate based glasses as photonics devices.     

Upconversion Properties of Er3+/Yb3+ Co-doped TeO2–TiO2–K2O Glasses

The Er³⁺/Yb³⁺ co-doped TeO₂–TiO₂–K₂O glasses were prepared by conventional melting procedures, and their upconversion spectra were performed. The dependence of luminescence intensity on the ratio of Yb³⁺/Er³⁺ was studied, and the relationship between green upconversion luminescence intensity and Er³⁺ concentration is discussed in detail. The 546 nm green upconversion luminescence intensity is optimised in the studied glasses either when the Yb³⁺/Er³⁺ ratio is 25/1 and Er³⁺ concentration is 0.1 mol%, or when the Yb³⁺/Er³⁺ ratio is 10/1 and Er³⁺ concentration is 0.15 mol%. These glasses could be one of the potential candidates for LD pumping microchip solid-state lasers.     

Characterization of the electrical properties of Y2O3-doped CeO2-rich CeO2–ZrO2 solid solutions

Electrical properties of Y₂O₃-doped CeO₂-rich ZrO₂–CeO₂ system were characterized with a view point of its point-defect structural scheme. Theoretical calculation of partial electronic and ionic conductivity from total conductivity was done to investigate the combined homovalent and aliovalent doping effect on the overall electrolytic property. According to our study, combined homovalent and aliovalent doping can be one of the key solutions to overcome the fatal disadvantage of limited electrolytic stability of doped ceria system by which properly enhances the ionic conductivity and suppresses the electronic conductivity all at once. Feasibility and limitation of Y₂O₃-doped CeO₂-rich ZrO₂–CeO₂ system as a potential alternative electrolyte material for low or intermediate temperature SOFC were discussed.     

Spectral-Luminescent Properties of Yb3+ in SOCl2–GaCl3

Optics and Spectroscopy - The absorption and luminescence spectra and the excited state lifetime of Yb3+ in SOCl2–GaCl3–Yb3+ solutions are measured. Information on the Stark splitting...     

Manifestation of up-conversion in Yb3+/Tm3+ doped Li2O–Y2O3–SiO2 glass system

In this study, we have investigated the principal role of Y₂O₃ on the emission features of Tm³⁺ ion and up-conversion phenomenon in Tm³⁺ and Yb³⁺ co-doped Li₂O–Y₂O₃–SiO₂ glass system. The concentration of Y₂O₃ is varied from 0 to 5 mol% while that of Yb³⁺ and Tm³⁺ is fixed. When the glasses are doped with Tm³⁺ ions, the intense blue and red emissions were observed, whereas Yb³⁺ doped glasses exhibited NIR emission at about 980 nm. When the glasses are co-doped with Tm³⁺ and Yb³⁺ ions and excited at 900 nm, the blue and red emission lines were observed to be reinforced and strengthened with increase in the concentration of Y₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄ → ³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to co-doping. The reasons for enhancement in the intensity of various emission bands due to co-doping have been identified and discussed with the help of rate equations for various emission transitions.     

Optical Properties of (ZrO2)1 – x(Y2O3)х (х = 0–0.037) Crystals Grown by Directional Crystallization of the Melt

Optics and Spectroscopy - The luminescent and optical properties of materials based on zirconium(IV) oxide grown by crystallization of ZrO2 melts with 0, 2.0, 2.5, 2.8, and 3.7 mol % of Y2O3 are...     

Control of Crystallization Kinetics and Study of the Thermal, Structural and Morphological Properties of an Li2O–B2O3–Al2O3 Vitreous System

A glass matrix with nominal composition 50Li₂O·45B₂O₃·5Al₂O₃ (mol%) was synthesized, and its physical properties were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and atomic force microscopy (AFM). The glass transition temperature T _g, the crystallization-onset temperature T _x,, the crystallization peak temperatures T _c1 and T _c2, and the fusion peak temperatures T _m1 and T _m2 were determined from at least two glass matrix phases to be approximately 382, 457, 486, 574, 761, and 787?°C, respectively, at 5?°C/min heating rate. Heat treatments at 450?°C for an increasing sequence of time intervals allowed control over the amount of crystallization. Additional information on the crystallization kinetics for the LBA glass matrix was gathered from AFM images, DTA thermograms, and XRD diffractograms. The latter technique showed that LiBO₂ (ICDD-16568) and Li₃AlB₂O₆ (ICDD-51754) phases are formed in the glass?Cceramic system. Debye?CScherrer analysis of the XRD peaks revealed a competition between the evolutions of crystal phases during heat treatment. Activation energies for crystallization, obtained from theoretical models applied to the DTA data showed that the crystallization is heterogeneous. The AFM images demonstrated that this heterogeneous crystallization starts at the surface of the LBA glass matrix and identified crystal sizes in agreement with the results of the Debye?CScherrer analysis. Our study shows that thermal and structural characterization techniques can be combined with theoretical results drawn from well-tested models to offer a unified view of crystallization in a glass?Cceramics system.     

Crystallographic Features of the Structure of Cast and Quenched Cobalt–Niobium Alloys

Technical Physics - Specific features of structure formation at the β → α (fcc → hcp) polymorphic transformation in Co–Nb binary alloys have been investigated by...     

Polymer–Salt Synthesis of Yb:YAG Nanopowders and Study of Their Structure and Luminescent Properties

Optics and Spectroscopy - Nanopowders of ytterbium-doped yttrium aluminum garnet are synthesized by the polymer–salt method and their crystal structure and spectral-luminescent properties are...     

Influence of LiB3O5 Structure on Microstructure and Optical Properties of ZrO2 Thin Films Prepared by Electron Beam Evaporation

ZrO2 thin films were deposited by using an electron beam evaporation technique on three kinds of lithium triborate (LIB3O5 or LBO) substrates with the surfaces at specified crystalline orientations. The influences of the LBO structure on the structural and optical properties of ZrO2 thin films are studied by spectrophotometer and x-ray diffraction. The results indicate that the substrate structure has obvious effects on the structural and optical properties of the film: namely, the ZrO2 thin film deposited on the X-LBO, Y-LBO and Z-LBO orients to m(-212), rn(021) and o(130) directions. It is also found that the ZrO2 thin film with m(021) has the highest refractive index and the least lattice misfit.     

Distinctive Features of the Absorption Spectra of Titanium and Iron Ions in α‐Al2O3:Ti,Fe Crystals

In the UV and visible radiation regions, the absorption spectra of Al₂O₃:Ti,Fe single crystals grown under oxidizing conditions by the Verneuil method are investigated. A considerable residual absorption in the regions 200–300 and 400–600 nm is revealed, which depends strongly on the conditions of growing (the growth rate and temperature drops) and which is caused by transitions in an impurityvacancy complex with charge transfer (IVC CT) O^2––Ti⁴⁺...Fe³⁺ and by conversion of the state of titanium ions Ti⁴⁺ Ti³⁺. The reversible conversion of the state of titanium ions Ti³⁺ Ti⁴⁺ on bending strain of specimens is established.     

Structure and Properties of SnO2–In2O3–Ag–N Coatings Formed by a Complex Method on Copper

Russian Physics Journal - The aim of this work is to analyze the structure and properties of a coating of the SnO2–In2O3–Ag–N composition formed on copper by a complex method...     

Surface Modification of ZrO2–3Y2O3 with Highintensity Pulsed N2+ Ion Beams

Russian Physics Journal -     

Influence of sintering conditions on the electrical properties of 10% ZrO2–10% Y2O3–CeO2 (mol%)

Yttria–zirconia doped ceria, 10% ZrO₂–10% Y₂O₃–CeO₂ (mol%) (CZY) and 0.5 mol% alumina-doped CZY (CZYA), prepared through oxide mixture process, were sintered by isothermal sintering (IS) and two-step sintering (TSS) having as variable the temperature and soaking time. The electrical conductivity of sintered samples was investigated in the 250 to 600 °C temperature range by impedance spectroscopy in air atmosphere. The microstructure was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Alumina, as additive, improves the grain boundary conductivity of samples sintered at temperatures lower than 1500 °C. Concerning the sintering mode, two-step sintering (TSS) proved to be a good procedure to obtain CZYA samples with high electrical conductivity and density (> 95%) at relatively low sintering temperature and long soaking time.