Structural and Thermal Validations of Y<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript>18</Subscript> Composites Synthesized via Citrate Sol-Gel Spontaneous Combustion Method

The fabrication of single-phase superconductors enabled promising advancements in a wide range of technological applications. Numerous parameters including processing temperature, thermal cycle, chemical composition, doping, and atmosphere will be carefully addressed and optimized. This paper investigates phase stability and compound formation of Y₃Ba₅Cu₈O_y (Y-358) preform powders which were sintered at different temperatures. The precursor powder synthesized via chemical route and employing spontaneous combustion technique, respectively. The presence of Y-358 and YBa₂Cu₃O_7-δ (Y-123) phases in composites sintered at different temperatures with varied phase fractions were further confirmed through Rietveld refinement. The formation of Y-123 phase is dominant in all samples and composite was sintered at 900 °C, which was exhibited higher as compared to Y-358 phase content. The decomposition of different phases present in the composites and reaction temperatures were investigated with simultaneous differential thermal and thermogravimetry analysis.     

Electrical and Structural Properties of RE<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript>18</Subscript> (RE=Y,Sm and Nd) Superconductors

This paper presents the synthesis and characterization of the new superconducting compounds with nominal composition, RE₃Ba₅Cu₈O₁₈, RE=Y, Sm and Nd. The onset critical temperatures of the present samples are 97.5, 97 and 95 K for the RE=Y, Sm and Nd, respectively. The first two values are the highest for the RE–Ba–Cu–O superconductors recorded to date. The RE₃Ba₅Cu₈O₁₈ samples crystallize in the orthorhombic system, with increased unit cell volume as Sm and Nd replace the element Y.     

Superconducting Performance,Structure, Microstructure,and Trapped Field of Top-Seeded Melt-Processed Bulk Y<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The sintering temperature for the production of Y₃Ba₅Cu₈O₁₈ (Y-358) preform powders synthesized in sol-gel spontaneous combustion technique was optimized. A large single-grain bulk Y-358 crystal was fabricated employing a top-seeded melt-growth technique utilizing the optimally sintered preform powders (i.e., at 900 ^°C for 12 h). Structural, microstructural, elemental, and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscopy, and SQUID, respectively. The structural characterization indicated that the sample is highly textured in (00l) direction. The Y-358 phase fractions were estimated in both preform powders and bulk sample using Rietveld refinement. The onset of superconducting transition is observed at 92.5 K, and the curve is very sharp indicative of the high quality of the produced bulk sample. The field dependence of critical current density (J_c) was determined at 77 K, and the self-field J_c was found to be ～26 kA/cm². A magnetic field of 0.27 T was trapped by the sample at 77 K.     

Determining the absolute thermo emfs of conductors using a Y<Subscript>1</Subscript>Ba<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript> rod

The voltage drop on a 110-mm-long Y₁Ba₂Cu₃O_{7 − δ} (YBCO) rod with a diameter of 7 mm bearing a current of 1 A has been studied as a function of the temperature. It is shown that YBCO rods can be used to measure the absolute thermo emf of conductors in a range of temperatures up to the onset of breakage of the superconducting state. The thermo emf of Ni, Cu, and W conductors was determined.     

Controlled magnetoresistance in Y<Subscript>3/4</Subscript>Lu<Subscript>1/4</Subscript>Ba<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>-CuO composites at 77 K

We have studied the low-temperature magnetoresistance of Y_3/4Lu_1/4Ba₂Cu₃O₇-CuO composites obtained by fast sintering technique and established a relation between the probing to critical current density ratio j/j _c and the shape of the magnetoresistance curve ρ(H). For j/j _c<1, the electric resistance arises at a threshold value of the magnetic field strength H _c. For j/j _c≥1, a linear variation of ρ(H) at 77 K in the range from 0 to 14 Oe can be provided by selecting the CuO content (in the 15–30 vol % interval) and the j value (in the 0.003–0.2 A/cm² range). In the latter case, the slope dρ/dH (i.e., the sensitivity of the electric resistivity with respect to the magnetic field) is 1–20 mΩ cm/Oe and the relative field-induced increase in the resistivity ρ₀=(ρ(H)−ρ(H=0))/ρ(H=0) amounts to 1320 and 685% at H=200 and 35 Oe, respectively. Composites possessing controlled magnetoresistance are promising materials for the active elements of magnetic field sensors capable of operating at a practically convenient liquid nitrogen temperature.     

Two-Dimensional Nanogranularity of the Oxygen Chains in the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.33</Subscript> Superconductor

The organization of dopants in high-temperature superconductors provides complex topological geometries that control superconducting properties. This makes the study of dopants’ spatial distribution of fundamental importance. The mobile oxygen ions, y, in the CuO₂ plane of YBa₂Cu₃O_{6 + y} (0.33 < y < 0.67) form ordered chains which greatly affect the transport properties of the material. Here, we visualize and characterize the two-dimensional spatial organization of these oxygen chains using scanning micro X-ray diffraction measurements in transmission mode on a thin single-crystal slab with y = 0.33 (T _c = 7 K) near the critical doping for the insulator-to-metal transition. We show the typical landscape of percolation made of a granular spatial pattern due the oxygen chains segregating in quasi-one-dimensional needles of ortho-II (O-II) phase embedded in an insulating matrix with low density of disordered oxygen interstitials.     

The Effect of Excess Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Addition on the Mechanical Properties of Melt-Processed YBCO Superconductor

In this study, two kinds of melt-processed YBCO samples with Y₂O₃ addition were fabricated and their microstructures were defined by XRD analysis and polarized light optical microscopy. The mechanical properties of these compounds have been investigated by measuring the Vickers hardness. The superconducting transition temperature was determined by inductive measurements for oxygenated and non-oxygenated samples. The compacted powders were located on a crucible with a buffer layer of Y₂O₃ and a crucible with Y₂O₃ powder freely poured to avoid liquid to spread on the furnace plate. It was found that the sample located on crucible with freely poured Y₂O₃ powder has shown almost single crystal and indicated a very sharp transition curve.     

Paramagnetism and Superconductivity in Eu<Subscript>0.7</Subscript>Sm<Subscript>0.3</Subscript>Ba<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript>

Magnetic properties of sintered Eu_0.7Sm_0.3Ba₂Cu₃O_7?δ were investigated both in dc and ac magnetic fields. The dc response reflects the interplay between the rare earth ion paramagnetic and the superconducting charge carrier subsystems, respectively. The harmonic susceptibilities exhibit special features: the second harmonic is anomalously high and the third harmonic in zero dc-field has reversed temperature dependence with respect to the theoretical models. The magnetic relaxation at low fields is monotonous and occurs as a two-stage relaxation, each stage obeying logarithmical time dependence with different rates. At high fields, the relaxation is nonmonotonous with a peak at intermediate time suggesting a temporary re-entrance of irreversibility when the flux-line density increases in the center of the sample because of the redistribution of the vortices toward that region.     

Production of the Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> transparent nanostructured ceramics

The nanocrystalline Y₃Al₅O₁₂ ceramics with different phase compositions, microstructures, and optical characteristics have been prepared by low-temperature consolidation of the Y₃Al₅O₁₂ powder at pressures from 6 to 7.7 GPa in the temperature range from 250 to 550°C. The conditions have been defined for obtaining transparent nanostructured ceramics Y₃Al₅O₁₂ having grains of size 20–40 nm and a transmission coefficient in the visible region of 40–45%. The criteria for the transparency of the nanostructured ceramics have been formulated and the ways of an improvement of its optical characteristics are discussed.     

Plasma-chemical Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles for Doping of High-Temperature Superconductors

Ferrite nanoparticles (Fe₃O₄) have been produced by the direct low-pressure plasma-chemical synthesis. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), vibration magnetometry (VSM), and Mössbauer spectroscopy (NGR) were used for measurements, showing that the produced nanoparticles have an average size of 9.4 nm, a crystalline phase of magnetite, possess a property of superparamagnetism at room temperature, and have a blocking temperature of 89 K. The peculiarities of nanoparticle behavior in the magnetic field, related to a large specific surface area, are discussed.     

Investigation of Structural and Magnetic Effects of Cobalt Doping in ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles

We study structural and magnetic properties of magnetic ceramic Co _x Zn_1?x Fe₂O₄ nanoparticles synthesized by the co-precipitation method and optimize its size and magnetic property for possible application in wastewater treatment. The effects of long stirring time under boiling condition and the introduction of the third metal ion to the structure are investigated. To study the microstructural and magnetic characteristic of the samples, X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM) analyses are carried out. The diffracted peaks of XRD pattern confirm the formation of spinel phase. In addition, we study the effect of Co doping on the peak positions in the spinel structures. To evaluate crystallite size and other lattice parameters of the samples, we use the Rietveld method as a nearly exact approximation instead of Scherrer formula. Thus, the Rietveld refinement method has been utilized and structural and lattice parameters of the samples are extracted using Reflex program. In contrast with other works, our nanoparticles show superparamagnetic behavior, larger surface area, and better crystallinity with no calcination which originates from the condition of the synthesis method.     

The influence of the cooling rate on bulk metallic glass formation in Mg<Subscript>80</Subscript>Cu<Subscript>15</Subscript>Y<Subscript>5</Subscript> and Mg<Subscript>80</Subscript>Cu<Subscript>10</Subscript>Y<Subscript>10</Subscript>

The Mg–Cu–Y system is known to be one of the best glass formers among the various existing magnesium alloys. The compositions chosen for the current study were Mg₈₀Cu₁₅Y₅ and Mg₈₀Cu₁₀Y₁₀. Different casting processes yielded four different microstructures that were analyzed by means of X-ray diffraction, scanning electron microscopy, high resolution scanning electron microscopy, and energy-dispersive X-ray spectroscopy chemical analysis. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mold held at different temperatures (cooled to −195 °C with the aid of liquid nitrogen, held at room temperature and heated up to 300 °C) and melt-spinning. Detailed microstructure study was then performed on the melt-spun specimen using transmission electron microscopy and high resolution transmission electron microscopy. The above-mentioned investigation revealed a crystalline rather than amorphous structure. The observed microstructure could not be explained on the basis of current models referring to the frequency of nucleation events.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> co-stabilized ZrO<Subscript>2</Subscript>-WC composites

Y₂O₃ + Nd₂O₃ co-stabilized ZrO₂-based composites with 40 vol% WC were fully densified by pulsed electric current sintering (PECS) at 1350 °C and 1450 °C. The influence of the PECS temperature and Nd₂O₃ co-stabilizer content on the densification, hardness, fracture toughness and bending strength of the composites was investigated. The best combination of properties was obtained for a 1 mol% Y₂O₃ and 0.75 mol% Nd₂O₃ co-stabilized composite densified for 2 min at 1450 °C under a pressure of 62 MPa, resulting in a hardness of 15.5 ± 0.2 GPa, an excellent toughness of 9.6 ± 0.4 MPa.m^0.5 and an impressive 3-point bending strength of 2.04 ± 0.08 GPa. The hydrothermal stability of the 1 mol% Y₂O₃ + 1 mol% Nd₂O₃ co-stabilized ZrO₂-WC (60/40) composites was compared with that of the equivalent 2 mol% Y₂O₃ stabilized ceramic. The double stabilized composite did not degrade in 1.5 MPa steam at 200 °C after 4000 min, whereas the yttria stabilized composite degraded after less than 2000 min. Moreover, the (1Y,1Nd) ZrO₂-WC composites have a substantially higher toughness (~9 MPa.m^0.5) than their 2Y stabilized equivalents (~7 MPa.m^0.5).     

Structural and electrical properties of Ba<Subscript>5</Subscript>SmTi<Subscript>3</Subscript>V<Subscript>7</Subscript>O<Subscript>30</Subscript> ceramics

Polycrystalline sample of Ba₅SmTi₃V₇O₃₀ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray preliminary structural studies reveal that the material has orthorhombic structure at room temperature. Detailed electrical (dielectric and impedance) properties of the material studied by using a complex impedance spectroscopy (CIS) technique in a wide temperature range (33–450 °C) at different frequencies (10²–10⁶ Hz) reveal that the relative dielectric constant of the material increases with rise in temperature and thus bulk has a major contribution to its dielectric and electrical properties. The bulk resistance of the material decreases with rise in temperature exhibiting a typical negative temperature coefficient of resistance (NTCR) behavior. The nature of the temperature variation of conductivity and value of activation energy, suggest that the conduction process is of mixed-type (ionic–polaronic and space charge). The existence of ferroelectricity in the compound was confirmed from polarization study.     

Preparation and Properties of MPMG YBCO Bulk with Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Layer

In this study, four kinds of melt-processed YBCO samples were fabricated with the MPMG procedure. The compacted powders were located on a crucible with a buffer layer of Y₂O₃ to avoid liquid to spread on the furnace plate. Their microstructures were defined by XRD analysis and polarized light optical microscopy. The microstructure investigations indicated that the 123 grains were very big and fine and dispersed 211 particles remained in the samples. Resistivities of the samples were measured by a standard continuous dc four-probe method. Magnetization measurements were made and flux jumps were observed at a relatively higher temperature for Y1060. The critical current density, J _c , values of the samples, measured by VSM in 5 T magnetic field, exceeded 0.6×10³ A⋅cm⁻² at 77 K and 4 T.     

Reactions of V<Subscript>2</Subscript>O<Subscript>5</Subscript>, Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>, and Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> with AlN

Reactions of vanadium, niobium, and tantalum pentoxides with aluminum nitride have been studied using X-ray diffraction. At temperatures from 1000 to 1600°C, we have identified various V, Nb, and Ta nitrides. The composition of the niobium and tantalum nitrides depends on the reaction temperature. The tendency toward nitride formation becomes stronger in the order V₂O₅ < Ta₂O₅ < Nb₂O₅.     

Relaxation of optical excitations in crystals of the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system with radiation defects

The photoluminescence and short-time persistence (afterglow) kinetics in pure and doped Y₂O₃-Al₂O₃ crystals excited with UV laser pulses (12 ns, 337 nm) were studied using samples irradiated with gamma quanta from a ⁶⁰Co source to a dose from 10⁴ to 10⁷ Gy. The relaxation time of the samples studied increases, with decreasing symmetry of the crystal lattice, in the following order: garnet—orthoaluminate—ruby—yttria. The afterglow duration and intensity significantly decrease in gamma-irradiated crystals, which is explained by the predominant recombination of close electron-hole pairs. Garnet-neodymium crystals are characterized by high radiation stability and fast relaxation kinetics.     

Preparation and characterization of new dielectric ceramics Ba<Subscript>5</Subscript>LnTi<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>18</Subscript> (Ln = La,Nd)

Two new A₆B₅O₁₈ type cation-deficient perovskites Ba₅LnTi₂Nb₃O₁₈ (Ln = La, Nd) were prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Both compounds crystallize in the trigonal system. Ba₅LaTi₂Nb₃O₁₈ has a dielectric constant of 56.6, a high quality factors (Q_u × f > 16,700 at 4.3331 GHz), and a relatively large temperature coefficient of resonant frequency (_f) + 142 ppm°C^–1 at room temperature; Ba₅NdTi₂Nb₃O₁₈ has a higher dielectric constant of 47.3 with high quality factors Q_u × f > 15,000 at 4.6830 GHz, and _f + 128 ppm°C^–1.     

Crystallization and microstructures of Y-Si-Al-O-N glass-ceramics containing main crystal phase Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>

A glass with the nominal composition of 28Y48Si24Al83O17N (in equal percentage) was chosen as parent glass in this paper to prepare Y₃Al₅O₁₂-based glass-ceramics. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to assess the crystallization process of the parent glass. YAG as the only crystalline phase appears in all glass-ceramics produced under 1250°C. A small amount of O’-Sialon secondary phase starts to precipitate from parent glass samples as heat treatment temperature increases to 1250°C. Grain size of the dendrite crystal which corresponds to YAG phase increases and the dendrite branches get thickened as heat treatment temperature increases. Moreover, grain size of YAG phase resulting from two-stage heat treatment is much smaller than that of YAG phase obtained by one-stage heat treatment. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass-ceramics and for heat treatments of YAG/β-SiAlON materials.     

Recombination processes in the Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> scintillator

The roentgenoluminescence spectra, temperature-dependent activator luminescence, optically stimulated luminescence, and the effect of IR irradiation on the yield and spectral composition of the low-temperature roentgenoluminescence and thermoluminescence curves of the Y₃Al₅O₁₂:Ce³⁺ scintillator have been studied in the temperature range 85–295 K. The results, coupled with earlier data, suggest that the Ce³⁺ ions in the garnet crystal studied form Ce³⁺ p hole centers and increase the concentration of electronic F ^?-centers responsible for the IR stimulation band at 940 nm. The reduction in roentgenoluminescence yield on cooling Y₃Al₅O₁₂:Ce³⁺ to below 230 K is due to the significant localization of excited carriers at defects, which show up in thermoluminescence peaks and optical stimulation spectra. The low-temperature Ce³⁺ luminescence in Y₃Al₅O₁₂:Ce₃₊ seems to result from the recombination of activator-bound excitons.