Hydrothermal Synthesis,Luminescence, and Phase Stability of Solid Solution Nanocrystals Based on Y3NbO7 and ZrO2

Cubic solid solution nanocrystals in the zirconia (ZrO₂)–yttrium niobate (Y₃NbO₇) system were directly formed at 180°C–240°C from the precursor solution mixtures of NbCl₅, ZrOCl₂, and YCl₃ under mild hydrothermal conditions in the presence of aqueous ammonia. The lattice parameter corresponding to cubic phase linearly changed according to the Vegard's law in the wide composition range of ZrO₂ (mol%) = 10–90 in the ZrO₂–1/4Y₃NbO₇ system. The progress of the formation of nanocrystalline solid solutions based on the Y₃NbO₇ was assisted via the presence of ZrO₂ component as a promoter with the same fluorite‐type structure. The optical band gap of the solid solutions was in the range 3.4–3.7 eV. Broadband emissions centered at 360–380 and 390 nm were observed for the nanocrystalline cubic solid solutions and pure cubic Y₃NbO₇, respectively, under excitation at 240 nm Xe lamp. The nanosized cubic crystallites of the solid solutions were maintained after heat treatment up to 800°C for 1 h air. The cubic phase of the solid solutions in the ZrO₂–1/4Y₃NbO₇ system was maintained after heat treatment at 1400°C in air.     

Ceramic pigments from CoxNi3-xP2O8 (0 ≤ x ≤ 3) solid solutions

Co_xNi_3-xP₂O₈ (0 ≤ x ≤ 3) solid solutions were synthesized via the chemical co-precipitation method. Variation of unit cell parameters and interatomic distances indicated that these solid solutions with the Ni₃P₂O₈ structure are stable between 800 and 1200 °C in compositions with 0 ≤ x ≤ 1.5 and between 800 and 1000 °C when (0 ≤ x ≤ 3). When (2.5 ≤ x ≤ 3.0), the solid solutions lead to the Co₃P₂O₈ structure, being stable between 800 and 1000 °C.The yellow colour of the Ni₃P₂O₈ compound changes to pink or red when Co(II) ions are incorporated in the structure as Ni₃P₂O₈ solid solutions are formed. Bands corresponding to second and third electronic transitions of the Co(II) ions in octahedral coordination appear in the 450–600 nm in the UV-V spectra, and they are responsible of the observed changes in the colour. Absorbance in the visible spectra was also obtained from enamelled samples but a new band at 650 nm with considerable absorbance when x > 1.0 increased the blue amount, and colour of the enamelled samples was yellowish brown, brown, green and blue.     

Synthesis,structural characterization,and photoluminescence properties of TTB‐type PbTa2O6:Eu3+ phosphor

Undoped and Eu³⁺‐doped tetragonal tungsten bronze (TTB) PbTa₂O₆ phosphors were synthesized by using solid‐state reaction method. Synthesized samples were characterized by XRD, SEM‐EDS, and photoluminescence analyses. XRD results revealed TTB‐type crystal structure with single phase up to 10 mol% Eu³⁺ doping concentration. In SEM‐EDS analyses, elemental composition of Pb decreased with the increasing concentration of Eu³⁺. Emissions at the excitation wavelength of 398.5 nm were observed at 593.2 and 618.8 nm due to ⁵D₀→⁷F₁ transitions and ⁵D₀→⁷F₂ transitions, respectively. Emission increased with the increasing Eu³⁺ doping concentration up to 10 mol% and not observed concentration quenching.     

The influence of mechanical activation on the structure and phase formation of an electro-thermal explosion in the Ti–Zr–C system

The Ti_xZr_1-xC solid solutions were synthesized by electro-thermal explosion under pressure in the (Ti + Zr + C) blends mechanically activated in hexane (MA-ETE). The effect of mechanical activation (MA) duration on reaction blend characteristics, ETE parameters, phase composition, and microstructure formation in solid solutions was investigated. At MA, the Ti + Zr blend deforms metal crystal lattices for 20 min, complete amorphization occurs for 40 min, and the carbide grains form a cubic structure for 90 min. The single-phase Zr_0.50Ti_0.50C solid solution with a grain size of 3–5 μm and a submicron composite with a grain size of 0.1–0.2 μm containing the Ti_0.86Zr_0.14C and Zr_0.74Ti_0.26C solid solutions were synthesized in a one-stage process for the first time without any additional thermotreatment. The influence of mechanical activation on diffusional mass transfer of reactants, structure, and phase formation is discussed.     

Structural,dielectric and optical analysis of Li1.1−yNb0.9-3yTi0.1+4yO3 M-phase solid solutions

The present paper reports the structural, dielectric and optical analysis of the M-phase Li_1.1−yNb_0.9-3yTi_0.1+4yO₃ (y=0.00, 0.045, 0.09, 0.11, 0.135) solid solutions in the Li₂O–Nb₂O₅–TiO₂ ternary system prepared by conventional solid state reaction method. High density (relative density>91%) ceramics were obtained by sintering the solid solutions at 1100 °C. XRD spectra revealed these ceramics to exhibit hexagonal structure and the superstructure formation was observed for higher Ti content (≥28 mol%) samples. Plate-like shape and closely packed grains were formed with low porosity (≤10%). Particle size was obtained in the range of 392–235 nm using TEM images. Relative permittivity changed from 46 to 31 while temperature coefficient of resonant frequency ranged from −93.5 to 57.5 at 1 MHz frequency. The maximum photoluminous intensity of 203.13 for the emission peak at 453 nm (blue emission) was observed for the sample y=0.00.     

Impedance spectroscopy studies on PbFe0.5Nb0.5O3 –BiFeO3 multiferroic solid solution

(1-x) PbFe_0.5Nb_0.5O₃ (PFN) – (x) BiFeO₃ (BFO) (PFN – BFO) multiferroic solid solution (x = 0.1, 0.2, 0.3 and 0.4) were synthesized by single step solid state reaction method. Single phase was confirmed in all the samples through room temperature (RT) X-ray Diffraction (XRD) with monoclinic structure (Cm space group). Transmission Electron Microscopy (TEM) studies confirm the high crystallinity of the materials with the average particle size of 100 nm. The temperature (313–528 K) and frequency (100 Hz – 5 MHz) dependent impedance, modulus and DC conductivity of PFN – BFO solid solutions were investigated. An impedance spectroscopy result shows a significant contribution from the grains (bulk) to the conductivity and exhibits non-Debye type of relaxation. The bulk (grain) resistance reduces as the temperature increases corresponds to negative temperature coefficient of resistance (NTCR) behaviour. Electric modulus exhibits thermally dependent relaxation phenomena in the material. The Bergmann modified KWW function fitted to the imaginary modulus with non-Debye type of relaxation. DC conductivity of PFN – BFO solid solutions was found to follow the Arrhenius behaviour.     

Dielectric properties and related ferroelectric domain configurations in multiferroic BiFeO3–BaTiO3 solid solutions

Dielectric properties and ferroelectric domain configurations of multiferroic xBaTiO₃–(1 ? x)BiFeO₃ (x = 0.10–0.33) solid solutions synthesized by conventional solid-state reaction, were reported. A structural transition from rhombohedral to pseudo-cubic structures appeared around x = 0.33, and the formation of impurity phase of Bi₂Fe₄O₉ was effectively depressed by doping BaTiO₃. Dielectric constants of xBaTiO₃–(1 ? x)BiFeO₃ solid solutions decreased with increasing the frequency, and the degree of decrease was related to the doping content of BaTiO₃. Transmission electron microscopy images revealed that the ferroelectric domain configurations in the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry, exhibited a wavy character whereas a predominant intricate domain structure with fluctuating mottled contrast was observed in the multiferroic BiFeO₃–BaTiO₃ solid solution with pseudo-cubic phase structure. The presence of 1/2{1 1 1} superlattice spots in the selected area electron diffraction patterns taken from the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry indicated that the ordered regions have a doubled perovskite unit cell.     

Europium‐Activated KSrPO4–(Ba,Sr)2SiO4 Solid Solutions as Color‐Tunable Phosphors for Near‐UV Light‐Emitting Diode Applications

This article reports the structural and luminescence characteristics of Eu²⁺‐activated solid solutions of (KSrPO₄)_1?x·((Ba,Sr)₂SiO₄)_x for 0 ≤ x ≤ 1. These phosphors were prepared by a sol‐gel/Pechini method. The lattice parameters of the solid solutions are linearly dependent on x. The reliability factor from Rietveld analysis is nearly constant and independent of x, indicating KSrPO₄·(Ba,Sr)₂SiO₄ forms an ideal solid solution. The emission spectra consist of two distinct broad bands, which depend on x: blue ranging from 430 to 470 nm and green–yellow ranging from 515 to 570 nm. Both emission peaks red‐shift as x increases due to the crystal field effect and an anomalous transition. The emission intensity of these solid solutions is also a function of x and is comparable to that of LiCaPO₄:Eu²⁺ (QE = 81%) at x = 0.1, suggesting that these color‐tunable solid solutions are promising for applications in solid‐state white lighting.     

Optical,thermal and dielectric properties of Bi4(TiO4)3 ceramic powders

Bismuth titanate (Bi₄(TiO₄)₃) ceramic powders have been synthesized by using a solid state reaction method. Prominently intense blue emission at 480 nm has been measured with an excitation at 418 nm. The reason for the observance of such a blue emission from this ceramic powder has been explained. The phase formation has been investigated by X-ray diffraction analysis (XRD). The morphology and composition of the ceramic powders have been studied from the measurement of SEM and EDS profiles. FTIR and Raman spectra have also been recorded to analyze the presence of functional groups and Raman active modes in the Bi₄(TiO₄)₃ ceramic powders. The sintering temperature has been optimized to be 1100 °C based on the measured TG–DTA profiles of the as prepared material. Besides these, dielectric properties of ceramic powder in the frequency range of 200 Hz–3 MHz at 300 K have also been carried out.     

Two‐Step Carbothermal Synthesis of AlN–SiC Solid Solution Powder Using Combustion Synthesized Precursor

In the present work, a two‐step carbothermal reduction method is employed to prepare the AlN–SiC solid solution (AlN–SiCss) powders by using a combustion synthesized precursor. The precursor is prepared by low‐temperature combustion synthesis (LCS) method using a mixed solution of aluminum nitrate, silicic acid, polyacrylamide, glucose, and urea. The synthesized LCS precursor exhibits a porous and foamy uniform mixture of Al₂O₃ + SiO₂ + C consisting of flaky particles. The carbothermal reduction in the LCS precursor is carried out in two steps. First, the precursors are calcined at 1600°C in argon for 3 h. Subsequently, the precursors are further calcined at 1600°C–1900°C in nitrogen for 3 h. The results indicate that the precursor calcined at and above 1850°C in nitrogen for 3 h yields the single‐phase AlN–SiCss powders. The synthesized AlN–SiCss powder exhibits near‐spherical particles with diameter of 200–500 nm. The experimental and thermodynamical results reveal that the formation of AlN–SiCss occurs via the diffusion of AlN into SiC by virtue of formation of a highly defective β′ intermediate during the second step reaction.     

Strain properties of (1-x)Bi0.5Na0.4K0.1TiO3-xBi(Mg2/3Ta1/3)O3 electroceramics

A ternary solid solution of Bi_0.5Na_0.5TiO₃–Bi_0.5K_0.5TiO₃–Bi(Mg_2/3Ta_1/3)O₃ (BNKT-xBMT) lead-free electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (T_F-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d₃₃* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase.     

Structure,Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents of (1 − x)Ba0.6Sr0.4La4Ti4O15–xBa5Nb4O15 Solid Solutions

(1 ? x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xBa₅Nb₄O₁₅ (x = 0.05, 0.1, 0.15 and 0.2, BSLT–BN) ceramic samples were prepared by co‐firing the mixtures of Ba_0.6Sr_0.4La₄Ti₄O₁₅ and Ba₅Nb₄O₁₅ powders. Crystal structure, microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of the BSLT–BN series ceramics were investigated. X‐ray diffraction patterns reveal that all the samples exhibit a hexagonal perovskite structure, which implies that the BSLT–BN mixtures form solid solutions. With increasing Ba₅Nb₄O₁₅ content, the diffraction peaks shift to low angles and the sintering temperature of BSLT–BN decreases. Raman spectra analysis reveals the shifting and splitting of the vibration modes. The microwave dielectric properties of the well‐sintered (1 ? x)BSLT–xBN ceramics vary with Ba₅Nb₄O₁₅ content. The dielectric permittivity of the ceramics exhibits a slight decreasing trend. The quality factor varies in the range of 45 000–11 200 GHz, whereas near‐zero temperature coefficients of the resonant frequency may be achieved by changing the Ba₅Nb₄O₁₅ content. TSDC was utilized to explore the extrinsic loss mechanism associated with defects. TSDC relaxation peaks are mainly generated by oxygen vacancies, and the Ba₅Nb₄O₁₅ content has a significant influence on the TSDC spectra.     

Phase evolution and chemical stability of Nd-doped natural garnet waste form by microwave sintering

Advanced materials and processes are needed to immobilize fission products in the form of chemically durable waste. Nd-doped Ca₃Zr₂Fe₂SiO₁₂ (GZG) ceramics with different sintering temperatures (1100–1300 °C), sintering times (0.5–6 h) and solid solutions (0 ≤ x ≤ 2.5) were prepared by microwave sintering. The results show that by adjusting a series of key parameters, natural garnet structures with excellent chemical stability are obtained. XRD shows that a single phase of solid solution can be obtained by increasing the sintering temperature and controlling the actinide solid solution below the solid solution limit. The sintering temperature only affects the compactness of the solid solution. Thermodynamic calculations show that high temperature is favorable for the synthesis of GZG, and it is positive and irreversible. The normalized leaching rate of Nd³⁺ in the GZG structure is approximately ～ 10^?6 g m^?1 d^?1. The release form of Nd in aqueous solution is inner diffusion. The experimental results show that the naturally occurring garnet structure is an excellent waste form.     

Structural,microstructural, and magnetic studies of Y3Fe5-xNixO12 garnet nanoparticles

This paper reports the structural and magnetic properties of a series of Y₃Fe_5-xNi_xO₁₂ (x = 0, 0.05, 0.1, and 0.2) nanopowders synthesized by the citrate combustion method. We have discussed the change in different properties with the variation in calcination temperatures as well as the Ni ion substitution in yttrium iron garnet. X-ray diffraction study confirmed the desired garnet phase formation in all the calcined powders, and the crystallinity improved with an increase in calcination temperature. The crystallite sizes were observed in the range 47–52 nm and 84–94 nm for the samples calcined at 800 and 1000 °C, respectively. Scanning electron micrographs confirmed that the grains were in the nanometre range (132–170 nm) at 800 °C and increased (351–363 nm) at 1000 °C. Larger grains at high calcination temperature resulted in the enhanced saturation magnetization and a decrease in coercivity. Curie temperature (T_c) was observed in the range 558–560 K for all the calcined Y₃Fe_5-xNi_xO₁₂ samples. Nickel substitution for iron sites in Y₃Fe_5-xNi_xO₁₂ decreased the saturation magnetization and enhanced the coercivity. This could be related to the substitution of Ni ions for tetrahedral iron sites, which changed the magnetic exchange interactions of different lattice sites. The magnetic anisotropy constant (K) increases with the enhancement of calcination temperature, whereas it decreases with nickel ion substitution in Y₃Fe_5-xNi_xO₁₂. This study suggests that the structural and magnetic properties can be tuned by Ni substitution for the Fe ions in Y₃Fe₅O₁₂ garnets at different calcination temperatures, which make them promising candidates for various technological applications.     

Phase equilibrium in binary La2O3-Dy2O3 and ternary CeO2-La2O3-Dy2O3 systems

Cerium oxide doped with oxides of rare earth elements is a multifunctional material, a wide range of uses which is associated with its unique physicochemical properties. Phase diagrams of multicomponent systems are the physicochemical basis for the creation of new materials with improved characteristics.In this work, phase equilibria in ternary CeO₂–La₂O₃–Dy₂O₃ and binary La₂O₃–Dy₂O₃ systems in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal section of the phase diagram of the CeO₂–La₂O₃–Dy₂O₃ system at a temperature of 1500 °С is constructed. No new phases have been detected in the system. It was found that in the studied ternary system solid solutions are formed on the basis of (F) modification of CeO₂ with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln₂O₃.In the La₂O₃–Dy₂O₃ binary system (1500–1100 °С) three types of solid solutions are formed: based on hexagonal modification A-La₂O₃, monoclinic modification B-Dy₂O₃ and cubic modification C-Dy₂O₃ separated by two-phase fields (A+B) and (B+C), respectively. The boundaries of the regions of homogeneity of solid solutions based on A-La₂O₃ are determined by compositions containing 35–40, 20–25, 15–20 mol% Dy₂O₃ at 1500, 1250, 1100 °C, respectively. From the obtained data it follows that the solubility of Dy₂O₃ in the hexagonal modification of lanthanum oxide is 39 mol% at 1500 °C, 23 mol. % at 1250 °C and 16 mol% at 1100 °C. The limits of existence of solid solutions based on monoclinic B-modification are determined by compositions containing 30–35, 65–60 (1250 °С), 35–40, 55–60 (1100 °С) 40–45, 70–75 (1500 °C) mol% Dy₂O₃.In the studied system, with a decrease in temperature from 1500° to 1100°C, there is a decrease in the solubility of La₂O₃ in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%.     

Nanocrystaline solid solution CeO2–Bi2O3

Nanocrystalline powders of solid solution CeO₂–Bi₂O₃ were synthesized by self-propagating room temperature reaction (SPRT) procedure with composition (Ce_1?xBi_xO_2?δ where the x = 0.1–0.5). X-ray diffraction analyses show that for x < 0.50 a solid solution with fluorite structure is formed. Rietveld's structure refinement method was applied to characterize prepared powders and its microstructure (size–strain). The lattice parameters increase according to Vegard's rule with increasing of Bi concentration. The average crystallite size is about 2–3 nm. Spectroscopic ellipsometry and Raman scattering measurements were used to characterize the samples at room temperature. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas increase of Bi content provokes a small decrease of optical absorption edge in comparison with pure ceria. Specific surface area of obtained powders was measured by Brunauer–Emmet–Teller (BET) method.     

The effect of reaction temperature on the structural and magnetic properties of nano CoFe2O4

Nano cobalt ferrites (CoFe₂O₄) were co-precipitated at various reaction temperatures (60, 70 and 80 °C) for 1 h. The reaction temperature greatly influenced the crystallite size and the magnetic behaviours of the nano CoFe₂O₄. The mean crystallite size ranged from 9 to 15 nm with the increase in the reaction temperature and the intensity of metal oxide vibrations at 568–550 cm⁻¹ were also inclined. The synthesized samples were in the stoichiometric ratio of 1:2 (Co:Fe) with roughly spherical morphology. The synthesized cobalt nanoferrites exhibited ferromagnetism at room temperature and 5 K, and the saturation magnetization increased from 6.4 to 20 emu/g with the crystallite size.     

Influence of rare-earth La3+ ion doping on microstructural,magnetic and dielectric properties of Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) ferrite nanoparticles

A series of La³⁺ ion doped magnesium nickel ferrites, Mg_0.5Ni_0.5Fe_2-xLa_xO₄ (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La³⁺ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La³⁺ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La³⁺ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La³⁺ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications.     

Preparation and characterization of LnMgAl11O19 (Ln=La,Nd, Gd) ceramic powders

Lanthanide hexaaluminate powders of LaMgAl₁₁O₁₉ (LMA), NdMgAl₁₁O₁₉ (NMA) and GdMgAl₁₁O₁₉ (GMA) were synthesized via the solid state reaction or sol–gel and calcination method. The LMA and NMA powders synthesized by the sol–gel and calcination method at 1600 °C for 8 h exhibit a single hexaaluminate phase with magnetoplumbite structure; however, the GMA powder synthesized by the sol–gel and calcination method at 1600 °C for 8 h contains both a hexaaluminate phase and a small amount of second phase GdAlO₃ with a perovskite structure. The powders synthesized by the solid state reaction method at 1500 °C for 4 h have a small particle size of 1–3 μm, and a large specific surface area and a good uniformity. The powders synthesized by the sol–gel and calcination method at 1600 °C for 8 h have a particle size of 5–20 μm, and exhibit to a certain extent agglomeration.     

Microwave-assisted polyol synthesis of sub-micrometer Y2O3 and Yb-Y2O3 particles for laser source application

Sub-micrometer powder (100–150 nm diameter) of Yb-doped yttrium oxide was obtained, for the first time, by microwave-assisted polyol (diethylene glycol, DEG) method. This method is based on fast and homogeneous increase of temperature, due to the microwave heating, and on addition of the hydrolysing agent (water) at high temperature. This promotes a fast nucleation followed by a controlled growth of nuclei. Different procedures were used to process the as-synthesized powders. In some cases washing by ultrapure water was used to dissolve nitrate and DEG by-products, this treatment allowed the use of a lower calcination temperature (150–200 °C less) to obtain the crystalline phase. Analysis of the calcined powder showed different levels of structures: from nanocrystal (10–15 nm), to primary particles (100–150 nm), to micrometer soft aggregates (2–4 μm). The microwave-assisted polyol method resulted an easy way to dope yttria with the desired amount of Yb³⁺. This work was carried out in order to prepare particles to be used as rare-earth doped Y₂O₃ and YAG polycrystalline transparent ceramic for laser source applications.