X-Ray Diffraction Study of Ba6-3x (Eu1/2 Nd1/2)8+2x Ti18O54 Microwave Dielectric Ceramics Prepared by Sol-Gel Method

Perfectly-sintered Ba_6-3x (Eu_1/2 Nd_1/2)_8+2x Ti₁₈O₅₄ (x = 2/3) (BENT) microwave dielectric ceramics was fabricated successfully with BENT powders prepared by Sol-Gel process. The lattice parameters of BENT ceramic powders were determined by method of X-ray diffraction in ordinary temperature. Orthorhombic lattice type (space group Pbam) of BENT in ordinary temperature was determined, its pattern was indexed and its polycrystalline X-ray diffraction data were listed. By analysis of its X-ray diffraction data, it could be concluded that Eu and Nd coexisted in the single phase and could not be distinguished in BENT ceramics. The increasing dielectric losses of BENT could be explained basically by the disorder of Eu ions and Nd ions occupied in Al-sites.     

Microstructure and microwave dielectric properties of Ba6-3xSm8+2xTi18O54 ceramics with various BaxSr1-xTiO3 additions

The Ba6-3xSm8+2xTi18O54 (x=2/3) microwave dielectric ceramics were prepared by traditional solid sate reaction technique. The ex-periment was based on the Ba6-3xSm8+2xTi18O54 (BST) microwave dielectric ceramics doped with a certain amount of Bi2O3, then the effects of BaxSr1-xTiO3 additives on the structure and microwave dielectric properties of Ba6-3xSm8+2xTi18O54 ceramics were investigated using X-ray diffraction and scanning electron microscopy. In this study, the small amount substitution of Sr for Ba was effective for the microwave dielec-tric properties of BST, especially the τf could be tuned to near zero. The result showed that the BST possessed excellent dielectric properties when the addition of Bi2O3 and BaxSr1-xTiO3 was 1 wt.% respectively: εr=79.6, Q?f=10789 GHz, τf=-1.5 ppm/oC.     

Sintering characteristics and microwave dielectric properties of 0.5Ca0.6La0.267TiO3-0.5Ca(Mg1/3Nb2/3)O3 ceramics prepared by reaction-sintering process

0.5 Ca_(0.6)La_(0.267)TiO_3-0.5 Ca(Mg_(1/3)Nb_(2/3))O_3(5 CLT-5 CMN) ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = +8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.     

CaTiO3–Sm0.9Nd0.1AlO3 ceramics with a moderate dielectric constant and a high quality factor prepared by sol–gel auto combustion method

CaTiO₃–LnAlO₃ (Ln = La, Nd, Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant ε_r, a high quality factor Q × f, and a small temperature coefficient of resonant frequency τ_f, making this system promising for microwave devices. However, its high synthesis temperature and sintering temperature limit its industrial applications. In our work, single phase 0.7CaTiO₃–0.3Sm_0.9Nd_0.1AlO₃ (7CT–3SNA) was synthesized via the sol–gel auto combustion method using citric acid as fuel at a relatively low temperature. After being calcined at 600 °C for 2 h, well-crystallized 7CT–3SNA powders with 30–50 nm average particle size were achieved, suggesting good sintering activity. The new and narrow order band at about 800 cm⁻¹ in the Raman spectra indicates a high ordering degree in the B site of 7CT–3SNA solid solution. Compared with the solid–state reaction method and co-precipitation method, the 0.7CT–0.3SNA ceramics fabricated by the current method possess a much lower calcination temperature, a similar ε_r value, and an improved Q × f value. The optimum microwave dielectric properties of ε_r = 43.54, Q × f = 54375 GHz, and τ_f = −6.3 × 10⁻⁶/°C are obtained for the CTSA ceramics derived from the sol–gel auto combustion process. Therefore, the 7CT–3SNA ceramics prepared in this study are potential dielectric materials for microwave applications, indicating that the sol–gel auto combustion method is a good alternative strategy for the fabrication of CaTiO₃–LnAlO₃ ceramics.     

Studies on BaO-Y2O3-TiO2 Microwave Dielectric Ceramics

BaO-Y₂O₃-TiO₂ microwave dielectric ceramics with the rich area of TiO₂ were fabricated by a solid-state reaction method using BaCO₃, Y₂O₃, TiO₂ powders as starting materials. The sintering characteristics, phase composition, micro-structures and microwave dielectric properties of BaO-Y₂O₃-TiO₂ microwave dielectric ceramics with different k values sintered at different temperatures were investigated. The results showed that the sintering temperature of BaO-Y₂O₃-TiO₂ microwave dielectric ceramics was lower (about 1240 °C), and the sintered ceramics with the major phase of Y₂Ti₂O₇ had excellent dielectric properties. When k = 4, ɛ_r and tanδ were about 78.3 and 3 × 10⁻³ respectively. When k=5, ɛ_r and tanδ were about 53 and 9 × 10⁻⁴ respectively.     

Effect of Nd2O3 doping on the electrical properties of Ba0.96Ca0.04Ti0.90Sn0.10O3 ceramics

The Ba_(0.96)Ca_(0.04)Ti_(0.90)Sn_(0.10)O_3-xNd_2 O_3(x = 0-0.08%) ceramics were prepared via traditional solid-state sintering method. The influences of Nd3+ substitution on the phase structure, dielectric properties,piezoelectric and ferroelectric properties of the ceramics were investigated. All the samples possess pure BaTiO_3-type perovskite structure. MPB with orthorhombic and tetragonal phase coexist at around x = 0.03-0.04. Nd~(3+) doping decreases both Tc and T_(O-T) to lower temperature. All the samples exhibit an intermediate state with the coexistence of ferroelectric and diffuse relaxor ferroelectric behavior with the addition of Nd~(3+). The electric properties of the ceramics were optimized at x = 0.03 with d33, K_p, ε_r and P_r values of 545 pC/N, 51.9%, 24,412 and 10.74 μC/cm~2.     

Preparation and characterization of Ce_(0.8)La_(0.2–x)Y_xO_(1.9) as electrolyte for solid oxide fuel cells

In this study, ultrafine Ce0.8La0.2–x Y x O1.9（for x=0, 0.05, 0.10, 0.15, 0.20） powders were successfully prepared by the sol-gel method.The samples were characterized by fourier transform infrared（FTIR）, thermogravimetric and differential scanning calorimetry（TG-DSC）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, AC impedance and thermal expansion measurements.Experimental results indicated that highly phase-pure cubic fluorite electrolyte Ce0.8La0.2–x Y x O1.9 powders were obtained after calcining at 600 °C.The as-synthesized powders exhibited high sintering activity, the Ce0.8La0.2–x Y x O1.9 series electrolytes which have higher relative densities over 96% could be obtained after sintered at 1400 °C for 4 h.Ce0.8La0.15Y0.05O1.9 electrolyte sintered at 1400 °C for 4 h exhibited higher oxide ionic conductivity（σ800 oC=0.057 S/cm）, lower electrical activation energy（E a=0.87 e V） and moderate thermal expansion coefficient（TEC=15.5×10-6 K-1, temperature range 25–800 °C）.     

Investigation of Structural and Diffuse Phase Transition of New Nano Lead-Free System xBAO – yBZT − (1 − x − y) BCT

We present in this article the latest development of single-phase nanocrystalline ceramics, x(BiAlO₃) ? y(BaZr_0.2Ti_0.8O₃) ? (1 ? x ? y) (Ba_0.7Ca_0.3TiO₃), abbreviated as xBAO ? yBZT ? (1 ? x ? y) BCT with (x, y) = (0, 0.50), (0.01, 0.49), (0.03, 0.47), and (0.1, 0.4), which were prepared using a high-energy ball milling technique. In the current study, BZT ? xBCT has been selected as a host system to be incorporated into BiAlO₃. Their properties of structure, relative dielectric permittivity (ε), diffuse phase transition (γ), peak broadening (δ _γ ), and deviation from Curie–Weiss law (ΔT _C) were systematically investigated. However, the decreasing trend of Curie temperature (T _c) in the system does not obey the Vegard’s law. Analysis of X-ray diffraction patterns shows the solid solubility of (Bi³⁺, Ca²⁺) into A-site and that of (Zr⁴⁺, Al³⁺) into B-site of pure BaTiO₃ lattice of tetragonal symmetry with space group P4mm. The values of γ (1.75 to 1.63) confirmed that the ceramic has intermediate behavior between the relaxor and normal ferroelectric, which is evaluated by modified Curie–Weiss law. The high value of quality factor (115), when x = 0.01, y = 0.49 at 1-kHz frequency and temperature 323 K (50  °C), decreases with the increasing frequency.     

Effect of Yttrium Doping in Barium Zirconium Titanate Ceramics: A Structural, Impedance, and Modulus Spectroscopy Study

In the current article, we studied the effect of yttrium [Y³⁺] ions’ substitution on the structure and electric behavior of barium zirconate titanate (BZT) ceramics with a general formula [Ba_1?x Y_2x/3](Zr_0.25Ti_0.75)O₃ (BYZT) with [x = 0, 0.025, and 0.05] which were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that these ceramics have a single phase with a perovskite-type cubic structure. Rietveld refinement data confirmed [BaO₁₂], [ZrO₆], [TiO₆], and [YO₆] clusters in the cubic lattice. The Y³⁺ ions’ effects on the electric conductivity behavior of BZT ceramics as a function of temperature and frequency are described, which are based on impedance spectroscopy analyses. The complex impedance plots display a double semicircle which highlights the influences of grain and grain boundary on the ceramics. Impedance analyses showed that the resistance decreased with the increasing temperature and resulted in a negative temperature coefficient of the resistance property in all compositions. Modulus plots represent a non-Debye-type dielectric relaxation which is related to the grain and grain boundary as well as temperature-dependent electric relaxation phenomenon and an enhancement in the mobility barrier by Y³⁺ ions. Moreover, the electric conductivity increases with the replacement of Ba²⁺ by Y³⁺ ions may be due to the rise in oxygen vacancies.     

Evaluation of Dielectric Properties, Vibration Modes, and Crystal Structures in Ba[Zn(1?x)/3Ni x/3Nb2/3]O3 Ceramics

Microwave dielectric ceramics of Ba[Zn_(1?x)/3Ni _x/3Nb_2/3]O₃ (BZNN, x = 0.0, 0.5, 0.6, 0.7, 0.8) were sintered at 1773 K (1500 °C) for 3 hours by the conventional solid-state reaction method. To clarify the relationship between dielectric properties and crystal structures, vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection spectroscopy (FTIR)) and X-ray diffraction (XRD) were employed to study Ba[Zn_(1-x)/3Ni_x/3Nb_2/3]O₃ solid solutions. Crystal structures were determined as cubic perovskite structures, and no phase transition appears in substitution of Ni²⁺ to Zn²⁺ ions. Raman spectroscopy was used to discuss the correlation of dielectric properties with Raman shifts and full-width at half-maximum (FWHM) values, which indicate that dielectric properties are closely related to both FWHM values and A_1g(Nb) mode shifts. FTIR spectra and imaginary parts of dielectric constants were calculated to obtain the correlation between polar phonon modes and dielectric properties with Ni²⁺ concentration.     

Microwave electromagnetic and absorbing properties of Dy3+doped MnZn ferrites

Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM) and network analyzer(Agilent 8722ET).All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03.The average crystallite size was about 44?56 nm.The mi...     

Study on Ferroelectric and Dielectric Properties of La-Doped CaBi4Ti4O15-Based Ceramics

Research on bismuthlayer structuredferroelectricceramics as piezoelectric material with high Curie tem-perature ,strong anisotropic characters ,lowdielectricdissipationfactor and lowaging rate has attracted in-creasing interest[1,2].It can be used to manu…     

Effect of Y3＋, Gd 3＋and La3＋dopant ions on structural,optical and electrical properties of o-mullite nanoparticles

Dielectric ceramics of M(x) Al6(1–x) Si2 O13 doped mullite were synthesized via co-precipitation technique. The X-ray diffraction profiles revealed that these nanoparticles were crystallized well and the volume of mullite unit cell was increased as a function of the ionic radius of dopant ion. TEM images showed regular orthorhombic crystal morphology for the pure mullite sample. Meanwhile, the doped samples exhibited slightly distorted crystal morphology of larger particle sizes. DSC thermograms evinced that the exothermic peak temperature of mullite was shifted to the lower value with M3+ion insertion. The photoluminescence spectra were studied for mullite samples, and it was found that the intensity of the emission spectra was affected by the M3+ion type. It was found that, Y3+doped mullite achieved the minimum dielectric loss value of 0.01 in the radio wave frequency region(1 MHz). Meanwhile, Gd3+ doped mullite achieved the minimum dielectric loss value of 0.09 in the microwave frequency region(1 GHz).     

Synthesis and characterization of YAG: Ce3+ fluorescence powders by co-precipitation method

YAG:Ce³⁺(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate, yttrium nitrate, cerous nitrate as the starting materials and ammonium carbonate as precipitant. The products were characterized by X-ray powder diffraction, luminescence spectrometer, transmission electron microscope (TEM). The XRD results showed that the obtained YAG:Ce³⁺ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 °C and the TEM results showed that the grain diameters were about 100 nm. The YAG:Ce³⁺ fluorescence powders, synthesized by co-precipitation method, had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y_3-xCe_xAl₅O₁₂, the calcinations time was 2 h and the calcinations temperature was 1000 °C.     

Dielectric and microstructural properties of YAG:Dy3+ ceramics

Yttrium aluminium garnet(Y_3 Al_5 O_(12):YAG) singly doped with Dy3+ at different concentrations was prepared by solid state reactions using repeated heating cycles over the temperature range of 1300-1600 ℃. X-ray powder diffraction analysis confirms the presence of a well-crystallized YAG perovskite phase with cubic structure(by Rietveld refinement). The rare earth dopant is successfully integrated into the YAG host lattice without any major changes in the original structure. The temperature dependence,up to 250 ℃, of the conductivity, dielectric constant, dielectric loss, and loss tangent, at various frequencies of up to 5.0 MHz for undoped and doped crystals is compared to understand the electrical and structural characteristics. The experimental results reveal that Dy3+ dopants in YAG crystal significantly influence the conductivity, dielectric constant, and lossy mechanisms, which is probably due to the 3 d-AI ions and 4 f-Dy ions incorporated at different positions of both tetrahedral and octahedral symmetries in YAG:xDy3+ ceramics.     

Enhanced Dielectric Properties in Spark Plasma Sintered Zinc Titanate Ceramics

The ever increasing application of zinc titanate ceramics as a dielectric material in microwave devices and low temperature co-fired ceramics calls for the improvement in their dielectric properties. In this paper, the effect of different sintering techniques on the dielectric properties of zinc titanate have been discussed. Zinc titanate was prepared by ball milling 1:1 molar ratio of ZnO and TiO₂ for 12 h and calcined at 800 °C for 2 h. The presence of ZnTiO₃ and Zn₂TiO₄ phases were confirmed by X-ray diffraction and the dielectric properties of the sintered samples were studied using LCR meter. Samples consolidated by spark plasma sintering (SPS) showed highest densification (13% increase), higher dielectric permittivity (?_r = 25.17) and Q factor (Q factor = 162.78) with lower loss tangent values (tanδ = 0.00614) than that of microwave sintered samples (?_r = 21.86, Q factor = 99.08, tanδ = 0.01009) and conventionally sintered samples (?_r = 20.54, Q factor = 60.07, tanδ = 0.01665). The fabrication time was considerably reduced for the materials prepared via SPS than that prepared by conventional route with improved properties and also the dependence of dielectric properties on density was confirmed in this research work.     

Er and Gd Co-Doped Ceria-Based Electrolyte Materials for IT-SOFCs Prepared by the Cellulose-Templating Method

Ce_0.9?x Gd_0.1Er _x O_1.9?x/2 (0 ≤ x ≤ 0.1) (EGDC) powders were successfully synthesized with a fast and facile cellulose-templating method for the first time and characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The samples were calcined at a relatively low calcination temperature of 773 K (500 °C). The sintering behavior of the calcined EGDC powders was also investigated at 1673 K (1400 °C) for 6 hours. Calcined Ce_0.9?x Gd_0.1Er _x O_1.9?x/2 (0 ≤ x ≤ 0.1) powders and sintered Ce_0.9?x Gd_0.1Er _x O_1.9?x/2 (0 ≤ x ≤ 0.1) pellets crystallized in the cubic fluorite structure. It was found that the relative densities of the sintered EGDC pellets were over 95 pct for all the Er contents studied. Moreover, the effect of Er content on the ionic conductivity of the gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_1.90) was investigated. The highest ionic conductivity value was found to be 3.57 × 10^?2 S cm^?1 at 1073 K (800 °C) for the sintered Ce_0.82Gd_0.1Er_0.08O_1.91 at 1673 K (1400 °C) for 6 hours.     

Study on Dy2O3-Doped Medium Temperature Sintering (Ba,Sr)TiO3 Series Capacitor Ceramics

The influence of Dy₂O₃ doping on the properties of medium temperature sintering (Ba, Sr)TiO₃ series capacitor ceramics was studied by single factor various amount method, and the law of the influence on the medium temperature sintering (Ba, Sr)TiO₃ series capacitor ceramics was obtained. The dielectric materials used for multilayer ceramic capacitor was obtained, of which the dielectric constant was 1375, the dielectric loss was 0.0060, the density was 5.92 g·cm⁻³, the sintering temperature was less than 1150 °C, the capacitance temperature changing rate (ΔC/C) was less than ± 15%, the voltage withstand strength was more than 9.3 kV·mm⁻¹, and the crystal grain size was about 1 μm. The surface morphology of the sample doped with various amount Dy₂O₃ was analyzed by scanning electron microscope (SEM). The results showed that doping Dy₂O₃ could form defect solid solution, stop grain growth, fine crystal grain, widen curie peak, obtaining high dielectric constant and low dielectric loss, capacitance temperature property was suited for X7R character, in the (Ba,Sr)TiO₃ series ceramics. At the same time, the voltage withstand strength was enhanced greatly.     

Effect of V2O5–TeO2 Glass Addition on Dielectric Properties of CaCu3Ti4O12 Ceramics Prepared by Solid State Method

CaCu₃Ti₄O₁₂ (CCTO) is well known to have colossal dielectric constant in the range of 10⁵. However, CCTO has considerably high dielectric loss values (tanδ > 0.1) at room temperature and 1 kHz. In this work, addition of glass to CCTO was suggested in order to improve its dielectric properties. The effect of V₂O₅–TeO₂ (VT) glass addition on microstructure and dielectric properties of CCTO ceramics were investigated. Dielectric measurements were carried out for (1 ? x) CCTO-(x) V₂O₅–TeO₂ (x = 0, 0.03, 0.05, 0.10) samples in the frequency range of 10²–10⁶ Hz using impedance spectrometer. Electron micrographs showed that low melting VT glass addition facilitated the grain growth of CCTO. As VT glass amount increased, dielectric constant decreased. The drop, though within reasonable values (~10⁵), may related to the presence of grain boundary glassy phase which itself has low dielectric constant. However, the dielectric loss of the composite has decreased after VT glass addition. The low melting V₂O₅–TeO₂ glass aided in liquid phase sintering and improved the grain boundary resistance which resulted in decreased leakage currents.     

Chemical State, Site, Solid Solubility, and Magnetism of Fe in the Ferropericlase (Mg1–x Fe x )O Produced by Ball Milling of MgO and Fe

Ferropericlase (Mg_1–x Fe _x )O solid solution was prepared by ball milling of the mixture of MgO with a rock-salt structure and metal Fe powders in atmosphere and at room temperature. Differing from (Mg_1–x Fe _x )O prepared at high temperature by using MgO and FeO as starting materials, the solution of Fe in MgO is not continuous but limited in the ball milling process, and the solubility limit is less than 30 at. pct. About 92 pct of the Fe ions occupy the site of tetrahedral oxygen coordination in trivalent Fe (Fe³⁺) with high spin, whereas about 8 pct of the Fe ions occupy the site of octahedral oxygen coordination in bivalent Fe (Fe²⁺) with high spin. The Fe³⁺ and Fe²⁺ ions do not show a ferromagnetic but show a paramagnetic state. The as-milled (Mg_1–x Fe _x )O is metastable and decomposes to ferropericlase (Mg_1–y Fe _y )O (where y < x) and MgFe₂O₄ with spinel structure as annealed above 773 K (500  °C), and the content of Fe in the (Mg_1–y Fe _y )O increases with increasing annealing temperature. A bulk (Mg_1–x Fe _x )O was fabricated by annealing the as-milled (Mg_1–x Fe _x )O powders at 973 K (700  °C). It shows n-type conductivity, which is attributed to an electronic small polaron with an activation energy of 0.135 eV.