Synthesis, structure, and dielectric properties of a novel perovskite-based nanopowders via sol–gel method: (1–x)BaTiO3–xDyScO3

A sol–gel method was adopted to synthesize novel perovskite-based nanopowders: (1–x)BaTiO₃–xDyScO₃ (0 ≤ x ≤ 0.06), which exhibited a relatively pure pseudo-cubic perovskite structure when xerogel was calcined at 750 °C. Through the employment of PEG 400 as dispersant, narrow size distributed particles of ~15–20 nm were achieved. Pellets pressed from the nanopowders can be densified at a lower sintering temperature of 1150 °C, compared with 1475 °C by solid-state reaction method. The phase formation, microstructure, dielectric properties, and relaxor behavior of (1–x)BaTiO₃–xDyScO₃ were investigated systematically. With an increasing DyScO₃ doping concentration in BaTiO₃, a tetragonal to pseudo-cubic phase transition appeared at x = 0.03, and two different doping behaviors (donor or acceptor-type) of Dy³⁺ in (1–x)BaTiO₃–xDyScO₃ were discussed. The grain growth of BaTiO₃ ceramics was inhibited, and the grain size was decreased to 200 nm for x = 0.06. The dielectric peak was broadened and the curie temperature dropped gradually, accompanied by an increased room-temperature permittivity. Furthermore, a typical relaxor behavior was observed at x = 0.05 and 0.06, according to the modified Curie–Weiss law.     

Series of thermally stable Li1+2x Mg4−x V3O12 ceramics: low temperature sintering characteristic,crystal structure and microwave dielectric properties

Series of novel low-firing microwave dielectric ceramics with the composition of Li_1+2x Mg_4?x V₃O₁₂ (?0.2 ≤ x ≤ 0.1) were prepared by a solid-state reaction process. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. As x increased from ?0.2 to 0.1, the optimized sintering temperature was reduced from 880 to 700 °C, the quality factors (Q × f) were effectively enhanced from 21,000 to 33,200 GHz. A good combined microwave dielectric properties with ε_r = 12.1, Q × f = 21,800 GHz, τ _f  = 1.8 ppm/°C were obtained for x = ?0.1.     

Effects of BaNb2O6 addition on microstructure and dielectric properties of BaTiO3 ceramics

(1 ? x)BaTiO₃–xBaNb₂O₆ [(1 ? x)BT–xBN] ceramics with x = 0, 0.005, 0.008, 0.01, 0.02, 0.03 were prepared by a conventional solid-state reaction route. The effect of BN addition on phase composition, microstructure and dielectric properties of BT-based ceramics were investigated by X-ray diffraction, scanning electron microscope and impedance spectroscopy. The results showed that a systematic structure change from the ferroelectric tetragonal phase to pseudo-cubic phase was observed near x = 0.01 at room temperature. It resulted in a considerable change of density, grain size and dielectric properties of the samples when BN was introduced. Meanwhile, it also lowered the sintering temperature of the ceramics. The dielectric constant peak and the variation rate of capacitance at Curie temperature are markedly depressed and broaden with increasing BN content. Especially, the ceramics with x = 0.008 and x = 0.01 showed good dielectric properties over the measured temperature range. Optimal dielectric properties of ε = 3,851, tanδ = 0.7 % at room temperature and Δε/ε₂₅ ≤ ±6.8 % (?55 to 125 °C) were obtained for the BT-based ceramics doped with 0.8 mol% BN, which was obviously superior to BaTiO₃ and BaNb₂O₆ ceramic, and it met the requirements of EIA X7R specifications.     

Structure and dielectric properties of Nd x Sr1−x TiO3 ceramics for energy storage application

Polycrystalline Nd-doped SrTiO₃ ceramics with the formula Nd _x Sr_1?x TiO₃ (NSTO, x = 0, 0.024, 0.056, 0.104, 0.152, 0.200) were prepared by solid state reaction route. X-ray diffraction (XRD) analysis confirmed the formation of monophasic compounds and indicated the structure to be changed from cubic to tetragonal by increasing Nd doping concentrations. A remarkable decrease in grain size from ~30 μm for un-doped SrTiO₃ ceramics to ~1 μm for Nd-doped SrTiO₃ ceramics with x = 0.024 was observed by scanning electron microscopy. The grain size had a degree of increasing with further increasing Nd doping concentration and reached ~3 μm when the x value was 0.200. The dielectric properties of NSTO ceramics were measured at 1 kHz in ambient temperature. It revealed that the dielectric constant dramatically increases for the reason of Nd doping, leading to a maximum value of 19,800 for as-sintered sample with x = 0.104. The breakdown strength of all Nd-doped SrTiO₃ samples was found to be higher than 10 kV/mm. The relationship between dielectric properties and the microstructure feature, as well as the defect structures correlated with the charge compensation induced by trivalent Nd³⁺ doping, was discussed tentatively.     

Structure and dielectric properties of Nd substituted Bi1.5MgNb1.5O7 ceramics

New pyrochlore ceramics Bi_(1.5?x)Nd _x MgNb_1.5O₇ with x = 0–0.6 were synthesized by doping Nd into the A site in the Bi_1.5MgNb_1.5O₇ pyrochlore. The Nd substituted Bi_1.5MgNb_1.5O₇ ceramics were prepared utilizing solid-state reaction and investigated by X-ray diffraction, scanning electron microscope and dielectric measurements. The crystal structure was characterized as single cubic pyrochlore phase for x ≤ 0.5 while the second phase appeared at x = 0.6. With increasing Nd content from 0 to 0.5, the lattice parameters decreased slightly and the average grain size pronouncedly reduced from ~7.5 to ~5.0 μm. The Nd incorporation resulted in attractive enhancement of the dielectric properties including the temperature coefficient of dielectric constant that was remarkably optimized with the lowest value of ?16 ppm/°C at x = 0.5. A good combination of low dielectric loss, superior temperature coefficient and high dielectric permittivity can be achieved for the composition of x = 0.5, which seems to be very appealing for the practical use in high-frequency multilayer ceramic capacitors.     

Phase structures and microwave dielectric properties of xCaTiO3–(1 − x)Sm0.9Nd0.1AlO3 ceramics

The xCaTiO₃–(1 ? x)Sm_0.9Nd_0.1AlO₃ (0.25 ≤ x ≤ 0.85) microwave dielectric ceramics were prepared by conventional solid state reaction method. The phase structures were characterized by X-ray diffraction, scanning electron microscope and Raman spectra. Solid solutions with the orthorhombic perovskite structure with octahedral tilting were formed from the x range of 0.25 to 0.85. Microwave dielectric properties of xCaTiO₃–(1 ? x)Sm_0.9Nd_0.1AlO₃ ceramics were investigated systematically. The optimum property of the ceramics was obtained for x = 0.65 sintered at 1,415 °C for 3 h: relative permittivity ε_r = 39.70, Q × f = 50,012 GHz, τ _f  = ?6.8 ppm/°C. xCaTiO₃–(1 ? x)Sm_0.9Nd_0.1AlO₃ ceramics provide a new promising material for application in the microwave technology with relative permittivity lying within the range from 39 to 44, high quality factor and near-zero τ _f .     

Crystal structure and optimized microwave dielectric properties of (1 − x) LiZn0.5Ti1.5O4–xTiO2 ceramics for application in dielectric resonator

Microwave dielectric ceramics with the composition of (1?x) LiZn_0.5Ti_1.5O₄ (LZT)–xTiO₂ (0.05 ≤ x ≤ 0.4) were prepared by a solid-state reaction route. XRD patterns revealed that the samples consist of LiZn_0.5Ti_1.5O₄ and rutile TiO₂, and the amount of rutile TiO₂ phase increased with increasing the x values. The microwave measurements show that the dielectric properties of ceramics can be improved with increasing x values. When x = 0.1, the temperature coefficient of resonant frequency (τ _f ) of 0.9LZT–0.1TiO₂ ceramic can be adjusted to a near-zero value of ?1 ppm/°C, and permittivity (ε_r) and Q × f value are 26 and 45,000 GHz, respectively. These results indicate that 0.9LZT–0.1TiO₂ ceramic can be a candidate in microwave dielectric resonators.     

Non-Ohmic and dielectric properties of Ba-doped CaCu3Ti4O12 ceramics

The microstructure, dielectric and electrical properties of Ca_1?x Ba _x Cu₃Ti₄O₁₂ (where x = 0, 0.025, and 0.05) ceramics were investigated. Our microstructural analyses revealed that Ba²⁺ doping ions preferentially form in a secondary phase, and are not introduced into the CaCu₃Ti₄O₁₂ lattice. Grain growth rate of CaCu₃Ti₄O₁₂ ceramics was significantly inhibited by the Ba-related secondary phase particles, resulting in a large decrease in their mean grain size. The dielectric permittivity of CaCu₃Ti₄O₁₂ ceramics decreased with increasing Ba content. Their loss tangent decreased after addition of CaCu₃Ti₄O₁₂ with 2.5 mol% of Ba²⁺, and increased with increasing Ba contents to 5.0 mol%. The nonlinear coefficient and breakdown field of the Ca_1?x Ba _x Cu₃Ti₄O₁₂ ceramics were significantly enhanced by adding 2.5 mol% of Ba²⁺, followed by a slight decrease as Ba²⁺ concentration was increased to 5.0 mol%. Using impedance spectroscopy analysis, it was revealed that variations in dielectric and non-Ohmic properties are associated with electrical response of grain boundaries. This supports the internal barrier layer capacitor model.     

(1 − x)CaTiO3–x(Li0.5Nd0.5)TiO3 for ultra-small dielectrically loaded antennas

Microwave (MW) dielectric ceramics based on the solid solution (1 ? x)CaTiO₃–x(Li_0.5Nd_0.5)TiO₃ (0.25 ≤ x ≤ 1.0) were prepared by conventional solid-state synthesis using the mixed oxide route. Compositions closest to zero τ_f (+65 ppm/°C) were obtained at x = 0.8 where ε_r = 110 and the microwave quality factor, Qf ₀ ? 2600 GHz for samples sintered at 1300 °C. To reduce the sintering temperature and compensate for any Li₂O loss during fabrication, ≤0.5 wt% 0.5Li₂O–0.5B₂O₃ was added as a sintering aid in the form of raw oxides (LBR) and also as a pre-reacted glass (LBG). 0.5 wt% LBR was the most effective, reducing the temperature to achieve optimum density by ~50 °C with no significant deterioration of microwave properties (ε_r = 115, τ_f = +65 ppm/°C and Qf ₀ ? 2500 GHz). The high permittivity and relatively low sintering temperatures (1250 °C) are ideal for the development of low cost ultra-small dielectric loaded antenna, assuming the system can be tuned closer to zero by fractionally increasing x.     

Phase structure and microwave dielectric properties of Zr(Zn1/3Nb2/3)xTi2−xO6 (0.2 ≤ x ≤ 0.8) ceramics

The phase structure, morphology and microwave dielectric properties of Zr(Zn_1/3Nb_2/3)_xTi_2?xO₆ (0.2 ≤ x ≤ 0.8) ceramics were investigated as a function of the amount of (Zn_1/3Nb_2/3)⁴⁺ substitution by the solid-state reaction technique. X-ray diffraction analysis showed the co-existence of the solid solution ZrTiO₄ (x = 0.2) or ZrTi₂O₆(x = 0.4–0.5) as the main phase and TiO₂ as the second phase, and the single-phase region for substituted ZrTi₂O₆ was obtained with x ≥ 0.5. As increasing x from 0.2 to 0.8, the grain growth was promoted, moreover the dielectric constant ε_r and the temperature coefficient of resonant frequency τ_f dropped from 53.8 to 39.2 and from +106.2 to ?25.5 ppm/°C respectively, and the Q × f values increased from 33,200 to 43,200 GHz. Ceramics with good microwave dielectric properties: ε_r = 41.7, Q × f = 42,100 GHz and τ_f = ?15.5 ppm/°C was obtained at x = 0.6.     

Microstructure and enhanced electrical properties of (1−x)(Na0.5K0.44Li0.06)NbO3–x(Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free ceramics

Environment-friendly lead-free piezoelectric ceramics (1?x)(Na_0.5K_0.44Li_0.06)NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ doped with 1.0 mol% MnO₂ were synthesized by conventional solid-state sintering method. The phase transition behavior and electrical properties of the ceramics is systemically investigated. It was found that all the ceramics formed pure perovskite phase with 0.0 ≤ x ≤ 0.1, and the phase structure of the ceramics gradually transformed from orthorhombic to tetragonal phase with increasing x. Coexistence of the orthorhombic and tetragonal phase is formed in the ceramics with 0.04 ≤ x ≤ 0.06 at room temperature, and enhanced dielectric, ferroelectric and piezoelectric properties are achieved in the two phase’s region. The ceramics in the mixed phase region exhibits the following optimum electrical properties: d ₃₃  = 130–147 pC/N, ε _r  = 642–851, P _r  = 5.51–12.44 μC/cm². The Curie temperature of the ceramics with mixed phase region was found to be 353–384 °C. The significantly enhanced dielectric properties, ferroelectric properties and piezoelectric properties with high cubic-tetragonal phase transition temperatures (T _c ) make the KNLN–xBCZT ceramics showing the promising lead-free piezoelectrics for the practical applications.     

Phase transition and piezoelectric properties of (1−x)(K0.42Na0.58)(Nb0.96Sb0.04)O3–x(Bi0.5Na0.5)0.90Mg0.10ZrO3 lead-free ceramics

(1?x)(K_0.42Na_0.58)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Na_0.5)_0.90Mg_0.10ZrO₃ [(1?x)KNNS–xBNMZ] lead-free ceramics have been prepared by the normal sintering, and effects of BNMZ content on their phase structure, microstructure, and electrical properties have been systematically investigated. These ceramics with 0.045 ≤ x ≤ 0.05 possess a rhombohedral–tetragonal (R–T) phase boundary, as confirmed by the temperature dependence of dielectric properties and X-ray diffraction patterns. The grain size of the ceramics first increases and then decreases as the BNMZ content increases, and the ceramic with x = 0.06 possesses much smaller grains (<1 μm), resulting in the abnormal electrical and phase transition behavior. In addition, the Mg²⁺ was homogenously distributed in the ceramic matrixes. These ceramics with R–T phase boundary show enhanced dielectric, ferroelectric, and piezoelectric properties as compared with a pure KNN, and optimum electrical properties (e.g., P _r ~ 16.23 μC/cm², E _C ~ 7.58 kV/cm, ε _r ~ 2,663, tan δ ~ 0.034, d ₃₃ ~ 434 pC/N, k _p ~ 0.47, and T _C ~ 244 °C) were found in the ceramic with x = 0.0475. We believe that the (1?x)KNNS–xBNMZ ceramic is a promising candidate for lead-free piezoelectric devices.     

Microwave dielectric properties of ZnO–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–<Emphasis Type="Italic">x</Emphasis>TiO<Subscript>2</Subscript> ceramics prepared by reaction-sintering process

The ZnO–Nb₂O₅–xTiO₂ (1 ≤ x ≤ 2) ceramics were fabricated by reaction-sintering process, and the effects of TiO₂ content and sintering temperature on the crystal structure and microwave dielectric properties of the ceramics were investigated. The XRD patterns of the ceramics showed that ZnTiNb₂O₈ single phase was formed as x ≤ 1.6 and second phase Zn_0.17Nb_0.33Ti_0.5O₂ appeared at x ≥ 1.8. With the increase of TiO₂ content and sintering temperature, the amount of the second phase Zn_0.17Nb_0.33Ti_0.5O₂ increased, resulting in the increase of dielectric constant, decrease of Q × f value, and the temperature coefficient of resonant frequency (τ _f ) shifted to a positive value. The optimum microwave dielectric properties were obtained for ZnO–Nb₂O₅–2TiO₂ ceramics sintered at 1075 °C for 5 h: ε _r  = 45.3, Q × f = 23,500 GHz, τ _f  = +4.5 ppm/°C.     

Growth and properties of HfxZn1−xO thin films on flexible PET substrate using pulsed laser deposition

Hf-doped ZnO thin films with different Hf contents of target (Hf_xZn_1?xO 0 ≤ x ≤ 10 at.%) were deposited on flexible PET substrates under different oxygen pressure using pulsed laser deposition. Microstructures, optical and electrical properties of the films were studied. The results show that the as-deposited Hf_xZn_1?xO (0 ≤ x ≤ 5 at.%) films crystallized in ZnO hexagonal wurtzite structure with a highly preferred c-axis orientation. The films exhibited a transmission of higher than 80 % in the visible region. With increasing Hf content, the lattice constants increased; the morphology of the films deteriorated. The sheet resistance reached a minimum value of 16 Ω/□ when the doping level was about 0.5 at.%.     

Synthesis and photoluminescence of Ca1-xTiO3:xEu3+ nanoparticles

Ca_1-xTiO₃:xEu³⁺ nanoparticles (NPs) with the size ranging from 27 nm to 135 nm were prepared by means of a chemical co-precipitation method. The structural and optical properties of the NPs were investigated, and the influence of Eu doping content and sintering temperature on the photoluminescence of the Ca_1-xTiO₃:xEu³⁺ NPs were examined. An obvious red emission band centered at 615 nm were observed under the excitation with 395 nm for the Ca_1-xTiO₃:xEu³⁺ NPs. X-ray photoelectron spectroscopy analyses suggest that Eu³⁺ is incorporated into not only the Ca-site, but also Ti-site of CaTiO₃ crystal lattice. Our study shows the promise of the Ca_1-xTiO₃:xEu³⁺ NPs as a red nanophosphor.     

Elastic and Thermal Properties of Double Doped Orthovanadate: Eu1−x (La0.254Y0.746) x VO3

We present the effect of A-site double doping (La_0.254Y_0.746) on elastic and thermal properties of EuVO₃ in a wide doping range (0≤x≤1), using a modified rigid ion model (MRIM). Various lattice distortions and their relation to bulk modulus has been investigated systematically. The effect of the lattice distortions on thermodynamic properties of Eu_1?x (La_0.25Y_0.74) _x VO₃ has been explored by an atomistic approach. The computed results emphasize that the Debye temperature decreases while the specific heat increases with increase in doping concentration (x). The computed temperature dependent (1 K≤T≤300 K) specific heat trends are in accordance with the corresponding experimental data at various compositions. Future scope of MRIM has also been discussed.     

Effects of La3+ addition on the phase transition,microstructure, dielectric and piezoelectric properties of Ba0.9Ca0.1Ti0.9Zr0.1O3 ceramics prepared by hydrothermal method

Lead-free Ba_0.9Ca_0.1Ti_0.9Zr_0.1O₃–xLa (x = 0.000, 0.005, 0.010, 0.015, 0.020, 0.025) ceramics were prepared by hydrothermal method and were assisted by fast microwave sintering. The effects of La³⁺ addition on the phase transition, microstructure, dielectric and piezoelectric properties were investigated. Single orthorhombic phase was observed in the composition of x ≤ 0.010 and the coexistence of orthorhombic and tetragonal phase were detected at x = 0.015 and 0.020, which is characterized by the broadening of (002)/(200) peaks at around 2θ ~ 45°. The ceramics show cubic phase when the x was increased to 0.025. The grain size was affected significantly by the La³⁺ content, reaching a maximum value of ~8.2 μm at x = 0.010. The dielectric constant decreases with the addition of small amount of La³⁺ and then increases sharply at x ≥ 0.015, exhibiting a PTC behavior at x = 0.020, while no T _C was observed at x = 0.025. The Curie temperature (T _C ) always decrease with the introduction of La³⁺ and the dielectric loss shows a minimum value at x = 0.015. The piezoelectric constant (d ₃₃ ) measured at 50 °C of the ceramics were increased after the partial substitution of La³⁺ because of the enhancement of coexistence of orthorhombic and tetragonal phases at this temperature. Ferroelectric and piezoelectric properties can not be detected when x was increased to 0.02 while they were observed again with further addition.     

Phase composition and microwave dielectric properties of (Zn,Ni)TiNb2O8 solid solution

The Zn_1?xNi_xTiNb₂O₈ (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were synthesized by the conventional solid-state reaction method. The crystal structure and microwave dielectric properties were investigated by XRD, SEM and dielectric measurements. The XRD patterns of Zn_1?xNi_xTiNb₂O₈ ceramics showed that (Zn, Ni)TiNb₂O₈ phase and (Ni, Zn)_0.5Ti_0.5NbO₄ phase were obtained. With the increase of sintering temperature and Ni content, the amount of the second phase [(Ni, Zn)_0.5Ti_0.5NbO₄] enhanced, resulting in the increase of dielectric constant and the decrease of Q × f value. Moreover, the temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Ni content. In conclusion, the excellent microwave dielectric properties were obtained for Zn_0.7Ni_0.3TiNb₂O₈ ceramics sintered at 1,125 °C for 4 h: ε_r = 41.36, Q × f = 31,760 GHz, τ_f = ?9.2 ppm/°C. Furthermore, to realize the zero value for τ_f, a proper adjustment of Ni doping and sintering temperature can be feasible in this system.     

Ba<Subscript>1−x</Subscript>La<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (x = 0.0, 0.2, 0.4, 0.6) hollow microspheres: material parameters,magnetic and microwave absorbing properties

Ba_1?xLa_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6) hollow ceramic microspheres (HCMs) have been prepared by combining self-reactive quenching method with heat treatment. Their material parameters, magnetic and microwave absorbing properties were investigated. It was observed that after doping of lanthanum, the material parameters showed a little change except hexagonal crystal disappearing. And the magnetic properties of HCMs were decided by lanthanum content and material parameters. With the lathanum increases from 0.0 to 0.6, the saturation magnetization (Ms) values initially increased, and then decreased sharply to a minimum value, and increased again, moreover, the coercive force (Hc) values were reduced first, and then increased, and decrease to a minimum value. Absorbing properties tests indicate that after La³⁺-doped, at 2 mm thickness, the effective absorbing band (<?10 dB) was reduced to 4.7, 5 and 4.4 GHz, respectively, the minimum reflectance would decrease in low substituted level (x ≤ 0.4) and increase in high level (x = 0.6), and the frequency shifts to low frequency with the increasing of doping content. In 1.5–3 mm range, with the increasing of thickness, the absorption peak of Ba_1?xLa_xFe₁₂O₁₉ (x = 0.2, 0.4, 0.6) HCMs shifts to low frequency and the absorption intensity increases, the effective absorbing band can up to 10, 8.1 and 8 GHz, respectively.     

Glass-free LTCC microwave ceramic-Ca1−x(La0.5Na0.5)xWO4

The structure and microstructure of the Ca_1?x(La_0.5Na_0.5)_xWO₄ (0.1 ≤ x ≤ 1.0) ceramics were investigated using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) method. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 10–14 GHz. Continuous solid solutions Ca_1?x(La_0.5Na_0.5)_xWO₄ (0.1 ≤ x ≤ 1.0) with Scheelite structure (space group: I4₁/a) could be densified at 850 °C/2 h. The dielectric permittivity increased slightly with the increase in substitution amount. The Q × f value decreased with the increase of x up to x = 0.5, and then increased with further increase of x. The Q × f value increased when the sintering temperature increased from 850 to 950 °C for the x < 0.5 compositions, whereas it decreased with the increase in sintering temperature for the x > 0.5 compositions. The τ _f value changed a little with the variation of x. All samples exhibited negative τ _f values. Addition of 30 mol% TiO₂ to the x = 0.9 composition improved the τ _f to ?9.3 ppm/°C with ε_r = 14.4 and Q × f = 14,255 GHz after sintering at 850 °C/2 h. The chemical compatibility of Ca_0.1(La_0.5Na_0.5)_0.9WO₄ + 30 mol% TiO₂ composite with silver (Ag) powders was also investigated. The composite showed inert behavior with Ag when cofired at 875 °C for 2 h. However small amount of Na_0.86WO₃ impurity phase was detected in the co-fired specimen.