Layered perovskite structured La5−xSrxTi4+xSc1−xO17 microwave ceramics for dielectrically loaded antennas

The crystal structure, microstructure and dielectric properties of layered perovskite structured La_5−xSr_xTi_4+xSc_1−xO₁₇ (x=0–0.8) ceramics prepared by a solid state reaction route were investigated. X-ray diffraction and Raman spectroscopy analysis revealed the formation of single phase orthorhombic (Pnnm) symmetry. The microwave dielectric properties (ε_r, Q×f_o and τ_f) of samples have been investigated as a function of composition. ε_r and τ_f increased while Q×f_o decreased with an increase in x. The sample x=0.6 exhibited ε_r=54.8, Q×f_o= 12,260 GHz and τ_f=6.7 ppm/°C which may be a suitable candidate material for dielectrically loaded antenna applications. The complex impedance spectroscopy analysis of the sample x=0.6 revealed that the sample is highly insulative with two electro-active regions (bulk and grain boundary).     

Structural characteristics and microwave dielectric properties of Zn1−xBixVxW1−xO4-based ceramics for LTCC applications

Herein, the improvement of the microwave dielectric properties and sintering characteristics of Zn_1?xBi_xV_xW_1?xO₄(x = 0–0.15)-based ceramics is reported. The results showed that an appropriate amount of doping could not only reduce the optimum sintering temperature from 1100° to 900°C, but also enhance the densification of the microstructures and increase the Q×f value from 5351 to 42525 GHz. Additionally, various structural parameters including the phase composition, crystal structure, vibrational and chemical bond characteristics that are correlated with the dielectric properties were systematically investigated. By considering the chemical bond characteristics, the first-principles calculations and the acquired Raman spectra, the interaction between W-O is stronger than Zn-O in the ZnWO₄ structure, while the interaction between V-O is stronger than Bi-O in BiVO₄. Interestingly, when the Zn_0.97Bi_0.03V_0.03W_0.97O₄-based ceramics were sintered at 900 °C, improved microwave dielectric properties were acquired (ε_r =18.32, Q×f=42525 GHz, τ_f=?67.51 ppm/°C), which provides a promising candidate in low-temperature co-fired ceramics technology.     

Crystalline structure and electrical properties of YCoxMn1−xO3 solid solutions

Solid solutions corresponding to YCo_xMn_1−xO₃ system with x=0.2...0.7 have been studied. The powders were prepared by solid state reaction of corresponding oxides. Sintered bodies were obtained firing between 1250 and 1350 °C. The incorporation of 25 at.% of Co in the Yttrium manganite induced the appearance of a perovskite-type phase with orthorhombic symmetry and Space Group Pbnm. This feature was extended at least up to an amount of 70 at.% of Co. The increase of the Co content from 25 to 70 at.% led to a monotonic decrease of the orthorhombicity factor b/a. Electrical measurements have shown a semiconducting behaviour for all solid solutions with the perovskite-type structure. The room temperature conductivity increased with Co until the 33 at.% of Co, and then decreased. The 60/40 Co/Mn composition showed an increase of the electrical conductivity in comparison to the 50/50 composition and a corresponding decrease of the activation energy. Small polaron hopping mechanism is supposed to control the conductivity.     

A novel TiO2/ZrxTi1−xO2 composite photocatalytic films

TiO₂/Zr_xTi_1−xO₂ composite films have been prepared by sol–gel method and their photocatalytic activity and stability have been investigated for the first time. Their surface morphology and average surface roughness are characterized by AFM. TiO₂ P25 and pure sol–gel TiO₂ films have also been prepared and investigated for comparison. Films with smaller crystallite size and larger surface roughness have been obtained by introduction of Zr_xTi_1−xO₂ intermediate layers between TiO₂ layers and substrate in the composite films. The results show that the photocatalytic activity and stability of the composite films are higher than those of pure sol–gel TiO₂ and TiO₂ P25 films.     

Multiscale study of ferroelectric–relaxor crossover in BaSnxTi1−xO3 ceramics

A systematic study of BaSn_xTi_1−xO₃ solid solutions (x = 0–0.20) by a combined field-induced dielectric and ferroelectric analysis with Raman and PFM investigations was realized, in order to obtain new insights concerning the composition-induced modification of the structural phase transitions and ferroelectric–relaxor crossover induced by the increase of Sn addition. The ceramics prepared via solid state reaction and sintering at 1400 °C/4 h showed average tetragonal symmetry for x ≤ 0.15 and cubic for x = 0.20. However, the dielectric and Raman analysis demonstrated that x = 0.05 and x = 0.15 are characterized by a coexistence of phases, which enhances their macroscopic properties (polarization for x = 0.05 and permittivity for x = 0.15). The domain structure shows a gradual modification when increasing Sn addition. No detectable domain structure has been found for x ≥ 0.15. All the compositions show local d₃₃(V) hysteresis loops at room temperature.     

Mesoporous CexZr1−xO2 solid solutions supported CuO nanocatalysts for toluene total oxidation

Mesoporous Ce_xZr_1−xO₂ solid solutions were prepared by the surfactant-assisted method and used as support of CuO nanocatalysts for catalytic total oxidation of toluene. The prepared CuO/Ce_xZr_1−xO₂ catalysts have a wormhole-like mesoporous structure with high surface area and uniform pore size distribution, and the CuO nanoparticles were highly dispersed on the surface of Ce_xZr_1−xO₂. The doping of ZrO₂ in CeO₂ promotes the dispersion of active copper species and enhances the reducibility of copper species. The effect of Ce/Zr ratio, calcination temperature and CuO loading amount on the catalytic performance of CuO/Ce_xZr_1−xO₂ was investigated in detail. The 400 °C-calcined 8%CuO/Ce_0.8Zr_0.2O₂ catalyst exhibits the highest activity with the complete toluene conversion temperature of 275 °C at the condition of GHSH = 33,000 h⁻¹ and the toluene concentration of 4400 ppm. The interfacial interaction between CuO and the Ce_xZr_1−xO₂ support, highly dispersed CuO nanoparticles and the nature of the support contribute to the high catalytic activity of mesoporous CuO/Ce_xZr_1−xO₂ nanocatalysts.     

Enhanced electrocaloric,pyroelectric and energy storage performance of BaCexTi1−xO3 ceramics

BaCe_xTi_1−xO₃ (BCT) ceramics with compositions x = 0, 0.1, 0.12 and 0.15 were synthesized using conventional solid state reaction route. Systematic exploration of enhancing electrocaloric effect (ECE) in BaTiO₃ by rare earth dopant Ce is presented. BaCe_0.12Ti_0.88O₃ exhibited an electrocaloric strength of ∼0.35 K m/MV at 351 K, which caters the need for a series of high-level ECE material. Further, the temperature dependence of pyroelectric coefficient is established for all compositions. The pyroelectric figure of merits (FOMs) for current responsivity (F_i), voltage responsivity (F_v), detectivity (F_d) and energy harvesting (F_e and F_e^*) are calculated and the results reveal that x = 0.1 could be a technologically superior candidate for pyroelectric devices. Further, BaCe_0.15Ti_0.85O₃ exhibited highest electrical energy storage performance of 115 kJ/m³ compared with 71 kJ/m³ in BaTiO₃. Our findings in this work may provide a better understanding for developing high ECE materials combined with pyroelectric and energy storage performance of Ce substituted BaTiO₃ ceramics.     

Synthesis and thermoelectric properties of (NaxCa1−x)3Co4O9 ceramics

(Na_xCa_1−x)₃Co₄O₉ (x=0.05−0.2) ceramics with a layered crystal structure were prepared by a sol–gel method followed by a low-temperature sintering procedure. The electrical conductivity and Seebeck coefficient of the complex oxide ceramics were measured from 400 to 900 °C. Their electrical conductivity and power factor increase with increasing temperature, while the thermal conductivity is very weakly dependant on the temperature. Na dopant amount has a remarkable effect on electrical and thermal transport properties. The figure of merit in the ceramic samples is smaller than that of traditional thermoelectric alloys.     

The significant role of the glycine-nitrate ratio on the physicochemical properties of CoxZn1−xO nanoparticles

In this study, Co_xZn₁⁻_xO (X = 0, 0.06, 0.18, 0.36, 0.54, and 1) nanoparticles were synthesized by one-step solution combustion synthesis method. The critical role of X values and fuel (glycine)-to-oxidizer (F/O) ratios (0.75, 1, and 1.25) were investigated on the physicochemical properties of synthesized particles. X-ray diffraction (XRD) results showed that by increasing the X molar fraction, up to 0.36 mol. %, at the F/O ratios of 0.75, 1, and 1.25, crystallite size decreases from 31 to 26, 39 to 31, and 64 to 43 nm, respectively. ZnO-Co₃O₄ mixed oxide nanopowders were directly crystallized at X = 0.54 in all F/O ratios. Semi-quantification evaluations of XRD results showed that the F/O ratio had a direct effect on the quantities of the crystallized and the content of the amorphous phases. According to the vibrating sample magnetometer analysis results (VSM), the greatest magnetization saturation (M_s) value of 30 emu/g was obtained at X = 1 and F/O ratio of 1.25. Calorimetry analysis revealed that by increasing the content of the doping agent, ie, cobalt ion, up to the molar fraction of 0.18, dark green color is observed in the specimens, and the deepest green color was obtained at F/O = 1 .     

Investigation of the Intrinsic Activity of ZrxCe1−xO2 Mixed Oxides in the CO + NO Reactions: Influence of Pd Incorporation

The intrinsic activity of various Zr _x Ce_1–x O₂ mixed oxides and after a Pd deposition has been investigated in the CO + NO reactions from temperature-programmed experiments performed under stoichiometric conditions. It has been found that the activity of Zr _x Ce_1–x O₂ depends on either the specific surface area or the number of Ce cations and their intrinsic activity, Zr_0.5Ce_0.5O₂ being the most active support. The addition of palladium strongly enhances the catalytic activity of the supports probably due to a synergistic effect between CeO₂ and the metal since the initial activity of palladium-based catalysts is directly related to their Ce content. Such a catalytic enhancement has been explained by a bifunctional mechanism involving active sites probably composed of Pd and ceria. A strong deactivation operates leading to the disappearance of the beneficial effect of ceria. Such a deactivation seems to be dependent on the support composition, Pd supported Zr_0.25Ce_0.75O₂ being the most resistant to deactivation.     

Intrinsic factors affecting the microwave dielectric properties of Mg2Ti1−x(Mg1/3Sb2/3)xO4 ceramics

The effect of crystal structure on the microwave dielectric properties of Mg₂Ti_1−x(Mg_1/3Sb_2/3)_xO₄ (0.025≤x≤0.15) ceramics was investigated. A single phase having a cubic inverse spinel structure formed over the entire range of compositions, in specimens sintered at 1450 °C for 4 h. The structural characteristics of these ceramics were quantitatively evaluated by applying the Rietveld refinement method to the X-ray diffraction data. The largest bond strength between the cation and the oxygen ion and hence the highest quality factor (Qf) of the specimens were obtained at x=0.05. Although the ionic polarizability (3.29 Å³) of (Mg_1/3Sb_2/3)⁴⁺ was larger than that (2.93 Å³) of Ti⁴⁺, the dielectric constant (K) of the specimens decreased owing to the decrease of rattling effect with increasing x. In addition, the temperature coefficient of resonant frequency (TCF) decreased with decreasing K values. Typically, a high Qf value of 229,000 GHz was obtained for the specimens with x=0.05.     

The relationship between the micro-mechanism and macroscopic dielectric properties in Ba1−xBixTi1−x−yZn0.75xW0.25x+yO3+y systems

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO₃ ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε_r, dielectric stability and dielectric loss) in Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10¹² Ω cm. These features suggested that the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment.     

Finite size effect on Sm3+ doped Mn0.5Zn0.5SmxFe2−xO4 (0≤x≤0.5) ferrite nanoparticles

Samarium doped Mn–Zn ferrite nanoparticles of composition Mn_0.5Zn_0.5Sm_xFe_2−xO₄ (0≤x≤0.5) have been synthesized by a chemical co-precipitation method for developing low Curie temperature stable ferrofluid. These samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Paramagnetic Resonance (EPR) spectroscopy and search coil method analytical techniques for their structural, morphological and magnetic properties. X-ray diffraction patterns confirmed the formation of crystalline single spinel phase of as grown nanoparticles. Lattice parameter and lattice strain increases with the increase in Sm³⁺ content. SEM images revealed the presence of ultrafine particles and their agglomerated structures in higher Sm³⁺ ions concentration analogues. The stoichiometry of the final product agreed well with the initial substitution composition as evidenced by EDS data. Electron paramagnetic resonance (EPR) spectra proved the ferromagnetic nature of nanoparticles. The magnetic measurements by search coil method showed superparamagnetism for x=0, 0.1 the samples with saturation magnetization of 23.95 emu/g for Mn_0.5Zn_0.5Fe₂O₄ sample which increases with rise in Sm³⁺ ions content. The results are explained and correlated with the structural, morphological and magnetic properties for developing stable kerosene based ferrofluid by using these nanoparticles.     

Electro-catalytic characterization and dye degradation of Ti1−x(Bi)xO2 in acidic solution

The authors in this study used the sol–gel process to prepare Bi-doped TiO₂ as a novel electrocatalyst. Results show that Bi can be doped successfully into TiO₂ from 1% to 90%. The electrical conductivity of a 1% Bi-doped TiO₂ particle-suspended solution is increased nearly twice that of pure TiO₂. The electro-catalyzing property of the synthesized Bi-doped TiO₂ catalyst was performed under acidic conditions toward a methyl blue dye solution. The observed removal percentage of methyl blue dye was from 5% to 75%. The optimized electro-catalyzing condition was observed at 5% Bi-doped TiO₂ with a working voltage of 5 V.     

Perovskite forming ceramics of the system SrxLa1−x TiIVx+yCoIIyCoIII1−x−2yO3 for NTC thermistor applications

The paper reports the preparation, structure and electrical properties of oxide ceramic semiconductors based on the series Sr_xLa_1−x Ti^IV_x+yCo^II_yCo^III_1−x−2yO₃ with perovskite type stucture: 0<x<1, 0<y<(1−x)/2. The study starts from LaCoO₃ which is highly conductive yielding metallic condutivity above 330°C. The upset trigonal distortion of LaCoO₃ is reduced when Sr^II/Ti^IV is substituted for La^III/Co^III corresponding to increasing values of x and also when 2 Co^III are introduced for Ti^IV/Co^II into the lattice corresponding to increasing values of y. At high values of x and y othorhombic distortion occurs. At the same time, the interaction between the Co^III atoms of LaCoO₃ is increasingly interrupted providing increasing values of the the resistivity value ρ_25°C and of the B_25/100°C value deduced from measurements at 25 and 100°C according to ρ(T )=ρ_25°C e^B/T. The range of variation of x an y makes possible to prepare ceramics with desired electrical properties within the limits of ρ_25°C=1.1 Ωcm, B=1910 K and ρ_25°C=1 bis 8×10⁶ Ωcm at B-values up to 6500 K. Dependent on composition, NTC ceramics for thermistor or insurance applications are accessible. Thermistors do not show aging even at higher temperature, e.g. at 500°C, provided the single phase state is achieved as a result of mixed oxide preparation and sintering. Hence, high temperature thermistor applications are also made possible. The semiconductor behavior can be understood using the conventional polaron state hopping model.     

Dielectric properties of compositionally graded Ba1−xLaxTi1−x/4O3 thick films

Compositionally graded thick films based on lanthanum-substituted barium titanate solid solutions Ba_1−xLa_xTi_1−x/4O₃ (BLT, x=0.02, 0.04, 0.06) are prepared by tape casting and their phase structures, surface morphologies, dielectric and tunability properties have been examined. Compared with single-layered BLT film, compositionally graded BLT02/04/06 film with three-layered sandwich-structure has better temperature stability in dielectric and tunability properties. Curie peak is broadened, dielectric loss is reduced, and more importantly, it has moderate permittivity and high tunability (>35%) in a temperature range of 25–75 °C, which is beneficial for practical applications of tunable devices.     

Electrochemical evaluation of LiZnxMn2−xO4 (x≤0.10) cathode material synthesized by solution combustion method

The spinel LiZn_xMn_2−xO₄ (x≤0.10) cathode materials have been synthesized by solution combustion method at 600 °C for 3 h. The structure and the morphology of LiZn_xMn_2−xO₄ were characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), respectively. All the obtained samples were identified as the spinel structure of LiMn₂O₄, the lattice parameters of samples decreased and the particle size increased as the Zn content increased. The effects of Zn-doping on the electrochemical characteristics of LiMn₂O₄ were investigated by galvanostatic charge–discharge experiments, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Among them, LiZn_0.05Mn_1.95O₄ particles presented outstanding cycling stability with a capacity retention of 82.9% at a discharge rate of 1 C (1 C=148 mA h g⁻¹) after 500 cycles. Spinel LiZn_0.05Mn_1.95O₄ had reversible cycling performance, revealing that doping LiMn₂O₄ with Zn improves its electrochemical performance.     

Preparation and characterisation of LaNixCo1−xO3 thin films on polycrystalline Al2O3-substrates

The perovskite LaNi_xCo_1−xO₃ exhibits metallic conductivity with a change from p- to n-type conduction around x=0·5, thus being a candidate for electrodes or buffer layers in thin film technology. Thin films of LaNi_xCo_1−xO₃ have been grown onto polycrystalline Al₂O₃ substrates by Chemical Solution Deposition (CSD) of nitrate solutions in ethanol/butylacetate. The solutions were applied by dip-coating. After pyrolysis the compounds are formed in air at temperatures between 600°C and 750°C. Formation of the perovskite phase was confirmed by grazing angle X-ray diffraction. Electron micrographs revealed that the obtained films were smooth and crack-free and consisted of nanocrystalline LaNi_xCo_1−xO₃ particles. The thickness of the films was between 200 nm and 400 nm, depending on the conditions of the dipcoating procedure. Specific conductivities of the film were measured using the van der Pauw-method and were found to be around 400 S/cm for LaNiO₃ and around 1 S/cm for LaCoO₃ at room temperature.