Preparation of V doped lanthanum silicate electrolyte ceramics by combustion method and study on conductance mechanism

Vanadium doped La_9.33Si_6−xV_xO_26+0.5x (x = 0.5, 1.0, 1.5) (LSVO) electrolyte powder was prepared by combustion method at 600°C for 5-7 min. The powder was sintered at 1500°C for 3 hours to prepare LSVO ceramics. XPS, IR, XRD, and EIS analysis show that V⁵⁺ doping replaces Si⁴⁺ in [SiO₄] to form [Si(V)O₄] tetrahedron. With the increase in x, the lattice volume increase. When x = 2.0, the LaVO₄ phase was formed, indicating that the limit doping amount of V⁵⁺ replacing Si⁴⁺ is x ≤ 1.5. The conductivity of LSVO increases significantly with the increase in x (x ≤ 1.0), which attributed to the defect reaction caused by V⁵⁺ doping. The addition of the interstitial oxygen Oi* in 6₃ channels and the increase of lattice volume leads to increased conductivity. When x = 1.0, the highest conductivity is 1.46 × 10⁻² S·cm⁻¹ (800°C). The doping enhancement conductivity mechanism is the Interstitial oxygen defect-Lattice volume composite enhancement mechanism.     

Visible light active heterostructured photocatalyst system based on CuO plate-like particles and SnO2 nanofibers

In this study, CuO–SnO₂ p-n type heterostructures were produced and tested for the degradation of methylene blue and 4-nitrophenol under visible light irradiation. CuO particles were produced in plate-like morphology using hydrothermal synthesis. SnO₂ nanofibers were obtained by electrospinning. Structural, morphological, optical and semiconducting property characterization of heterostructured CuO–SnO₂ and individual phases were performed. The photocatalytic activity was found to change depending on the amount of CuO particles in heterostructured samples. Among others, the sample with 0.35 wt.% CuO–SnO₂ showed the highest photocatalytic efficiency with a degradation rate constant ~2 h⁻¹. Active specie scavenger tests revealed that the decomposition reaction occurs through direct oxidation mechanism by the holes in the valence band of SnO₂ in pure samples whereas in CuO–SnO₂ samples and radicals also form and involve in the reactions. Further, the photocatalytic degradation mechanism was revealed using relative band potentials and p-n junctions of the heterostructured photocatalyst.     

Poling tuning: A plausible solution for minimizing microphony and secondary pyroelectric coefficient in ferroelectrics

This study proposes the idea of reducing the microphony effect and secondary pyroelectric coefficient in pyroelectric detectors by tuning the poling orientation. Mathematically, it has been shown that piezoelectric strain coefficients get altered by changing the poling direction. Eventually, for a couple of materials it has been demonstrated that microphony and secondary pyroelectric coefficient can be diminished by poling them at a given orientation. The poling angle nullifying secondary pyroelectric coefficient was found to be 58.2°, 47.1°, and 78.9° for (PZN-0.08PT), (PMN-PT), and (BCT-0.48BZT) respectively while no such value existed for (PZT-5A).     

Temperature deformation of 1-3 cylindrical curved composite

Piezoelectric composites will cause different degrees of deformation when ambient temperature changes during transportation, storage and use, affecting the performance and reliability seriously. The deformation measurement of cylindrical piezoelectric composites based on fiber Bragg grating (FBG) measurement is presented in this paper. The deformation and electromechanical properties of cylindrical piezoelectric composites over a wide range of temperature, from 233 K to 373 K, are investigated in detail. The deformation of piezoelectric composites in different directions is calculated. Adding deformation information, the frequency constant and dielectric constant data are modified. The results show that, at 233 K, the relative change of curvature of the cylindrical composite material in the arc direction is 0.024% and the relative change of deformation in the width and thickness direction are 0.018% and 0.026%, respectively. When the environment's temperature is increased to 100℃, the relative change of curvature in the arc direction is 0.019% and the relative changes of deformation in the width and thickness direction are 0.019% and 0.008%, respectively. After adding the deformation information, the most evident changes of frequency constant and dielectric constant are between 303 K and 333 K, the rate of change (slope) of frequency constant and the dielectric constant are −1.82983 (decreasing) and 3.85591 (increasing), respectively.     

Crystal structure and magneto-dielectric properties of Co-Zr co-substituted Co2Z hexaferrites

A series of Ba_1.5Sr_1.5Co_2+xZr_xFe_24-2xO₄₁ hexaferrites (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) were successfully prepared by the conventional solid-state reaction method. It was found that as the Co²⁺ and Zr⁴⁺ ions entered the hexaferrite structure, the lattice parameters increased, whereas the relative density increased when x = 0.00-0.03 and then decreased. A suitable amount of substitution increased the DC resistivity, reduced the magnetic and dielectric losses, and made the ${\mu }^{\prime }$ and ${\epsilon }^{\prime }$ closer to each other. At x = 0.03, the relative density and DC resistivity of the samples reached their maxim. Besides, both the magnetic and dielectric losses were lowest within the frequency range of 10 MHz-1 GHz. Meanwhile, the hexaferrite was impedance matched to free space, and the miniaturization factor was about 15. Therefore, this low-loss ferrite with almost equal permeability and permittivity could be meaningful for antenna miniaturization and high-frequency applications.     

Fabrication of tunable bandgap epitaxial β-(AlxGa1−x)2O3 films using a spin-coating method

β-(Al_xGa_1−x)₂O₃ films have several critical properties of interest to the research community, including a wide bandgap that may be used in the development of new electronic, optoelectronic, and photonic devices. Here we demonstrate the first time fabricated metal-alkoxide-based spin-coated single-phase epitaxial β-(Al_xGa_1−x)₂O₃ films on c-sapphire substrates with $(\overline{2}01)$ orientation and good crystallinity that is comparable to the films fabricated using other film deposition techniques, such as molecular beam epitaxy and chemical vapor deposition. Using this technique, we generated films with broad Al compositions (x) of 0.3, 0.5, and 0.7 with bandgap energies of 5.15, 5.56, and 6.16 eV, respectively, estimated from the X-ray photoelectron spectroscopy inelastic energy-loss spectra. Photoluminescence emission spectra in the ultraviolet and visible (blue) wavelength range highlighted several intrinsic defects in the film structure that functioned as luminescence centers, including self-trapped exciton and recombining donor-to-acceptor band. Detailed analysis of the structural and optical properties of β-(Al_xGa_1−x)₂O₃ epitaxial films revealed that this low-cost and scalable solution-deposition approach coupled with a spin-coating technique could be used to fabricate β-(Al_xGa_1−x)₂O₃ films with tunable properties.     

Anisotropic crack propagation behavior for the silicon-bond coat layer in a multilayer coated system

This study sought to examine the relationship between the degradation mechanism, thermal stress, and crack propagation behavior in environmental barrier coating (EBC) systems. An EBC system composed of a mullite topcoat (TC), Si-bond coat (BC), and SiC substrate was prepared by atmospheric plasma spraying. Heat exposure tests were conducted to evaluate the microstructure of the EBC system at 1300°C for 1, 10, 50, and 100 h. The fracture resistance of the Si BC for the in-plane (direction parallel to each layer, 0.4–0.6 MP) and through-thickness directions (direction from the TC to substrate, 1.7–2.1 MP) differed because a thermal compressive stress was induced for the in-plane direction owing to the mismatch of the thermal expansion coefficients for each layer, which acted as a barrier for crack propagation. However, cracks tended to propagate in the in-plane direction because they were not affected by the in-plane compressive stress. These results clearly showed that Si BC exhibited in-plane anisotropy and crack propagation after heat exposure, which were the major sources of delamination of the EBC system.     

Enhanced Energy Storage of Dielectric Nanocomposites at Elevated Temperatures

Enhancing the performance of dielectric capacitors toward higher energy density and higher operating temperatures has been drawing increased interest. Therefore, in this investigation, research efforts were dedicated to the fabrication and characterization of nanocomposites in order to enhance the energy density at both room temperature and elevated temperature. The dielectric capacitors are fabricated using nanocomposites composed of BaTiO nanoparticles with polyimide (PI) matrix aiming at combining the high relative dielectric permittivity of the ceramic filler and the high breakdown strength of the polymeric matrix. Dielectric energy storage performance is assessed for nanocomposites with volume fractions ranging from 0 to 20% under operating frequency from 20 Hz to 1 MHz and temperatures ranging from 20 to 120C. It is observed that with the increase of temperature, the capacitance increased while the energy density slightly decreased but significantly higher than pure polymer samples. The highest energy density was found for BaTiO/PI nanocomposites with 20% volume fraction, 9.63 J/cm at 20C and 6.79 J/cm at 120C. Overall, testing results indicate that using nanocomposites of BaTiO/PI as a dielectric component shows promise for implementation to preserve high energy density values up to temperatures of 120C.     

Temperature‐insensitive strain behavior in 0.99[(1−x)Bi0.5(Na0.80K0.20)0.5TiO3−xBiFeO3]–0.01Ta lead‐free piezoelectric ceramics

Lead‐free 0.99[(1?x)Bi_0.5(Na_0.80K_0.20)_0.5TiO₃?xBiFeO₃]–0.01Ta (BNKT20–100xBF–1Ta) lead‐free piezoelectric ceramics were fabricated through conventional solid state sintering method. Results showed that change of BF content in the BNKT20–100xBF–1Ta induced a phase transition from ferroelectric to ergodic relaxor phase with a significant disruption of the long‐range ferroelectric order. A large electric‐field‐induced strain of 0.36% (at 80 kV/cm driving field, corresponding to a large signal of ~450 pm/V) which is derived from a reversible field‐induced ergodic relaxor to ferroelectric phase transformation, was obtained in the composition with x=0.01 near the ferroelectric‐ergodic relaxor phase boundary. Moreover, an attractive property for application in nonlinear actuators demanding enhanced thermal stability was obtained in this material, which showed a temperature‐insensitive strain characteristic in the temperature range from room temperature to 100°C.     

Novel mullite-cordierite ceramic refractory fabricated from halloysite and talc

This research work aims to fabricate industrial refractory bricks using cheap and abundant kaolin DD₃ constituted of Halloysite. The fabrication process consists on mixing the crushed raw materials (Kaolin/Clay, Fireclay, Talc) with the respective proportions and an optimized granulometry, shaped by a uniaxial hydrostatic pressure of 250 bars, followed by drying at 100°C and sintering at 1300°C. The addition of Talc - at first with water, Fireclay and AP/DD₃- as a source of MgO promotes the increase of Cordierite formation in order to obtain high heat resistance shock and reduced thermal expansion. Three assays are studied with AP Clay and DD₃ Kaolin weight ratios (100/0, 50/50 and 0/100) % corresponding to (ER₀, ER₁ and ER₂) respectively. Mineralogical analysis results of the new refractory bricks, indicate the presence of Mullite and Cordierite as major phases besides Corundum and Quartz as minor phases. All products (ER₀, ER₁ and ER₂) are found to be argillaceous refractory with Alumina concentration (40 < Al₂O₃ < 45%, FC 40 group) and a melting point higher than 1600°C. The mechanical resistance of the samples is of the same order of magnitude; reaching 51 MPa.     

Sodium Excess Ta‐Modified (K0.5Na0.5)NbO3 Ceramics Prepared by Reactive Template Grain Growth Method

Lead‐free sodium excess Ta‐modified (K_0.470Na_0.545)(Nb_0.55Ta_0.45)O₃ (KNNT) ceramics were synthesized by a conventional and reactive templated grain growth methods, and their degree of grain orientation, microstructure, dielectric, ferroelectric, and field‐induced strain properties were systematically investigated. A high degree of grain orientation (Lotgering factor F = 80%) was obtained in textured KNNT ceramics. Results showed that textured KNNT ceramics exhibit high grain orientation, dielectric constant, and field‐induced strain as compared to nontextured samples of the same composition. Room temperature unipolar field‐induced strain of K_0.5Na_0.5NbO₃ (KNN) ceramics was enhanced from 0.080% for nontextured sample to 0.115% for textured sample, and their corresponding dynamic piezoelectric coefficients () were improved from 320 pm/V to 460 pm/V, respectively.     

Effects of Sr-doping on the giant magnetocaloric effect of EuTiO3

The magnetic properties and magnetocaloric effect of Eu_1−xSr_xTiO₃ (x=0–0.1) compounds are investigated. With slight Sr-doping, the ferromagnetic (FM) coupling significantly increased and FM exchange is dominant in the delicate balance. A giant reversible magnetocaloric effect (MCE) and large refrigerant capacity (RC) for Eu_1−xSr_xTiO₃ compounds were observed. The values of −ΔS_M^max are evaluated to be around 10 J/kg K under a magnetic field change of 1 T and 21 J/kg K under a magnetic field change of 2 T, respectively. But, the values of RC are increased with the more Eu in EuTiO₃ to be substituted by Sr. Therefore, the giant reversible MCE and large RC make the Eu_1−xSr_xTiO₃ compound a good candidate for magnetic refrigerant working at low-temperature and low-field.     

Effects of SiC on phase transformation and microstructure of spark plasma sintered α/β-SiAlON composite ceramics

α/β-SiAlON/SiC composite ceramic tool materials were prepared via spark plasma sintering. The effects of content and size of SiC particles and sintering temperature on phase composition, mechanical properties, and microstructure were investigated. The results indicated that SiC restrained the transformation of β-SiAlON to α-SiAlON, but higher SiC content (≥10 wt.%) resulted in a higher Vickers hardness of the composite. The large size of SiC particles raised the densification temperature of α/β-SiAlON composites, and small SiC particles benefited to improve microstructure. There were more equiaxed α-SiAlON grains and β-SiAlON with a larger aspect ratio (${\overline{\alpha }}_{95}$ = 5.1) in the α/β-SiAlON composite containing 100 nm SiC. The sample containing 10 wt.% 100 nm SiC particles sintered at 1700°C had the optimal properties with a Vickers hardness and fracture toughness of 18.5 ± .2 GPa, 6.4 ± .2 MPa m^1/2, respectively.     

Effects of Nb/TiC/TaC/VC and Co addition on the microstructure and properties of WC-based cemented carbides

A series of WC-based cemented carbides with Nb/TiC/TaC/VC and Co was prepared through spark plasma sintering (SPS) at a low sintering temperature of 1300°C, and their microstructures and mechanical properties were investigated. The nonstoichiometric multicomponent carbide Nb/TiC/TaC/VC with a rock-salt structure ($Fm\overline{3}m$) has a high atomic solution capacity. In the sintering process, partial WC and Co may dissolve in Nb/TiC/TaC/VC. With a high concentration of carbon vacancies, Nb/TiC/TaC/VC plays a beneficial role as a mass transfer intermediary. Good mass transfer facilitates the formation of a more accommodating and stable bonding between WC, Nb/TiC/TaC/VC, and Co, thereby preserving the hardness of the sintered bulks and preventing the initiation and propagation of cracks. When 6 wt.% Nb/TiC/TaC/VC and 4 wt.% Co are added to WC, the sintered bulk with fine grains exhibits superior hardness (23.27 ± .63 GPa) and toughness (10.45 ± .56 MPa·m^1/2).     

Synchrotron x-ray spectroscopy investigation of the Ca1−xLnxZrTi2−x(Al,Fe)xO7 zirconolite ceramics (Ln = La,Nd, Gd,Ho, Yb)

When incorporating actinides into zirconolite for high-level radioactive waste immobilization, Al³⁺ and Fe³⁺ ions generally act as charge compensators. In this study, we rationally designed a series of (Ln = La, Nd, Gd, Ho, Yb) to unravel the dopant solubility and evolutions of the crystalline phase and local environment of cations through synchrotron X-ray methods. It was found that single zirconolite phase is difficult to obtain and the fraction of perovskite have an increase with x from 0.1 to 0.9 in . Formation of both zirconolite-2M and zirconolite-3O phases was observed in and . Phase transformation from zirconolite-2M to 3O occurs at x = 0.7 for while x = 0.9 for . The solubility of and to form single zirconolite-2M can reach to 0.9 f.u. and 0.7 f.u., respectively. The evolution of lattice parameters of zirconolite in is greatly related to the ionic radii of cations and substitution mechanism among the cations. X-ray absorption near edge spectroscopy revealed that Fe³⁺ ions replace both five- and six-coordinated Ti sites and the ratio of TiO₅ to TiO₆ decreases when increasing dopant concentration in the . For the local environment of Zr⁴⁺, the major form is ZrO₇ with a trace of ZrO₈.     

Nickel element doping impacts on structure features and Faraday effects of magneto-optical transparent holmium oxide ceramics

The nickel element doped holmium oxide (Ho₂O₃:Ni) transparent magneto-optical ceramics were fabricated by vacuum sintering and the dopant impacts on structure features and Faraday effects were investigated. The starting oxide powders were synthesized by pyrolyzing the resulting layered holmium-based hydroxide nanosheets prepared from a chemical precipitation route using the sodium hydroxide as precipitant at the freezing temperature. Upon high-temperature sintering, the ${\mathrm{Ni}}_i^{••}$ defect is introduced by Ni²⁺ substitution for Ho³⁺ to form the interstitial solid solution. The 1 at.% Ni²⁺ doped Ho₂O₃ ceramic sample exhibits an in-line transmittance of ∼70.04% at 1 550 nm with a relative density of ∼99.88%, while more Ni²⁺ incorporation (e.g., 2‒5 at.%) even leads to a completely opaque state. The magneto-optical transparent Ho₂O₃:1%Ni ceramic developed in this work has Verdet constants of ∼−195, −65, and −29 rad/(T·m) at 635, 1 064, and 1 550 nm, respectively, which are ∼1.8-fold higher than the commercial terbium gallium garnet crystal or ∼1.4-fold higher than the pure Ho₂O₃ ceramic. This material also possesses relatively large figure of merit of ∼14.6°/T at 1 064 nm and relatively high thermal conductivity of ∼7.5 W/(m·K) at room temperature.     

Quantification of Yttria in Stabilized Zirconia by Raman Spectroscopy

The relationship between Y₂O₃ content in tetragonal and cubic ZrO₂ phases and the shift of the Raman band at ～645/cm was investigated. With increasing Y₂O₃ content, the 645/cm Raman band position decreases to lower Raman shift values. A fit of x = Y₂O₃ content in wt% and y = Raman band position in per cm, was found to be valid for low Y₂O₃‐stabilized t‐ZrO₂, t′′‐ZrO₂ transition, and fully stabilized c‐ZrO₂. Modeling the change in lattice parameters due to the incorporation of Y₂O₃ in ZrO₂ as obtained from Rietveld‐refined XRD data confirms that the peculiar sigmoidal form of the band shift with Y₂O₃ content is mainly due to a variation of the amount of oxygen vacancies. The resultant method is highly attractive in fields of Y₂O₃ determination in ZrO₂ materials where a fast, spatially resolved, and nondestructive analysis is required.     

Enhancement in magnetic permeability of Ni-Co-Zn ferrites using CuO doping for RF and microwave devices

Novel soft magnetic ferrite materials will play a crucial role in next-generation trillion-dollar sensor technologies related to 5G communications and internet of things as these materials can achieve improved wireless power/signal transfer efficiency with high operation frequency. In this work, Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrites with high permeability and low magnetic loss were prepared for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO dopant (x = 0 wt% to 20 wt%) were employed during the synthesis of Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (μ’ of 4-10) and relatively low magnetic loss tangent ( of 0.01-0.1) has been achieved at frequency range between 100 and 800 MHz. Addition of CuO, especially up to 3 wt%, can cause a significant increase in permeability. Real part of the permeability of 3.87 and 10.9 has been achieved for undoped and 3 wt% CuO doped specimens, while noticeable reduction in magnetic losses has been observed for the doped sample measured at 400 MHz. The resonance frequency of synthesized ferrites has also been shifted into GHz range, when higher concentration of CuO dopants (>5 wt%) were employed.