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Abstract ZnAl2O4 and CuAl2O4 spinel nanoparticles were prepared by a modified Pechini method and used with the natural chitosan (CS) and shellac (SH) polymers to form novel composite membranes as promising food packaging materials. The selection of ZnAl2O4 and CuAl2O4 spinel nanoparticles was based on their antibacterial characteristics, availability, and economy. Using a straightforward and adaptable solution mixing and casting method, the bio-composites were created. The mechanical, physical, antibacterial, homogeneity and air permeability properties of composite films were investigated. The film structure was evaluated in terms of component interactions using FTIR spectra. The addition of 10% SH increased the tensile strength, percentage strain at maximum load, Young’s modulus, and burst strength by 114–101%, 3.6–8.4, 103–119, and 179–153% for low and middle M.wt./CS respectively. Chitosan/shellac-CuAl2O4 composite has superior properties compared to ZnAl2O4 composite. In general, 0.05% spinel provides a composite having better qualities than that of 0.1 additions. Middle M.wt. chitosan provides a composite with superior properties compared to that of low M.wt. The incorporation of ZnAl2O4 or CuAl2O4 enhanced the thermal stability of the SH/CS composite. ZnAl2O4 provides superior thermal stability than CuAl2O4. When shellac/CS film structure is treated with the previously indicated ZnAl2O4 or CuAl2O4 formulation, the % swelling decreases along with an increasing in the gel fraction. The antimicrobial assessment using inhibition zone diameter and shake flask methods showed that a composite of 1:9 shellac/chitosan/0.05% of CuAl2O4 exerted the highest Gram-positive antibacterial activity against B. mycoides (21 mm), and C. albicans (22 mm). So, these enhancements make chitosan/shellac/ZnAl2O4 or CuAl2O4 composite films a good alternative to producing food packaging materials.

ZnAl2O4 and CuAl2O4 spinel nanoparticles were prepared by a modified Pechini method and used with the natural chitosan (CS) and shellac (SH) polymers to form novel composite membranes as promising food packaging materials. The selection of ZnAl2O4 and CuAl2O4 spinel nanoparticles was based on their antibacterial characteristics, availability, and economy. Using a straightforward and adaptable solution mixing and casting method, the bio-composites were created. The mechanical, physical, antibacterial, homogeneity and air permeability properties of composite films were investigated. The film structure was evaluated in terms of component interactions using FTIR spectra. The addition of 10% SH increased the tensile strength, percentage strain at maximum load, Young's modulus, and burst strength by 114–101%, 3.6–8.4, 103–119, and 179–153% for low and middle M.wt./CS respectively. Chitosan/shellac-CuAl2O4 composite has superior properties compared to ZnAl2O4 composite. In general, 0.05% spinel provides a composite having better qualities than that of 0.1 additions. Middle M.wt. chitosan provides a composite with superior properties compared to that of low M.wt. The incorporation of ZnAl2O4 or CuAl2O4 enhanced the thermal stability of the SH/CS composite. ZnAl2O4 provides superior thermal stability than CuAl2O4. When shellac/CS film structure is treated with the previously indicated ZnAl2O4 or CuAl2O4 formulation, the % swelling decreases along with an increasing in the gel fraction. The antimicrobial assessment using inhibition zone diameter and shake flask methods showed that a composite of 1:9 shellac/chitosan/0.05% of CuAl2O4 exerted the highest Gram-positive antibacterial activity against B. mycoides (21 mm), and C. albicans (22 mm). So, these enhancements make chitosan/shellac/ZnAl2O4 or CuAl2O4 composite films a good alternative to producing food packaging materials. [ABSTRACT FROM AUTHOR]

Pore-closed ZnAl 2 O 4 ceramic can hardly be pressureless sintered from conventional (>100 nm) powder, which restricts the fabrication of the transparent ceramic by capsule-free hot isostatic pressing technique. This work focused on the effect of yttrium-doping on the microstructural evolution in the sintering of a ∼180-nm ZnAl 2 O 4 powder. At a concentration of 300 or 600 ppm, the yttrium ions segregated along the grain boundaries and contributed to ordered nanostructures, which could suppress abnormal grain growth in both air sintering and hot isostatic pressing. The optimized Y-doped ZnAl 2 O 4 transparent ceramic owned good visible light transmittance (>65 %) and a wide transmission range (6.0 μm at the 60 % transmittance) at a thickness of 1.5 mm, as well as high thermal conductivity (24.9 W·m−1·K−1) and reasonable mechanical properties (Vickers hardness of 12.9 GPa and Young's modulus of 281.3 GPa), meeting the application requirements for infrared windows. [ABSTRACT FROM AUTHOR]

The ZnAl2-xCrxO4 (x = 0.0–0.1) ceramics were synthesized using microwave-hydrothermal method. The as synthesized powders were sintered at 1250 °C/4 h. All samples exhibit a cubic crystal structure and belong to Fd-3m space group. The lattice constant (a) increased from 8.085 Å (x = 0.0) to 8.128 Å (x = 0.04) and decreased for higher concentrations. The Fourier transform infrared spectra (FTIR) show tetrahedral and octahedral absorption bands in the region, 400 - 480 cm−1 and 480 – 682 cm−1, respectively. The X-ray photoelectron spectroscopy confirmed the valence states of Zn, Al, Cr, and O. The UV-vis spectra reveal a red shift with Cr3+ doping, reducing the bandgap energy (Eg) from 3.66 eV (x = 0.02) to 3.39 eV (x = 0.10). The electrochemical performance of the present samples was investigated using cyclic voltammetry (CV) and galvanostatic charge/discharge (GDC). The sample x = 0.10 exhibits high specific capacity of 143.671 F/g at a scan rate 5 mV/s. Therefore, the present samples may be useful for energy storage devices. Highlights: The ZnAl2-xCrxO4 (x = 0.0–0.1) ceramics were synthesized using microwave-hydrothermal method. The UV-vis spectra reveal a red shift with Cr3+ doping, reducing the bandgap energy (Eg) from 3.66 eV (x = 0.02) to 3.39 eV (x = 0.10). The sample x = 0.10 exhibits high specific capacity of 143.671 F/g at a scan rate 5 mV/s. [ABSTRACT FROM AUTHOR]

Palladium (Pd)-based catalysts are widely used for CO2 hydrogenation reactions due to the capability to activate H2, which enhances the overall CO2 conversion. However, most of the current Pd catalysts reported show high CO2 conversion only at higher temperature, and the exploration of efficient catalyst enabling low temperature conversion (180–300 °C) is of importance. In this study, a series of Pd-B/ZnAl2O4 catalysts were synthesized via in-situ doping, resulting in the Pd crystal transformation induced from crystal to amorphous. The catalytic hydrogenation activity of the amorphous Pd-B catalyst reaches its zenith at a Pd-B mole ratio of 1:2, accompanied by the superior catalysis stability in CO2 hydrogenation. Various characterization techniques, including XRD, CO-DRIFTS, H2-TPR, XPS and TEM, were used to investigate the properties of the Pd-B/ZnAl2O4 catalyst. The results showed that the Pd-B/ZnAl2O4 catalyst exhibited higher dispersion and better CO2 conversion efficiency compared to unmodified Pd catalyst. Additionally, the methanol space–time yields are nearly doubled when the B decoration is employed. At 280 °C, CO2 conversion was improved and methanol selectivity remained at ~ 65%. This study provides valuable insights into the design and optimization of Pd-B based catalysts for CO2 hydrogenation at low temperatures. [ABSTRACT FROM AUTHOR]

Transition metal ions, such as Cr3+, Fe3+, and Ni2+, are widely recognized activators for efficient broadband near‐infrared (NIR) phosphors. However, the potential of Mn2+ ions as NIR‐emitting activators is relatively overlooked due to their typically narrowband emission in the visible spectral region and relatively weak absorption. Herein, a heavy Mn2+‐doped Zn1‐xAl2O4: xMn2+ (ZAO: xMn2+) phosphor is presented that exhibits a single NIR emission band peaked at 830 nm with a bandwidth of 135 nm under excitation at 450 nm. Through comprehensive structural and spectral analysis, this NIR band is attributed to the emission originating from Mn2+ ions within the MnO6 octahedra. Importantly, the formation of Mn2+–Mn2+ dimers breaks the spin‐forbidden rule and significantly enhances the transition probability, as supported by the excited state dynamic analysis. Consequently, the optimal ZAO: 0.70Mn2+ sample shows high internal/external photoluminescence quantum yields of 85.8%/36.9%, along with good thermal stability demonstrated by the emission intensity at 423 K retains 60% of that at 298 K. Finally, a prototype NIR pc‐LED device is fabricated by combining ZAO: 0.70Mn2+ phosphor with a 450 nm blue diode chip, generating an NIR output power of 28.84 mW at 100 mA. This study provides novel insights into high‐performance Mn2+‐activated NIR phosphors. [ABSTRACT FROM AUTHOR]

Scientists have been searching for new microwave dielectric materials due to the need for miniaturization and weight reduction of wireless patch antenna. The sol–gel method was used to prepare the TiχZn(1-χ)Al2O4 (x = 0.25) microwave dielectric ceramic nanoparticles and various measurements were carried out. The distinctive peaks of titanium and zinc aluminate with the typical face-centered cubic structure was noticed in the X-ray diffraction (XRD) patterns. Fourier transform infrared spectroscopy (FTIR) was used to confirm the functional groups, field-emission scanning electron microscopy (FESEM) was used to analyze the crystalline structure and the elemental composition was confirmed using energy dispersive spectroscopy (EDS). The substitution of Zn2+ for Ti2+ in ZnAl2O4 nanoparticles increased crystallite size, affecting dielectric permittivity. The dielectric permittivity (εr) of TiχZn(1-χ)Al2O4 nanoparticles was calculated using a 100 KHz to 1 MHz LCR spectrometer. It can be demonstrated that the Ti0.25Zn0.75Al2O4 sample has εr 22.78–23.45, making it a viable material for millimeter-wave applications. Additionally, a prototype patch antenna with dimensions 2.5 cm × 1.5 cm was fabricated using these dielectric ceramic nanoparticles and tested using a network analyzer, which exhibited a return loss of −12.82 dB at an operating frequency of 2.12 GHz.

Three series of nanocrystalline phosphors based on ZnAl2O4 spinel co-doped with Cr3+, Er3+ and Yb3+ ions in the dopant concentration ratios 1:1:3, 1:1:5 and 1:1:7 were obtained by sol–gel citrate method. Unlike conventional high-temperature solid-state synthesis, the applied method makes it possible to obtain single-phase cubic spinel materials for all three series at a minimal annealing temperature of 700 °C. In this way, fine powders with an average grain size of 31–33 nm were obtained. The lattice parameters of the phosphors triply co-doped with Cr3+, Er3+ and Yb3+ ions are in the range of 8.094–8.087 Å, systematically higher than the corresponding values for single Cr-doped ZnAl2O4, thus proving incorporation of larger Er and Yb ions into the ZnAl2O4 spinel structure. Photoluminescence properties of ZnAl2O4:Cr,Er,Yb nanocrystalline phosphors were studied at the ambient conditions. The phosphors exhibit a characteristic photoluminescence related to d–d transitions in Cr3+ ions and up-conversion emission of Er3+ ions. The intensity of these emissions is dependent on the concentrations ratio of the activators and the annealing temperature. [ABSTRACT FROM AUTHOR]

In this work, crystallization, thermal expansion and wetting behavior of ZnO–Al 2 O 3 –SiO 2 (ZAS) glass were first investigated. The results showed that ZnAl 2 O 4 was precipitated from ZAS glass after crystallization treatment. Crystallization increased the coefficient of thermal expansion (CTE) of ZAS glass ceramic due to the high CTE of ZnAl 2 O 4. In addition, ZAS glass exhibited good wettability on the surface of MgAl 2 O 4 substrate. On this basis, ZAS glass was used to join MgAl 2 O 4 ceramic, and the microstructure and mechanical properties of joints obtained with different cooling methods were investigated. The flexural strength of joints was related to the content of ZnAl 2 O 4 crystals in the brazing seams. Additional nucleation and crystallization treatment during cooling process improved the crystallinity of brazing seam, resulting in better matching of the CTE of brazing seam with that of MgAl 2 O 4 ceramic. The maximum flexural strength of joints reached 201 MPa, which was equivalent to the strength of MgAl 2 O 4 ceramic. [ABSTRACT FROM AUTHOR]

ZnAl2O4 nanocrystallites doped with Cr3+ ions with mean sizes ranging from 2 to 16 nm were synthesized by the hydrothermal method. Chromium ions occupy the aluminum positions, which symmetry depends on the crystallite size. The smallest nanocrystals have a much larger unit cell than the bigger ones. The metal to ligand distance increases when the size of the nanocrystals decreases. This causes the nephelauxetic effect, which is for the first time (to our knowledge) observed as a size effect. It was also observed that ZnAl2O4:Cr3+ nanocrystals with size larger than 10 nm possesses the same spectroscopic properties as monocrystal. [ABSTRACT FROM AUTHOR]

ABSTRACTRefractories subject to loading and unloading repeatedly because of physical effects and thermal stress attack in the service process, which is an important issue shortening the service life of the thermal equipment. Therefore, researches of predicting the service life of refractories under cyclic loading have the guiding significance. The present work investigated the synthesis of ZnAl2O4 and discussed its effects on the alumina castables. The results show that the optimized generation temperature of ZnAl2O4 phase is 1400°C and the hysteresis loop in the curves of cyclic loading reveals a general trend of first sparse and then dense. The cycle times of the specimen with 3 wt.% ZnAl2O4 is 50 times, and the time from starting to loop to fracture is about 4300 s. The fatigue resistance of the specimen with 3 wt.% ZnAl2O4 is superior to ZA-0 and ZA-1.5. The new method of cyclic loading was innovatively adopted in refractories, which provide data and theoretical support for the thermal shock evaluation methods.

Catalysts with different ZnAl2O4 contents impregnated in beta zeolite were synthesized and their catalytic activity in glycerol dehydration to allyl alcohol was investigated. The materials were characterized by XRD, XRF, FTIR, DRIFTS‐ pyridine, NH3‐TPD, and N2 physisorption. In addition, the surface electrostatic potential maps were generated by a molecular mechanics approach. The XRD patterns indicated a high dispersion of the ZnAl2O4, evidenced by the absence of reflections in the diffractograms, except for the sample containing the highest spinel content. The FTIR spectra indicated the presence of zinc aluminate spinel in the zeolite matrix. The DRIFTS‐pyridine and NH3‐TPD analyses indicated that the incorporation of ZnAl2O4 modifies the acidic properties of the zeolite concerning the number, type, and distribution of acid sites. The N2 physisorption tests showed the maintenance of the micro and mesoporous properties of H‐BEA after modification, despite the reduction of the specific area and pore volume values. The samples impregnated with the ZnAl2O4 phase showed larger mesopores sizes, which may favor its catalytic performance. The catalytic tests indicated the allyl alcohol production for the impregnated materials, which the best results were obtained by the sample containing 2 % of ZnAl2O4, with 90.65 % glycerol conversion and 37 % allyl alcohol selectivity due to appropriate tuning of the acidic and textural properties, as well as the presence of basic sites evidenced by CO2‐TPD analysis and electrostatic potential maps. The presence of acid‐base sites is essential to conduct hydrogen transfer, according to the proposed mechanism, generating allyl alcohol. Finally, the results with a longer reaction period showed greater stability for the sample impregnated with low spinel content, whose coke deposition was smaller, which may be related to the larger size of secondary mesopores. [ABSTRACT FROM AUTHOR]

Refractories subject to loading and unloading repeatedly because of physical effects and thermal stress attack in the service process, which is an important issue shortening the service life of the thermal equipment. Therefore, researches of predicting the service life of refractories under cyclic loading have the guiding significance. The present work investigated the synthesis of ZnAl2O4 and discussed its effects on the alumina castables. The results show that the optimized generation temperature of ZnAl2O4 phase is 1400°C and the hysteresis loop in the curves of cyclic loading reveals a general trend of first sparse and then dense. The cycle times of the specimen with 3 wt.% ZnAl2O4 is 50 times, and the time from starting to loop to fracture is about 4300 s. The fatigue resistance of the specimen with 3 wt.% ZnAl2O4 is superior to ZA-0 and ZA-1.5. The new method of cyclic loading was innovatively adopted in refractories, which provide data and theoretical support for the thermal shock evaluation methods. [ABSTRACT FROM AUTHOR]

Thick ZnO/ZnAl2O4 coatings were synthesized on zinc alloy Z1 substrates through plasma electrolytic oxidation (PEO) for different anodization times. The prepared coatings were characterized by scanning SEM, XRD, diffuse reflectance and photoluminescence spectroscopy in order to establish the relationship between their structural and optical properties and PEO processing parameters. Under different PEO processing conditions (anodization time—1–10 min and applied voltage—370 and 450 V) ceramic coatings with a mean thickness of 2–12 μm were prepared. XRD analysis explored the coating structure composed of zinc oxide (wurtzite) and zinc aluminate spinel. The content of ZnAl2O4 in the coatings grows with increasing the applied voltage and anodization time. Photoluminescence (PL) measurements showed that the PEO coatings have several bands in the visible and near-infrared regions associated with their composite structure. The PL spectra significantly depend on the PEO processing parameters due to varying ZnO and ZnAl2O4 content in the coatings. The insight in the relationship between the ZnAl2O4 structure and the photoluminescent properties of ZnO/ZnAl2O4 coatings has been provided using the combination of XRD and luminescence spectroscopy. [ABSTRACT FROM AUTHOR]

The development of sapphire-compatible optical sources is highly valued due to the potential cost-effective applications in sapphire-based integrated devices. In this work, a screen printing technique assisted by a molten salt flux was used to synthesize (hk0)-textured ZnAl 2 O 4 : Nd, Ce sub-micron films deposited over the sapphire substrate. The study is focused at controlling Ce concentration in the emitting layers, as well as determining the key parameters to be met for the development of ZnAl 2 O 4 -based films of high efficiency and remarkable optical properties. A degree of crystallinity of the ZnAl 2 O 4 -based films, and a precise adjustment of texture are the keys parameters for further improvement of NIR luminescence efficiency. Specifically, (hk0)-textured films were developed at sintering temperature of around 1300 °C, which contributed to a higher NIR emission intensity as compared to that of (hkl)-untextured films. Therefore, the design process carried out in this work promotes a feasible way to achieve a high NIR emission performance, demonstrating the validity of the approach for a wide range of applications. Modulating the texture of ZnAl 2 O 4 : Nd, Ce sub-micron films growth over sapphire substrates to enhance the NIR luminescence. [Display omitted] [ABSTRACT FROM AUTHOR]

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Photoactive Cu-doped ZnO–ZnAl2O4 ceramic nanocomposites and coatings were prepared by polymer-salt method. The luminescent spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction methods were used for the study the structure, morphology and materials properties. The nanocomposites consist of small hexagonal ZnO and cubic ZnAl2O4 nanocrystals having size about 10 nm. The study of luminescence properties shows that prepared nanocomposites can be used as light down-converters that transfer short-wave ultraviolet (UV-C) radiation into long-wave ultraviolet (UV-A) and visible spectral range. These nanocomposites can be very attractive in photovoltaic applications as spectral down-converters. Also obtained nanocomposites demonstrate the ability to generate chemically active singlet oxygen under UV-A radiation and blue light. The experiments show that Cu-doped ZnO–ZnAl2O4 materials demonstrate antibacterial activity against gram-positive bacteria. [ABSTRACT FROM AUTHOR]

We implemented a simple and inexpensive aqueous sol-gel process to synthesize ZnAl2O4 nanoparticles to study its potential application as a gas sensor. Compared to traditional ceramic methods, the synthesis was conducted at lower temperatures and reaction times (5 h from 200 °C). The crystalline evolution of the oxide was investigated. The effect of the calcination temperature (200–1000 °C) on the crystallites' size (16–29 nm) and the ZnAl2O4 powder's surface morphology was also analyzed. Measurements confirmed the formation of bar-shaped granules (~0.35 μm) made up of nanoparticles (~23 nm). The surface area of the powders was 60 m2/g. Pellets were made from the powders and tested in sensing carbon monoxide and propane gases, showing a high sensitivity to such gases. The sensor's response increased with increasing temperature (25–300 °C) and gas concentration (0–300 ppm). The oxide showed a higher response in propane than in carbon monoxide. We concluded that the ZnAl2O4 is a good candidate for gas sensing applications. [ABSTRACT FROM AUTHOR]

In order to determine the catalytic stability, PtSn structured catalysts supported on thin films of MgAl2O4 or ZnAl2O4 deposited on α‐Al2O3 spheres were studied through five reaction‐regeneration cycles in the n‐butane dehydrogenation. Bimetallic catalysts show good catalytic stability along the five reaction‐regeneration cycles. Among the different synthesized catalysts, the PtSn/Sp‐Zn‐CN catalyst showed the best catalytic behaviour, showing very good values of yields to butenes and excellent catalytic stability along the cycles, even better than the one of a structured commercial catalyst used industrially for the dehydrogenation of paraffins. The characterization results by temperature‐programmed reduction and X‐ray photoelectron spectroscopy showed some modifications in the metallic phase of the catalysts after the cycles, mainly in the Sn/Pt surface ratios and in segregation effects in some catalysts. However, the transmission electron microscopy (TEM) results are conclusive in the sense that, after the cycles, the bimetallic catalysts maintained a very high proportion of particles with sizes between 1–2 nm, and therefore, preserved a high metallic dispersion. [ABSTRACT FROM AUTHOR]

Pristine and Cu-doped ZAO nanosheets have been successfully synthesized using the hydrothermal path. XRD analysis confirmed ZAO's single-phase cubic spinel structure. The morphology of ZAO changed significantly from micro-hexagons to nanosheets with the doping of Cu ions. The XPS spectra of Cu doped ZAO confirm the presence of Zn, Al, O and Cu at 2+ , 3+ , 2− and 2+ oxidation states, respectively. The bandgap of Cu-doped ZAO nanosheets is less than that of pure ZAO. Due to the tunable bandgap, the synthesized material can be used as a potential candidate for energy-based applications. [ABSTRACT FROM AUTHOR]

In this study, ZnAl2O4 catalyst was synthesized with the capability of transforming eugenol to vanillin through One-Pot Catalytic Oxidation. ZnAl2O4 was synthesized from Zn(CH3COO)2.2H2O and Al2O3 using the wet-impregnation method, and characterized by FTIR, XRD, and SEM. One-Pot Catalytic Oxidation was conducted by heating under reflux at 150oC using nitrobenzene and a certain amount of ZnAl2O4 catalyst (4% and 7%) for 2 and 3 hours of reaction. Catalytic Oxidation is also carried out without catalyst as a comparison. The vanillin product was confirmed by GC and spectral data achieved from UV-Vis, FTIR, and mass spectrometry. The results revealed that transforming eugenol to vanillin using ZnAl2O4 catalyst provides a better selectivity value than without using the catalyst, is 100% for the use of 4% catalyst in 2 hours, while without catalyst gives 88% in 3 hours. In addition, the use of 4% catalyst in 3 hours gives 94% for selectivity of vanillin, and the use of 7% catalyst gives selectivity values at 82% and 85%, respectively for 2 hours and 3 hours. The conversion rate of the use of catalyst and without catalyst gives the perfect rate at 100%, but the use of catalyst produces better vanillin with percent yield at 2.485 for 2 hours, and 3.22% for 3 hours, while without catalyst have percent yield of vanillin at 1.94% for 3 hours.

Undoped and Sm3+ doped ZnAl2O4 nanopowders were synthesized using the co-precipitation method and annealed at 750 ℃ for 3.5 h. The aim of this study was to investigate the effect of varying the Sm3+ concentration on the ZnAl2O4 structure, morphology, and optical properties. The X-ray diffraction analysis confirmed that the samples have a face-centred cubic structure. Crystallite size decreased with an increase in Sm3+ concentration. Scanning electron microscopy revealed that the addition of Sm3+ slightly influence the morphology of the samples. Transmission electron microscopy confirmed a slight decrease in particle sizes. Energy-dispersive X-ray spectroscopy analysis confirmed the anticipated elemental composition. Ultraviolet–visible spectroscopy showed an increase in bandgap compared to the host. Photoluminescence analysis indicated that doping with Sm3+ induced defects within ZnAl2O4. The emission peaks observed around 380, 401, 451, 500, and 739 nm are attributed to host material. The emission peaks at 564, 601, and 649 nm correspond to the 5G5/2 → 6H5/2, 6H7/2, and 6H9/2 transition of Sm3+, respectively. The highest luminescence intensity was found for the 0.5 % Sm3+ sample. The CIE colour chromaticity diagram showed that the emission colour could be tuned from bluish to nearly white to orange.

Humidity sensitivity is evaluated for chemically synthesized ZnAl2O4/Al devices. We succeeded in synthesizing the ZnAl2O4/Al device by applying chemical techniques only. Hydrothermal treatment for the anodized aluminum (AlOx/Al) gives us the device of the ZnAl2O4/Al structure. All fabrication processes were conducted under 400 °C. The key was focusing on ZnAl2O4 as the sensing material instead of MgAl2O4, which is generally investigated as the humidity sensor. The evaluation of this ZnAl2O4/Al device clarified its effectiveness as a sensor. Both electrical capacitance, Cp, and the resistivity, Rp, measured by an LCR meter, obviously responded to the humidity with good sensitivity and appreciable repeatability. Our synthesis technique is possible in principle to improve on the process for the device with a complex structure providing a large surface area. These characteristics are believed to expand the application study of spinel aluminate devices as the sensor. [ABSTRACT FROM AUTHOR]

In this paper, ZnO was used as a sintering aid as well as reactant in the reactive flash sintering (RFS) of zinc-containing ceramic materials at room temperature (25 °C). The RFS of ZnO-based ceramics, both ZnAl 2 O 4 and Zn 2 TiO 4 , were achieved with the application of a high electric field. Contrary to previous reports, the RFS of ZnAl 2 O 4 was divided into two stages according to temperature changes, and the effect of the reaction exotherm on the RFS was presented for the first time in this paper. In addition, the RFS produced a larger grain size of ZnAl 2 O 4 than conventional sintering did. [ABSTRACT FROM AUTHOR]

Transparent glass-ceramics based on ZnO–Al 2 O 3 –SiO 2 (ZAS) glass system exhibit excellent optical and mechanical properties that are dependent on crystal grains. Gahnite (ZnAl 2 O 4) was the main phase that crystallized in ZAS glass-ceramics via thermoelectric coupling treatment. The morphology and size of ZnAl 2 O 4 crystal were controlled by the electric field strength. Introduction of thermoelectric coupling field led to the refinement and dispersion of large and agglomerated ZnAl 2 O 4 crystal grains, which improved the transmission and Vickers' hardness of the ZAS-based glass-ceramics. Theoretical calculations revealed that crystal phase is the area of low electric field strength, which resulted in the migration of Zn ions (Zn2+) from glass phase to the ZnAl 2 O 4 crystal regions under the effect of thermoelectric coupling field. The decrease in the amount of Zn2+ in glass phase further limited its grain growth, and refinement of ZnAl 2 O 4 grains was achieved. This research shows an efficient and rapid approach to refine grains in ZAS glass-ceramics by application of thermoelectric coupling treatment. • In this work, it is the first time use of thermoelectric coupling field to precipitate ZnAl 2 O 4 nanocrystals in ZnO–Al 2 O 3 –SiO 2 glass-ceramics. • The application of a thermoelectric coupling field was used to refine and uniformly distribute ZnAl 2 O 4 crystals in ZnO–Al 2 O 3 –SiO 2 glass-ceramics. • The mechanism of a thermoelectric coupling field on crystal refinement is explained in detail, which provides ideas for the refinement and uniformly distribution of crystal grains. [ABSTRACT FROM AUTHOR]

Zinc aluminate ZnAl2O4 particles were synthesized using a spray pyrolysis technique. Aerosol droplets of the mixture of the zinc nitrate with concentration varied from 0.03 to 0.3 M and aluminum nitrate from 0.06 to 1.2 M were pyrolyzed in air at temperatures ranging from 600 to 800°C. The molar ratio of Al to Zn was in the range of 2–4. The produced ZnAl2O4 powders in single spinel phase have the primary and secondary particle sizes in the range of 10–30 nm and 0.5–7 μm, respectively. The primary particle size increased with the reaction temperature but decreased with precursor concentration (PC). The relative density of the particles increased with reaction temperature but decreased slightly with solution concentration at the constant pyrolysis temperature of 800°C. Particles synthesized under high PC with the molar ratio of Al/Zn equal to 4 tend to have an annona squamosal‐like exterior appearance but essentially mesoporous interior structure, with the highest surface area to 97 m2/g. The single spinel phase of ZnAl2O4 particles synthesized with molar ratios of Al/Zn equal to 3.5 or 4 may be explained by the increased solid solubility of Al in the ZnAl2O4 structure due to the nanosize effect. [ABSTRACT FROM AUTHOR]

• The development of crystalline phases and microstructures of Mg 4 Nb 2 O 9 -ZnAl 2 O 4 -TiO 2 dielectric ceramics was investigated. • The synergistic effect of ZnAl 2 O 4 -TiO 2 co-doping promoted the Mg 4 Nb 2 O 9 ceramic densification. • The long-range order on the NbO6 octahedra was enhanced by co-doping ZnAl 2 O 4 and TiO 2 to Mg 4 Nb 2 O 9. • A dielectric constant of 13.1 and a high Qxf value of 366,000 GHz could be obtained for 0.7Mg 4 Nb 2 O 9 −0.15ZnAl 2 O 4 −0.15TiO 2. This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg 4 Nb 2 O 9 -(0.3-x)ZnAl 2 O 4 -xTiO 2 ternary system. Crystalline phases and microstructure of Mg 4 Nb 2 O 9 -ZnAl 2 O 4 -TiO 2 dielectric ceramic composites were investigated and correlated with the relevant dielectric properties. It was observed that the addition of Ti4+ substituted Nb5+ in the Mg 4 Nb 2 O 9 structure, which promoted the decomposition of Mg 4 Nb 2 O 9 to form the second phase, Mg 5 Nb 4 O 15 , during sintering. The synergistic effect of ZnAl 2 O 4 -TiO 2 co-doping promoted the Mg 4 Nb 2 O 9 ceramic densification. The sample (0.7Mg 4 Nb 2 O 9 -(0.3-x)ZnAl 2 O 4 -xTiO 2) with x = 0.15−0.2 exhibited dielectric constants of 13–14, larger than those of ZnAl 2 O 4 , Mg 4 Nb 2 O 9 and Mg 5 Nb 4 O 15 , due to the NbO 6 octahedra distortion resulting from the substitution of Al3+/Ti4+ for Nb5+ in Mg 4 Nb 2 O 9 and Mg 5 Nb 4 O 15. The long-range order of the NbO 6 octahedra was enhanced by co-doping ZnAl 2 O 4 and TiO 2 , thereby enhancing the Qxf value. A dielectric constant of 13.1, Qxf value of 366,000 GHz and a τ f of −60.8 ppm/°C were obtained from 1300 °C sintered 0.7Mg 4 Nb 2 O 9 -0.15ZnAl 2 O 4 -0.15TiO 2. These results show that 0.7Mg 4 Nb 2 O 9 -0.15 ZnAl 2 O 4 -0.15TiO 2 ceramic is a good candidate for microwave electronic device applications. [ABSTRACT FROM AUTHOR]

ZnAl 2 O 4 nanocrystalline particles were prepared using the solution combustion method using a new combustion fuel, Leucine. The prepared samples' structural, microstructural–elemental composition, and optical characteristics were investigated using XRD, SEM-EDS, and UV–Visible spectroscopy. As-synthesized ZnAl 2 O 4 nanoparticles are polycrystalline, with no secondary phases, and crystallized in a cubic - spinel structure. The polycrystalline nature of the prepared sample is due to the exothermicity of fuel and oxidizer, which demonstrate that the fuel utilized (Leucine) provided adequate energy for the production of nanoparticles in their as-synthesized form, as supported by adiabatic temperature through thermodynamic calculations. The thermodynamic calculations also include a universal method to estimate the specific heat capacity at constant pressure. Furthermore, even after 2 h of calcination at 600 °C, ZnAl 2 O 4 exhibits a single phase with no secondary phases, indicating the material stability and single-phase nature. The crystallinity of ZnAl 2 O 4 nanoparticles was observed to increase with increasing annealing temperature. SEM micrographs of as-synthesized samples exhibit the formation of dense particles, voids, and pores in the as-synthesized sample. In addition, tiny aggregates were detected on the surface of more prominent clusters, which reduced as the calcination progressed. In addition, calcined samples exhibit a greater optical reflectance than as-synthesized samples. Tauc's graphs were used to compute the optical energy bandgap. The calculated energy band gap is redshifted to that of the bulk material. The bandgap energy decreases upon calcination, suggesting that the prepared materials have a larger crystallite size or more crystallinity. Correlations were found between the T ad , and the structural and optical properties of the prepared samples. The findings suggest that Leucine could be used as a novel combustion fuel to produce crystalline ZnAl 2 O 4 nanoparticles in their as-synthesis form. [ABSTRACT FROM AUTHOR]

In this work, 4CuO-TiO2-2Nb2O5 (CTN) composite oxide was added to ZnAl2O4 as sintering aid. XRD analysis revealed that trace amount of new phases formed in the ceramic samples with CTN, which might promote the low temperature sintering of ZnAl2O4 ceramics. The sample with 2 wt% CTN addition sintered at 1125 °C can achieve the highest thermal conductivity of 8.6 W/m·K and the lowest microwave dielectric loss of 3.59 × 10−4. The sintering temperature and thermal conductivity of ZnAl2O4 ceramics decreased while the dielectric constant and loss increased with the increase of the CNT contents. ZnAl2O4 ceramics can be sintered at a low temperature of 950 °C with the CTN content increasing to 10 wt%, which make it a potential material for the low temperature co-fired ceramics (LTCC) application. [ABSTRACT FROM AUTHOR]

In this paper, high enthalpy atmospheric plasma spraying technology is used to prepare ceramic powders with ZnAl2O4 phase and TiO2 as secondary phase by solid phase reaction with nano ZnO, Al2O3 and TiO2 as raw materials. The composite ceramic coating is prepared by spray pelleting with adhesive polyvinyl alcohol (PVA). The microstructure and phase composition of AZT coating are analyzed, and the effect of spraying power on microwave dielectric properties of AZT coating is explored. The results show that the contrast powder of AZT coating has a great change, ZnAl2O4 decomposes partially in high temperature plasma flame, and TiO2 precipitates in non stoichiometric form. The dielectric property test shows that the dielectric constant ε′ of the coating increases with the increase of spraying power. The tangent value of loss angle tanδ is in the range of 0.11-0.15, it shows a trend of first increasing and then decreasing. When the power is 60 kW, the dielectric constant reaches the lowest 6.38 and the loss tangent reaches the lowest 0.11. [ABSTRACT FROM AUTHOR]

In this paper, ZnAl2O4 powders were synthesized by molten salt method at 800 ~ 1 200 ℃ for 3 h in the mixed molten salt medium of KCl and LiCl using Al(OH)3, calcined Al2O3 and nano-Al2O3 as different aluminum sources respectively. The effects of aluminum source types on the synthesis temperature, phase composition and microstructure of the synthesized products were mainly analyzed by XRD, SEM, laser particle size analysis, and specific surface analysis. On this basis, the effects of reaction temperature and the mass ratio of molten salt to raw material (Ws / Wr) on the synthesis of ZnAl2O4 powders were discussed. The results show that the type of aluminum source significantly affect the formation temperature of ZnAl2O4 and powder performances. Compared with calcined Al2O3, the speed of ZnAl2O4 formation is faster with Al(OH)3 and nano-Al2O3 as the aluminum sources, and the pure phase ZnAl2O4 can be synthesized at 900 ℃. When calcined Al2O3 is used as an aluminum source, and the Ws / Wr ratio is 3∶1, the as-synthesized ZnAl2O4 powder exhibits best dispersibility, but higher temperatures easily lead to the agglomeration of powders. The formation of ZnAl2O4 can be promoted by the appropriate Ws / Wr ratio, and the particle size is the smallest when the Ws / Wr ratio is 4∶1. The ZnAl2O4 still retains the initial size and morphology of original Al2O3 raw material, indicating that the synthesis of ZnAl2O4 by molten salt method is mainly followed the "template synthesis mechanism". [ABSTRACT FROM AUTHOR]

Highly efficient photocatalytic degradation of Congo red dye under simulated sunlight irradiation was achieved on a ZnAl2O4/15%CeO2 photocatalyst. The results of structural and functional group characterization of ZnAl2O4/CeO2 photocatalyst shows that the sample only contain X-ray diffraction peaks of ZnAl2O4 and CeO2, no other impurities, which can increase light absorption capacity, increase specific surface area and suppress charge recombination than that of single phase of ZnAl2O4 or CeO2. Compared to pure ZnAl2O4 and CeO2 or ZnAl2O4/5%CeO2 and ZnAl2O4/10%CeO2 composites, the ZnAl2O4/15%CeO2 photocatalyst exhibited substantially improved simulated sunlight photocatalytic activity for photocatalytic degradation of Congo red dye under simulated sunlight irradiation, with the optimal dye concentration of 25 mg/L, optimal catalyst content of 50 mg/L and optimal pH value of 3 were obtained. The enhanced photocatalytic activity of ZnAl2O4/15%CeO2 photocatalyst can be attributed to the synergistic effect of light absorption capacity, specific surface area, and active site. Finally, the photocatalytic mechanism of ZnAl2O4/CeO2 photocatalyst was proposed on the basis of energy band theory and characterization results. [ABSTRACT FROM AUTHOR]

In this study, we report the photodegradation of a pharmaceutical pollutant namely the tetracycline (TC) onto the spinel ZnAl2O4. The semiconductor ZnAl2O4 was synthesized by chemical route and characterized by X-ray diffraction, scanning electron microscopy and optical analysis. The capacitance potential (C−2–E) measurements showed that the oxide exhibit n-type conduction, supported by a negative thermo-power. The degradation of TC was performed by combined adsorption/photocatalysis processes. The result showed that 30 min of contact time was sufficient to reach 42% of the adsorption capacity; the photodegradation rate of TC was evaluated on ZnAl2O4 under optimal operating parameters pH ~ 4.4, catalyst dose (1 g/L), and initial TC concentration (20 mg/L). The kinetic shows that the TC disappears almost completely (92%) and follows a second order model with a half photocatalytic lifetime of 21 min for a TC concentration of 20 mg/L. The mechanism of the antibiotic tetracycline photodegradation on ZnAl2O4 indicated that the O 2 · - radicals and the holes are mainly responsible for the oxidation of TC. The process can be qualified as clean remediation and is a part of a sustainable development perspective. [ABSTRACT FROM AUTHOR]

In this study, well-separated Fe-doped ZnAl2O4 nanosheets were synthesized by a co-precipitation assisted hydrothermal method (220 °C). The as-synthesized nanosheets were characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV- diffuse reflectance spectroscopy and vibrating sample magnetometer studies. The diffraction patterns reveal that there is no noticeable effect of doped Fe ions on the crystal structure of ZnAl2O4. This also confirms the crystallinity and pure spinel structure formation. In addition, no characteristic diffraction peaks related to any impurity, cluster formation, or secondary phase of Fe were detected. The XPS spectra of Fe-doped ZnAl2O4 confirms the presence target elements such as Zn, Al, O, and Fe. It is also confirmed the existence of mixed oxidation states, i.e., Fe2+ and Fe3+, in the optimized sample ZAO-Fe-3 (i.e., 3% of Fe ions doped ZnAl2O4). TEM images of pure ZnAl2O4 show a micro-hexagonal structure, whereas the Fe-doped ZnAl2O4 exhibits nanosheet-like structure. DRS analysis confirms that Fe doping modifies the bandgap energy of ZnAl2O4 with increasing Fe content. The M–H hysteresis curves of Fe-doped ZnAl2O4 exhibited clear room temperature ferromagnetism. [ABSTRACT FROM AUTHOR]

We implemented a simple and inexpensive aqueous sol-gel process to synthesize ZnAl2O4 nanoparticles to study its potential application as a gas sensor. Compared to traditional ceramic methods, the synthesis was conducted at lower temperatures and reaction times (5 h from 200 °C). The crystalline evolution of the oxide was investigated. The effect of the calcination temperature (200–1000 °C) on the crystallites’ size (16–29 nm) and the ZnAl2O4 powder’s surface morphology was also analyzed. Measurements confirmed the formation of bar-shaped granules (~0.35 μm) made up of nanoparticles (~23 nm). The surface area of the powders was 60 m2/g. Pellets were made from the powders and tested in sensing carbon monoxide and propane gases, showing a high sensitivity to such gases. The sensor’s response increased with increasing temperature (25–300 °C) and gas concentration (0–300 ppm). The oxide showed a higher response in propane than in carbon monoxide. We concluded that the ZnAl2O4 is a good candidate for gas sensing applications.

Nanostructured materials doped with Cr+3 have potential applications. However, it has been reported that heat treatment can modify the oxidation state of Cr+3, resulting in the formation of toxic Cr+6 in host matrices such as TiO 2 , Al 2 O 3 , SiO 2 , ZrO 2 , and Fe(OH) 3. The possibility of this occurrence in nanostructured ZnAl 2 O 4 :Cr+3 has not been previously considered. In this study, we report the effect of annealing temperatures within the range of 600–1300 °C on the structure, morphology, optical properties, and, more specifically, the chromium oxidation state of ZnAl 1.94 Cr 0.06 O 4 nanoparticles obtained through the coprecipitation method. The obtention of single-phase systems with a crystal size ranging from 5.25 nm to 142.75 nm was determined by X-ray diffraction and Rietveld refinement. At 800 °C, a more significant oxidation of Cr+3 was observed, evident in the increased absorption intensity of UV–vis bands associated with Cr+6 and a reduction in magnetic susceptibility at ambient temperature. At 1200 °C, a complete reduction of Cr+6 occurred, leading to the appearance of bands related to Cr+3 in the UV–vis absorption spectra and increased magnetic susceptibility; the results were confirmed by X-ray photoelectron spectroscopy. The outcomes of this study offer new insights into the thermal stability of chromium in ZnAl 2 O 4 nanoparticles. [Display omitted] • Nanoparticles of ZnCr 0.06 Al 1.94 O 4 were obtained in the range from 600 to 1300 °C. • A mixture of Cr+3 and Cr+6 is present between 600 and 1100 °C. • The presence of Cr+6 is favored at 800 °C. • At 1200 °C or higher, a genuine solid solution of ZnAl 2 O 4 :Cr+3, cr+6 free, is formed. [ABSTRACT FROM AUTHOR]

Abstract NiAl2O4, CuAl2O4, and ZnAl2O4 aluminate spinel nanoparticles were synthesized by sol-gel auto combustion method using diethanolamine (DEA) as a fuel. The effects of calcination temperature on structure, crystallinity, morphology, and optical properties of MAl2O4 (M = Ni, Cu, Zn) have been investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence (PL) spectroscopy. The XRD and FT-IR results confirm the formation of single-phase spinel structure of NiAl2O4, CuAl2O4, and ZnAl2O4 at 1200, 1000, and 600 °C, respectively. The direct band gap of these aluminate spinels, calculated from UV-DRS spectra using the Kubelka-Munk function, is found to increase with calcination temperature. The PL spectra demonstrate that NiAl2O4 gives the highest blue emission intensity, while CuAl2O4 and ZnAl2O4 exhibit a very strong violet emission. During fluorescence process, the ZnAl2O4 emits visible light in only violet and blue regions, while NiAl2O4 and CuAl2O4 emissions extend to the green region. It seems therefore that the transition metal type and intrinsic defects in these aluminate powders are responsible for these phenomena.

• Glass-ceramics containing ZnAl 2 O 4 and β-quartz solid solution nanocrystals were prepared. • Compared with the specimen with simultaneous precipitation of ZnAl 2 O 4 and β-quartz solid solution nanocrystals, glass-ceramics with sequential crystallization of ZnAl 2 O 4 and β-quartz solid solution nanocrystals show smaller grain size and more uniform structure and higher transparency. • Ion-exchange depth of layer increased significantly with the crystallization, which was related to the reduction in content of zinc and five coordinated aluminum in the residual glass matrix. • It was found that ionexchange process took place at the boundaries between nanocrystals and glass matrix, which was also considered to be responsible for the enhanced depth of layer. Crystallization of glass has significant effects on glass structure and the resultant ion-exchange behaviors. In this work, transparent glass-ceramics (GCs) with sequential crystallization of ZnAl 2 O 4 and β-quartz solid solution nanocrystals (NCs) were prepared, and effects of the crystallization on microstructure and ion-exchange properties were investigated. Compared with the specimen with simultaneous precipitation of ZnAl 2 O 4 and β-quartz solid solution NCs, GCs with sequential crystallization of ZnAl 2 O 4 and β-quartz solid solution NCs show smaller grain size and more uniform structure and higher transparency. Ion-exchange depth of layer (DOL) increases significantly with the crystallization of the specimens due to the reduction in content of zinc and five coordinated aluminum in the residual glass matrix. High residual compressive stress and Vickers hardness can be obtained after ion-exchange in KNO 3 molten salt. [ABSTRACT FROM AUTHOR]

Zn0.9Mg0.1Al2O4 + x wt.% TiO2 (0 ≤ x ≤ 3) microwave dielectric ceramics with relatively high thermal conductivity were prepared by solid-phase reaction. The effects of TiO2 on the crystal phase, micromorphology, microwave dielectric properties, and thermal conductivity of the Zn0.9Mg0.1Al2O4 ceramics were studied. X-ray diffraction analysis, scanning electron microscopy, laser flash measurements, and network analysis were used in this study. The results showed that a small amount of nonstoichiometric compounds appeared in the Zn0.9Mg0.1Al2O4 ceramics with increasing TiO2 content. At the same time, TiO2 doping promoted growth of crystal grains, opened the ion-exchange channels in the system, promoted the sintering reaction, and reduced the sintering temperature of the Zn0.9Mg0.1Al2O4 ceramics. Moreover, addition of TiO2 suppressed the microscopic lattice disorder and macroscopic segregation, leading to an improvement in the dielectric properties and thermal conductivity of the composite ceramics. The Zn0.9Mg0.1Al2O4 + 2 wt.% TiO2 ceramic sintered at 1500°C exhibited the best dielectric performance and thermal conductivity with a dielectric constant of 8.57, Q × f product of 18,0861 GHz, temperature coefficient of resonance frequency of −41.5 ppm/°C, and thermal conductivity of 19.67 W/(m K). [ABSTRACT FROM AUTHOR]

ZnO–B2O3–Na2O–Al2O3–SiO2 (ZBNAS) glass/Al2O3/AlN biphasic ceramics are prepared by a standard tape casting process and solid phase sintering. The low‐temperature co‐fired ceramic (LTCC) tapes are sintered at 850 °C for 2 h under a nitrogen atmosphere. The new phase of ZnAl2O4 is formed by the reaction between glass phase and ceramic fillers during the sintering process. The addition of AlN improves the comprehensive properties of the ZBNAS glass/Al2O3 composites. The samples with 30 wt% AlN exhibit a thermal conductivity of 5.48 W m−1 K−1, a low dielectric constant of 2.99 and a dielectric loss of 0.029 at 18 GHz, and a coefficient of thermal expansion (CTE) of 6.98 × 10−6 °C−1. The obtained composite ceramic with good comprehensive performance may be the promising candidates for high‐power devices. [ABSTRACT FROM AUTHOR]

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Magnetically recyclable Zn0.95−xCr0.05MnxAl2O4 nanoparticles were synthesized via hydrothermal and heat treatment techniques. The crystal structure, morphology, and photoelectrochemical and magnetic properties of the samples were characterized by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray energy-dispersive spectroscopy (XEDS), ultraviolet–visible (UV–Vis) spectroscopy, photoluminescence spectra (PL), vibrating-sample magnetometer (VSM), electrochemical impedance spectra (EIS) and transient photocurrent responses, and the photocatalytic activity of the samples were evaluated by the photodegradation of methyl orange (MO) dye under simulated sunlight irradiation. The experimental results show that Zn0.95−xCr0.05MnxAl2O4 nanoparticles possess a cubic spinel structure without impurity phases. Cr and Mn ions are successfully substituted in the lattice site of Zn2+ and enter the ZnAl2O4 matrix. The morphology of the samples exhibits irregular spherical or ellipsoid particles with small particle size and good dispersion. The average crystallite size and the bandgap decrease with an increase in Mn ion concentration. Meanwhile, the co-doped samples exhibit obvious room-temperature ferromagnetism, the photoluminescence intensity decreases and a luminescence quenching phenomenon occurs. In addition, Zn0.95−xCr0.05MnxAl2O4 nanoparticles exhibit excellent photocatalytic activity and possess better photocatalytic reusability in degradation of MO aqueous solution. [ABSTRACT FROM AUTHOR]

Low-temperature sintering of gahnite (ZnAl2O4) ceramic, which has the potential to exhibit higher thermal conductivity than alumina but sinters densely at a moderate temperature of approximately 1500°C, has been investigated. When adding only 5 wt.% Cu-Nb-O additive, the sintering temperature was lowered significantly to 960°C. The sample fired at 960°C for 2 h exhibited a relative permittivity (εr) of 9.1, a quality factor multiplied by resonant frequency (Q × f) value of 30,000 GHz (at a measurement frequency of approximately 13 GHz), and a temperature coefficient of resonant frequency (τf) of −69 ppm/K, being relatively satisfactory values. However, the thermal conductivity of the sample was 9.3 W/m-K, which exceeds that of conventional low-temperature co-fired ceramic (LTCC) materials but is only one-third of that of the pure gahnite sample (27 W/m-K). Our analysis revealed that the main cause was the incorporation of the Cu component into the gahnite lattice. These results enable the proposal of guidelines for the development of new LTCC materials with high thermal conductivity. [ABSTRACT FROM AUTHOR]

We report the preparation method and broadband emission characteristics of nickel ion-doped ZnAl 2 O 4 transparent ceramics. The transparent ceramics were prepared with melting-vaporing procedure, for the first time, to the best of our knowledge, and possesses the ultrabroad band emission spectra ranging from 1050 to 1550 nm under the excitation of a 980 nm laser. The analysis of crystal structure of this ceramics shows that the diffraction peaks of the crystal-phase match perfectly with ZnAl 2 O 4 crystal. This material shows high luminance efficiency and has great potential for broad band optoelectronic materials and devices including optical coherence tomography imaging system and optical communication measurement instruments. [ABSTRACT FROM AUTHOR]