Synthesis of Fe/ZnO composite nanocatalyst and its sonophotocatalytic activity on acid yellow 23 dye and real textile effluent

Nanocatalysts such as ZnO, Fe and Fe/ZnO composite were synthesized for better treatment of dye than the conventional treatment methods. The catalysts were characterized using SEM, EDAX, BET surface area, XRD and DRS. The degradation of acid yellow 23 dye in aqueous solution has been investigated using sonolysis, photolysis and sonophotocatalysis. The effect of different conventional operating parameters such as initial solution pH, gas purging (Argon, Oxygen, Air and Nitrogen) and H₂O₂ addition, under sonolysis (13 and 25 mm probe tip diameter) and photolysis (UV light), showed a maximum of 41 % colour removal for 0.0187 mmol/L dye solution under photolysis with 88.2 mmol/L H₂O₂ addition. Among the catalysts used, 98 % dye colour removal was obtained with 0.2 g/L Fe/ZnO composite under 60 min of sonophotolysis that had been benefitted by the synergistic effects. The HPLC spectrum of the untreated dye and treated dye supports the claim of eradication of the parent dye compound. Sonophotocatalytic treatment of real textile effluent in the presence of 6 g/L Fe/ZnO composite and 264.6 mmol/L H₂O₂ reduced the COD level from 792 to 174.4 mg/L in 240 min to meet the allowable effluent discharge standard into running water streams. The studied treatment methods were found to be effective for the degradation of acid yellow 23 dye and subsequently in real textile effluent too.     

Synthesis of acetone reduced graphene oxide/Fe3O4 composite through simple and efficient chemical reduction of exfoliated graphene oxide for removal of dye from aqueous solution

A simple and effective technique for reduction of graphene oxide at low temperature (70 °C) using acetone was reported for the first time. Magnetically recoverable acetone reduced graphene oxide (ARGO)/Fe₃O₄ composite was synthesized by uniformly decorating Fe₃O₄ on ARGO. The synthesized ARGO/Fe₃O₄ composite was characterized by the powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform-infrared spectroscopy and thermogravimetric analysis. An organic dye rhodamine 6G was used as an adsorbate for investigating the adsorption characteristics of the composite. The adsorption kinetic data were best described by the pseudo-second-order model, and equilibrium was achieved within 2 h. Dye adsorption was favored in basic conditions (pH 9–11) and governed by intraparticle diffusion process. The maximum dye adsorption on the composite was 93.37 mg/g at 293 K, and it followed the Langmuir–Freundlich model. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the dye adsorption onto composite was feasible, spontaneous and exothermic. The ARGO/Fe₃O₄ composite was easily controlled in magnetic field for desired separation, leading to an easy removal of the dye from wastewater, which holds great potential for dye decontamination.     

Ultra-sensitive room-temperature H<Subscript>2</Subscript>S sensor using Ag–In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanorod composites

Ultra-sensitive H₂S sensors operated at room temperature were fabricated using Ag–In₂O₃ nanorod composites synthesized using sol–hydrothermal method followed by NaBH₄ reduction process. TEM proved that the In₂O₃ was nanorod structures of?~?110 nm in length and?~?35 nm in diameter. Ag nanoparticles with diameters from 10 to 15 nm homogeneously decorated on the surfaces of the In₂O₃ naonorods. XRD and XPS analysis proved that the Ag elements existed as zero-valent metallic silver on the surface of the In₂O₃ nanorods. Ag nanoparticles could enhance the formation of chemisorbed oxygen species and interactions between H₂S molecules and oxygen species due to spillover effect, and the electron transfer between Ag and In₂O₃ nanorods also enhanced the sensing properties. Therefore, the H₂S sensors based on the Ag–In₂O₃ nanorod composites showed significantly improved sensing performance than those based on the pure In₂O₃ nanorods. The optimized content of Ag nanoparticles is 13.6 wt%. Operated at room temperature, the H₂S sensors made of 13.6 wt% Ag–In₂O₃ nanorod composites exhibited an ultra-high response of 93719 to 20 ppm H₂S and a superior detection limit of 0.005 ppm. The sensor also showed good reversibility, good selectivity, excellent reproducibility and stability for detection of H₂S gas.     

Quaternary co-electrodeposition of the Cu2ZnSnS4 films as potential solar cell absorbers

Cu₂ZnSnS₄ (CZTS) films are successfully prepared on Mo substrate by electrochemical epitaxial method. An electrolyte contains 0.124 M CuSO₄·5H₂O, 0.14 M ZnSO₄, 0.13 M SnCl₂·2H₂O, 0.16 M Na₂S₂O₃·5H₂O, 2.25 M NaOH, 1.36 M C₆H₅Na₃O₇, 1.00 M C₄H₆O₆. The equilibrium potential for quaternary co-electrodeposited solution is set at ?1.1 ～ ?1.20 V. The results show that elements are deposited in the following sequence: Cu/S/Zn/S/Cu/S/Sn/S…. The ternary and quaternary compounds are formed with the increasing temperature during annealing. Finally the CZTS film can be well formed at 550 °C. The resistivity of CZTS is about 5.6 × 10⁴ Ω cm.     

Biomimetic fabrication of α-Fe2O3 with hierarchical structures as H2S Sensor

A facile sol–gel method is developed for the fabrication of α-Fe₂O₃ with quasi-honeycomb like structures inherited from Papilio paris butterfly wings. The exquisite hierarchical architecture is faithfully maintained in α-Fe₂O₃ from the skeleton of butterfly wings at the levels from macro to nano-scales. When used as a chemical sensor, the obtained α-Fe₂O₃ replica (P-α-Fe₂O₃) showed a much higher performance than that of the compared α-Fe₂O₃ nanoparticles synthesized under the same condition without biotemplate (S-α-Fe₂O₃). The P-α-Fe₂O₃-based sensor has a sensitivity of 19.2–50 ppm H₂S, which is four times more than that of S-α-Fe₂O₃, accompanied by a rapid response/recovery time within 1/10 s even at a relatively low working temperature of 180 °C. Compare to the S-α-Fe₂O₃, surface area of which cannot be detectable, the high sensing feature of P-α-Fe₂O₃ would be attributed to the relatively high-specific surface area 24.12 m²/g thus fabricated together with the unique 3D-network structures, which provide channel for the diffusion of H₂S. This strategy is expected to be used in fabrication of other kinds of metal oxide with unique structures for the potential application in gas sensor.     

Cerium ion redox system in CeO2–xFe2O3 solid solution at high temperatures (1,273–1,673 K) in the two-step water-splitting reaction for solar H2 generation

CeO₂–xFe₂O₃ (x = 0.026–0.214) solid solutions with different Ce:Fe mole ratios (Ce:Fe = 9.5:0.5–7.0:3.0) were prepared as reactive ceramics with the combustion method for solar hydrogen production. The prepared CeO₂–xFe₂O₃ solid solutions were characterized by X-ray diffractometry, ICP atomic emission spectrometry, and Mössbauer spectroscopy. Two-step water-splitting reaction with the CeO₂–xFe₂O₃ solid solution proceeded at 1,673 K for the O₂-releasing reaction and at 1,273 K for the H₂-generation reaction by irradiation of an infrared imaging lamp as a solar simulator. The amounts of H₂ gas evolved in the H₂-generation reaction with CeO₂–xFe₂O₃ solid solutions were 0.97–1.8 cm³/g, the evolved H₂/O₂ ratio was approximately equal to 2 of the stoichiometric value. The amounts of H₂ and O₂ gases were independent of the Ce:Fe mole ratio in the CeO₂–xFe₂O₃ solid solution. It was suggested that the O₂-releasing and H₂-generation reactions with the CeO₂–xFe₂O₃ solid solution were repeated with the reduction and oxidation of Ce⁴⁺–Ce³⁺ enhanced by the presence of Fe³⁺–Fe²⁺.     

Aqueous synthesis of CdSe and CdSe/CdS quantum dots with controllable introduction of Se and S sources

A new and convenient route is developed to synthesize CdSe and core–shell CdSe/CdS quantum dots (QDs) in aqueous solution. CdSe QDs are prepared by introducing H₂Se gas into the aqueous medium containing Cd²⁺ ions. The synthesized CdSe QDs are further capped with CdS to form core–shell CdSe/CdS QDs by reacting with H₂S gas. The gaseous precursors, H₂Se and H₂S, are generated on-line by reducing SeO₃ ^2? with NaBH₄ and the reaction between Na₂S and H₂SO₄, and introduced sequentially into the solution to form CdSe and CdSe/CdS QDs, respectively. The synthesized water-soluble CdSe and CdSe/CdS QDs possess high quantum yield (3 and 20 %) and narrow full-width-at-half-maximum (43 and 38 nm). The synthesis process is easily reproducible with simple apparatus and low-toxic chemicals. The relatively standard deviation of maxima fluorescence intensity is only 2.1 % (n = 7) for CdSe and 3.6 % (n = 7) for CdSe/CdS QDs. This developed route is simple, environmentally friendly and can be readily extended to the large-scale aqueous synthesis of QDs.     

Oxygen storage and release behavior of delafossite-type CuFe1−x Al x O2

Delafossite-type solid solution, CuFe_1?x Al _x O₂, was synthesized and its oxygen storage capacity (OSC) was investigated under oxidation/reduction cycle using a pulse injection method. CuFe_1?x Al _x O₂ was synthesized by heating at 1100–1150 °C in N₂ flow. OSC values for x = 0.1 and 0.3 were larger than that for x = 0 above 500 °C, indicating that substitution of Fe³⁺ by Al³⁺ improved OSC. For x = 0.5–1.0, temperature at which OSC increased steeply shifted upward. Results of X-ray diffraction (XRD) after the thermogravimetry and differential thermal analysis (TG–DTA) measurement in air for CuFe_1?x Al _x O₂ (x = 0–0.7) indicated that oxidative decomposition of delafossite phases to CuO and spinel-type phase occurred. In addition, Cu reduction temperature estimated by the temperature programmed reduction using H₂ (H₂-TPR) shifted to higher temperature with increasing Al content. The XRD results of the samples after H₂ and O₂/He pulse injection suggested that the oxygen storage/release behavior was caused by reversible oxidation/reduction process between CuFe_1?x Al _x O₂ delafossite and (Fe_1?x Al _x )₃O₄ spinel phase +Cu.     

Evaluation of magnetic nanoparticles performance as photocatalyst for the catalytic treatment of direct red 28 dye in synthetic and real water effluents

Integrated water resources management practice is gaining popularity as an alternative water source due to the limited supply of freshwater. The present study was carried out on the photocatalytic degradation of Direct red 28 (DR-28) dye using magnetic nanoparticles (MNPs; Fe₃O₄) as a photocatalyst. The study was conducted on the photocatalytic degradation of DR-28 dye in synthetic dye effluent water, to understand the effects of different photoreaction parameters on the degradation kinetics. The influence of different parameters such as time, amount of photocatalyst, concentration of H₂O₂ and pH was investigated. At the optimum dosage of MNPs (0.6?g/L) with 4?mmol/L of H₂O₂, significant photocatalytic degradation of DR-28 dye (93.2%) was observed. The kinetic study revealed that the photocatalytic degradation followed pseudo-first-order kinetics. The degradation performance of Fe₃O₄ nanoparticles as a photocatalyst for DR-28 dye was compared with titanium dioxide (TiO₂) and it was found that the performance of Fe₃O₄ as a photocatalyst is superior to TiO₂ photocatalyst. The real dye effluent was also degraded at optimum conditions and promising results were achieved.     

Influence of hydrothermal treatment on the microstructure and oxidation resistance of a Zn4B2O7·H2O (4ZnO·B2O3·H2O) coating for C/C composites

Antioxidant modification for C/C composites by in situ hydrothermal synthesise at 140 °C of a 4ZnO·B₂O₃·H₂O crystallite coating has been successfully achieved. The influence of hydrothermal time on the phase composition, microstructure of the as-prepared Zn₄B₂O₇·H₂O (4ZnO·B₂O₃·H₂O), and its antioxidant modification for C/C composites were investigated. Samples were characterised by XRD, SEM, isothermal oxidation test and TG-DSC. Results show that, 4ZnO·B₂O₃·H₂O crystalline coating is achieved on the surface of C/C composites after the hydrothermal treatment at 140 °C for time in the range of 2–12 h. A smooth and crack-free 4ZnO·B₂O₃·H₂O layer can be obtained when the hydrothermal time reaches 8 h. Isothermal oxidation test demonstrates that the oxidation resistance of C/C composites is improved. The as-modified composites exhibit only 1.52 g·cm^?2 weight loss after oxidation at 600 °C for 15 h, while the non-modified one shows a 6.57 g·cm^?2 weight loss after only 10 h oxidation. For the uncoated C/C composite the oxidation rate is approximately linear with time (non-protective oxidation), thus at 15 h exposure one can estimate the mass loss to be 6.57 g·cm^?2 after 10 h for direct comparison with the coated samples.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Thermal,structural and in vitro dissolution of antimicrobial copper-doped and slow resorbable iron-doped phosphate glasses

This paper focuses on investigating and comparing the effects of CuO and Fe₂O₃ addition on the bioactive response of glass having composition [xCuO or Fe₂O₃ + (100 ? x) (0.2CaO + 0.2SrO + 0.1Na₂O + 0.5P₂O₅)] (in mol%), where x is ranging from 0 up to 5. The addition of CuO was found to increase the hot processing window and the dissolution rate leading to a fast surface layer precipitation. Using IR and Raman spectroscopies, we related this change in the bioactive response of this glass to the progressive depolymerization of the glass network induced by the addition of CuO. On the other hand, the addition of Fe₂O₃ was found to reduce the hot processing window and the dissolution rate as no depolymerization of the network occurs due to the formation of P–O–Fe bonds at the expense of P–O–P bonds. All the glasses were found to dissolve congruently and in a controlled manner. Finally, the antimicrobial properties of the copper-doped glasses were examined and compared to bioactive glasses which are known to exhibit good antimicrobial properties. The CuO addition leads to higher antimicrobial properties than the commercial bioactive glass S53P4 and total bacterial elimination could be obtained.     

Study of the electrochemical oxidation and reduction of C.I. Reactive Orange 4 in sodium sulphate alkaline solutions

Synthetic solutions of hydrolysed C.I. Reactive Orange 4, a monoazo textile dye commercially named Procion Orange MX-2R (PMX2R) and colour index number C.I. 18260, was exposed to electrochemical treatment under galvanostatic conditions and Na₂SO₄ as electrolyte. The influence of the electrochemical process as well as the applied current density was evaluated. Ti/SnO₂–Sb–Pt and stainless steel electrodes were used as anode and cathode, respectively, and the intermediates generated on the cathode during electrochemical reduction were investigated. Aliquots of the solutions treated were analysed by UV–visible and FTIR-ATR spectroscopy confirming the presence of aromatic structures in solution when an electro-reduction was carried out. Electro-oxidation degraded both the azo group and aromatic structures. HPLC measures revealed that all processes followed pseudo-first order kinetics and decolourisation rates showed a considerable dependency on the applied current density. CV experiments and XPS analyses were carried out to study the behaviour of both PMX2R and intermediates and to analyse the state of the cathode after the electrochemical reduction, respectively. It was observed the presence of a main intermediate in solution after an electrochemical reduction whose chemical structure is similar to 2-amino-1,5-naphthalenedisulphonic acid. Moreover, the analysis of the cathode surface after electrochemical reduction reveals the presence of a coating layer with organic nature.     

Enhanced electrochemical reduction of hydrogen peroxide by Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowire electrode

Crystalline Co₃O₄ nanowire arrays with different morphologies grown on Ni foam were investigated by varying the reaction temperature, the concentration of precursors, and reaction time. The Co₃O₄ nanowires synthesized under typical reaction condition had a diameter range of approximately 500–900 nm with a length of 17 µm. Electrochemical reduction of hydrogen peroxide (H₂O₂) of the optimized Co₃O₄ nanowire electrode was studied by cyclic voltammetry. A high current density of 101.8 mA cm^?2 was obtained at ?0.4 V in a solution of 0.4 M H₂O₂ and 3.0 M NaOH at room temperature compared to 85.8 mA cm^?2 at ?0.35 V of the Co₃O₄ nanoparticle electrode. Results clearly indicated that the Ni foam supported Co₃O₄ nanowire electrode exhibited superior catalytic activity and mass transport kinetics for H₂O₂ electrochemical reduction.     

Effect of Additives on Calcium Sulfate Hemihydrate Whiskers Morphology from Calcium Sulfate Dehydrate and Phosphogypsum

The influence of P₂O₅ on the whiskers morphology of CaSO₄ · 0.5H₂O was discussed by using CaSO₄ · 2H₂O as raw materials and the hydrothermal process at 140°C for 2 h. The result indicated whiskers were obtained by adding 0.2% P₂O₅, with a smooth surface, uniform diameter (～1–3 µm), and an aspect ratio of about 45. The aspect ratio of whiskers decreased as the addition amount of P₂O₅ increased. Raw phosphogypsum (PG) was ground by using a planetary ball mill and then washed using distilled water in order to reduce the P₂O₅ content. Washed PG constituted ～50% of the sample, with an agglomerate size of 32.6 µm, and contained 0.43 wt% P₂O_5. The influence of glycerol on the morphology of CaSO₄ · 0.5H₂O whiskers was investigated by also using the hydrothermal method. The aspect ratio of whiskers first increased and then decreased while the amount of glycerol increased. The whiskers were also prepared by using added 1.3 wt% calcium oxide (CaO) PG at 140°C for 2 h and the effect of phosphorus on whiskers growth can be decreased.     

The characterization and preparation of core–shell structure particles of carbon-sphere@NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>@PPy as microwave absorbing materials in X band

An excellent PPy/NiFe₂O₄/CS microwave absorbing materials with a three-layer core–shell structure, was synthesized successfully by two reaction steps of solvothermal reaction and in situ polymerization. The surface morphology, phase structure and chemical components of the composite have been characterized by a scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscope. The results suggest that the surface of CS is covered by NiFe₂O₄ completely and PPy wraps the obtained NiFe₂O₄/CS successfully. The conductivity and the saturation magnetization (Ms) of the resulting PPy/NiFe₂O₄/CS composites are 0.38 S/cm and 46 emu/g, respectively. The vector network analysis shows the composite performs better microwave absorbing ability than that of CS and NiFe₂O₄/CS. The maximum reflection loss of the composite with 1.97 mm coating thickness is ?53 dB at 10.5 GHz and the bandwidth of reflection loss less than ?10 dB is 3.4 GHz (8.9–12.3 GHz). This ternary composite with light weight, thin thickness and strong absorbing capacity can be an attractive candidate in the field of microwave absorption.     

Application of BICOVOX catalyst for hydrogen production from ethanol

Catalytic activity of cobalt-doped bismuth vanadate [Bi₄(V_0.90Co_0.10)₂O_11?δ ; BICOVOX] powder, prepared by a solution combustion synthesis and calcined at 800 °C (BICOVOX-800), for hydrogen production using low-temperature steam reforming of ethanol, has been reported in this paper. The effects of reaction temperature (250–400 °C) and feed concentration (H₂O/EtOH = 2.5:1 and 23:1 mol ratio) on the steady-state ethanol conversion and selectivity of H₂, CO₂, CO, and CH₄ have been investigated (up to 30 h). It is observed that with an increase in reaction temperature and H₂O/EtOH mole ratio, H₂ and CO₂ selectivity increases and CO and CH₄ selectivity decreases. The maximum H₂ selectivity and ethanol conversion are observed to be 63 and 88%, respectively, for H₂O/EtOH = 23:1 mol ratio at 400 °C. The XRD results show that the fresh BICOVOX-800 has pure γ-phase and is highly crystalline. The used catalyst (more than 150 h total) is detected to have less crystallinity and to partially decompose into Bi₂O₃ and BiVO₄ phases.     

Greenhouse gases mitigation by CO<Subscript>2</Subscript> reforming of methane to hydrogen-rich syngas using praseodymium oxide supported cobalt catalyst

This study focuses on the potential of hydrogen-rich syngas production by CO₂ reforming of methane over Co/Pr₂O₃ catalyst. The Co/Pr₂O₃ catalyst was synthesized via wet-impregnation method and characterized for physicochemical properties by TGA, XRD, BET, H₂-TPR, FESEM, EDX, and FTIR. The CO₂ reforming of methane over the as-synthesized catalyst was studied in a tubular stainless steel fixed-bed reactor at feed ratio ranged 0.1–1.0, temperature ranged 923–1023 K, and gas hourly space velocity (GHSV) of 30,000 h^?1 under atmospheric pressure condition. The catalyst activity studies showed that the increase in the reaction temperature from 923 to 1023 K and feed ratio from 0.1 to 1.0 resulted in a corresponding increase in the reactant’s conversion and the product’s yields. At 1023 K and feed ratio of 1.0, the activity of the Co/Pr₂O₃ catalyst climaxed with CH₄ and CO₂ conversions of 41.49 and 42.36 %. Moreover, the catalyst activity at 1023 K and feed ratio of 1.0 resulted in the production of H₂ and CO yields of 40.7 and 40.90 %, respectively. The syngas produced was estimated to have H₂:CO ratio of 0.995, making it suitable as chemical building blocks for the production of oxygenated fuel and other value-added chemicals. The used Co/Pr₂O₃ catalyst which was characterized by TPO, XRD, and SEM-EDX show some evidence of carbon formation and deposition on its surface.     

CeO<Subscript>2</Subscript> and Co<Subscript>3</Subscript>O<Subscript>4</Subscript>–CeO<Subscript>2</Subscript> nanoparticles: effect of the synthesis method on the structure and catalytic properties in COPrOx and methanation reactions

CeO₂ and Co₃O₄–CeO₂ nanoparticles were synthesized, thoroughly characterized, and evaluated in the COPrOx reaction. The CeO₂ nanoparticles were synthesized by the diffusion-controlled precipitation method with ethylene glycol. A notably higher yield was obtained when H₂O₂ was used in the synthesis procedure. For comparison, two commercial samples of CeO₂ nanoparticles (Nyacol^®)—one calcined and the other sintered—were also studied. Catalytic results of bare CeO₂ calcined at 500 °C showed a strong influence of the method of synthesis. Despite having similar BET area values, the CeO₂ synthesized without H₂O₂ was the most active sample. Co₃O₄–CeO₂ catalysts with three different Co/(Co + Ce) atomic ratios, 0.1, 0.3, and 0.5, were prepared by the wet impregnation of the CeO₂ nanoparticles. TEM and STEM observations showed that impregnation produced mixed oxides composed of small CeO₂ nanoparticles located both over the surface and inside the Co₃O₄ crystals. The mixed oxide catalysts prepared with a cobalt atomic ratio of 0.5 showed methane formation, which started at 200 °C due to the reaction between CO₂ and H₂. However, above 250 °C, the reaction between CO and H₂ became important, thus contributing to CO elimination with a small H₂ loss. As a result, CO could be totally eliminated in a wide temperature range, from 200 to 400 °C. The methanation reaction was favored by the reduction of the cobalt oxide, as suggested by the TPR experiments. This result is probably originated in Ce–Co interactions, related to the method of synthesis and the surface area of the mixed oxides obtained.     

Phase structure and microwave dielectric properties of Mn-doped (1−x)ZrTi2O6–xZnNb2O6(x = 0.13–0.53) ceramics

(1?x)ZrTi₂O₆–xZnNb₂O₆(x = 0.13–0.53) ceramics doped with 0.7 wt% MnCO₃ were prepared by solid-state reaction and they were all sintered well in air at 1,270 °C. XRD analysis suggested there were a two-phase region for ZrTi₂O₆–TiO₂(x = 0.20–0.33) and a single-phase region for ZrTi₂O₆(x = 0.40–0.53) because (Zn_1/3Nb_2/3)⁴⁺ preferentially substituted Ti⁴⁺ sites, and thereafter Zr⁴⁺ sites. The addition of Mn, working as acceptors to receive the electrons left by the lost oxygen, raised the Q × f value dramatically. For 0.7 wt% MnCO₃ doped (1?x)ZrTi₂O₆–xZnNb₂O₆ ceramics, with the increase of x, the ε_r and the τ_f dropped from 53.4 to 41.0 and from +95 ppm/°C to ?35 ppm/°C respectively, and the Q × f value increased from 26,300 GHz to 48,100 GHz. At last, 0.69ZrTi₂O₆–0.31ZnNb₂O₆+0.7 wt % MnCO₃ ceramics showed excellent dielectric properties: ε_r = 45.3, Q × f = 43,300 GHz and τ_f = ?0.5 ppm/°C. Another advantage is that the sintering atmosphere was in air, which is benefit to the commercial application.