This study deals with the effects of Bi doping on the structural, optical, dielectric, and electrical properties for ZnO nanoparticles synthesized by the sol–gel method. X-ray diffraction measurements revealed that all samples crystallized with a hexagonal wurtzite structure, and, as the Bi concentration increased from 0 mol% to 7 mol%, the crystallite size increased from 36.10 nm to 47.78 nm. Scanning electron microscopy observation showed that the morphology of ZnO particles is affected by the Bi doping concentration, forming spherical and rod-shaped particles. The optical band gap for the samples determined by UV–Visible spectra gradually decreased from 3.257 eV to 3.065 eV with the Bi content increasing. Impedance analysis showed only one semicircle in all the samples, indicating that the contribution of grain boundaries is greater than that of the grains. The dielectric properties of ZnO were improved by doping Bi, the dielectric loss was significantly reduced from 10.4 to 0.2, and the dielectric constant stabilized at around 180 in the high-frequency region. It was also found that the conductivity was improved by doping Bi, with the highest conductivity corresponding to the 5% Bi content. Additionally, the 5% Bi-doped ZnO has the best dielectric properties, with a dielectric constant of 180 and a dielectric loss lower than 0.2 within the temperature range of 100–200°C at an operating frequency of 1 MHz. These results suggest that Bi-doped ZnO nanocrystals may be promising candidates for dielectric applications.

In this study, we report on the humidity-sensing behavior of Al-doped SnO 2 materials to evaluate the effect of Al on enhanced sensing performance and propose a structural defects-dominating sensing mechanism of SnO 2 . The diffractograms peaks are found to be broadened and shifted upon doping with the Al, reflecting the successful substitution of the Al. The variations of the UV band gap values regulate the concentration of electrons in the conduction band, which has significant implications for the electrical performance. The PL spectroscopy indicates the occurence of the lattice defects with the Al concentration increasing. Furthermore, Al-doped SnO 2 humidity sensor exhibits better hysteresis and response properties as the introduction of Al modifies inner structure of SnO 2 . The possible chemical mechanisms for the enhancement on the humidity sensitivity induced by the surface defects in the prepared Al doping SnO 2 materials is also proposed.

This study investigated the effects of N doping on the structural, optical, dielectric and electrical properties for ZnO nanoparticles synthesized via a sol–gel method. X-ray diffraction revealed that all samples crystallized in the hexagonal wurtzite structure and crystallite size decreased from 30.36 to 26.18 nm with increasing N content from 0 to 20

The present investigation reports the variations of the microstructure and electrical properties due to a change in the ZnSb2O6 content of ZnO varistors. The impact of the ZnSb2O6 additive on both microstructure and electrical properties in ZnO varistors is studied via the X-ray diffraction (XRD) and an impedance analyzer. Zn7Sb2O12 spinel phase and single hexagonal ZnO phase are detected in ZnO varistors with the addition of ZnSb2O6. The ZnO varistors with 5 mol% ZnSb2O6 have the highest nonlinear coefficient (43.2) and the lowest leakage current density (3.96 A cm(-2)). The resistivity of grain boundary rho(gb) increases continuously with the increasing content of ZnSb2O6 as demonstrated by impedance measurements. Additionally, low values of dielectric loss at high frequencies suggest a ZnO varistor doped with ZnSb2O6 is suitable for high frequency device applications.

The low-melting Bi2O3–B2O3–SiO2–ZnO glasses doped with two different modifier oxides (BaO and MgO) are synthesized using sol-gel method. The prepared samples are characterized using various experimental techniques such as differential thermal analysis (DTA), X-ray diffraction (XRD), and the impedance instrument to study their structure, thermal, and dielectric properties. The X-ray diffraction patterns reveals the amorphous properties of all the samples, while crystallization of BaO1.3 and BaZn2Si2O7 is formed and the diffraction peaks become weak with the increase of MgO content. The porous characteristics were observed in the scanning electron microscopy (SEM) images and the pore size distribution is mainly in the meso- and macro-range. The glass transition temperature decreases from 474.4 to 471.7 °C with the increase of MgO content, while the glasses become more thermally stable against crystallization. The glass structure is shown that Bi3+ cations were incorporated in the glass structure as pyramidal [BiO3] and octahedral [BiO6] units. With the concentration of MgO increases, the [BO4] units would transform to [BO3] and form non-bridging oxygens, which may destroy the original network structure of glasses and result in the increase of dielectric loss and dielectric constant. Furthermore, the decrease in chemical stability with the content of MgO increases can be attributed to the weakening of the glass structure.

The tetragonal rutile Sb doped Sn O 2 (0, 0.5, 1 at.%) is successfully synthesized by hydrothermal method. The XRD analysis shows that the average crystallite size of SnO 2 decreases from 29.59 to 20.53 nm with the increase of the doping concentration. SEM images depict the spherical grain morphology of the SnO 2 sample. With the increase of the doping ratio, the optical bandgap value of the SnO 2 samples increases from 3.6 to 3.86 eV and then decreases to 3.47 eV, showing a trend of first increasing and then decreasing. XPS results indicate that oxygen vacancy defects and substitutional defects(Sb Sn )are formed into the SnO 2 lattice, which changes the electronic effect of Sn element to tune the oxygen vacancy concentration. The humidity‐sensitive testing data shows that 1 at.% Sb‐doped SnO 2 humidity sensor presented excellent sensitivity and linearity at a working frequency of 100 Hz as compared to the pure SnO 2 sample.

Colossal permittivity materials have aroused great interest due to their unique advantages in high-performance capacitors and micro-electronic devices. Nevertheless, the unbalance of their dielectric constant and dielectric loss impedes their application. The present work describes a study of the structure and dielectric properties of Ta 0.02 Ag x Ti 0.98- x O 2 (0 ≤ x ≤ 0.08) (TAT) ceramics synthesized through the sol–gel process and the solid-state reaction method. The impacts of (Ag, Ta) additives on the microstructure and electrical properties of the TiO 2 ceramic have been studied by x-ray diffraction, photoluminescence emission spectroscopy, and scanning electron microscopy. In the light of the experimental results, it can be concluded that the addition of Ta 5+ can restrict the solid solution limits of Ag + in TiO 2 , while second phases can form when both Ta and Ag are doped. The scanning electron microscopy images reveal that doping TAT ceramics with Ag not only increases densification but also alters the fracture surface from transcrystalline to intergranular. The co-doped samples with x ≥ 0.04 doping level exhibit colossal permittivity more than 10 4 and a dielectric loss tangent less than 2.5. The Ag dopant is discovered to have a substantial influence on the dielectric properties of Ta-doped TiO 2 ceramics. The Ta 0.02 Ag 0.08 Ti 0.9 O 2 ceramics have a dielectric permittivity of 8.5 × 10 3 (tested at 1 kHz) and a dielectric loss tangent of 1.24 (measured at 1 kHz) that meet the specifications of ceramic capacitors. The study has found that the electron-pinned defect-dipoles were responsible for the massive dielectric permittivity mechanism in co-doped TiO 2 ceramics.

Zinc oxide materials doped with different carbon contents are successfully synthesized. The results show that the synthesized samples are all ZnO with hexagonal wurtzite structure. The crystallite size increases with the increase of carbon doping. The size of the samples is about 400–500 nm, and the doped samples have the phenomenon of carbon microsphere adhesion. In addition, with the increase of carbon doping, the optical band gap value of the sample decreases from 3.16 to 2.79 eV, showing a decreasing trend. The results of Raman spectroscopy show that the increase of carbon doping can cause the crystal quality of the sample to decrease and the oxygen vacancy concentration to decrease. Photoluminescence spectroscopy finds that all ZnO samples have oxygen vacancy defects and deep‐level double ionized oxygen vacancies. The carbon‐doped samples show an increase in the proportion of interstitial zinc (Zn i ) defects and a decrease in the O Zn concentration of substitutional defects.

In this paper, the influence of Ca‐doping on microstructure and electrical characteristics of ZnO varistor ceramics is studied. With the increase of the doping concentration of calcium, the ZnO ceramics show strong directional growth along the Ca 2 MnO 3.5 phase and the intensity of the X‐ray diffraction peaks of the Ca 2 MnO 3.5 phase increase obviously, which indicates that the phase structure of ZnO ceramics is significantly affected by the calcium concentration. The average grain size of 0, 1, 2, and 3 mol% Ca‐doped ZnO ceramics is 7.2, 5.2, 4.8, and 4.2 µm, respectively, confirming the doping of Ca restrained the growth of grain in ceramics. The varistor ceramics doped with 1 mol% Ca have a density of 4.37 g cm −3 , with a nonlinear coefficient of ∼41 at room temperature. They can be used to protect the electrical circuits from over voltages in the range of 280–460 V. Moreover, the ZnO ceramics show good temperature stability and the nonlinear coefficient changes slightly when the temperature changes from 25 to 150 °C; especially for varistor ceramics with 2 mol% Ca, the nonlinear coefficient is stable at about 37.

In this study, Ag-doped titanium dioxide samples with different concentrations have been prepared by sol–sel method. The existence of anatase and rutile in Ag-doped TiO2 is proved and the mineral phase structure of the main host is determined. Furthermore, the presence of the rutile crystal phase and Ag dopants is found to be critical for enhancing the dielectric and optical properties. Infrared spectroscopy is used to identify the presence of functional groups. Ag doping turns out to reduce the band gap and increase the absorption rate by studying the optical properties of Ag-doped TiO2 powders. Based on the results, the principles of dielectric constant, dielectric loss, and AC conductivity as the function of frequency are explained in detail. The studies on the dielectric properties of Ag-doped TiO2 samples have shown that the excellent dielectric property of all samples is obtained when the molar concentration contained in the sample is 5 mol% Ag ions.

The rod-like (Bi, Co) co-doped ZnO powders were directly synthesized by refluxing method and the effect of reaction time on its structure and optical properties was explored. These powders were consolidated into dense varistors discs by compaction, sintering, and evaluated for their non-linear I – V characteristics. X-ray diffraction (XRD) results revealed that the doped ZnO nanopowders have a hexagonal wurtzite structure and the Bi 2 O 3 phase is found. The half-height width of the (002) plane of the ZnO phase decreases as the reaction time increases, which indicates the improvement of the crystal quality. Scanning electron microscope (SEM) results show that the samples present a uniform rod-like structure. As the refluxing time increases from 2 to 4 h, the average length of ZnO composites increases from 900 to 2250 nm and decreases to 530 nm for 6 h. The presence of functional groups and the chemical bonding is confirmed by Fourier transformation infrared spectra (FTIR). X-ray photoelectron spectroscopy (XPS) demonstrates that Bi element is successfully doped into ZnO in the trivalent valence state while Co element in the form of divalent and trivalent states. The Z-2 varistor ceramics sintered in air at 1200 °C for 2 h showed the highest nonlinear coefficient of 30.8 and the strongest breakdown voltage of 282.8 V/mm. These studies demonstrate the feasibility of direct synthesis of doped ZnO powders for varistor ceramics by refluxing method.

Bi2O3-SiO2-B2O3 low-melting glass powders with different Bi2O3 contents (45–60 mass%) are synthesized using sol-gel method. The structure, crystallization behavior, thermal properties, chemical stability and physical characteristics of the samples are systematically investigated. The broad peak in X-ray diffraction patterns confirms the amorphous properties of all the glass samples. The infrared absorption spectra analysis shows that [BiO3], [BiO6], [BO3] and [BO4] are the main structure units of the glass powders. The [BO3] groups are converted into more stable [BO4] groups with rising the Bi2O3 content. The glass transition temperature (Tg) decreases from 478.56 to 456.24 °C when the Bi2O3 contents increases from 45 to 60 mass%. Both the glass softening temperature (Tf) and the crystallization temperature (Tp) decline with the increase of Bi2O3 content. In addition, the results revealed that the chemical stability decreases gradually and the volume resistivity of glass powders decreases from 3.08 × 1014 Ω cm to 2.04 × 1011 Ω cm as the content of Bi2O3 increases.

B2O3 doped ZnO-BaO (ZBO) varistors, denoted as ZBO-xB2O3 (where x = 0 wt.%, 0.02 wt.%, 0.04 wt.% and 0.08 wt.% of B2O3) are successfully prepared via a sol–gel method. The effects of B2O3 additive on the microstructure, electrical properties, and stability of ZBO varistor are studied using x-ray diffraction, ultraviolet–visible spectroscopy (UV–Vis), and field emission scanning electron microscopy. A single hexagonal ZnO phase is detected in ZBO-xB2O3 with B2O3 added. Secondary phase Zn5B4O11 that is formed after adding B2O3 can replace other secondary phases in the samples. The average grain size increases from 11.71 µm to 37.56 µm as the B2O3 content increases from 0 wt.% to 8 wt.%. The band gap of the as-prepared ZBO-xB2O3 increases gradually from 3.01 eV to 3.14 eV with increasing B2O3 contents. It is shown that ZBO-0.02B2O3 possesses the highest nonlinear coefficient of 49.2, while ZBO-0.04B2O3 exhibits the lowest leakage current density of 3.922A/cm2. Furthermore, ZBO-0.04B2O3 is able to demonstrate the best frequency stability, while ZBO-0.02B2O3 displays the best temperature stability. Thus, based on the collective results, adding an appropriate amount of B2O3 to ZBO varistor can enhance its performance in all aspects.

The effects of ammonium polycarboxylate (AMP) on the dispersion of zinc oxide nanopowders were investigated in this study. Good dispersibility and stability in ZnO suspension with a dispersant content of 0.5 wt.% at pH 10 was observed by field emission scanning electron microscopy, and was confirmed by sedimentation experiments. The adsorption state of AMP on the surface of nano-sized ZnO powder was examined by Fourier transform infrared spectroscopy. For the ZnO nanopowders with various AMP amounts in the alkaline region, a maximum absolute zeta potential of 55.8 mV was measured at pH 10, which correlated well with the saturation amount of adsorbed AMP. Compacted varistor discs were prepared from the nano-origin ZnO powders before and after AMP absorption, showing sintered densities of 97.6% and 98.4%, respectively. The advantages of AMP were clearly seen in grain structuring, in addition to the enhanced densification and homogeneous microstructures for obtaining a high nonlinear coefficient.

The ZnO-Bi 2 O 3 -MnO 2 -Co 2 O 3 -based (ZBMCO) varistors were prepared via the sol–gel method. The effects of B 2 O 3 additive on the phase composition, microstructure, sintering temperature and electrical properties of the ZBMCO ceramics were studied. A single hexagonal ZnO phase was detected in all ZBMCO- x B 2 O 3 varistors sintered at high temperature (1100°C). Secondary phases Mn 0.31 Bi 1.69 O 2.85 , Zn 3 B 2 O 6 , Bi 24 B 2 O 39 and Bi 2 O 3 were detected in ZBMCO-1.0 wt.%B 2 O 3 varistors at a lower sintering temperature (900°C, 1000°C). The average grain size increased remarkably in the range of 15.27–26.12 μ m with an increase of the B 2 O 3 content. The ZBMCO-1.0 wt.%B 2 O 3 varistor showed the maximum relative density of 97.2% with high nonlinear coefficient (56.5) and low leakage current (0.07 μ A/cm 2 ) at 1100°C. The E 1mA decreased noticeably from 865 V/mm to 64 V/mm with an increase of the sintering temperature. When the sintering temperature is lower at 1000°C, the varistor exhibits relatively good electrical properties ( α = 48.7, I L = 0.68 μ A/cm 2 ). These results demonstrate that low melting point B 2 O 3 plays multiple roles in grain growth and microstructure.

The organic-inorganic hybrid material originated from metal-lophthalocyanine and layered double hydroxide has been identified as bifunctional catalyst for the oxidation of ethylbenzene to acetophenone. The hybrids exhibited excellent catalytic activity in the selective oxidation through O-2/NHPI (N-hydroxyphthalimide) system with excellent selectivity of acetophenone. The hybrid could accelerate not only the formation of hydroperoxide, but also the decomposition of hydroperoxide. Further, the catalyst also exhibited high activity in the transformation of 1-phenylethanol to acetophenone. The present catalytic system could also catalyze the aerobic oxidation of varied alkyl arenes under the optimized reaction conditions. A series of controlled experiments suggested that the basicity of the hybrid benefited for the catalytic activity, and synergistic effect might exist between the basicity and the activity of metal-lophthalocyanine during the oxidation. On the basis of obtained results and Hammett experiment, a possible mechanism of the oxidation of ethylbenzene under the hybrid in the presence O-2/NHPI has been proposed.

Ce-doped Bi 2 O 3 nanopowders were prepared by reverse titration chemical coprecipitation from Bi 3+ and Ce 4+ containing aqueous solution. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the as-synthesized materials. The XRD patterns indicated that the peaks can be easily indexed to β-Bi 2 O 3 and no diffraction peaks of Ce or other impurity phases were detected in the prepared samples. The calculated average crystalline size decreased from 31.72 to 11.96 nm when the Ce content increased from 1 wt% to 10 wt%. The morphology changed from flake-like into the spherical-like with increase in Ce content. The electric conductivity of Ce-doped Bi 2 O 3 electrolyte was also investigated by two probe DC method. Conductivity analysis exhibited that the rate of conductivity increased with increasing Ce 2+ ratio, when the Ce concentration was up to 5 wt%, the as-synthesized Ce-doped Bi 2 O 3 electrolyte showed the maximum value of conductivity(0.295 S·cm –1 ).

In this article, monodisperse ZnO composite nanoparticles were successfully prepared by sol–gel mixed precursor method. Subsequently, carbon as the shell was homogeneously coated on the surface of the ZnO composite nanoparticles via a simple adsorption and calcination process. Microstructural studies of the as-obtained powders were carried out using the techniques of the x-ray powder diffraction, scanning electron microscopy, field emission scanning electron microscopy, transmission electron microscopy with energy dispersive x-ray spectroscopy, and Fourier transform infrared spectroscopy. The results show that the pink ZnO composite powders were fully coated by carbon. Based on the results, the effect of glucose content on the microstructure of the synthesized composites and the electrical properties of the ZnO varistors sintered in air at 1150°C for 2 h were also fully studied. As the amount of glucose increased, the thickness of carbon can be increased from 2.5 nm to 5 nm. In particular, the ZnO varistor fabricated with the appropriate thickness of the carbon coating (5 nm) leads to the superior electrical performance, with present high breakdown voltage (V b = 420 V/mm) and excellent nonlinear coefficient (α = 61.7), compared with the varistors obtained without carbon coating.

Varied metallophthalocyanine intercalated layered double hydroxides (LDHs) as bifunctional hybrid catalysts for selective epoxidation have been prepared and characterized. Systematic characterizations suggested the successful intercalation of the metallophthalocyanines into the interlayer of ZnAl LDHs. The synthesized hybrid exhibited excellent catalytic activity in the selective epoxidation of various olefins through O2/isobutaldehyde system. The basicity of the hybrid benefits to the selectivity of epoxide, and the bifunctional roles of the catalyst in the reaction have been discussed and verified by a series of controlled experiments. On the basis of obtained results, a probable mechanism of the epoxidation by the hybrid has been proposed and detailedly investigated. Under the catalysis of metallophthalocyanines intercalated LDHs in the presence of O2/isobutaldehyde, the production of epoxide undergoes two reaction paths. And two types of intermediates, namely acylperoxy radical and peroxyacid, are formed in the reaction, and the former is predominant.

A heterogeneous bifunctional hybrid catalyst originated from copper tetrasulfophthalocyanine (CuPcTs) and hydrotalcite for Baeyer–Villiger (B-V) oxidation has been prepared and characterized. XRD, FTIR, DR UV-Vis and SEM characterization indicate that CuPcTs molecule has been successfully intercalated into the layer of ZnAl hydrotalcite. And the synthesized hybrid exhibited excellent catalytic activity in the B-V oxidation for various ketones under mild conditions. Its bifunctional role in the reaction through O2/benzaldehyde has been discussed and verified by controlled experiments. The study indicates that the designed catalyst not only catalyzes the oxidation of benzaldehyde to perbenzoic acid, but also accelerates the transformation of ketone to lactone or ester.