Microstructure Of ZnO Research Articles

Sintering temperature dependence of varistor properties and impedance spectroscopy behavior in ZnO based varistor ceramics

ZnO based varistor ceramics were prepared by a solid state reaction route, and the phase composition, microstructure and electrical properties were also investigated by XRD, SEM, a V–I source/measure unit and impedance spectroscopy. Results show that all the samples consist of mainly ZnO grains and secondary phases including Bi2O3, Zn7Sb2O12, Y2O3, Nd-rich and Y-containing Bi-rich phases. With the increase of sintering temperature, the number of grain boundaries and varistor voltage per grain boundary decreases, and the breakdown field (E1mA) decreases from 556.4 to 319.4 V/mm. The nonlinear coefficient value (α) is in the range of 60–70, the leakage current density values (JL) of all the varistor ceramics are <3 μA/cm2. Typically, the varistor ceramic sintered at 1,050 °C exhibits good electrical properties of E1mA = 556.4 V/mm, α = 61 and JL = 1.55 μA/cm2. Meanwhile, a schematic model for the electrical microstructure of ZnO based varistor is proposed with an equivalent circuit of Rg (RgbCgb) by impedance spectroscopy.

Influence of WO3‐Doping on the Microstructure and Electrical Properties of ZnO–Bi2O3 Varistor Ceramics Sintered at 950°C

The phase evolution, microstructure, and electrical properties of WO3‐doped ZnO–Bi2O3‐based varistors were investigated for different amounts x (0 ≤ x ≤ 1.60 mol%) of the dopant. When x was less than 0.40, the dissolved W6+ in the β‐Bi2O3 acted as a donor in the grain boundaries and reduced the electrical properties of the ZnO varistors. However, when x was 0.40 mol%, which meant an amount of WO3 equal to that of Bi2O3, the electrical properties dramatically increased, which means the W6+ donor effect is removed at the grain boundaries because a new Bi2WO6 phase was formed in the grain‐boundary regions. The Bi2WO6 phase has high oxygen conductivity at high temperatures; it transfers more oxygen to the grain boundaries in order to further enhance the electrical properties. For x values higher than 0.40 (i.e., an addition of WO3 that is greater than the content of Bi2O3), the electrical properties were steadily reduced in comparison to the composition with x = 0.40. This could be explained by the reduced amount of Co, Mn, and Al at the grain boundaries and in the ZnO grains as a result of their incorporation into the ZnWO4 phase. The electrical properties of the ZnO grains and the grain boundaries were in agreement with the results of the impedance spectroscopy analysis.

Microstructure and properties of ZnO doped CaO–Al2O3–SiO2 ceramic for LTCC applications

The effects of ZnO content and sintering temperature on the microstructure, bending strength, coefficient of thermal expansion and dielectric properties of Li2O–Al2O3–SiO2 glass–ceramic are presented. The prepared Li2O–Al2O3–SiO2 glass–ceramic could be used for the application of LTCC substrate. Glass powders were produced by conventional melt-quenching technique. The sintering and crystallization behavior of glass powders was explored using scanning electron microscopy, differential thermal and X-ray diffraction analyses. The crystalline phase formation in the calcination of Li2O–Al2O3–SiO2 samples has shown a major phase of Li2OAl2O37.5SiO2 and two minor phases ZrO2 and CaMgSi2O6. Increasing ZnO content at the expense of SiO2 was shown to not only promote the densification and lower the linear shrinkage, but also enhance the bending strength and the coefficient of thermal expansion of the glass–ceramic. The linear shrinkage and density of samples will decrease with the increasing sintering temperature.

A positron annihilation study of ZnO prepared by thermal oxidation at different temperatures

ZnO particles were prepared from Zn nanoparticles by thermal oxidation in air, over a temperature range of 500 to 900 oC. The microstructure of ZnO was investigated by SEM and XRD, showing that the thermal oxidation temperature affected the particle growth mechanism, morphology, and microstructure. Positron annihilation spectroscopy indicated that the thermal oxidation process has an important influence on the zinc-related vacancies and their clusters in the ZnO particles.

Sintering effect on electrical properties and aging behavior of quaternary ZnO–V2O5–Mn3O4–Nb2O5 ceramics

The microstructure, electrical properties, dielectric characteristics, and DC-accelerated aging behavior of ZnO–V2O5–Mn3O4–Nb2O5 ceramics were systematically investigated at various sintering temperatures. Analysis of the microstructure indicated that ZnO–V2O5–Mn3O4–Nb2O5 ceramics are composed of ZnO grain as a primary phase, and Zn3(VO4)2, ZnV2O4, and VO2 as the minor secondary phases. The increase in sintering temperature increased the average grain size from 5.9 to 14.3 μm, whereas it decreased the sintered density from 5.54 to 5.40 g/cm3. The breakdown field decreased from 5,671 to 1,443 V/cm with the increase in sintering temperature. The nonlinear coefficient exhibited a maximum value (47) at 900 °C and a minimum value (17.8) at 950 °C. The varistors sintered at 950 °C exhibited the highest stability; variation rates for the breakdown field, for the nonlinear coefficient, and for the leakage current density were +0.4, −0.6, and +22.2 %, respectively, after application of a stress of 0.85 E1 mA/85 °C/24 h.

The Microstructure of Aging ZnO, AZO, and GZO Films

The Microstructure of Aging ZnO, AZO, and GZO Films

The Microstructure of Aging ZnO, AZO, and GZO Films

The Microstructure of Aging ZnO, AZO, and GZO Films

Simple and rapid preparation of spherical flower-like ZnO and their photocatalytic property

The influences brought about by different microstructure of ZnO on its special chemical and optical properties have been widely discussed. Precipitates from the mixed solution of oleic acid with Zn(NO3)2 and KOH were investigated using SEM, TEM, XRD, Raman, and FTIR. The obtained microstructure of the ZnO precipitates was proved to be a unique hierarchical structure consisted of 5 nm thick nanosheets. The catalytic property of the received flower-like ZnO was explored, and it was found that the photodegradable property of rhodamine B was largely improved when the precipitates were heat treated at 500 °C for 2 h due to a high crystallinity with a heat treatment, and the decomposition of the oleic acid molecules.

Alignment-controlled hydrothermal growth of well-aligned ZnO nanorod arrays

ZnO nanorod arrays (ZNAs) were prepared via a two-step seeding and solution hydrothermal growth process. Effects of preparing parameters such as seed layer, colloid concentration, substrate and precursor concentration, on the alignment control of ZNAs were systematically investigated. The deviation angle of ZnO nanorods was measured to evaluate the alignment of arrays. Results show that seed layer not only controls the vertical orientation of ZNAs, but also the compactness of ZNAs. Altering colloid concentration and substrate can influence the microstructure of ZnO seed layer and affect the ordered alignment of ZNAs. The precursor concentration has an insignificant effect on the alignment of ZNAs but has great impact on the morphology of ZNAs. Alignment-controlled and well-aligned ZnO nanorods with different diameter and aspect ratio can be obtained by properly controlling the preparing parameters. A growth mechanism was proposed for the growth of ZnO nanorods.

Reduction of thermal conductivity in dually doped ZnO by design of three-dimensional stacking faults

A design paradigm for fabrication of high quality thermoelectric material was demonstrated by using wurtzite ZnO based materials. To prepare the three-dimensional stacking faults in the microstructure of ZnO, Ga2O3 and In2O3 which were guided by atomistic simulation were selected as doping oxides in wurtzite ZnO. TEM microanalysis experimentally confirmed two kinds of stacking faults which were along the basal-plane (i.e. {0001}) and pyramidal-plane (i.e. {10–14}) in the microstructure of ZnO dually doped with small amount of Ga2O3 and In2O3. Also, EDS analysis results indicated the dopant segregation effect at stacking faults which was predicted by our atomistic simulation results. By varying doping levels, it was found that the (Ga0.004, In0.004)Zn0.992O with dense three-dimensional stacking faults revealed low lattice thermal conductivity (1.7 W m−1 K−1 at 773 K) and high thermo-electric performance (ZT: 0.19 at 773 K) in the present work. Based on all experimental results, it is expected that the combined method of atomistic simulation, microanalysis and processing route design will provide us great opportunity for design of three-dimensional stacking faults in the microstructure of ZnO with high performance.

Microstructure and photoluminescence of ZnO：Cd nanorods synthesized by hydrothermal method

High-quality ZnO and Cd-doped ZnO nanorods with different Cd-doping concentrations are synthesized by using the hydrothermal method. Microstructures and photoluminescence of the samples are systematically investigated by SEM, X-ray diffraction (XRD), Raman scattering spectrum and photoluminescence (PL) spectrum. Results of XRD analysis indicate that ZnO and ZnO:Cd crystallites exhibit a hexagonal wurtzite structure. SEM shows that the nanorods become smaller due to Cd doping. There is an internal tension which induces the decrease of optical band gap in Cd-doped nanorods. Cd-doping increases the intensity of violet emission peak near 2.90 eV and the blue emission peak located at 2.67 eV appears when the doping concentration is up to 2%. This study can be used for developing blue-violet-emitting devices.

Evolution of microstructure and related optical properties of ZnO grown by atomic layer deposition

A study of transmittance and photoluminescence spectra on the growth of oxygen-rich ultra-thin ZnO films prepared by atomic layer deposition is reported. The structural transition from an amorphous to a polycrystalline state is observed upon increasing the thickness. The unusual behavior of the energy gap with thickness reflected by optical properties is attributed to the improvement of the crystalline structure resulting from a decreasing concentration of point defects at the growth of grains. The spectra of UV and visible photoluminescence emissions correspond to transitions near the band-edge and defect-related transitions. Additional emissions were observed from band-tail states near the edge. A high oxygen ratio and variable optical properties could be attractive for an application of atomic layer deposition (ALD) deposited ultrathin ZnO films in optical sensors and biosensors.

Microstructure and electrical properties of Dy2O3-doped ZnO–Bi2O3 based varistor ceramics

The Dy2O3-doped ZnO–Bi2O3 based varistor ceramics were prepared by a solid state reaction route, and the microstructure and electrical properties were also investigated. The results show that a multiphase composition exists in all samples. With increasing content of Dy2O3, the average size of ZnO grains decreases and the threshold voltage greatly increases. The nonlinear coefficient of the ceramics is in the range of 4.7–60.2, the threshold voltage is in the range of 364.6–884V/mm, and the leakage current is between 1.77μA/cm2 and 159.1μA/cm2. Typically, the varistor ceramics with 0.60mol.% Dy2O3 sintered at 1050°C exhibit excellent electrical properties with the threshold voltage of 872.5V/mm, the nonlinear coefficient of 60.2 and the leakage current of 5.46μA/cm2. The results show doping Dy2O3 is a promising route for the production of the higher threshold voltage of ZnO–Bi2O3 based varistor ceramics.

Microstructure and varistor properties of Y2O3-doped ZnO–Pr6O11–CoO–Cr2O3–La2O3 ceramics

The microstructure, electrical properties, and aging behavior of Y2O3–doped ZnO–Pr6O11–CoO–Cr2O3–La2O3 varistor ceramics have been systematically investigated for different amounts of Y2O3. As the amount of Y2O3 increased, the sintered density increased from 4.97. 5.18, and 5.20 g/cm3 and the average grain size decreased from 4.1, 3.9, and 3.7 μm. The breakdown field increased from 8953 to 9731 V/cm with an increase in the amount of Y2O3. The varistor ceramics doped with 0.5 mol% in the amount of Y2O3 exhibited the highest nonlinear coefficient of 60.9. The varistor ceramics doped with 1.0 mol% in the amount of Y2O3 exhibited a surprisingly excellent stability by exhibiting –0.5% in the variation rate of the breakdown field and 2.5% in the variation rate of the nonlinear coefficient for aging stress of 0.95 EB/150 °C/24 h.

Sol–gel derived ZnO–CeO2 thin films on glass substrate

The microstructure and optical properties of crystalline ZnO–CeO2 thin films on glass substrate at various preheating temperatures, annealing temperatures and time were investigated. The relative intensity ratio values of the diffraction peaks of ZnO–CeO2 thin films and grain growth behavior were related to the preheating temperature, annealing temperature, and time. A suitable thermal treatment results in higher surface energy, which improves the surface morphology of the grown film. The ZnO–CeO2 thin films present high transparency (over 70%) in the visible region of the optical spectrum.

Effects of in content on the microstructure and the roughness of ZnO:In films

We investigated the changes in the preferred orientation and microstructure of ZnO:In films with increasing In content. ZnO and ZnO:In films with In contents of up to 50 at.% were deposited on Si (111) substrates by using pulsed laser deposition and were subsequently characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The structural analysis of the films revealed that as the In content was increased, the preferred orientation of the films changed from a c-axis to a random orientation at In content of 10 at.% and finally became a a-axis orientation at In content of 20 at.%. The column grain size and values of root-mean-square (RMS) roughness showed a gradual decrease with increasing In content. As the In content was increased to 10 at.%, the initial orientation of the nuclei changed from a c-axis to a random orientation; nuclei with a preferred an a-axis orientation were dominant for an In content of 20 at.%, reflecting a deterioration in the tetrahedral coordination of ZnO. Consequently, the growth direction of the grains changed, and the preferred orientation of the grains affected the microstructure.

Defects in semipolar ZnO grown on (112) LaAlO3/(La,Sr)(Al,Ta)O3 substrate by pulsed laser deposition

The microstructure of semipolar ZnO deposited on (112) LaAlO3/(La,Sr)(Al,Ta)O3 was investigated by transmission electron microscopy. The ZnO shows an in-plane epitaxial relationship of with oxygen-face sense polarity. The misfit strain along and is relieved through the formation of misfit dislocations with the Burgers vectors and , respectively. The line defects in the semipolar ZnO are predominantly perfect dislocations, and the dislocation density decreases with increasing ZnO thickness as a result of dislocation reactions. Planar defects were observed to lie in the M-plane and extend along 〈0001〉, whereas basal stacking faults were rarely found.

The Structural, Optical and Electrical Properties of Spray Deposited Fluorine Doped ZnO Thin Films

ABSTRACTHighly transparent and conducting Fluorine doped zinc oxide thin films were deposited using spray pyrolysis method on glass substrates held at 450 °C. The X-ray diffraction study revealed that as the dopant concentration increases in ZnO films, the intensity of the preferential orientation of (002) reflection decreased and (101) was found to increase up to 5 at. % F. The crystallite size was varied from 40 to 50 nm with dopant concentration. The optical band gap of the un-doped films was 3.30 eV and it increased to 3.34 eV for 3 at. % F. The refractive index of the films was increased from 2.05 to 2.18 with the increase of dopant concentration from 0 to 5 at. %. The scanning electron microscopy results depicted that the microstructure of ZnO: F films highly influenced by the fluorine doping. After annealing the films in hydrogen atmosphere, the resistivity of the films decreased as increase the dopant concentration and it is 4×10−3 Ω cm for 3at. % F beyond which it increased. The mobility of the charge carriers was 14 cm2/ V sec and the carrier concentration was 7.8×1019 cm3 obtained for the films doped with 3 at. % of fluorine concentration in the starting solution.

XANES and XPS Study on Microstructure of Mn-Doped ZnO Films

Microstructure of ZnO:Mn films with various Mn concentration was investigated with XANES and XPS. The experimental results revealed a substitution of Mn in ZnO and also excluded the existence of Mn oxides or metallic manganese clusters. The substitutional Mn presented a divalent state and all the ZnO:Mn films were n-type. Room temperature ferromagnetism monotonously decreases with the decrease of the electron carrier concentration. The observed ferrmagnetism should come from the carrier-mediated exchange.

Synthesis, characterization, and electrical conductivity of ZnO with different morphologies

ZnO samples with different morphologies were prepared using a simple direct precipitation method with Zn (NO 3 ) 2 ⋅ 6H 2 O and NH 3 ⋅ H 2 O as raw materials. The morphology and purity of the ZnO powders were studied via scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffraction. Factors influencing the morphology of ZnO, such as NH 3 ⋅ H 2 O concentration and aging temperature, were studied. Photoluminescence spectra and Raman spectra were also used to analyze the native crystal defects of the ZnO samples. The results showed that the ZnO samples prepared in this work possessed a hexagonal wurtzite structure with high purity. In addition, NH 3 ⋅ H 2 O concentration and aging temperature were essential in controlling the morphologies of ZnO. The electrical conductivities of ZnO with different morphologies were different, which mainly depends on the different native crystal defects of the ZnO samples. With adjustment of the experimental parameters, ZnO samples with different morphologies were synthesized, the concentration of the reactant (NH 3 ⋅ H 2 O) and aging temperature played important roles on the morphologies of the ZnO, and the electrical conductivity of ZnO showed that the influence of the crystal morphology on the electrical conductivity of the ZnO mainly depends on the different native crystal defects. ► Different morphological ZnO were prepared by a direct precipitation method. ► Factors Influencing on the morphology of ZnO were studied. ► Influence of crystal morphology on the electrical conductivity of ZnO was discussed. ► The microstructure of ZnO were studied by Raman scattering.