Influence of praseodymium oxide/cobalt oxide ratio on microstructure and electrical properties of zinc oxide varistor ceramics

The microstructure and electrical properties of varistor ceramics, which are composed of (99.5–x–y)ZnO+xPr₆O₁₁+yCoO+0.5Dy₂O₃ system, were investigated with Pr₆O₁₁/CoO mole ratio (x/y=0.5/0.5, 0.5/1.0, 1.0/0.5, 1.0/1.0) and sintering temperature. The density of varistor ceramics with Pr₆O₁₁=1.0 was almost constant with sintering temperature, whereas it was increased noticeably in Pr₆O₁₁=0.5. Increasing Pr₆O₁₁ content enhanced the densification for any CoO content and the density was greatly affected not by CoO content but by Pr₆O₁₁ content. The varistor ceramics with Pr₆O₁₁/CoO=0.5/1.0 exhibited a higher nonlinearity than any other composition ratios. In particular, the varistor ceramics sintered at 1350 °C. exhibited the best electrical properties, with nonlinear exponent of 37.8, leakage current of 7.6 μA, and dissipation factor of 0.059. It was found that Pr₆O₁₁/CoO ratio greatly affects various characteristics of varistor ceramics.     

Microstructure, electrical properties, and degradation behavior of praseodymium oxides-based zinc oxide varistors doped with Y2O3

The microstructure, electrical properties, and degradation behavior of Pr-based zinc oxide varistors, which are composed of Zn-Pr-Co-Cr-Y oxides were investigated according to Y₂O₃ additive content in the range 0.5–4.0 mol%. The majority of the Sadded Y₂O₃ were segregated at the multiple ZnO grain junctions and grain boundaries. The average grain size was markedly decreased in the range 27.3–8.6 m with increasing Y₂O₃ additive content. Y₂O₃ acted as an inhibitor of grain growth. Additions of Y₂O₃ increased the varistor voltage in the range 36.90–686.58 V/mm, increased the nonlinear exponent in the range 3.75–87.42, decreased the leakage current in the range 115.48–0.047A, increased the barrier height in the range 1.06–2.16 eV, and decreased the donor concentration in the rang 1.87 × 10¹⁸–0.19 × 10¹⁸ cm^–3. Y₂O₃ acted as an acceptor, as a result of the decrease of donor concentration. All Pr-based ZnO varistors doped with Y₂O₃ exhibited very predominant degradation characteristics, which show a nearly symmetric I-V after the stress. In particular, since 4.0 mol% Y₂O₃-added ZnO varistor has not only very excellent non-ohmicity, but also very stable degradation behavior, it is estimated to be sufficiently used to various application fields.     

ZnO-Nb2O5掺杂SnO2基陶瓷研究

通过常压烧结制备SnO2基陶瓷,研究了ZnO、Nb2O5单掺杂及ZnO-Nb2O5复合掺杂对SnO2基陶瓷的烧结性能及电阻率的影响。采用SEM及XRD对试样分别进行了微观结构观察及物相分析。研究表明,掺杂ZnO能提高陶瓷的体积密度,但对于降低电阻率的影响不明显,当ZnO掺杂量在0.5%～0.75%(质量分数)时,SnO2基体积密度可达到6.67～6.73g/cm3;掺杂Nb2O5不能有效提高烧成陶瓷的体积密度,但能显著降低SnO2基陶瓷的电阻率;0.5%(质量分数)ZnO～1.5%(质量分数)Nb2O5复合掺杂在1450℃下烧成的陶瓷可得到较好的性能,其体积密度可达到6.61g/cm3,常温电阻率为867.84Ω.cm。     

Ferroelectric properties of barium calcium titanate ceramics doped with bismuth oxide

Ferroelectric properties of Bi doped (Ba_1 − xCa_x)_0.925Bi_0.05TiO₃ (Bi-BCT, 0.10 < x < 0.30) ceramic prepared by the solid-state technique have been studied. An interesting double-like hysteresis (P-E) loop at room temperature (300 K) with the remarkable linear dielectric response was observed over a certain electric field range. Room temperature P-E loops before and after de-aging, as well as those at different values of field cycling, could exclude the possibility that the double P-E loops might result from the antiferroelectric components and the electric field induced paraelectric-ferroelectric (PE-FE) transition near Curie temperature (T_c) in Bi-BCT, and verify that there exists a diffusional aging effect in Bi-BCT. A symmetry-conforming short-range ordering (SC-SRO) of point defects is suggested to be responsible for the observations of the interesting double-like P-E loop in Bi-BCT.     

Microstructures and electrical properties of copper oxide doped terbium oxide ceramics

The effects of copper oxide (CuO) on the microstructure and electric properties of nonstoichiometric compound terbium dioxide (Tb₄O₇) ceramics were investigated. Results included a reduction in the sintering temperature to 1,100 °C, a grain size of 4.2 μm, and a density of 96.2 %, which are larger than the values in previous investigation for Tb₄O₇ ceramics (grain sizes between 0.4 and 1.0 µm). Among the sintered ceramics, the sample doped with 10.0 wt% CuO showed the maximum nonlinear coefficient α = 43.5, which is obviously greater than α = 3.03 of the pure sample. Doping with 10.0 wt% CuO also exhibited nonlinearity α = 2.14 even at 1,123 K. In addition, the impedance spectra of the sample doped with 5.0 mol% CuO showed the largest grain boundary semicircle; 0 and 20 % samples showed both inductive and capacitive reactance.     

Electrical properties and stability against DC accelerated aging stress of lanthania doped praseodymia-based zinc oxide varistor ceramics

The microstructure, electrical properties, and stability against DC accelerated aging stress of the varistor ceramics, which are composed of ZnO–Pr₆O₁₁–CoO–Cr₂O₃–La₂O₃-based ceramics, were investigated for various La₂O₃ contents. The increase of La₂O₃ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0 mol%. The highest nonlinearity was obtained from 0.5 mol% La₂O₃, in which the nonlinear exponent is 81.6 and the leakage current is 0.1 μA. As the La₂O₃ content increased, the donor concentration increased in from 0.64 × 10¹⁸ to 16.89 × 10¹⁸/cm³ and the barrier height greatly decreased with increasing La₂O₃ content, reaching a maximum (1.47 eV) in 0.5 mol% La₂O₃. The varistors doped with 0.5 mol% La₂O₃ exhibited high stability, in which the variation rates of varistor voltage, nonlinear exponent, and leakage current were −1.14%, −3.7%, and +100%, respectively, for stressing state of 0.95 V _{1 mA}/150 °C/24 h.     

Optical properties of zinc oxide thin films doped with aluminum and lithium

Aluminum doped Zinc Oxide (AZO) and Lithium doped Zinc Oxide (LZO) thin films are obtained by Pulsed Laser Deposition (PLD) method. These films are characterized by using Spectroscopic Ellipsometry (SE), X-ray Diffraction (XRD) and Photoluminescence (PL). By modeling the ellipsometry spectra we get the dielectric functions, the optical band gap E_g, and the electrical properties. Our results show the influence of the processing parameters on the optical and structural properties of doped ZnO thin films. The post-annealing treatment applied to AZO thin films, changes strongly the optical properties, by lowering the resistivity and red-shifting the band gap.     

Optical properties of praseodymium oxide films

The refractive index n_f, absorption index k_f and absorption coefficient α of vacuum-deposited films of praseodymium oxide prepared under different conditions have been evaluated from the transmittance T data at different wavelengths in the visible region. The optical energy gap was estimated to be approximately 3.40 eV.     

Visible photocatalytic properties of vanadium doped zinc oxide aerogel nanopowder

Vanadium-doped zinc oxide nanoparticles have been synthesized by sol-gel method. In our approach the water for hydrolysis used in the synthesis of nanopowder was slowly released followed by a thermal drying in ethyl alcohol at 250 °C. The obtained nanopowder was characterized by various techniques such as particle size analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). In the as-prepared state, the powder with an average particle size of 25 nm presents a strong luminescence band in the visible range. From photoluminescence excitation (PLE) the energy position of the obtained PL band depends on the excitation wavelength and this PL band can be also observed under visible excitations. This result is very promising for visible photo catalysis applications, which was confirmed by methylene blue photo-degradation using visible lamp as a light source.     

Preparation and properties of mullite-bonded porous SiC ceramics using porous alumina as oxide

Mullite-bonded porous silicon carbide ceramics were prepared by an in situ reaction bonding technique and sintering in air with SiC, porous Al₂O₃, and graphite as starting materials. The pores in the ceramics were formed by burning graphite and by stacking particles of SiC and Al₂O₃. The surface of SiC was oxidized to SiO₂ at high temperature. With a further increase in temperature, SiO₂ reacted with Al₂O₃ to form mullite. The reaction-bonding characteristics, phase composition, open porosity, mechanical strength as well as the microstructure of porous SiC ceramics were investigated.     

Preparation and dielectric properties of microwave ceramics based on doped zinc titanates

We have studied the dielectric properties of microwave ceramic materials in the binary system Zn₂TiO₄-TiO₂ and examined the effect of doping with Sn²⁺, Sb³⁺, Bi³⁺, and Mg²⁺ on the dielectric properties and microstructure of the ceramics. The doped Zn-Ti-O ceramics are thermally stable and have ? = 18–33 and tan δ from 0.0001 to 0.007. Our results demonstrate that the doped Zn-Ti-O ceramics are potentially attractive for microwave applications, in particular for use as ceramic components (resonator substrates) of miniature antennas.     

Nonlinear electrical properties of zinc oxide ceramics with B2O3 additions

The effect of B₂O₃ additions on theI-V behavior of ZnO-based ceramics (ZnO-Bi₂O₃-Co₃O_-4- MnO_2-NiO-TiO₂) and its changes in response to an applied dc current was studied. The introduction of B₂O₃ was shown to reduce shrinkage during sintering and raise the nonlinearity factor and the voltage drop across the sample at a fixed current density. The effect of B₂O₃ on the stability ofI-V behavior depends on the temperature at which the electrical contacts were formed.     

Dielectric and piezoelectric properties of neodymium oxide doped lead zirconate titanate ceramics

The dielectric and electromechanical properties of lead zirconate titanate [Pb(Zr, Ti)O₃] ceramic added with neodymium oxide have been systematically studied employing the vector impedance spectroscopic (VIS) technique. The specimens were prepared using the mixed oxide route by adding different mol% of Nd2O₃ (01 to 7mol%) in [Pb(Zr, Ti)O₃] near morphotropic phase boundary. Piezoelectric equivalent circuit parameters R, L, C_a in series and C_b in parallel have been determined by simulating /Z/ and Θ plots. Electromechanical coupling coefficients and strain constants for the radial modes show a peak at about 3 mol%, the dielectric constant peaks at about 1 mol% and voltage constants peak at about 0–75 mol% of Nd₂O₃.     

Study of the properties of undoped and fluorine doped zinc oxide nanoparticles

ZnO and ZnO:F nanoparticles were successfully prepared by precipitation in the presence of oxalic acid. This procedure yields ZnO and ZnO:F nano-arrangements of different lengths consisting of chains of quasi-spherical nanoparticles of ∼ 30 nm in size. Only the wurtzite ZnO structure was detected for both undoped and fluorine doped ZnO nanoparticles. By absorption and photoluminescence measurements, a diminishing of singly ionized oxygen vacancies was detected when fluorine is present in the nanoparticles; while a blue shift of the exciton absorption was observed. Additionally, by NIR reflectance measurements, the creation of free carriers by the fluorine doping of ZnO nanoparticles was observed.     

锌钛掺杂三氧化钨陶瓷的热电性能

利用传统工艺制备TiO2以及ZnO掺杂的WO3陶瓷,利用X射线衍射以及扫描电镜对其微观结构进行分析,并且在273~973 K进行热电性能的测量,发现晶粒尺寸有着微小的变化,而且有第二相的生成。所有不同浓度的样品在测量范围内均为负值,说明仍是n型氧化物热电材料。实验发现掺杂浓度为0.5%(摩尔分数),温度达到973K时有着最高的功率因子为0.052μW/m·K2。     

Thermal conductivity of silicon carbide ceramics doped with beryllium oxide

The thermal conductivity of silicon carbide ceramics containing up to 3 wt % BeO was measured in the temperature range 300–1300 K. The effective thermal conductivity was found to rise notably with increasing BeO content in the range 1.3–1.5 wt % BeO and to decrease exponentially with increasing porosity.     

Rare earth doped zinc oxide nanowires

Zinc oxide (ZnO) nanowires were grown via thermal transport and subsequently doped with different concentrations of Tm, Yb, and Eu using ion implantation and post annealing. High ion fluences lead to morphology changes due to sputtering; however, freestanding nanowires become less damaged compared to those attached to substrates. No other phases like rare earth (RE) oxides were detected, no amorphization occurs in any sample, and homogeneous doping with the desired concentrations was achieved. Photoluminescence measurements demonstrate the optical activation of trivalent RE-elements and the emission of the characteristic intra-4f-luminescence of the respective RE atoms, which could be assigned according to the Dieke-diagram. An increasing RE concentration results into decreasing luminescence intensity caused by energy transfer mechanisms to non-radiative remaining implantation defect sites. Furthermore, low thermal quenching was observed due to the considerable wide band gap of ZnO.     

Physical properties of natively textured yttrium doped zinc oxide films by sol-gel

Sol-gel derived yttrium doped ZnO films of various thicknesses have been deposited by the dip coating technique. The investigations of microstructural, electrical and optical properties of post heat-treated films in air as a function of thickness have been made. It is found that high quality films are obtained at an annealing temperature of 550 ^∘C. The (002) preferential growth of both the doped and undoped ZnO films changes to (101) as the thickness of the films were increased. The full width at half maximum of (002) X-ray peak decreases with annealing temperature and the lattice constant is found to approach the value of bulk ZnO. Natively textured films have been obtained for film having thickness greater than 0.8 μm. The thinner films are found to be non-textured with high resistivity. The formation of the textured surface of the film is linked to the suppression of c-axis (002) orientation and the columnar growth in the thick film.     

Durability of doped zinc oxide/silver/doped zinc oxide low emissivity coatings in humid environment

The relationship between internal stress of doped zinc oxide films and durability of doped zinc oxide/silver/doped zinc oxide low emissivity (low-e) coatings in humid environment was investigated. Aluminum, titanium, tin, chromium, silicon, gallium, magnesium, boron, barium, and calcium were chosen as a doping element in sputtering targets. Ratios of dopant/zinc in the oxide targets were 4/96-5/95 at.%. Films were formed by radio frequency sputtering. Doping of barium and calcium to the zinc oxide film led to a large increase in the internal stress. Doping of the other elements resulted in decreasing the internal stress. It was concluded that durability of the low-e coatings in humid environment closely correlated with the internal stress of the oxide layers.