Effects of doping and temperature on nonlinearity of WO3 varistor

J. Phys. D: Appl. Phys.

Yao

2001

Tungsten oxide thin films with different stoichiometry have been deposited on Si (111) wafers by pulsed laser deposition (PLD) technique under different conditions. The structural properties and infrared emissivity of WO3 thin films were analysed using a scanning accessory of a transmission electron microscope (STEM), x-ray diffraction (XRD), Raman spectra (RS) and Fourier transform infrared (FT-IR) spectra. Thin films deposited at 200 °C on Si showed an amorphous structure, while those annealed in air at 300 and 400 °C showed nanocrystalline and porous triclinic structures. These porous and nanocrystalline structures could be used to improve electrochromic colour efficiency and responsing, recovery properties. However, samples deposited at 200 °C and annealed at 240 °C for 0.5 h in oxygen showed a triclinic structure with average 10 nm crystallites. Nanocrystalline WO3 thin films on Si (111) synthesized by this technique might find applications in infrared emittance modulation systems.

Section: Introductionmentioning

confidence: 99%

Fabrication and characterization of electrochromic nanocrystalline WO₃/Si (111) thin films for infrared emittance modulation applications

Fang

J. Phys. D: Appl. Phys.

Yao

2001

“…1, we can see that (001) peak rather than (020) peak has the highest intensity at this temperature. With the data in Table 2, the average lattice constants of thin films deposited at 400 C were calculated to be a a = 7.314 (3) 3 . The average grain size of the thin film deposited at 400 C on ITO was calculated to be about 24 nm by using Scherrer's formula.…”

Section: Resultsmentioning

confidence: 99%

“…Tungsten trioxide is one of the most important electro-chromic materials, which are used in gas and humidity sensors, and low voltage varistors [1][2][3]. It has been recognized that WO 3 can be colored through electro, photo, gas, laser induced and thermochromism processes [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Preparation and Electrochromic Properties of Nanocrystalline WO3 Thin Films Prepared by Pulsed Excimer Laser Ablation Technique

Fang

Sun

et al. 2001

phys. stat. sol. (a)

Tungsten oxide thin films with different stoichiometry have been deposited on In 2 O 3 : SnO 2 glass (ITO) and Si wafer by pulsed laser deposition (PLD) technique at different deposition temperatures and oxygen pressure. The structural properties of WO 3 thin films were analyzed by using a scanning accessory of transmission electron microscope (STEM), X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), Raman spectrum (RS). Thin films deposited at 200 C on ITO showed amorphous structure, those deposited at 300 and 400 C on ITO showed nanocrystalline triclinic structure. As for samples deposited at 400 C, in which the crystals keep nanocrystalline, cyclic voltammograms at sweep rate of 50 mV/s shows that no long-term degradation was noted at least up to 1000 cycles, and durability was verified to 8000 cycles in the voltage range between --1.2 and 1.4 V. Its open and porous structure is suitable for Li-ions going into and out, and induced improved cycle stability and reversibility.

“…At the same time, varistors based on other ceramic systems are also under investigation and development because of the need for even better properties, such as low voltage and high dielectric constants. Since Makarov and Trontelj [1] found that Na 2 CO 3 -and MnO 2 -doped WO 3 ceramics exhibited non-linear current-voltage characteristics, some investigations [2][3][4][5][6] have been done to further clarify the physical mechanism of microcosmic electrical transport and to improve its electrical properties.…”

Section: Introductionmentioning

confidence: 99%

Improved Stability of Mn-Doped WO3 Varistor via Doping Cr2O3

Zhao

Zhu

et al. 2007

KEM

In this paper, the effect of Cr2O3 addition on the electrical properties and microstructures of WO3-MnO2 ceramics was studied. The samples were fabricated by the conventional solid phase reaction techniques. The current-voltage curves and impedance spectra of sintered samples were measured at room temperature. The samples without Cr2O3 doping exhibit the max nonlinear coefficient α above 8 in current region from 1mA to 10mA and an unstable characteristic of current-voltage curve for repeat measuring cycle, while the samples doped with Cr2O3 display lower nonlinearity with α about 5 and an improved stability of current-voltage curve at the same conditions. The impedance measurements indicate that the influence on electrical properties comes from grain boundary as well as grain. SEM shows the doping of Cr2O3 into WO3-MnO2 ceramics suppresses obviously the growth of WO3, and XRD analysis reveals the coexistence of WO3 phases with some manganese tungstates and chromium tungstates. The problems related to electrical transporting mechanism were discussed simply.