Amorphous-to-crystalline transition of silicon-incorporated anodic ZrO2 and improved dielectric properties

Koyama, Shun; Aoki, Yoshitaka; Nagata, Shinji; Kimura, Hisamichi; Habazaki, H.

doi:10.1016/j.electacta.2010.01.063

Cited by 16 publications

(21 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast, it has been realized that capacitances of crystalline anodic oxides on Zr-Ti alloys become higher than those on titanium and zirconium [11]. Recently, we have also found marked enhancement of the capacitance of crystalline anodic ZrO 2 by the incorporation of silicon species, although SiO 2 has low relative permittivity [12]. Thus, foreign species-incorporated anodic ZrO 2 is of interest as a dielectric.…”

Section: Introductionmentioning

confidence: 81%

Formation and dielectric properties of anodic oxide films on Zr–Al alloys

Koyama

Aoki

Nagata

et al. 2010

J Solid State Electrochem

View full text Add to dashboard Cite

Zr-Al alloys containing up to 26 at.% aluminum, prepared by magnetron sputtering, have been anodized in 0.1 mol dm -3 ammonium pentaborate electrolyte, and the structure and dielectric properties of the resultant anodic oxide films have been examined by grazing incidence X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy and AC impedance spectroscopy. The anodic oxide film formed on zirconium consists of monoclinic and tetragonal ZrO 2 with the former being a major phase. Two-layered anodic oxide films, comprising an outer thin amorphous layer and an inner main layer of crystalline tetragonal ZrO 2 phase, are formed on the Zr-Al alloys containing 5 to 16 at.% aluminum. Further increase in the aluminum content to 26 at.% results in the formation of amorphous oxide layer throughout the thickness. The anodic oxide films becomes thin with increasing aluminum content, while the relative permittivity of anodic oxide shows a maximum at the aluminum content of 11 at.%. Due to major contribution of permittivity enhancement, the maximum capacitance of the anodic oxide films is obtained on the Zr-11 at.% Al alloy, being 1.7 times than on zirconium at the formation voltage of 100 V.

show abstract

Section: Introductionmentioning

confidence: 81%

Formation and dielectric properties of anodic oxide films on Zr–Al alloys

Koyama

Aoki

Nagata

et al. 2010

J Solid State Electrochem

View full text Add to dashboard Cite

show abstract

“…16 A good correlation between the migration rates of cations and their single metal-oxygen bond energies has been reported. [17][18][19] The cation species with lower metal-oxygen bond energies migrate faster toward the film/electrolyte interface. The metal-oxygen bond energies decrease in the following order: Si 4+ 16 .…”

Section: Discussionmentioning

confidence: 99%

Improved Thermal Stability of Efficient Proton-Conducting Anodic ZrO2-WO3 Nanofilms by Incorporation of Silicon Species

Ye¹,

Aoki

Tsuji

et al. 2011

J. Electrochem. Soc.

View full text Add to dashboard Cite

Novel proton-conducting amorphous anodic ZrO 2 -WO 3 -SiO 2 films, 200 nm thick, are prepared by anodizing of sputter-deposited Zr 37 W 47 Si 16 at 100 V with current decay for 1.8 ks in 0.1 mol dm −3 phosphoric acid electrolyte at 20 • C. The resultant anodic films have been characterized using electrochemical impedance spectroscopy, transmission electron microscopy, glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The addition of silicon species to the anodic ZrO 2 -WO 3 film significantly enhanced the thermal stability. Even after thermal treatment at 300 • C in dry Ar atmosphere, the anodic ZrO 2 -WO 3 -SiO 2 films revealed stable proton conductivity in the temperature range of 50-225 • C, while the anodic ZrO 2 -WO 3 on the Zr 43 W 57 loses the proton conductivity by annealing at 250 • C. The anodic film on the Zr 37 W 47 Si 16 consisted of two layers, comprising an outer thin ZrO 2 layer, free from tungsten and silicon species, and an inner main layer containing all zirconium, tungsten and silicon species. The results in this study suggest that the conductivity deterioration at high annealing temperatures is associated with the diffusion-induced formation of a poorly-conducting layer near the alloy/anodic oxide interface. Anodizing of valve metals, including aluminum, titanium, zirconium, niobium, hafnium and tantalum, leads to formation of barriertype (compact) or self-organized nanoporous anodic oxide films, depending on the electrolytes used. The oxide films formed are dielectrics or semiconductors with useful properties that make them of great interest for many applications, including solid electrolytic capacitors, solar cells, photocatalysis, electrochromic devices, and self-cleaning materials. [1][2][3][4][5] It is known that anodic films usually contain hydrogen species, 6 and the authors recently reported that amorphous ZrO 2 -WO 3 nanofilms, prepared by anodizing of Zr-50 at% W alloy in phosphoric acid electrolyte, revealed efficient proton conductivity even below 200• C. 7ZrO 2 -WO 3 is an attractive acid catalyst with its Brønsted acidity being comparable to fully anhydrous hydrogen fluoride. 8 As a consequence of its strong acidity, the anodic ZrO 2 -WO 3 films may have exhibited the efficient proton conductivity. Such proton-conductive nanofilms are of great interest for application to an electrolyte membrane for intermediate-temperature fuel cells (ITFCs), operating between 100-400• C. 9 The ITFCs have several advantages over polymer electrolyte fuel cells, which operates below 100• C under fully hydrated conditions. 10, 11 The fuel cell operation at intermediate temperatures allows the use of non-precious metal electrocatalysts 12 and a range of fuels including hydrocarbons 13 and facilitates simpler module designs compared with high-temperature solid oxide fuel cell.14 Currently, tailoring of solid electrolytes with high conductivity at intermediate temperatures is a key to develop ITFCs.Although the authors found the proton-conducting amorphous anodi...

show abstract

“…At the silicon content of 16 atom %, the average ox value is 21.7, being slightly smaller than that of pure zirconium. 25 Larger ox value of the anodic film formed at 100 V on the Zr-10 atom % Si film in comparison with that at 20 V may be associated with an amorphous-to-crystalline transition of the anodic film. The formation voltage dependence of ox becomes less significant for the anodic films on the Zr-16 at % Si film, probably because the relative thickness of the outer crystalline layer is reduced largely by the increase in silicon content to 16 atom %.…”

Section: Journal Of the Electrochemical Society 157 ͑12͒ C444-c451 ͑mentioning

confidence: 99%

“…The silicon-free outer layer is relatively thin, for both the Zr-10 and 16 atom % Si films, due to the low transport number of cations in amorphous anodic zirconia. 15,25 Since crystalline anodic oxide films are usually developed on zirconium metal, the outer silicon-free amorphous layer should be more readily crystallized during anodizing, compared with the inner silicon-containing layer. In addition, it has been reported that an amorphous-to-crystalline transition of anodic oxides during anodizing of niobium and Ti-Si alloys is initiated at the location that an air-formed oxide film is present before anodizing.…”

Section: Journal Of the Electrochemical Society 157 ͑12͒ C444-c451 ͑mentioning

confidence: 99%

See 1 more Smart Citation

Phase Transformation and Capacitance Enhancement of Anodic ZrO[sub 2]–SiO[sub 2]

Koyama¹,

Aoki²,

Sakaguchi

et al. 2010

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Capacitance enhancement of anodic oxide films on zirconium by adding silicon is reported here with correlation to the phase transformation of the oxide. The anodic oxide film formed on zirconium consists mainly of monoclinic ZrO 2 , which changes to tetragonal ZrO 2 phase on the Zr-5.5 atom % Si. Further increase in the silicon contents to 10 and 16 atom % results in the formation of amorphous oxide up to 30 V, above which two-layered films, comprising an outer crystalline tetragonal-phase oxide layer and an inner amorphous layer, are developed. The relative thickness of the outer crystalline layer to the total film thickness increases with formation voltage. The highest capacitance of the anodic oxide films is obtained on the Zr-10 atom % Si. The changes in capacitance, permittivity and formation ratio of anodic oxide films with alloy composition are discussed with phase transformation and growth process of anodic oxides. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3503592͔ All rights reserved.Manuscript submitted August 9, 2010; revised manuscript received September 23, 2010. Published October 22, 2010 ZrO 2 is an important inorganic material for high-temperature applications, due to many useful properties such as high strength and stability at high temperatures, oxide ion conductivity at elevated temperatures and radiation-resistant properties. These features make ZrO 2 attractive for oxygen sensors, solid oxide fuel cells, and nuclear materials. Moreover, in recent years, zirconia-based materials, including ZrO 2 -SiO 2 , have been proposed as a promising high-gate dielectric material for metal-oxide-semiconductor ͑MOS͒ transistors. 8,9 Anodizing is the most simple and easiest method to form dielectric oxides, and this has been extensively used to form dielectric oxide films on aluminum and tantalum for electrolytic capacitor applications. Tantalum electrolytic capacitors are widely used in electronics industry, but due to limitation of natural resources of tantalum and for high demand of increasing capacitance, alternative abundant materials that form oxides with higher permittivity, such as niobium and titanium, have been studied. [10][11][12][13][14][15][16] Zirconium forms usually crystalline anodic oxide films, in contrast to the formation of amorphous anodic oxides on a range of valve metals, including aluminum, bismuth, niobium, tantalum and tungsten. 17 The crystalline structure of anodic zirconium oxide films is influenced by surface treatments prior to anodizing and electrolyte for anodizing. When magnetron-sputtered zirconium is anodized in ammonium pentaborate electrolyte without pretreatment of the deposited surface, crystalline oxide films, consisting mainly of monoclinic ZrO 2 , are developed. 9 The monoclinic phase of ZrO 2 is thermodynamically the most stable at ambient temperature, but amorphous and high-temperature stable phases of cubic or tetragonal ZrO 2 are also often found in the anodic oxide films formed on chemically polished zirconium, particularly at low formation voltage...

show abstract

Amorphous-to-crystalline transition of silicon-incorporated anodic ZrO2 and improved dielectric properties

Cited by 16 publications

References 49 publications

Formation and dielectric properties of anodic oxide films on Zr–Al alloys

Formation and dielectric properties of anodic oxide films on Zr–Al alloys

Improved Thermal Stability of Efficient Proton-Conducting Anodic ZrO2-WO3 Nanofilms by Incorporation of Silicon Species

Phase Transformation and Capacitance Enhancement of Anodic ZrO[sub 2]–SiO[sub 2]

Contact Info

Product

Resources

About