Inter-relationship between structure and dielectric properties of crystalline anodic zirconia

Habazaki, H.; Shimizu, K.; Nagata, Shinji; Asami, K.; Takayama, Koichi; Oda, Y.; Skeldon, P.; Thompson, G.E.

doi:10.1016/j.tsf.2004.12.002

Cited by 43 publications

(51 citation statements)

References 19 publications

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“…The outer ~15 % of the film thickness has slightly light appearance, suggesting the presence of boron species in this region. Figure 5 shows the GIXRD patterns of the sputter-deposited zirconium and Zr-Al alloy specimens anodized to 100 V. The anodic oxide film formed on the sputter-deposited zirconium at 100 V consists of a mixture of monoclinic ZrO 2 and a high-temperature stable phase ZrO 2 , with the former being a major phase, as reported previously [11]. The anodic oxide film formed on the Zr-5 at.% Al alloy also consists of a mixture of monoclinic and high-temperature stable phase ZrO 2 , but latter phase becomes more dominant compared with that on zirconium.…”

Section: Transmission Electron Micrographssupporting

confidence: 60%

“…This means that film properties superior to both anodic oxide films on two individual metals cannot be obtained when the anodic oxides are amorphous. 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].…”

Section: Introductionmentioning

confidence: 76%

“…For zirconium, the slope changes at 60 V, probably associated with phase transformation from a high-temperature stable phase (cubic or tetragonal) ZrO 2 to monoclinic ZrO 2 in the anodic oxide films [11]. The voltages for all Zr-Al alloys increase approximately linearly to 100 V with anodizing time.…”

Section: Voltage-time and Current-time Curvesmentioning

confidence: 97%

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

Koyama

Aoki

Nagata

et al. 2010

J Solid State Electrochem

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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.

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Section: Transmission Electron Micrographssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 76%

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

Koyama

Aoki

Nagata

et al. 2010

J Solid State Electrochem

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“…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 voltages. 18,19 It is also reported that the film structure is dependent on the electrolyte for anodizing.…”

mentioning

confidence: 99%

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

Koyama¹,

Aoki²,

Sakaguchi

et al. 2010

J. Electrochem. Soc.

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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...

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“…It is known that defect-free, high-capacitance composite anodic oxide films can be formed on substrates by anodizing a Ti-62.5 at% Zr alloy [45][46][47][48][49][50][51]. Therefore, a simple fabrication process for creating a micro-porous Ti-Zr alloy with large surface area must be developed to create novel Ti-Zr capacitors.…”

Section: Introductionmentioning

confidence: 99%

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

Kikuchi

Yoshida

Matsuura

et al. 2014

Journal of Physics and Chemistry of Solids

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Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173 K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Micro-porous metallic titanium with a low oxygen content (0.42 wt%) and a large surface area (1.794 m 2 g -1 ) can be successfully obtained by reduction under optimal conditions. Key words: Titanium, Calcium, Calciothermic reduction, Nano-particles, Electrolytic capacitor IntroductionMetallic calcium can easily reduce a large number of metal oxides directly to metals because calcium has a strong reducing ability. The reduction of metal oxides with a calcium reductant in calcium chloride molten salt at high temperature, well known as the calciothermic reaction, has long been widely investigated by many researchers. During oxide reduction, calcium chloride molten salt acts as a suitable solvent and has a high solubility for calcium and calcium oxide as a byproduct formed by reduction. [11] are formed via reduction of these oxides with a calcium reductant in calcium chloride molten salt. The residual oxygen in the reduced metal decreases continuously by deoxidation with a calcium reductant [4]. Pure metals, alloys, and intermetallic compounds with a lower residual oxygen content can be successfully fabricated by a one-step reduction technique. Reduction with a calcium reductant is a simpler technique for the production of these metals without complicated processes such as the Kroll process, although reduction is a batch-type production method.In recent years, a method for the successive reduction of metal oxides was developed by electrolysis in calcium chloride and calcium oxide mixture molten salts. Ono and Suzuki reported that calcium oxide in molten calcium chloride becomes the reductant source for the reduction of metal oxides during constant-voltage electrolysis [12]. For example, metallic calcium formed electrochemically at a cathode reacts with metal oxides, and reduced metals with a low residual oxygen content can be formed (OS (Ono and Suzuki) Kyoto process). Metallic titanium [13][14][15], niobium [16], nickel [17], and other alloys and intermetallic compounds [18,19] can be formed via the OS process. In addition, the electrochemical decomposition of carbon dioxide gas by an advanced OS process using ...

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Inter-relationship between structure and dielectric properties of crystalline anodic zirconia

Cited by 43 publications

References 19 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

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

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

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