Neue Beobachtungen zum System TiO2Ta2O5

Mertin, Wilhelm; Gruehn, R.; Schäfer, Harald

doi:10.1016/0022-4596(70)90125-8

Cited by 22 publications

(12 citation statements)

References 30 publications

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“…Dense specimens were heated to different temperatures for varying amounts of time, and then either cooled slowly (maximum 5°C/min) or quenched directly into water (∼500 °C/sec). Previous XRD studies on undoped Ta 2 O 5 indicated that quenching was required to maintain the H‐Ta 2 O 5 structure at room temperature, but those studies were based upon powder specimens that were crushed and ground after their final heat treatment 13,19,22,23 . For the current study, uncrushed ceramic specimens held at a given temperature for the same amount of time exhibited identical room temperature XRD patterns whether they were quenched or cooled slowly to room temperature.…”

Section: Resultsmentioning

confidence: 80%

“…The lower‐temperature phase (L‐Ta 2 O 5 ) appears to be orthorhombic 12–18 . It has been speculated that the stable high‐temperature phase (H‐Ta 2 O 5 ) is tetragonal, 13,19,20 but at room temperature, H‐Ta 2 O 5 specimens in metastable form exhibit monoclinic (or triclinic) symmetry that is slightly distorted from tetragonal 21–23 …”

Section: Introductionmentioning

confidence: 99%

“…[12][13][14][15][16][17][18] It has been speculated that the stable high-temperature phase (H-Ta 2 O 5 ) is tetragonal, 13,19,20 but at room temperature, H-Ta 2 O 5 specimens in metastable form exhibit monoclinic (or triclinic) symmetry that is slightly distorted from tetragonal. [21][22][23] Phase equilibria studies have verified that, up to levels of B12.5%, TiO 2 is incorporated into the modulated block structure of L-Ta 2 O 5 and forms a solid solution with H-Ta 2 O 5 . 13,22,23 Additions of TiO 2 lower the temperature of the L ) H-Ta 2 O 5 phase transformation, with a minimum transformation temperature of B11501C occurring at approximately 9% TiO 2 .…”

Section: Introductionmentioning

confidence: 99%

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Preparation of Dense Ta₂O₅‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Brennecka

Payne

2006

Journal of the American Ceramic Society

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A hybrid solution‐coated powder method was used to reduce the sintering temperature of TiO2‐modified Ta2O5 ceramics. This simple and effective method allowed chemical homogenization and densification to take place below a densification‐impeding phase transformation, something that has not been achieved by traditional mixed oxide processing. Combining the coated powder method with a two‐stage heat treatment (by which specimens were first densified and then transformed into the high dielectric constant H‐Ta2O5 phase) enabled the realization of dense and homogeneous 92Ta2O5–8TiO2 ceramics with dielectric constant values up to 280 at room temperature.

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Section: Resultsmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Preparation of Dense Ta₂O₅‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Brennecka

Payne

2006

Journal of the American Ceramic Society

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“…After reinterpretation of data collected from Sc 2 O 3 ‐stabilized crystals, Stephenson and Roth 16 later proposed a monoclinic unit‐cell for the prototypic high‐temperature structure of H‐Ta 2 O 5 . Several reports have confirmed the presence of three different phases of metastable H‐Ta 2 O 5 , with a relatively close agreement for the temperatures of the respective transformations, but significant uncertainty still exists regarding the symmetry and exact structure(s) of the phases 15,17,18–22 . Two different groups have reported on the defect chemistry of pure and doped H‐Ta 2 O 5 , 23–26 and noted that TiO 2 ‐containing specimens were more stable than pure specimens at intermediate temperatures.…”

Section: Introductionmentioning

confidence: 90%

Phase Transformations in the High‐Temperature Form of Pure and TiO₂‐Stabilized Ta₂O₅

Brennecka

Payne

Sarin

et al. 2007

Journal of the American Ceramic Society

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The high‐temperature forms of undoped tantalum pentoxide (H‐100Ta2O5) and TiO2–modified Ta2O5 (H‐92Ta2O5–8TiO2) were investigated by in situ synchrotron X‐ray diffraction and Raman scattering measurements. Two unquenchable and reversible phase transformations were observed in pure H‐Ta2O5, while only one was detected for TiO2‐stabilized H‐Ta2O5. Diffraction studies were consistent with displasive transformations, but hot‐stage Raman spectroscopy indicated the existence of transient intermediate forms during the transformations. Use of complementary techniques enabled the reinterpretation of phase transformations in light of a newly proposed crystal structure model for H‐Ta2O5,1 and emphasized the structural contributions of the oxygen sublattice.

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“…The properties of solid solutions are well defined when the concentration of the solute ions is within the solubility limit. This limit is approximately 4‐8 at% for tantalum and 8‐18 at% of niobium …”

Section: Brief Literature Overviewmentioning

confidence: 96%

Electrical conductivity and defect disorder of tantalum‐doped TiO₂

et al. 2017

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The present work reports the electrical properties of polycrystalline Ta-doped TiO 2 (0.39 at.% Ta) determined in situ at elevated temperatures (1173-1323 K) in the gas phase of controlled oxygen activity (10 À12 Pa to 10 5 Pa). The effect of oxygen activity on the electrical conductivity and thermoelectric power of TiO 2 is discussed in terms of defect disorder, including (1) the intrinsic electronic disorder that is governed by electronic compensation in the strongly reducing regime, (2) the extrinsic electronic disorder that is governed by electronic charge compensation in the reducing regime, and (3) the extrinsic ionic disorder that is governed by ionic compensation in the oxidizing regime. It is shown that tantalum ions are incorporated into the titanium sublattice of TiO 2 leading to the formation of donor-type energy levels. The Arrhenius-type plot of the electrical conductivity data leads to the determination of the formation enthalpy terms. The obtained results are considered in terms of the effect of tantalum and oxygen activity on the defect disorder and the associated key performance-related properties in the light-induced partial water oxidation. K E Y W O R D SPoint defects, electrical properties, oxides, titanium dioxide | INTRODUCTIONTitanium dioxide is the promising material for water oxidation using solar energy. [1][2][3][4][5] This process, leading either to partial or total water oxidation, may be applied in water purification and the generation of solar fuel, respectively. Intensive research aims at processing TiO 2 with enhanced performance in these applications.The most commonly applied research strategy in processing TiO 2 with enhanced performance is based on the incorporation of a range of extrinsic ions into the TiO 2 lattice.2-5 The influence of the extrinsic ions on the performance in solar energy conversion by TiO 2 has been commonly considered to be determined by reduction of the band gap, which leads to enhanced absorption of sunlight. While the effect of the band gap on light absorption is obvious, the recent studies show that the solar-to-chemical energy conversion by oxide semiconductors and the related charge transfer is profoundly influenced by a range of the key performance-related properties, KPPs, such as the concentration of surface active sites, charge transport, Fermi level and the band gap. [5][6][7] It is shown that the KPPs are defect related. For example, titanium vacancies are the anodic active sites for water oxidation. 5-7 Therefore, these can be modified by defect engineering. 5-7The aim of the present work, which is part of a larger research program on the effect of KPPs of TiO 2 on the solar-to-chemical energy conversion, is the determination of the effect of tantalum on the semiconducting properties

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Neue Beobachtungen zum System TiO2Ta2O5

Cited by 22 publications

References 30 publications

Preparation of Dense Ta₂O₅‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Preparation of Dense Ta₂O₅‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Phase Transformations in the High‐Temperature Form of Pure and TiO₂‐Stabilized Ta₂O₅

Electrical conductivity and defect disorder of tantalum‐doped TiO₂

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Neue Beobachtungen zum System TiO2Ta2O5

Cited by 22 publications

References 30 publications

Preparation of Dense Ta2O5‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Preparation of Dense Ta2O5‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Phase Transformations in the High‐Temperature Form of Pure and TiO2‐Stabilized Ta2O5

Electrical conductivity and defect disorder of tantalum‐doped TiO2

Contact Info

Product

Resources

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Preparation of Dense Ta₂O₅‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Preparation of Dense Ta₂O₅‐Based Ceramics by a Coated Powder Method for Enhanced Dielectric Properties

Phase Transformations in the High‐Temperature Form of Pure and TiO₂‐Stabilized Ta₂O₅

Electrical conductivity and defect disorder of tantalum‐doped TiO₂