Phase equilibrium investigations and thermodynamic modelling of the ZrO2-Ta2O5 system

Löffler, Mario; Fabrichnaya, Olga; Hutterer, Patrick; Lepple, Maren

doi:10.1016/j.jeurceramsoc.2023.08.004

Cited by 11 publications

(8 citation statements)

References 46 publications

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“…Our observed powder XRD patterns closely match observations from previous studies on bulk Ta 2 O 5 [17,18,55] and Ta 2 O 5 thin films [39,56]. Figure 1 compares an integrated pattern collected at ambient conditions with calculated profiles of the proposed Ta 2 O 5 phases.…”

Section: Methodssupporting

confidence: 86%

Phase comparison and equation of state for Ta₂O₅

Brennan,

Rehn,

Huston

et al. 2024

J. Phys.: Condens. Matter

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Tantalum pentoxide (Ta2O5) is among the most technologically useful heavy transition metal oxides. Unfortunately, its crystal structure is the subject of long-standing and unresolved disagreement. Among other consequences, this uncertainty has made it impossible to formulate a robust high pressure equation of state for Ta2O5. Here, we report the results of high pressure X-ray diffraction experiments indexed against a comprehensive list of proposed Ta2O5 phases. Five of the proposed phases produce good matches to experimental observations, and the compressibility parameters for these phases are all consistent within uncertainty. This means that regardless of the particular phase chosen, the Ta2O5 equation of state can be described with bulk modulus K0 = 138 ± 3.68 GPa and pressure derivative K′0 = 1.82 ± 0.45. Combining these experimental results with new density-functional theory calculations allows us to identify the λ phase as the best structural model of Ta2O5 at ambient conditions.

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Section: Methodssupporting

confidence: 86%

Phase comparison and equation of state for Ta₂O₅

Brennan,

Rehn,

Huston

et al. 2024

J. Phys.: Condens. Matter

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“…For the α‐Ta 2 O 5 and β‐Ta 2 O 5 phases, the formulas of (Ta 5+ ) 3 (O 2− ) 6 (O 2− , Va) 2 and (Ta 5+ ) 12 (O 2− ) 12 (O 2− , Va) 19 were used to separately describe the tetragonal α‐Ta 2 O 5 and orthorhombic β‐Ta 2 O 5 phases by Löffler et al 38 . based on their crystal structures.…”

Section: Resultsmentioning

confidence: 99%

“…based on their crystal structures. In order to express the larger solubility of Al 2 O 3 in the α‐Ta 2 O 5 and β‐Ta 2 O 5 phases, the formulas of Löffler et al 38 . were accepted in our optimization, and therefore they were modeled as (Al 3+ , Ta 5+ ) 3 (O 2− ) 6 (O 2− , Va) 2 and (Al 3+ , Ta 5+ ) 12 (O 2− ) 12 (O 2− , Va) 19 .…”

Section: Resultsmentioning

confidence: 99%

Phase equilibrium investigations of the Al₂O₃–Ta₂O₅ system: New experiments and thermodynamic modeling

Feng,

Zhao,

et al. 2024

J Am Ceram Soc.

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Phase equilibria in the Al2O3–Ta2O5 system have been studied by means of CO2 laser heater, high‐speed pyrometer, X‐ray powder diffraction, and scanning electron microscopy. The liquidus and invariant reaction temperatures in the whole composition region were measured by cooling trace tests. The monotectic reaction of Liquid 1→Liquid 2 + Al2O3 was determined to be at about 1547°C, but the typical microstructures for the miscibility gap were not directly observed in our experiments. The tetragonal AlTaO4 phases formed from as‐cast samples were found to congruently melt at 1669°C, and they could maintain stability during the cooling process but would gradually transform into orthorhombic and monoclinic polymorphs after heat treatment. Two eutectic reactions of Liquid → Al2O3 + T‐AlTaO4 and Liquid → T‐AlTaO4 + β‐Ta2O5 were measured to be at 1447°C and 36.7 mol%Ta2O5 and 1513°C and 63.5 mol% Ta2O5, respectively. Due to the undercooling effect, the invariant reaction temperatures determined by this work might be preliminary and need to be verified by more accurate methods. Our experiments confirmed that doping Al2O3 in Ta2O5 phases could improve phase stability of β‐Ta2O5. Finally, thermodynamic optimization of the Al2O3–Ta2O5 system was performed based on the obtained experimental data by means of the CALPHAD method. The self‐consistent thermodynamic parameters are helpful in further efforts for construction of Al2O3–Ta2O5‐based multicomponent thermodynamic database and the development of alumina–tantala‐based materials.

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“…In this work, hafnium chloride (HfCl 4 , 99.9% metals basis, Alfa Aesar) and tantalum chloride (TaCl 5 , 99.99% metals basis, Alfa Aesar) were used as precursors. The details of the procedure of sample synthesis can be found in Löffler et al 12 To analyze the qualitative and quantitative phases, powder XRD was carried out using a Bruker D8 instrument with Co Kα radiation (λ = 1.7889 Å) for the XRD analysis. The measurement range of 18 • ≤ 2θ ≤ 150 • with a step size of.0118 • was used, and the total measurement time was 22.5 h. The sintered pellet fragments were pulverized and then examined on a silicon sample carrier.…”

Section: Methodsmentioning

confidence: 99%

“…11 The thermodynamic modeling of the phases is based on the compound energy formalism accounting the crystal structure of the phases. The phases found in the system have the same structures as in the ZrO 2 -Ta 2 O 5 system and the same models as in the work by Löffler et al 12 are going to be used.…”

Section: Introductionmentioning

confidence: 99%

Phase equilibrium investigations and thermodynamic modeling of the HfO₂–Ta₂O₅ system

Löffler,

Fabrichnaya

2024

Int J Applied Ceramic Tech

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The HfO2–Ta2O5 system was investigated using two distinct methods: the equilibration method at temperatures ranging from 1 573 to 1 873 K and the differential thermal analysis method up to 2 473 K. To identify the phases, X‐ray diffraction (XRD) and scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM/EDX) were employed. The temperature of the eutectic reaction L→Hf6Ta2O17+Ta2O5 was measured to be 2 052 K and the eutectic composition to be 66.7 mol.% Ta2O5. The peritectic reaction L+HfO2→Hf6Ta2O17 was observed at a temperature of 2 287 K. The heat capacity of the Hf6Ta2O17 phase was measured using differential scanning calorimetry from 240 to 1 300K. The thermodynamic database for the HfO2–Ta2O5 system was derived.

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Phase equilibrium investigations and thermodynamic modelling of the ZrO2-Ta2O5 system

Cited by 11 publications

References 46 publications

Phase comparison and equation of state for Ta₂O₅

Phase comparison and equation of state for Ta₂O₅

Phase equilibrium investigations of the Al₂O₃–Ta₂O₅ system: New experiments and thermodynamic modeling

Phase equilibrium investigations and thermodynamic modeling of the HfO₂–Ta₂O₅ system

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Phase equilibrium investigations and thermodynamic modelling of the ZrO2-Ta2O5 system

Cited by 11 publications

References 46 publications

Phase comparison and equation of state for Ta2O5

Phase comparison and equation of state for Ta2O5

Phase equilibrium investigations of the Al2O3–Ta2O5 system: New experiments and thermodynamic modeling

Phase equilibrium investigations and thermodynamic modeling of the HfO2–Ta2O5 system

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Product

Resources

About

Phase comparison and equation of state for Ta₂O₅

Phase comparison and equation of state for Ta₂O₅

Phase equilibrium investigations of the Al₂O₃–Ta₂O₅ system: New experiments and thermodynamic modeling

Phase equilibrium investigations and thermodynamic modeling of the HfO₂–Ta₂O₅ system