Lattice structure of β-Ta2O5

Lehovec, K.

doi:10.1016/0022-5088(64)90036-0

Cited by 107 publications

(66 citation statements)

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“…The points refer to the experimental data and the line to the Rietveld refinement fit. The first row of ticks corresponds to the Bragg positions of the wodginite (C2/c) crystal structure, the second and third rows of ticks refer to the Ta 2 O 5 (Lehovec, 1964) and Nb 2 O 5 (Ercit, 1991) minority phases, respectively.…”

Section: Resultsmentioning

confidence: 99%

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A new approach for the determination of multiple cation locations and ordering, using the example of natural and heat-treated columbites

Kinast¹,

Isnard²,

Cunha³

et al. 2011

J Appl Cryst

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A new approach is proposed to determine unambiguously the location of four cations within the crystal structure of a natural AB 2 O 6 columbite-type compound and derivatives, when submitted to order-disorder transitions caused by heat treatments. This method is based on the successive use of electron microprobe analysis to determine the cation concentration, Mö ssbauer spectroscopy to identify the Fe occupation, and a crystal structure determination of the samples combining Rietveld refinements of both neutron and X-ray diffraction. This approach is tested successfully to investigate (Fe, Mn, Nb, Ta) natural minerals as well as oxides obtained by heat treatment of the initial AB 2 O 6 columbite-type compound.

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Section: Resultsmentioning

confidence: 99%

“…1. The oxidation of the sample during annealing in an air atmosphere also led to the formation of Ta 2 O 5 - (Lehovec, 1964) and Nb 2 O 5 -type (Ercit, 1991) phases whose concentrations are listed in Table 8.…”

Section: Sample Phasesmentioning

confidence: 99%

A new approach for the determination of multiple cation locations and ordering, using the example of natural and heat-treated columbites

Kinast¹,

Isnard²,

Cunha³

et al. 2011

J Appl Cryst

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“…Early X-ray diffraction studies [9,10] found that the orthorhombic Ta 2 O 5 phase consists of two-dimensional (2D) layers of Ta 2 O 3 in the ab plane, and two-fold coordinated O atoms that connect the Ta atoms in adjacent layers (forming linear chains of -Ta-O-Ta-O-Ta-) along the c direction. In the Ta 2 O 3 plane, it was understood that the Ta atoms form a triangular arrangement, but the arrangement of O atoms was unresolved, with many weak superstructure lines [10]. Later, Roth and coworkers reported that the Ta 2 O 3 plane consists of a disordered array of Ta atoms in octahedral and pentagonal bipyramidal arrangements, with an 11-fold increase of the lattice parameters in the b direction [11].…”

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confidence: 99%

“…1). These models assume a triangular sublattice of Ta, as shown in early experiments [9,10], with one or two Ta 2 O 5 units per unit cell. Recently, however, Andreoni and Pignedoli found that both the β and δ models have instability modes with imaginary vibration frequencies [21].…”

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confidence: 99%

“…This instability highlights the need to clearly identify the atomic structure of the orthorhombic Ta 2 O 5 phase in order to improve fundamental understanding of the material, and also to accelerate technological applications. An attempt to pinpoint the origin of the structural disorder [10][11][12][13][14] should also be made.In this Letter, we use first-principles calculations to determine the key structural motif of the orthorhombic phase of Ta 2 O 5 and the origin of structural disorder. We propose a new structural model that consists of two Ta 2 O 5 units per unit cell, is stable, and accounts very well for experimentally observed structural and electronic properties.…”

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Hidden Structural Order in OrthorhombicTa2O5

Lee

Kim

et al. 2013

Phys. Rev. Lett.

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We investigate using first-principles calculations the atomic structure of the orthorhombic phase of Ta2O5. Although this structure has been studied for decades, the correct structural model is controversial owing to the complication of structural disorder. We identify a new low-energy highsymmetry structural model where all Ta and O atoms have correct formal oxidation states of +5 and −2, respectively, and the experimentally reported triangular lattice symmetry of the Ta sublattice appears dynamically at finite temperatures. To understand the complex atomic structure of the Ta2O3 plane, a triangular graph-paper representation is devised and used alongside oxidation state analysis to reveal infinite variations of the low-energy structural model. The structural disorder of Ta2O5 observed in experiments is attributed to the intrinsic structural variations, and oxygen vacancies that drive collective relaxation of the O sublattice.Tantalum pentoxide (Ta 2 O 5 ) is one of the most extensively studied transition metal oxides due to its potential for technological applications such as anti-reflection coatings, photocatalysis, and high-k dielectrics for highdensity transistors [1][2][3]. It has recently attracted interest as the material of choice for resistance-change memory and the related memristor [4][5][6], however, its crystalline structure, which is critical to its unique structural and electronic properties, is still unclear.Ta 2 O 5 has an orthorhombic phase up to ∼ 1350 • C, above which a transition to a tetragonal phase occurs [7,8]. Although the low-temperature orthorhombic phase is of technological relevance, it has proven difficult to characterize structurally. Early X-ray diffraction studies [9,10] found that the orthorhombic Ta 2 O 5 phase consists of two-dimensional (2D) layers of Ta 2 O 3 in the ab plane, and two-fold coordinated O atoms that connect the Ta atoms in adjacent layers (forming linear chains of -Ta-O-Ta-O-Ta-) along the c direction. In the Ta 2 O 3 plane, it was understood that the Ta atoms form a triangular arrangement, but the arrangement of O atoms was unresolved, with many weak superstructure lines [10]. Later, Roth and coworkers reported that the Ta 2 O 3 plane consists of a disordered array of Ta atoms in octahedral and pentagonal bipyramidal arrangements, with an 11-fold increase of the lattice parameters in the b direction [11]. The superstructure periodicity was shown to change when aliovalent cations, such as W or Li, were incorporated in small amounts to stabilize the phase [12,13]. The superstructures consist of a set of small-unit basic structures and invoked the concept of infinitely adaptive structures [14] for nonstoichiometric Ta 2 O 5−x thatwithin certain composition limits-every composition orders into a different superstructure.Extensive theoretical studies have been made with regards to the bulk properties, dielectric response, and oxygen vacancies (and their diffusion) of Ta 2 O 5 [15][16][17][18][19][20][21][22][23]. In these studies, the low-temperature Ta 2 O 5 pha...

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Structural Analysis and Performance in a Dual‐Mechanism Conductive Filament Memristor

Tsai

Huang

et al. 2021

Adv Elect Materials

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The development of a dual‐filament model is vital for achieving better performance in next‐generation resistive random‐access memory (RRAM). In this work, the microstructure evolution and corresponding performance of a Cu/Ta2O5−x/Pt system are investigated at the atomic scale. By inducing intrinsic oxygen vacancies into tantalum oxide and applying copper as the active electrode, the RRAM device can exhibit the electrical properties of a dual‐mechanism filament. The device demonstrates a long retention time (104 s) and a large memory window of 106. By using high‐resolution transmission electron microscopy and high‐resolution X‐ray photoelectron spectroscopy, the conductive filament is found to consist of crystalline copper and oxygen vacancies. Moreover, with the growth kinetics of filaments from in situ transmission electron microscopy and curve fitting relevant to the conduction mechanism, the formation of filaments is promoted by field‐coalesced oxygen vacancies induced by the growth of copper filaments. Therefore, this work provides a unique perspective and a novel material engineering approach for tailoring RRAM devices and developing further applications in electronic technology.

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Lattice structure of β-Ta2O5

Cited by 107 publications

References 3 publications

A new approach for the determination of multiple cation locations and ordering, using the example of natural and heat-treated columbites

A new approach for the determination of multiple cation locations and ordering, using the example of natural and heat-treated columbites

Hidden Structural Order in OrthorhombicTa2O5

Structural Analysis and Performance in a Dual‐Mechanism Conductive Filament Memristor

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