Irradiation-induced structural transitions in Ti 2 AlC

Wang, Chenxu; Yang, Tonghai; Xiao, Jingren; Liu, Shaoshuai; Xue, Jianming; Wang, Jingyang; Huang, Qing; Wang, Yugang

doi:10.1016/j.actamat.2015.07.043

Cited by 54 publications

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References 36 publications

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“…The d=3.3Å of the (10-10) planes were perfectly matched with those of the reported Ti2AlC [5]. M2AX phase Ti2AlC possessed a hexagonal structure in which covalent Ti2C layers are intercalated with metallic Al layers (Fig.1b).…”

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confidence: 63%

The Morphology of TiiAlC (M2AX) and TiiC (MXene) Sheets Revealed by HAADF STEM Analysis

Bakardjieva

Klie

2018

Microsc Microanal

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The MAX phases are a family of materials composed of a transition metals (M), an A group element (A), and carbon and/or nitrogen (X) with a combination of metallic and ceramic properties [1]. The significance of the MAX phases stems from their laminated structure, where Mn+1Xn sheets are interleaved with atomically thin A layers. The M-X bonds consist of a mixture of covalent, metallic, and ionic bonds making M-X compounds exceptionally strong and hence appealing for new applications [2]. The family of graphene-analogous material, known as MXenes, was discovered recently by Barsoum´s group [3]. The MXenes are synthesized from the MAX phases by removal of A-layers through chemical etching, resulting in stand-alone 2D sheets. It was confirmed that the properties of the MXene layered compounds such as wetting, electrical and electrochemical properties can be tunable through selections of surface functional groups. As modified surfaces make MXenes interesting in multiple fields, for instance in energy storage systems and catalysis.In this study, the structural properties of individual Ti2C (MXene) sheets are investigated at the atomic level by STEM-EELS and EDX. The Ti2C compound was generated through selective etching of aluminum (Al) from of the Ti2AlC ternary M2AX. Ti2AlC was prepared by ball-milling of Ti:Al:TiC reagents in ratio 1:1.1:1 for 24 h using zirconia balls. The mixture was annealed at 1300°C for 2 hrs in argon atmosphere. The sintered compact was converted to a powder by milling. Ti2C MXene powder was prepared by immersing Ti2AlC powder in 1M of NH4HF2 solution for 2 days [4]. After treatment the suspension was washed several times using deionized water. TEM samples were prepared by crushing the powder and next dispersion in ethanol solution, treated in ultrasound for 5 min. A drop of suspension was placed on a Ni grid. The characterization was performed using the UIC microscope JEOL JEM-ARM200CF TEM/STEM with cold field emission source; CEOS probe aberration corrector, Gatan digital cameras, Oxford Energy Dispersive X-ray Spectroscopy (XEDS) and Gatan Electron Energy Loss Spectroscopy (EELS). EELS intensities were normalized with respect to the Ti peak.From the observations of lattice fringes, solid state obtained sample revealed to have well-crystallized M2AX-phase Ti2AlC structure (Fig.1a). The d=3.3Å of the (10-10) planes were perfectly matched with those of the reported Ti2AlC [5]. M2AX phase Ti2AlC possessed a hexagonal structure in which covalent Ti2C layers are intercalated with metallic Al layers (Fig.1b). According our STEM experiment the molar ratio of Ti:Al:TiC = 1:1.1:1 led to a stoichiometric Ti2AlC phase (Fig.1d). Fig.2a shows the HAADF STEM of Ti2AlC phase etched in NH4HF2 results for Ti2C sheets. It is found atomic Ti-C columns (Fig.2b) to be imaged even for single layer structures. The d=2.0Å of the (1-100) planes were matched with those of Ti2C. The layer stacking sequence of Ti atoms along the [0 0 0 1] is visible. In conclusion, we confirm that Al containing M2AX phases could be s...

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confidence: 63%

The Morphology of TiiAlC (M2AX) and TiiC (MXene) Sheets Revealed by HAADF STEM Analysis

Bakardjieva

Klie

2018

Microsc Microanal

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“…Similar to Ti 2 AlC, V 2 AlC and Cr 2 AlC phases have the isomorphous hexagonal symmetry structures (space group of P 6 3 / mmc ) with four V/Cr atoms in 4 f , two Al atoms in 2 d , and two C atoms in 2 a Wychoff positions, as shown in Fig. (a).…”

Section: Introductionmentioning

confidence: 97%

Structural Transitions Induced by Ion Irradiation in V₂AlC and Cr₂AlC

et al. 2016

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Nanolayered structural metallic ceramics, MAX phases, possess unique and highly attractive properties, including excellent radiation tolerance for some of them, whereas little is known about the detailed process of irradiation-induced structural transitions. In this study, the microstructural transformations and the stabilities of V 2 AlC and Cr 2 AlC induced by 1 MeV Au + ions irradiation over a wide range of fluences were investigated by grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). GIXRD analyses show different processes of phase transitions and amorphization tolerance under irradiation between these two MAX phases, which are consistent with the selected area electron diffraction (SAED) results and the high-resolution observations. TEM observations reveal that the nanolamellar structures are disturbed and respective phase transitions occur at relatively low fluences, with the formation of stacking faults. As the fluence increases, Cr 2 AlC becomes completely amorphous, while V 2 AlC are gradually transformed into facecentered cubic (fcc) structure from the original hexagonal close-packed (hcp) structure without amorphization, indicating that V 2 AlC is more tolerant of irradiation than Cr 2 AlC. Based on the phase contrast images and the electron-diffraction pattern (EDP) simulation of the microstructures, mechanisms of the phase transitions of V 2 AlC and Cr 2 AlC are proposed and the difference of the irradiation tolerance between them is discussed.

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“…However, the nature and mechanisms of atomic-scale damage resulting from exposure of these materials to radiation have been debated for many years. To date, there are three different explanations for the irradiation-induced transformation to the face-centered cubic (fcc) structures: decomposition into the corresponding binary fcc-structured carbides or nitrides with out-diffusion of the A elements 17 ; formation of a new fcc M n +1 (A, X n ) composition with A atoms randomly redistributed on the X sublattice 18 ; hex-to-fcc transformation due to mixing of both M and A cations onto the sublattice of the other 19 . In the absence of direct observation of local atomic rearrangements accompanying this order–disorder transformation, the precise mechanism cannot be accurately determined, giving rise to these conflicting explanations.…”

Section: Introductionmentioning

confidence: 99%

Disorder in Mn+1AXn phases at the atomic scale

et al. 2019

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Atomic disordering in materials alters their physical and chemical properties and can subsequently affect their performance. In complex ceramic materials, it is a challenge to understand the nature of structural disordering, due to the difficulty of direct, atomic-scale experimental observations. Here we report the direct imaging of ion irradiation-induced antisite defects in Mn+1AXn phases using double CS-corrected scanning transmission electron microscopy and provide compelling evidence of order-to-disorder phase transformations, overturning the conventional view that irradiation causes phase decomposition to binary fcc-structured Mn+1Xn. With the formation of uniformly distributed cation antisite defects and the rearrangement of X anions, disordered solid solution γ-(Mn+1A)Xn phases are formed at low ion fluences, followed by gradual transitions to solid solution fcc-structured (Mn+1A)Xn phases. This study provides a comprehensive understanding of the order-to-disorder transformations in Mn+1AXn phases and proposes a method for the synthesis of new solid solution (Mn+1A)Xn phases by tailoring the disorder.

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Irradiation-induced structural transitions in Ti 2 AlC

Cited by 54 publications

References 36 publications

The Morphology of TiiAlC (M2AX) and TiiC (MXene) Sheets Revealed by HAADF STEM Analysis

The Morphology of TiiAlC (M2AX) and TiiC (MXene) Sheets Revealed by HAADF STEM Analysis

Structural Transitions Induced by Ion Irradiation in V₂AlC and Cr₂AlC

Disorder in Mn+1AXn phases at the atomic scale

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Irradiation-induced structural transitions in Ti 2 AlC

Cited by 54 publications

References 36 publications

The Morphology of TiiAlC (M2AX) and TiiC (MXene) Sheets Revealed by HAADF STEM Analysis

The Morphology of TiiAlC (M2AX) and TiiC (MXene) Sheets Revealed by HAADF STEM Analysis

Structural Transitions Induced by Ion Irradiation in V2AlC and Cr2AlC

Disorder in Mn+1AXn phases at the atomic scale

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Structural Transitions Induced by Ion Irradiation in V₂AlC and Cr₂AlC