Ta3AlC2 and Ta4AlC3 − Single-Crystal Investigations of Two New Ternary Carbides of Tantalum Synthesized by the Molten Metal Technique

Etzkorn, Johannes; Ade, Martin; Hillebrecht, Harald

doi:10.1021/ic062231y

Cited by 120 publications

(84 citation statements)

References 36 publications

(34 reference statements)

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“…For Ta 5 AlC 4 , the Fermi-level is located at a very sharp peak and this is consistent with the fact that successful synthesis of Ta 5 AlC 4 has never been reported. 46 Our predictions of the contrasting stability of Ti 2 SC and Ti 2 PC crystals are consistent with the calculations by Du et al 16 and Hug et al 37 . Nevertheless, for those other phases, their less salient DOS topography at the Fermi-level could be outweighed by other factors in determining the phase stability, especially further in predicting whether a phase can exist or not.…”

Section: Methods Of Calculationsupporting

confidence: 91%

Electronic structure and optical conductivities of 20 MAX-phase compounds

2012

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Section: Methods Of Calculationsupporting

confidence: 91%

Electronic structure and optical conductivities of 20 MAX-phase compounds

2012

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“…However, our data on Ta 4 AlC 3 powder showed that Ta 4 AlC 3 has the same structure as Ti 4 AlN 3 [38]. Etzkorn et al [39] independently arrived at the same conclusion. We attempted to refine our XRD data to the structure proposed by Lin et al; however, this refinement was not possible since the experimental peak intensities differed strongly from the calculated intensities, in many cases by more than an order of magnitude.…”

Section: Polymorphism Of Max Phasesmentioning

confidence: 49%

“…In the first reports on Ti 4 AlN 3 [28], the stoichiometry was stated to be Ti 4 AlN 3- with  ≈ 0.1 (determined from Rietveld refinement of Xray and neutron diffraction data), i.e., the Ti 4 AlN 3 structure was reported to be slightly substoichiometric in N. This is supported by DFT calculations, which indicate that introduction of N vacancies in Ti 4 AlN 3- is energetically favorable compared to stoichiometric Ti 4 AlN 3 [52]. On the other hand, a recent calculation for -Ta 4 AlC 3 by Du et al [53] indicated that the introduction of only a small amount of C vacancies in Ta 4 AlC 3 results in reduced stability compared to the stoichiometric structure, and there are no experimental indications that -Ta 4 AlC 3 is understoichiometric in C [39]. Therefore, it is possible that the X-site vacancy-bearing abilities of the known 413 phases differ.…”

Section: Vacanciesmentioning

confidence: 99%

“…The breakthrough came from investigations on bulk synthesis in the Ta-Al-C system, where Ta 2 AlC was previously the only known MAX phase. Around 2006, Ta 4 AlC 3 was discovered independently by several groups [36,37,38,39,240,250], and Ta 3 AlC 2 was first reported by Etzkorn et al [39]. Initially, there was some debate regarding the exact structure of Ta 4 AlC 3 ; this debate was resolved by the finding [38] that Ta 4 AlC 3 has two polymorphs ( and , see section 2.2).…”

Section: Ion Bombardment Effectsmentioning

confidence: 99%

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The M+1AX phases: Materials science and thin-film processing

et al. 2010

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This article is a critical review of the M n+1 AX n phases ("MAX phases", where n =1, 2, or 3) from a materials science perspective. MAX phases are a class of hexagonal-structure ternary carbides and nitrides ("X") of a transition metal ("M") and an A-group element. The most well known are Ti 2 AlC, Ti 3 SiC 2 , and Ti 4 AlN 3 . There are ~60 MAX phases with at least 9 discovered in the last five years alone. What makes the MAX phases fascinating and potentially useful is their remarkable combination of chemical, physical, electrical, and mechanical properties, which in many ways combine the characteristics of metals and ceramics. For example, MAX phases are typically resistant to oxidation and corrosion, elastically stiff, but at the same time they exhibit high thermal and electrical conductivities and are machinable. These properties stem from an inherently nanolaminated crystal structure, with M n+1 X n slabs intercalated with pure A-element layers. The research on MAX phases has been accelerated by the introduction of thin-film processing methods.Magnetron sputtering and arc deposition have been employed to synthesize single-crystal material by epitaxial growth, which enables studies of fundamental materials properties. However, the surface-initiated decomposition of M n+1 AX n thin films into MX compounds at temperatures of 1000-1100 °C is much lower than the decomposition temperatures typically reported for the corresponding bulk material. We also review the prospects for low-temperature synthesis, which is essential for deposition of MAX phases onto technologically important substrates. While deposition of MAX phases from the archetypical Ti-Si-C and Ti-Al-N systems typically require synthesis temperatures of ~800 °C, recent results have demonstrated that V 2 GeC and Cr 2 AlC can be deposited at ~450 °C. Also, thermal spray of Ti 2 AlC powder has been used to produce thick coatings. We further treat progress in the use of first-principles calculations for predicting hypothetical MAX phases and their properties. Together with advances in processing and materials 3 analysis, this progress has led to recent discoveries of numerous new MAX phases such as Ti 4 SiC 3 , Ta 4 AlC 3 , and Ti 3 SnC 2 . Finally, important future research directions are discussed. These include charting the unknown regions in phase diagrams to discover new equilibrium and metastable phases, as well as research challenges in understanding their physical properties, such as the effects of anisotropy, impurities, and vacancies on the electrical properties, and unexplored properties such as superconductivity, magnetism, and optics. 4

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“…From Density Functional Theory (DFT) calculations, it has been predicted that the introduction of N or C vacancies in Ti 4 AlN 3−δ and V 4 AlC 3- , respectively, increases the phase stability relative to the stoichiometric 413 phases [18,19]. In contrast, a similar calculation for α-Ta 4 AlC 3 suggested that a small amount of C vacancies in Ta 4 AlC 3 reduces the stability compared to the stoichiometric structure [20], and there are no experimental indications that α-Ta 4 AlC 3 is understoichiometric in C [21][22]. Nevertheless, there is most likely a stoichiometry range for X-site vacancies for most MAX phases, as for the binary carbides and nitrides.…”

Section: Introductionmentioning

confidence: 98%