The double solid solution (Zr, Nb)2(Al, Sn)C MAX phase: a steric stability approach

Abstract

The addition of Nb and Sn to Zr2AlC is investigated, targeting the synthesis of a Zr-rich bulk MAX phase free of ZrC. The 211 phase formation in the two quaternary Zr-Nb-Al-C and Zr-Al-Sn-C systems is evaluated. Solubility over the entire compositional range in (Zr, Nb)2AlC and Zr2(Al, Sn)C is observed. In terms of effectiveness, the addition of Sn is preferred over the addition of Nb, as the former is selectively incorporated into the 211 structure. A combinatorial approach results in the formation of phase-pure (Zr0.8, Nb0.2)2(Al0.5, Sn0.5)C. The effect of the added solutes on the microstructure and crystallographic parameters is investigated. The addition of Nb and Sn reduces the distortion parameter of the trigonal prism compared to pure Zr2AlC. Therefore, an attempt is made to establish a more general stability criterion for the M2AC structure based on the steric relationship between the atoms in the M6A trigonal prism. Inspired by the Hume-Rothery rules, it is suggested that comparable atomic radii of the M- and A-atoms provide a good starting point to obtain a stable 211 MAX phase.

Ta-based 413 and 211 MAX phase solid solutions with Hf and Nb

“…1). In order to increase the amount of the 413 MAX phase, 50% of the Al content was substituted for Sn, in analogy with prior studies on the synthesis of phase-pure (Zr,Nb)2(Al,Sn)C [41] and (Zr,Ti)2(Al,Sn)C [20] MAX phase ceramics. In those studies, the enhanced stability of the 211 MAX phases over the competing binary phases (carbides, intermetallics) was associated with the trigonal prism distortion parameter and the relative size of the M and A atoms in the M6A prism [42].…”

“…These studies demonstrated experimentally that highly phase-pure bulk MAX phase ceramics can be produced by forming solid solutions on both M and A sites [42]. Apart from giving a comprehensive review of the importance of steric effects in MAX phase lattice distortions, one of these studies demonstrated that a reduced prismatic distortion in the crystal lattice due to smaller differences in the M and A atomic sizes could ensure the synthesis of phase-pure (Zr0.8,Nb0.2)2(Al0.5,Sn0.5)C MAX phase ceramics [41].…”

“…Moreover, the synthesis of (Ta1-x,Hfx)4(Al0.5,Sn0.5)C3 and (Ta1-x,Nbx)4(Al0.5,Sn0.5)C3 double solid solutions was explored in an attempt to produce MAX phase-based bulk ceramics with higher phase purity. This approach has already been successfully implemented in the synthesis of double solid solution (Zr,Nb)2(Al,Sn)C and (Zr,Ti)2(Al,Sn)C MAX phase ceramics [19,20].…”

Compatibility of Zr2AlC MAX phase-based ceramics with oxygen-poor, static liquid lead–bismuth eutectic

“…Note that only in those MAX phases reported to react and to form solid solutions with Bi/Pb, the stress field around the Al atoms was in tension when compared to the natural state of fcc Al. [41] in the Zr2(Al,Bi,Pb)C MAX phase solid solution, using the NPD data acquired from the hot pressed Zr2(Al,Bi,Pb)C ceramic, results in a reduced trigonal prism distortion of 1.080 (Zr2AlC = 1.101 [42]) and an increased octahedral distortion of 1.1103 (Zr2AlC = 1.034 [42]). Recent studies showed that aiming to reduce the trigonal prism distortion by making double solid solution MAX phases (i.e., solid solutions on both M and A sites of the 'host' MAX phase compounds) enhanced the phase purity of the produced ceramics [42,73].…”

Ab initio Study of the Structure, Elastic, and Electronic Properties of Ti3(Al1-nSin)C2 Layered Ternary Compounds

“…Hence, In this study, Ti3SiC2 and Ti3AlC2 are investigated as potential structural materials to expose their further potential for technological and industrial applications as they are considered promising candidates for applications where materials are subjected to extreme environments, like nuclear reactors 1,3,13,14,20 . Therefore, comprehensive knowledge of their electronic, structural stabilities and elastic properties is crucial so that our results will resolve some inconsistency where they exist in the reported properties of these materials.…”