Order and disorder in quaternary atomic laminates from first-principles calculations. Issue 47 (13th November 2015)

• Record Type: Journal Article
• Authors: Dahlqvist, Martin; Rosen, Johanna
• Is Part Of: Physical chemistry chemical physics. Volume 17:Issue 47(2015)
• Page Start: 31810
• Page End: 31821
• Publication Date: 2015-11-13
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp06021d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The stability of chemically ordered and disordered quaternary atomic laminates with highly ordered structures are predicted to be stable at typical synthesis temperatures T synthesis for TiM2 AlC2 (M = Cr, Mo, W) and Ti2 M2 AlC3 (M = Mo, W) when T synthesis < T disorder . Abstract : We report on the phase stability of chemically ordered and disordered quaternary MAX phases – TiMAlC, TiM2 AlC2, MTi2 AlC2, and Ti2 M2 AlC3 where M = Zr, Hf (group IV), M = V, Nb, Ta (group V), and M = Cr, Mo, W (group VI). At 0 K, layered chemically ordered structures are predicted to be stable for M from groups V and VI. By taking into account the configurational entropy, an order–disorder temperature T disorder can be estimated. TiM2 AlC2 (M = Cr, Mo, W) and Ti2 M2 AlC3 (M = Mo, W) are found with T disorder > 1773 K and are hence predicted to be ordered at the typical bulk synthesis temperature of 1773 K. Other ordered phases, even though metastable at elevated temperatures, may be synthesized by non-equilibrium methods such as thin film growth. Furthermore, phases predicted not to be stable in any form at 0 K can be stabilized at higher temperatures in a disordered form, being the case for group IV, for MTi2 AlC2 (M = V, Cr, Mo), and for Ti2 M2 AlC3 (M = V, Ta). The stability of the layered ordered structures with M from group VI can primarily be explained by Ti breaking the energetically unfavorable stacking of M and C where M is surrounded by C in a face-centered cubic configuration, and by M having a larger electronegativity than Al resulting in a fewer electrons available for populating antibonding Al–Al orbitals. The results show that these chemically ordered quaternary MAX phases allow for new elemental combinations in MAX phases, which can be used to add new properties to this family of atomic laminates and in turn prospects for tuning these properties.