Theoretical prediction, synthesis, and crystal structure determination of new MAX phase compound V2SnC

Qiang Xu,Salvatore Grasso,Chunfeng Hu,Haiming Zhang,Quanzheng Tao,Jun Lu,Johanna Rosén,Yanchun Zhou,Yunhui Niu,Anna Jiang

doi:10.1007/s40145-020-0391-8

Abstract

Guided by the theoretical prediction, a new MAX phase V2SnC was synthesized experimentally for the first time by reaction of V, Sn, and C mixtures at 1000 °C. The chemical composition and crystal structure of this new compound were identified by the cross-check combination of first-principles calculations, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and high resolution scanning transmission electron microscopy (HR-STEM). The stacking sequence of V2C and Sn layers results in a crystal structure of space group P63/mmc. The a- and c-lattice parameters, which were determined by the Rietveld analysis of powder XRD pattern, are 0.2981(0) nm and 1.3470(6) nm, respectively. The atomic positions are V at 4f (1/3, 2/3, 0.0776(5)), Sn at 2d (2/3, 1/3, 1/4), and C at 2a (0, 0, 0). A new set of XRD data of V2SnC was also obtained. Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy, satisfied Born-Huang criteria of mechanical stability, and positive phonon branches over the Brillouin zone. It also has low shear deformation resistance c44 (second-order elastic constant, cij) and shear modulus (G), positive Cauchy pressure, and low Pugh’s ratio (G/B = 0.500 < 0.571), which is regarded as a quasi-ductile MAX phase. The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.

Highlights

The layered machinable MAX phases are a large family of ternary carbides and nitrides with a general formula of Mn+1AXn, where M is an early transition metal, A is a group of IIIA or IVA elements, X is carbon or nitrogen, and n is an integer, commonly equal to 1, 2, or 3 [1,2,3]
The purpose of this study is to explore the existence of V2SnC and its crystal structure determination
We report on the full X-ray diffraction (XRD) pattern data of V2SnC for the first time

Summary

Introduction

The layered machinable MAX phases are a large family of ternary carbides and nitrides with a general formula of Mn+1AXn, where M is an early transition metal, A is a group of IIIA or IVA elements, X is carbon or nitrogen, and n is an integer, commonly equal to 1, 2, or 3 [1,2,3]. Like ceramics, they have low density, high strength and modulus, good corrosion, and hightemperature oxidation resistance; like metals, they are electrically conductive, relatively soft, readily machinable, resistant to thermal shock, and tolerant to damage [14,15]. These phases can be used as precursors for the two-dimensional (2D) materials MXenes by selectively etching out the group IIIA or IVA elements [16]. Mo2Ga2C, Mo2(Au1–xGax)2C, Ti2Au2C, and Ti3Au2C2 with the double A-layer phases have been reported [17,18,19,20]

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