Synthesis, crystallographic structure and thermodynamic properties of T2-Al2MgC2

Abstract T2-Al 2 MgC 2 was synthesized from the elements in a Mg-Al melt at 1000 °C using sealed Ta crucibles. Single crystals of T2-Al 2 MgC 2 were extracted by evaporating the Mg-Al matrix. The crystal structure of T2-Al 2 MgC 2 was refined for the first time on the basis of single-crystal X-ray diffraction. The crystal is trigonal (space group P-3m1, Z = 1) with lattice parameters of a = 3.3767(11) A, c = 5.807(2) A and V = 57.34(5) A 3 . Based on the refined crystal structure, DFT calculations were conducted to evaluate the thermodynamic properties and the electronic structure of the phase. The heat of formation of T2-Al 2 MgC 2 was calculated to be −23.6 kJ/mol of atoms at 298 K. The heat capacity of T2-Al 2 MgC 2 was measured by DSC from 300 to 871 K and calculated by DFT from 0 to 1000 K. Based on the calculated heat capacity, the entropy of formation of the phase at 298 K was determined to be 70.0 J/mol/K. The band structure and the electronic density of state of T2-Al 2 MgC 2 was calculated leading to an indirect band gap value of 1.73 eV.