Elastic, mechanical, electronic, and defective properties of Zr–Al–C nanolaminates from first principles

Abstract

By means of first principles calculations, Zr–Al–C nanolaminates have been studied in the aspects of chemical bonding, elastic properties, mechanical properties, electronic structures, and vacancy stabilities. Although the investigated Zr–Al–C nanolaminates show crystallographic similarities, their predicated properties are very different. For (ZrC)nAl3C2 (n = 2, 3, 4), the Zr–C bond adjacent to the Al–C slab with the C atom intercalated in the Zr layers is the strongest, but the one with the C atom intercalated between the Zr layer and Al layer is the weakest. In contrast, the situation for (ZrC)nAl4C3 (n = 2, 3) is just the opposite. For Zr–Al–C nanolaminates, the calculated bulk, shear and Young's modulus increase in the sequence of Zr2AlC < Zr3AlC2 < Zr2Al4C5 < Zr3Al4C6 < Zr2Al3C4 < Zr3Al3C5 < Zr4Al3C6. The (ZrC)nAl3C2 (n = 2, 3, 4) series exhibit the most outstanding elastic properties. In the presence of the external pressure, the bulk and shear moduli exhibit a linear response to the pressure, except for Zr2AlC and Zr3AlC2, both of which belong to the so‐called MAX phases. The two materials also exhibit very distinct properties in the strain‐stress relationship, electronic structures and vacancy stabilities. As the intercalated Al layers increase, the formation energy of VZr and VAl increases, while the formation energy of VC decreases.

Synergetic Effects of Strain Engineering and Carbon Vacancy Modification on Tin+1CnO2 MXene for Promising Catalytic Activity of Hydrogen Evolution Reaction

“…The stabilities of defective models were considered to gain deep insight into the HER catalytic activity of Ti n +1 C n O 2 , and the vacancy formation energy ( E f ( X )) of different species ( X ) was introduced as follows: , E f false( X false) = E def false( X false) − E matrix + μ X where E def ( X ) and E matrix are the total energies of the defective supercells and the matrix materials, respectively. And μ X is the chemical potential of the vacancy species such as a C vacancy, oxygen vacancy, or titanium vacancy.…”

“…The stabilities of defective models were considered to gain deep insight into the HER catalytic activity of Ti n+1 C n O 2 , and the vacancy formation energy (E f (X)) of different species (X) was introduced as follows: 46,47 E X E X E ( ) ( )…”

Synthesizinge a novel Zr2Al-GNS MAX phase ceramic with superior electrical properties using pressureless sintering technique

“…The presence of the Al element in the ceramic MAX phase can assist in forming a protective oxide layer to prevent the high-temperature steam oxidation process [ 26 ]. Because of the narrow cross section of the Zr element in neutrons applications, the Zr-Al-C MAX phases ceramic, such as Zr 3 AlC 2 and Zr 2 AlC, are superior candidates for using in fuel cladding coatings [ 27 , 28 ]. Therefore, a simple, cost-effective technique with uncomplicated equipment under low temperature preparing a high-purity ceramic MAX phase is in urgent demand.…”

Stability trend, weak bonding, and magnetic properties of the Al‐ and Si‐containing ternary‐layered borides MAB phases

“…38 However, it is very difficult to theoretically predict their mechanical behavior using the conventional First principles. To respond to this challenge, using a theoretical model of "bond stiffness" (k) proposed by Bai et al 4,39 which quantitatively characterizes the strength of chemical bonds and importantly shows the relative bonding strength among nanolaminates, the ratio of bond stiffness of the weakest and strongest bonds (k min /k max ) plays a critical role in the mechanical performance of ternary layered ceramics: the high damage tolerance and fracture toughness without indentation cracks are observed when the ratio is lower than 1/2, such as MoAlB 14 and most of MAX phases; 5 but above or around 1/2 cracks are indeed present in the Vickers' indentation, such as the (MC) n Al 3 C 2 40 and (MC) n Al 4 C 3 41,42 and MAX-phase Ti 2 SC 40 although the Ti-S bond is still weaker than Ti-C bond with k min /k max = 0.78. Therefore, k min /k max can be used as a theoretical judgment of the macro mechanical behavior of ternary layered ceramics from the micro bond stiffness.…”