No abstract

M n+1 AX n phases are a large family of compounds that have been limited, so far, to carbides and nitrides. Here we report the prediction of a compound, Ti 2 InB 2 , a stable boron-based ternary phase in the Ti-In-B system, using a computational structure search strategy. This predicted Ti 2 InB 2 compound is successfully synthesized using a solid-state reaction route and its space group is confirmed as P m2 (No. 187), which is in fact a hexagonal subgroup of P6 3 /mmc (No. 194), the symmetry group of conventional M n+1 AX n phases. Moreover, a strategy for the synthesis of MXenes from M n+1 AX n phases is applied, and a layered boride, TiB, is obtained by the removal of the indium layer through dealloying of the parent Ti 2 InB 2 at high temperature under a high vacuum. We theoretically demonstrate that the TiB single layer exhibits superior potential as an anode material for Li/Na ion batteries than conventional carbide MXenes such as Ti 3 C 2 .

Considering the recent breakthroughs in the synthesis of novel two-dimensional (2D) materials from layered bulk structures, ternary layered transition metal borides, known as MAB phases, have come under scrutiny as a means of obtaining novel 2D transition metal borides, so-called MBene. Here, based on a set of phonon calculations, we show the dynamic stability of many Al-containing MAB phases, MAlB (M = Ti, ). By comparing the formation energies of these MAB phases with those of their available competing binary M−B and M−Al, and ternary M−Al−B phases, we find that some of the Sc-, Ti-, V-, Cr-, Mo-, W-, Mn-, Tc-, and Fe-based MAB phases could be favorably synthesized in an appropriate experimental condition. In addition, by examining the strengths of various bonds in MAB phases via crystal orbital Hamilton population and spring constant calculations, we find that the B−B and then M−B bonds are stiffer than the M−Al and Al−B bonds. The different strength between these bonds implies the etching possibility of Al atoms from MAB phases, consequently forming various 2D MB, M 2 B 3 , and M 3 B 4 MBenes. Furthermore, we employ the nudged elastic band method to investigate the possibility of the structural phase transformation of the 2D MB MBenes into graphene-like boron sheets sandwiched between transition metals and find that the energy barrier of the transformation is less than 0.4 eV/atom.

Inspired by the successful synthesis of alkaline-earth-metals-based electrides [CaAlO](e) (C12A7:e) and [CaN]:e and high-throughput database screening results, we explore the potential for new electrides to emerge in the Sr-P system through a research approach combining ab initio evolutionary structure searches and experimental validation. Through employing an extensive evolutionary structure search and first-principles calculations, we first predict the new structures of a series of strontium phosphides: SrP, SrP, SrP and SrP. Of these structures, we identify SrP and SrP as being potential electrides with quasi-one-dimensional (1D) and zero-dimensional (0D) character, respectively. Following these theoretical results, we present the successful synthesis of the new compound SrP and the experimental confirmation of its structure. Although density functional calculations with the generalized gradient approximation predict SrP to be a metal, electrical conductivity measurement reveal semiconducting properties characterized by a distinct band gap, which indicates that the newly synthesized SrP is an ideal one-dimensional electride with the half-filled band by unpaired electrons. In addition to presenting the novel electride SrP, we discuss the implications of its semiconducting nature for 1D electrides in general and propose a mechanism for the formation of electrides with an orbital level diagram based on first-principles calculations.