cKey Laboratory of State Ethnic Affairs
Commission for Electronic and Information Engineering, Southwest Minzu
University, Chengdu 610041, China
Abstract: We have designed
Ti3AlB2 and two new layered ordered
double-transition metals MAX compound
Ti2ZrAlB2 based on the structure of
Ti3AlC2. By first-principles
calculations with density functional theory, their structure, phase
stability, elastic properties, electronic properties and thermal
properties have been further investigated. Results show that they are
all energetic, thermodynamically and mechanically stable. The bulk
modulus, shear modulus, Young’s modulus, Poisson’s ratio and Debye
temperature were computed to discuss their elastic and thermal
properties. Results show that they are all good ductile materials with
high melting points. Density of states and electron localization
function of these three phases were presented to research the chemical
bonds and explore the reason limiting their melting points.
Keywords: first-principles calculations, ordered
double-transition metals MAX, phase stability, thermal properties
Introduction
Since Nowotny et al synthesized the first member of
Mn+1AXn (MAX)
compounds–Ti3SiC2 in 1965 [1].
Hundreds of new carbides of this class were synthesized in the past
several decades [2-7]. As a new class of ceramic compounds,
Mn+1AXn crystallizes in the form of with
layered structures, where n varies from 1 to 3, M is an early transition
metal, A is primarily an element in group IIIA or IVA, X is the element
of C, B or N. This new class of ceramic materials usually have the
advantages of both metal and traditional ceramic materials, such as good
conductivity, thermal conductivity and easy processing similar to metal,
high temperature resistance, light weight, creep resistance and fatigue
resistance similar to traditional ceramic materials. These excellent
characteristics make them as potential candidates in a wide range of
technological applications [8-10]. In addition, based on the
structure of MAX compounds, a new class of 2D materials–MXenes, can
be gotten by selectively etching the A-layers and leaving the
Mn+1Xn layers intact [11-13]. This
will greatly increase the variety of 2D materials. What’s more,
theoretical and experimental studies show that the performance and
stability of double transition metal MXenes are better than that of
single transition metal MXenes. However, the double transition metal
MXenes should be obtained by chemical etching the corresponding double
transition metal MAX. For example, Rose et al [14] obtained a
set of novel MXenes–Mo1.33C from their independently
synthesized
(Mo2/3Sc1/3)2AlC
structure (Mo and Sc are chemically ordered in the same plane) by
selective etching of the Al and Sc elements. Anasori et al[15] have obtained 2D MXenes structures
Mo2TiC2Tx,
Mo2Ti2C3Txand Cr2TiC2Tx based on
the parent ordered double transition metal MAX phases.
In view of its application prospect in the industrial field and the
design requirements of two-dimensional double transition metal MXenes,
the design of double transition metal MAX structures has an important
scientific significance. Now many double transition metal MAX
[16-17], such as
(V0.5Cr0.5)n+1AlCn(n=2, 3) and
(Ti0.5Nb0.5)5AlC4,
have been successfully synthesized by introducing another solid solution
metal into the layered ceramic compounds in the laboratory. Liu et
al [18-19] also reported the crystal structure of two newly ordered
double transition metal MAX phases,
Cr2TiAlC2 and
Cr5/2Ti3/2AlC3, by
various techniques. By mixing and heating different elemental powder
mixtures method, Anasori et al [20] has successfully obtained
two newly double ordered transition metal MAX phases
Mo2TiAlC2 and
Mo2Ti2AlC3. And more and
more chemical ordered double transition metal MAX structures have been
synthesized in the laboratory [21]. However, both theoretical and
experimental studies focus on MAX (X=C, N), but there are few studies on
MAX (X=B) [22], and no report on the double transition metal MAB.
Ti3AlC2 is the most typical
representative of MAX phase, and the research on this phase is also the
most. Therefore, we design the aimed structures on the basis of
Ti3AlC2 structure.
As an effective way to predict condensed material structures and
properties, first-principles calculations can reproduce experimental
data at a high accuracy. So this method has been widely used in the
study field of material science [23-26]. In this study, based on the
structure of Ti3AlC2, we predicted
Ti3AlB2 and two
Ti2ZrAlB2 double transition metal MAX
phases and further investigate the phase stability and potential
properties of them by first-principle calculations.