Synergy of atom-probe structural data and quantum-mechanical calculations in a theory-guided design of extreme-stiffness superlattices containing metastable phases

Abstract

A theory-guided materials design of nano-scaled superlattices containing metastable phases is critically important for future development of advanced lamellar composites with application-dictated stiffness and hardness. Our study combining theoretical and experimental methods exemplifies the strength of this approach for the case of the elastic properties of AlN/CrN superlattices that were deposited by reactive radio-frequency magnetron sputtering with a bilayer period of 4 nm. Importantly, CrN stabilizes AlN in a metastable B1 (rock salt) cubic phase only in the form of a layer that is very thin, up to a few nanometers. Due to the fact that B1-AlN crystals do not exist as bulk materials, experimental data for this phase are not available. Therefore, quantum-mechanical calculations have been applied to simulate an AlN/CrN superlattice with a similar bilayer period. The ab initio predicted Youngʼs modulus (428 GPa) along the [001] direction is in excellent agreement with measured nano-indentation values (408±32 GPa). Aiming at a future rapid high-throughput materials design of superlattices, we have also tested predictions obtained within linear-elasticity continuum modeling using elastic properties of B1-CrN and B1-AlN phases as input. Using single-crystal elastic constants from ab initio calculations for both phases, we demonstrate the reliability of this approach to design nano-patterned coherent superlattices with unprecedented and potentially superior properties.

Atomistic Modeling‐Based Design of Novel Materials

“…The near future DFT applications for investigations of material properties and for prediction of novel materials with tailored technological specifications may be foreseen, and has already started, in four basic directions (for each area we provide several references, which coin the path): 1) finite temperature effects, [37,38,125,127,129,[131][132][133][134]160] 2) extended defects (grain boundaries, stacking faults, dislocations, etc. ), [8,98,[193][194][195][196][197][198][199][200][201][202][203][204][205][206][207][208][209] 3) materials of relevance for real applications (complex compositions, realistic conditions, etc. ), [31,63,68,159,160,176,179,[210][211][212][213][214][215] and 4) high-throughput search for novel materials [13,[215]…”

“…[1] In turn, they have become indispensable tools in modern materials science, offering fundamental insights into materials. As other examples, it is possible to i) decouple chemical and elastic contributions to de-mixing enthalpies, [5,6] ii) study separately, for example, polymorphic and ordering transformations, which are difficult to distinguish experimentally, [7] iii) characterize metastable phases, [8,9] iv) follow atomistic processes behind materials catastrophic failure, [10] or v) learn about the chemistry at the very quantum-mechanical level. For example, material response under extremely high pressures [2] or restricted loading modes [3,4] are hardly accessible experimentally, but rather straightforward to simulate.…”

“…For example, material response under extremely high pressures [2] or restricted loading modes [3,4] are hardly accessible experimentally, but rather straightforward to simulate. As other examples, it is possible to i) decouple chemical and elastic contributions to de-mixing enthalpies, [5,6] ii) study separately, for example, polymorphic and ordering transformations, which are difficult to distinguish experimentally, [7] iii) characterize metastable phases, [8,9] iv) follow atomistic processes behind materials catastrophic failure, [10] or v) learn about the chemistry at the very quantum-mechanical level. [11,12] On the other hand, modern high-performance computer clusters make possible to perform a vast number of similar simulations, [13] hence, probing the corresponding configurational space (being it, e.g., chemical composition, microstructure, or stress state), which would not be possible otherwise due to time and/or cost restrictions.…”

Quantum-Mechanical Study of Nanocomposites with Low and Ultra-Low Interface Energies

“…WSi2 and MoSi2, which crystallize in the tetragonal C11b structure, form a coherent nanocomposite where two conventional cells of each materials are stacked one on top of the other along the [001] direction (the interfaces are perpendicular to this direction) and alternate. It should be emphasized that, due to the periodic boundary conditions, which are applied to all nanocomposites in our calculations, the simulated nanocomposites form so-called superlattices [57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78] when the atomic planes continue from one phase into another.…”

An Ab Initio Study of Pressure-Induced Reversal of Elastically Stiff and Soft Directions in YN and ScN and Its Effect in Nanocomposites Containing These Nitrides

“…It would be, therefore, desirable to achieve the studied elasticity change under more easily reachable conditions. It is interesting to examine biaxial loading conditions (misfit strains) which are induced, for example, in coherent nanocomposites (such as superlattices [45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66]) when materials with slightly mismatching lattice parameters co-exist. In order to simulate the impact of similar strain conditions, we have performed a series of calculations for tetragonally deformed YN.…”