Prediction of Thermodynamically Stable Compounds of the Sc–N System under High Pressure

Abstract

Materials under high pressure often exhibit unusual physical and chemical behaviors. We investigated the Sc–N system under high pressure in the range of 0–110 GPa using variable-composition methodology implemented in Universal Structure Predictor: Evolutionary Xtallograpgy (USPEX) in conjunction with Vienna Ab Initio Simulation Package (VASP). The calculation led to prediction of new thermodynamically stable compounds, Sc 4 N 3 , Sc 8 N 7 , ScN 3 , and ScN 5 , and also phase transition of ScN 5 from triclinic to monoclinic at 104 GPa. These results are important to understand the structure of Sc–N compounds under high pressure and their elastic and electronic properties.

Synthesis and study of ScN thin films

“…Figure 5(b) demonstrates the measured indentation hardness (H) and modulus (E) of the ScN thin film samples as a function of R N2 whereas, Figure 5(c) illustrates the ratio of (H 3 /E 2 ) which corresponds to the resistance of ScN samples to plastic deformation as a function of H. As expected, Sc exhibits the lowest H and E values of 8(±1.3) and 79(±7) GPa, respectively. With nitridation, both H and E increases monotonically from 15 -27 GPa and 152 -268 GPa for the ScN samples, except for R N2 = 2.5%, which is close to the calculated value of 25 GPa for ScN [65]. At R N2 = 2.5%, the values maximizes at 34(±6.2) and 476(±157) GPa, respectively, which can be attributed to the highest density as estimated from the XRD data [66], smaller grain size and strong (111) and (222) texturing of the ScN sample [67].…”

Predictions on High-Power Trivalent Metal Pentazolate Salts

“…We further calculated the enthalpy of nitrogen-rich MN 15 and used other nitrides as references under pressures <50 GPa. The enthalpy of a MN 15 structure relative to the mixture of MN x ground states or other high-pressure compounds and nitrogen molecular phases − is described by the equation Δ H = [ H (MN 15 ) – H (MN x ) – (15 – x ) H (N)]/16. Here, H (MN 15 ) represents the free energy for one MN 15 formula unit.…”

“…It seems larger atomic radius requires less external pressure to stabilize isostructural MN 15 energetically. When mixing with P 4 1 2 1 2 nitrogen under such extreme conditions, both the high-pressure AlN 3 and ScN 5 , phase tends to transform into nitrogen-rich MN 15 structure, at a pathway of AlN 3 + 6N 2 → AlN 15 or ScN 5 + 5N 2 → ScN 15 (inset of Figure a). Considering the van der Waals (VDW) correction to the energy estimation especially for the molecular phases, we employ the PBE-D3 and optB86-vdW methods to relax all the structures above (see results in Figure S2).…”

“…The total enthalpy of MN and nitrogen mixture is used as the baseline (dashed line), as shown in panel a. The ground states of MN and nitrogen at different pressures are taken into account, including the hexagonal Wurtzite P 6 3 mc and cubic Rock-salt Fm 3̅ m for MN , and the α and P 4 1 2 1 2 phases for nitrogen. , Inset in panel a represents the enthalpy difference between MN 15 structure and the mixtures (dashed line in the inset) of stable high-pressure MN x compounds , and pure nitrogen phases.…”

Materials under high pressure: A chemical perspective

“…The success of EA methods is demonstrated in the large number of high-pressure crystal structures they have identified. These include hydrogen-rich phases with "non-classical" stoichiometries [161][162][163][164][165][166][167][168][169][170][171][172][173], elemental phases of boron [174,175] and sodium [176], binary systems ranging from Xe-O [177] to Sc-N [178] to Li-B [179,180] and Be-B, [181,182] (and the Li-Be-B ternary system [183]) alongside other ternary systems including Li-F-H [184] and La-B-H [185].…”