Structural stability, elemental ordering, and transport properties of layered ScTaN₂

Journal Article · Thu Sep 25 00:00:00 UTC 2025 · Physical Review Materials

DOI: https://doi.org/10.1103/1clz-gwtx · OSTI ID:3014939

Julien, Baptiste  ^[1]; Leahy, Ian A.  ^[1]; Smaha, Rebecca W.  ^[1]; Mangum, John S.  ^[1]; Perkins, Craig L.  ^[1]; Bauers, Sage R. ^[1]; Zakutayev, Andriy  ^[1]

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1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Ternary transition metal (TM) nitrides have gained significant attention in thin film research due to their promising properties for a broad range of applications. Particularly, some of the ternary TM nitrides have been predicted to adopt layered structures that make them interesting for thermoelectric conversion and quantum materials applications. Unfortunately, synthesis of TM ternary nitride films by physical vapor deposition often favors disordered 3D structures rather than the predicted 2D-like layered structure. In this study, we investigate the structural interplay in the Sc-Ta-N ternary system using a combinatorial approach. Combinatorial libraries S⁢c_𝑥⁢T⁢a_1−𝑥⁢N are synthesized following a two-step method: First, deposit film precursors by cosputtering and then process the resulting 3D-structured samples with rapid thermal annealing. Synchrotron grazing-incidence wide-angle x-ray scattering on films annealed at 1200 ⁢°⁢C for 20 min leads to the nucleation of ScTaN₂ layered structure (𝑃⁢6₃/𝑚⁢𝑚⁢𝑐) near stoichiometry. We find that the layered structure can accommodate large off-stoichiometry in the Ta-rich region (𝑥 < 0.5), facilitated by the alloying with quasi-isostructural Ta₅⁢N₆ compound that exists on a composition tie line at 𝑥 = 0. While focusing on ScTaN₂, we estimate the long-range order parameter in near-stoichiometric films to be 0.86, corresponding to a fraction of Sc/Ta antisites of 7%. Transport measurements on ScTaN₂ reveal a nearly temperature-independent high carrier density (10²¹ c⁢m⁻³), suggesting a heavily doped semiconductor or semimetallic character, consistent with a small positive Seebeck coefficient of +19 µV/K. The carrier mobility at 2 K is relatively small (9.5c⁢m² V⁻¹ s⁻¹) and the residual-resistivity ratio is minor, suggesting that electrical conduction is dominated by defects or disorder. Measured magnetoresistance suggests possible weak antilocalization at 2 K. This paper highlights the interplay between ScTaN₂ and Ta₅⁢N₆ crystal structures in stabilizing layered materials, emphasizes the importance of cation order/disorder for potential tunable alloys, and suggests that ScTaN₂ is a promising platform for exploring electronic properties.

• Research Organization: National Laboratory of the Rockies (NLR), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: AC02-76SF00515; AC36-08GO28308
• OSTI ID: 3014939
• Report Number(s): NLR/JA--5K00-94393
• Journal Information: Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 9 Vol. 9; ISSN 2475-9953
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English