Bulk and film synthesis pathways to ternary magnesium tungsten nitrides
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- Materials Science Center, National Renewable Energy Laboratory, Golden, CO 80401, USA, Department of Chemistry, Colorado State University, Fort Collins, CO, 80523, USA
- Materials Science Center, National Renewable Energy Laboratory, Golden, CO 80401, USA
- Department of Chemistry, Colorado State University, Fort Collins, CO, 80523, USA
- Department of Chemistry, Colorado State University, Fort Collins, CO, 80523, USA, School of Advanced Materials Discovery, Colorado State University, Fort Collins, CO, 80523, USA
Bulk solid state synthesis of nitride materials usually leads to thermodynamically stable, cation-ordered crystal structures, whereas thin film synthesis tends to favor disordered, metastable phases. This dichotomy is inconvenient both for basic materials discovery, where non-equilibrium thin film synthesis methods can be useful to overcome reaction kinetic barriers, and for practical technology applications where stable ground state structures are sometimes required. Here, we explore the uncharted Mg-W-N chemical phase space using rapid thermal annealing to reconcile the differences between thin film (on ambient or heated substrates) and bulk powder syntheses. Combinatorial co-sputtering synthesis from Mg and W targets in a N2 environment yielded cation-disordered Mg-W-N phases in the rocksalt (0.1 < Mg/(Mg + W) < 0.9), and hexagonal boron nitride (0.7 < Mg/(Mg + W) < 0.9) structure types. In contrast, bulk synthesis produced a cation-ordered polymorph of MgWN2 that consists of alternating layers of rocksalt-like [MgN6] octahedra and nickeline-like [WN6] trigonal prisms (denoted "rocksaline"). Thermodynamic calculations corroborate these observations, showing rocksaline MgWN2 is stable while other polymorphs are metastable. We also show that rapid thermal annealing can convert disordered rocksalt films to this cation-ordered polymorph, but only near the MgWN2 stoichiometry. Electronic structure calculations suggest that this rocksalt-to-rocksaline structural transformation should also drive a metallic-to-semiconductor transformation. In addition to revealing three new phases (rocksalt MgWN2 and Mg3WN4, hexagonal boron nitride Mg3WN4, and rocksaline MgWN2), these findings highlight how rapid thermal annealing can control polymorphic transformations, adding a new strategy for exploration of thermodynamic stability in uncharted phase spaces.
- Research Organization:
- National Renewable Energy Laboratory (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Renewable Energy Laboratory (NREL), Laboratory Directed Research and Development (LDRD) Program
- Grant/Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1993333
- Alternate ID(s):
- OSTI ID: 1995179
- Report Number(s):
- NREL/JA-5K00-86368; JMCCCX
- Journal Information:
- Journal of Materials Chemistry C, Journal Name: Journal of Materials Chemistry C Vol. 11 Journal Issue: 34; ISSN 2050-7526
- Publisher:
- Royal Society of Chemistry (RSC)Copyright Statement
- Country of Publication:
- United Kingdom
- Language:
- English
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