Ion exchange synthesizes layered polymorphs of MgZrN$_2$ and MgHfN$_2$, two metastable semiconductors

Christopher L. Rom; Matthew Jankousky; Maxwell Q. Phan; Shaun O'Donnell; Corlyn Regier; James R. Neilson; Vladan Stevanovic; Andriy Zakutayev

doi:10.1021/acs.chemmater.4c02748

paper

Ion exchange synthesizes layered polymorphs of MgZrN $_{2}$ and MgHfN $_{2}$ , two metastable semiconductors

arXiv:2412.02600 · doi:10.1021/acs.chemmater.4c02748

Abstract

The synthesis of ternary nitrides is uniquely difficult, in large part because elemental N $_{2}$ is relatively inert. However, lithium reacts readily with other metals and N $_{2}$ , making Li-M-N the most numerous sub-set of ternary nitrides. Here, we use Li $_{2}$ ZrN $_{2}$ , a ternary with a simple synthesis recipe, as a precursor for ion exchange reactions towards AZrN $_{2}$ (A = Mg, Fe, Cu, Zn). In situ synchrotron powder X-ray diffraction studies show that Li $^{+}$ and Mg $^{2 +}$ undergo ion exchange topochemically, preserving the layers of octahedral [ZrN $_{6}$ ] to yield a metastable layered polymorph of MgZrN $_{2}$ (spacegroup $R 3 m$ ) rather than the calculated ground state structure ( $I 41/ am d$ ). UV-vis measurements show an optical absorption onset near 2.0 eV, consistent with the calculated bandgap for this polymorph. Our experimental attempts to extend this ion exchange method towards FeZrN $_{2}$ , CuZrN $_{2}$ , and ZnZrN $_{2}$ resulted in decomposition products (A + ZrN + 1/6 N $_{2}$ ), an outcome that our computational results explain via the higher metastability of these phases. We successfully extended this ion exchange method to other Li-M-N precursors by synthesizing MgHfN $_{2}$ from Li $_{2}$ HfN $_{2}$ . In addition to the discovery of metastable $R 3 m$ MgZrN $_{2}$ and MgHfN $_{2}$ , this work highlights the potential of the 63 unique Li-M-N phases as precursors to synthesize new ternary nitrides.

Ion exchange synthesizes layered polymorphs of MgZrN2​ and MgHfN2​, two metastable semiconductors

Abstract

References in corpus (7)

Ion exchange synthesizes layered polymorphs of MgZrN $_{2}$ and MgHfN $_{2}$ , two metastable semiconductors