Abstract
The synthesis of ternary nitride materials 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 subset of ternary nitrides. Here, we use Li(2)ZrN(2), a ternary nitride compound with a simple synthesis recipe, as a precursor for ion exchange reactions toward 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)]. This reaction yields a metastable layered polymorph of MgZrN(2) (space group R3̅m) rather than the calculated ground state structure (I4(1)/amd). Diffuse reflectance 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 toward FeZrN(2), CuZrN(2), and ZnZrN(2) resulted in decomposition products (). This experimental outcome is explained by our computational results via the higher metastability of these phases compared to MgZrN(2). 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 experimental synthesis of metastable R3̅m polymorphs of MgZrN(2) and MgHfN(2), this work highlights the potential of the 63 known Li-M-N phases as precursors to synthesize many other ternary nitride materials.