Non-stoichiometric FexWN2: Leaching of Fe from layer-structured FeWN2

Non-stoichiometric FexWN2 (x∼0.72) was synthesized via leaching of Fe from layer-structured stoichiometric FeWN2 by soaking in sulfuric acid at ca. 50 °C. The synthesized products were characterized by powder X-ray diffraction (pXRD), secondary electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and magnetic measurements. Non-stoichiometric FexWN2 has the same symmetry unit cell as stoichiometric FeWN2 (P63/mmc), but the lattice parameters change: the a-axis expands by 0.16% while the c-axis decreases by 1.5%. Polycrystalline powder of FexWN2 showed similar morphologies as those of FeWN2. The calculated electronic structure of stoichiometric FeWN2 shows a more ionic-bonding character between Fe and N than that between W and N, which presumably allows for the partial Fe leaching from between the W–N prismatic layers. The magnetic susceptibility of FexWN2 smoothly decreases with increasing temperature from 3 to 300 K, unlike the broad maximum seen near 27 K in stoichiometric FeWN2.