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The hafnium nitrides are the various salts produced from combining hafnium and nitrogen. The two most important such are hafnium(III) nitride, HfN; and hafnium(IV) nitride, Hf₃N₄. None can be prepared from hafnium oxide, but must instead be prepared from the elemental metal or a different hafnium nitride salt; attempted nitridation of the oxide gives an oxynitride instead.

HfN is refractory and generally produced as a thin film coating, although zone annealing gives the bulk material. HfN adopts the rock-salt crystal structure. The surplus hafnium electron delocalizes, so that HfN is a metal, conducting at room temperature and superconducting below 8.8 K (−443.83 °F). Its bright gold color is a cheaper alternative to gilding.

The dark red semiconductor Hf₃N₄ does not form at room temperature, but requires high pressure, high temperature synthesis in a diamond anvil cell. At 18 GPa (180,000 atm) and 2,800 K (4,580 °F), it adopts the cubic crystal structure and repeats according to space group I{{{1}}}3d. At lower pressures, the cubic structure is believed metastable, decaying to the orthorhombic structure of zirconium(IV) nitride. That structure forms outright at 19 GPa and 2,000 K (3,140 °F), and another metastable tetragonal structure forms at 12 GPa and 1,500 K (2,240 °F). Computational studies suggest that it may catalyze polymerization of nitrogen at very high temperatures, through a catenary anion in HfN₁₀.

In systems with limited nitrogen, hafnium also forms Hf₃N₂, as well as a solid solution hafnium alloy.

References

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2. ^ Zerr, Andreas; Miehe, Gerhard; Riedel, Ralf (2003-03-01). "Synthesis of cubic zirconium and hafnium nitride having Th3P4 structure". Nature Materials. 2 (3): 185–189. doi:10.1038/nmat836. ISSN 1476-1122.
3. Christensen, A. Nørlund; Kress, W.; Miura, M.; Lehner, N. (1983-07-15). "Phonon anomalies in transition-metal nitrides: HfN". Physical Review B. 28 (2): 977–981. doi:10.1103/PhysRevB.28.977. ISSN 0163-1829.
4. ^ Kroll, Peter (2003-03-25). "Hafnium Nitride with Thorium Phosphide Structure: Physical Properties and an Assessment of the Hf-N, Zr-N, and Ti-N Phase Diagrams at High Pressures and Temperatures". Physical Review Letters. 90 (12). doi:10.1103/PhysRevLett.90.125501. ISSN 0031-9007.
5. ^ Zhang, Jin; Oganov, Artem R.; Li, Xinfeng; Niu, Haiyang (2017-01-18). "Pressure-stabilized hafnium nitrides and their properties". Physical Review B. 95 (2). doi:10.1103/PhysRevB.95.020103. ISSN 2469-9950.
6. Ushakov, Sergey V.; Navrotsky, Alexandra; Hong, Qi-Jun; van de Walle, Axel (26 Aug 2019) . "Carbides and nitrides of zirconium and hafnium". Materials. 2019 (12). Basel: MDPI. doi:10.3390/ma12172728.

• Hafnium compounds
• Nitrides
• Salts
• Refractory materials