# Nitride halide

A nitride halide is a mixed-anion [inorganic compound](https://www.edgepedia.org/inorganic-compound) that contains nitride ions (N³⁻) and halide ions (X⁻, where X is chlorine, bromine, or iodine in the best-studied families) in a single crystal lattice. The archetype is the layered transition-metal nitride halide MNX, where M is titanium, zirconium, or hafnium, and X is Cl, Br, or I; in the ionic limit these compounds can be written M⁴⁺N³⁻X⁻.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> The coverage below rests mainly on the MNX archetype, because the primary literature on the class is concentrated there; some generalisations to other metal systems are noted explicitly where the evidence supports them.

| Fact | Value |
|---|---|
| Ionic-limit formula of prototypic MNX | M⁴⁺N³⁻X⁻, with {X[M₂N₂]X} slabs separated by van der Waals gaps<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> |
| Structure types | α (FeOCl type) and β (SmSI or YOF type), all layered<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup><sup> • </sup><sup>[3](https://www.osti.gov/etdeweb/biblio/20346817)</sup> |
| Parent compounds | Band insulators, gaps larger than 2.5–4 eV, no magnetic or charge-density-wave order<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup> |
| Highest superconducting Tc | 25.5 K in Li₀.₄₈(THF)ᵧHfNCl (1998)<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> |
| LixZrNCl Tc | about 13 K (1996); a later source gives 13–15 K<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup><sup> • </sup><sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup> |
| Gas-solid synthesis window | NH₄Cl sublimed at 360 °C, reacted with Zr metal or ZrH₂ at about 400–800 °C<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> |
| High-pressure crystal growth | 3–5 GPa and 900–1200 °C with NH₄X flux<sup>[3](https://www.osti.gov/etdeweb/biblio/20346817)</sup> |
| Thorium phases | ThNF and ThNCl resist intercalation because interlayer chemical bonding dominates over van der Waals forces<sup>[4](https://pubs.rsc.org/en/content/articlehtml/2021/ra/d1ra05578j)</sup> |

## Structural families

The defining structural motif of the prototypic nitride halides is the sandwich slab. All three known structure types of MNX consist of {X[M₂N₂]X} slabs, in which a two-atom-thick nitride layer is capped on both sides by halide, and adjacent slabs interact only through van der Waals forces between the outward-facing halide anions.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> Equivalent descriptions give the double-layer composition [X–M–N–N–M–X] for M = Ti, Zr, Hf, and X = Cl, Br, I, separated by van der Waals gaps.<sup>[5](https://doi.org/10.1088/0268-1242/29/6/064005)</sup>

Two layered polymorphs exist. The α-form adopts the FeOCl structure and the β-form the SmSI structure.<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup> High-pressure growth of six β-MNX compounds (M = Zr, Hf; X = Cl, Br, I) showed that all crystallize in the rhombohedral space group R-3m with Z = 6; β-ZrNCl, β-ZrNBr, and β-HfNCl are isotypic with SmSI, while the other three adopt the YOF type.<sup>[3](https://www.osti.gov/etdeweb/biblio/20346817)</sup>

The layered architecture is what makes the intercalation chemistry possible, but it is not universal. First-principles calculations show that in thorium nitride halides, ThNF and ThNCl, interlayer chemical bonding plays a larger role than van der Waals interactions, in contrast to the isostructural ZrNCl and HfNCl. Calculated interlayer interaction energies are −82.29, −71.28, and −17.48 meV per atom for ThNF, ThNCl, and ZrNCl respectively, and exfoliation energies are 0.0719, 0.057, and 0.016 eV Å⁻². This is consistent with the experimental finding that ThNF and ThNCl cannot be intercalated by lithium or organic molecules, unlike ZrNCl and HfNCl.<sup>[4](https://pubs.rsc.org/en/content/articlehtml/2021/ra/d1ra05578j)</sup>

The class extends beyond the simple ternary MNX phases. In the Ca–Sr–N–Cl–Br system, quaternary bimetallic nitride halides, and the first quintinary nitride mixed halides were synthesized; all crystallize in R-3m with the anti-α-NaFeO₂ structure and show coexistent disorder of both cations and anions, with only nitride occupying a discrete crystallographic position.<sup>[6](https://doi.org/10.1039/c0dt00214c)</sup>

## Synthesis and stability

The historical route is ammonolysis: Juza and co-workers prepared various pure titanium and zirconium nitride halides during the 1960s using this technique.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> A later gas-solid route developed by Ohashi and co-workers heats ammonium chloride to 360 °C so that it decomposes and sublimes, then transports it in an ammonia stream to react with pure zirconium metal or zirconium dihydride at about 400–800 °C.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup>

Temperature control selects the polymorph and limits decomposition. The α-polymorphs of MNX (M = Ti, Zr; X = Cl, Br, I) form at reaction temperatures of about 180–500 °C, whereas the β-phases require about 600 °C. Above about 750 °C the products are instead binary nitrides of several compositions, including Zr₃N₄, Zr₃N, and ZrN, and MNₓ with M = Ti, Zr.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup> Single crystals of the β-phases can be grown from MN or MNX powders with NH₄X fluxes in sealed gold or platinum tubes at 3–5 GPa and 900–1200 °C.<sup>[3](https://www.osti.gov/etdeweb/biblio/20346817)</sup>


## Superconducting intercalated phases

The parent MNX phases with nominal M⁴⁺ (d⁰) configuration are band insulators with gaps larger than 2.5–4 eV, and show neither magnetic order nor charge-density-wave order.<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup> [Superconductivity](https://www.edgepedia.org/superconductivity) appears only after electron doping: intercalation of alkali, alkaline-earth, or rare-earth metals between the Cl[M₂N₂]Cl layers adds electrons, and the interlayer distance can be tuned by cointercalating solvent molecules.<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup>

The key results came in quick succession. Lithium-doped zirconium nitride chloride, LixZrNCl, was found to be superconducting with a critical temperature of about 13 K in 1996; a later review of the same compound gives a range of 13–15 K, and this discrepancy is unresolved in the sources. The maximum critical temperature, Tc = 25.5 K, was reached in 1998 in the lithium and tetrahydrofuran cointercalated compound Li₀.₄₈(THF)ᵧHfNCl.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup><sup> • </sup><sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup> The solvent matters: cointercalated solvent molecules tune the interlayer spacing, and Li₀.₄₈(THF)ᵧHfNCl holds the class record.<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup><sup> • </sup><sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup>

A useful comparison is with the binary nitrides. Rock-salt MN compounds (M = Ti, Zr, Hf) are three-dimensional superconductors with Tc = 5.5, 10.7, and 8.8 K respectively.<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup> The thorium phases stand outside this story entirely: because their interlayers are chemically bonded rather than van der Waals separated, they resist the intercalation that turns the Zr and Hf analogs into superconductors.<sup>[4](https://pubs.rsc.org/en/content/articlehtml/2021/ra/d1ra05578j)</sup>

## By the numbers

- **Critical temperatures.** Intercalated phases: 25.5 K (Li₀.₄₈(THF)ᵧHfNCl), 13–15 K or about 13 K (LixZrNCl, sources disagree). Binary MN: 5.5 K (TiN), 10.7 K (ZrN), 8.8 K (HfN).<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup><sup> • </sup><sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup>
- **Band gaps.** Parent d⁰ MNX polymorphs: larger than 2.5–4 eV, making them wide-gap insulators rather than semimetals.<sup>[2](https://ar5iv.labs.arxiv.org/html/1412.4447)</sup>
- **Synthesis windows.** α-phase 180–500 °C; β-phase about 600 °C; decomposition to binary nitrides above about 750 °C at ambient pressure; crystal growth at 3–5 GPa and 900–1200 °C.<sup>[1](https://doi.org/10.1524/zkri.2011.1350)</sup><sup> • </sup><sup>[3](https://www.osti.gov/etdeweb/biblio/20346817)</sup>
- **Interlayer binding.** [Interaction](https://www.edgepedia.org/interaction) energies of −82.29 (ThNF), −71.28 (ThNCl), and −17.48 meV per atom (ZrNCl); exfoliation energies of 0.0719, 0.057, and 0.016 eV Å⁻² respectively, implying that ThNF and ThNCl are more difficult to exfoliate than ZrNCl.<sup>[4](https://pubs.rsc.org/en/content/articlehtml/2021/ra/d1ra05578j)</sup>

## References

1. [Superconducting nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)](https://doi.org/10.1524/zkri.2011.1350)
2. [Unconventional superconductivity in electron-doped layered metal nitride halides MNX](https://ar5iv.labs.arxiv.org/html/1412.4447)
3. [High-pressure synthesis and crystal structures of beta-MNX (M = Zr, Hf; X = Cl, Br, I)](https://www.osti.gov/etdeweb/biblio/20346817)
4. [Investigation on the interlayer coupling and bonding in layered nitride-halides ThNF and ThNCl](https://pubs.rsc.org/en/content/articlehtml/2021/ra/d1ra05578j)
5. [Chemistry and superconductivity of intercalated metal nitride halides](https://doi.org/10.1088/0268-1242/29/6/064005)
6. [Structural and compositional tuning of layered subnitrides; new complex nitride halides](https://doi.org/10.1039/c0dt00214c)

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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Elements and inorganic substances › Halides, nitrides, and carbides › Nitrides and oxynitride materials › Nitride halides and nitride fluorides*

*Initially written Sep 17, 2026 · Edited: Oct 11, 2026; Oct 15, 2026*

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