Highly Coordinated Iron and Cobalt Nitrides Synthesized at High

Article pubs.acs.org/IC

Highly Coordinated Iron and Cobalt Nitrides Synthesized at High Pressures and High Temperatures Ken Niwa,*,† Toshiki Terabe,† Daiki Kato,‡ Shin Takayama,† Masahiko Kato,‡ Kazuo Soda,‡,§ and Masashi Hasegawa† †

Department of Crystalline Materials Science, ‡Department of Quantum Engineering, Graduate School of Engineering, and §Nagoya Synchrotron Radiation Center, Nagoya University, Nagoya, Japan S Supporting Information *

ABSTRACT: Highly coordinated iron and cobalt nitrides were successfully synthesized via direct chemical reaction between a transition metal and molecular nitrogen at pressures above approximately 30 GPa using a laser-heated diamond anvil cell. The synthesized novel transition metal nitrides were found to crystallize into the NiAs-type or marcasite-type structure. NiAs-type FeN could be quenched at ambient pressure, although it was gradually converted to the ZnS-type structure after the pressure was released. On the other hand, CoN was recovered with ZnS-type structure through a phase transition from NiAs-type structure at approximately a few gigapascals during decompression. Marcasite-type CoN2 was also synthesized at pressures above approximately 30 GPa. High-pressure in situ X-ray diffraction measurement showed that the zero-pressure bulk modulus of marcasite-type CoN2 is 216(18) GPa, which is comparable to that of RhN2. This indicates that the interatomic distance of the N−N dimer in marcasite-type CoN2 is short because of weak orbital interaction between cobalt and nitrogen atoms, as in RhN2. Surprisingly, a first-principles electronic band calculation suggests that the NiAs-type FeN and CoN and marcasite-type CoN2 exhibit metallic characteristics with magnetic moments of 3.4, 0.6, and 1.2 μB, respectively. The ferromagnetic NiAs-type structure originates from the anisotropic arrangement of transition atoms stacked along the c axis.

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INTRODUCTION Iron- and cobalt-based nitrides have attracted much attention because of their fundamental physical properties and industrial application in electronic devices.1 In particular, simple binary nitrides such as Fe−N and Co−N compounds have been prepared by various synthesis methods to thoroughly investigate their fundamental properties, focusing mainly on their magnetism.2−27 The late transition metals iron and cobalt preferentially form metal-rich nitrides, in contrast to early transition metals such as Ti and V,1 whereas theoretical studies have suggested that the transition metal mononitrides should show a variety of physical properties depending on the crystal structure.28−42 According to the synthesis experiments performed to date, iron and cobalt mononitrides crystallize into the zincblende (ZnS)4,5,11,16,17,20,26 or sodium chloride (NaCl)-type structure,7,20,22 although consistent evidence of NaCl-type mononitrides, especially NaCl-type FeN, in previous studies remains a controversial issue. Both the ZnS- and NaCl-type structures exhibit cubic symmetry, although the local atomic coordination varies depending on the size of the atoms that occupy the various interstitial sites. ZnS- and NaCl-type MX consists of tetrahedral (MX4) and octahedral (MX6) units, respectively. The atomic coordination affects the mechanical, physical, and chemical properties of materials.43−53 The high-pressure technique is one of the most effective and powerful tools for fabricating highly coordinated materials, because the high pressure directly © 2017 American Chemical Society

decreases the atomic size, inducing a change in the atomic coordination number and enhancement of orbital interaction. For example, the nanocrystalline bulk SiO2 stishovite, which is a six-coordinate form of silica, was synthesized via direct transformation of bulk glass at a pressure of approximately 15 GPa and temperatures of ≤2073 K.43 This nanocrystalline bulk stishovite was found to exhibit an extremely high fracture toughness of 13 MPa m1/2 and a Vickers hardness of 29 GPa. Tetrahedrally coordinated ZnS-type CdSe, a direct-gap semiconductor, is transformed to the octahedrally coordinated NaCl type at a pressure of approximately 8.5 GPa.44,45 This phase transition changes the material from a direct-gap semiconductor to an indirect-gap semiconductor. More recently, advanced high-pressure studies revealed that platinum-group elements form pernitrides (MN2, where M = Ru, Rh, Pd, Os, Ir, or Pt) via direct chemical reaction with molecular nitrogen at pressures exceeding a few tens of gigapascals.46−53 These new platinum-group pernitrides consist of MN6 octahedral units that are connected by a singly bonded N−N dimer. In addition, the orbital interaction between the platinum-group element and nitrogen atom produces a noteworthy mechanical strength and a variety of physical properties such as those of a metal, a semiconductor, or an insulator. On the basis of these previous studies, the use of high pressures has played an important role Received: February 25, 2017 Published: May 16, 2017 6410

DOI: 10.1021/acs.inorgchem.7b00516 Inorg. Chem. 2017, 56, 6410−6418

Article

Inorganic Chemistry

Figure 1. Synchrotron XRD profiles of (a) iron and (b) cobalt nitrides that were recovered after experiments at 35.0 and 39.9 GPa, respectively. The inset in panel a is the enlarged spectrum in the 2θ range above 30°. The labels NA hkl, ZS hkl, and M hkl correspond to the diffraction peaks of NiAs-, ZnS-, and marcasite-type nitrides, respectively. Simulated XRD profiles of high-pressure-synthesized phases of NiAs-type FeN, marcasite-type CoN2, and ZnS-type FeN and CoN are shown at the bottom.

Figure 2. Surface texture of ambient recovered samples from experiments with (a−c) Fe−N2 at 30.7 GPa and (d−f) Co−N2 at 50.2 GPa.

their crystal structure, electronic structure, and magnetic properties, are discussed on the basis of the results of highpressure experiments and a first-principles calculation. These findings offer new insight into the fundamental electronic and physical properties of transition metal nitrides.

in the development of novel materials involving a high atomic coordination number. In this study, we applied a high-pressure, high-temperature technique to synthesize novel highly coordinated 3d transition metal nitrides of iron and cobalt. There have been previous high-pressure experiments on the late 3d transition metal nitrides in the gigapascal pressure range.9,10,13,14,19,24 For example, Schwarz et al. reported the synthesis of Fe3N1.5 by high-pressure and -temperature treatment of Fe2N at 15 GPa and 1600 K.14 Hasegawa and Yagi performed direct nitriding experiments on iron and cobalt at 10 GPa.9·10 However, they synthesized the existing nitrides (Fe2N and Co2N) even by synthesis under nitrogen-rich conditions. Thus, novel nitrogenrich and highly coordinated late 3d transition metal nitrides have not been synthesized to date. On the other hand, it was very recently reported that incompressible TiN2 was successfully synthesized at 70 GPa and quenched to ambient pressure.54 This indicates that the chemical reaction at a much higher pressure leads to the formation of novel 3d transition metal pernitrides. We have, therefore, increased the pressure range to approximately 60 GPa. The details of the novel highly coordinated 3d transition metal nitrides, such as

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EXPERIMENTAL SECTION

Iron and cobalt nitrides were synthesized using a laser-heated diamond anvil cell (LHDAC) up to a pressure of approximately 60 GPa. A foil of a transition metal (Co or Fe, 99.9%, Nilaco Ltd.) was shaped into a square with dimensions of ∼80 μm × ∼80 μm and a thickness of ∼10 μm. The shaped foil was placed at the center of a sample chamber that was prepared in an indented stainless steel gasket using a pulsed infrared laser. Then, nitrogen was cryogenically loaded into the sample chamber, in which small ruby chips were also loaded to determine the chamber pressure.55 After being compressed to the desired pressure at room temperature, the transition metal foil was heated by irradiation with an infrared laser from both sides or one side to react the metal with molecular nitrogen under high pressures. The heated sample was characterized by high-pressure in situ X-ray diffraction (XRD) and Raman scattering measurements at room temperature. The highpressure in situ XRD experiments were conducted at the beamline NE1, the Photon Factory Advanced Ring of the KEK synchrotron facility or at Nagoya University beamline BL2S1 of Aichi Synchrotron 6411


Article

Inorganic Chemistry

Figure 3. Crystal structure of high-pressure-synthesized iron and cobalt nitrides, ZnS- and NiAs-type TMN and marcasite-type TMN2 (TM = Fe or Co) drawn by VESTA.58 Large and small spheres correspond to transition metal and nitrogen atoms, respectively. The bottom row shows the polyhedral representation of the crystal structures of the ZnS-, NiAs-, and marcasite-type nitrides. Radiation Center of the Aichi Science & Technology Foundation.56 The sample was irradiated with monochromatic X-rays parallel to the compression axis, and the diffracted X-rays were recorded on a chargecoupled device or imaging plate. The details of the high-pressure in situ XRD measurements are summarized in Table S1. High-pressure in situ Raman scattering measurements were also performed, as described previously.53 After the sample was returned to ambient pressure, it was examined with a scanning electron microscope equipped with an energy-dispersive spectroscopy (EDS) instrument. Furthermore, the electronic density of states (DOS) of the synthesized transition metal nitrides was calculated by a first-principles calculation using the WIEN2k code in the framework of the full-potential linearized augmented plane wave method with the generalized gradient approximation proposed by Perdew, Burke, and Ernzerhof.57

and they show no significant changes with respect to the synthesis pressure. Figure 1b shows the XRD profile of the sample recovered after the synthesis experiments using Co and N2 at 39.9 GPa. Many sharp diffraction peaks were observed, together with broad diffraction peaks of ZnS-type CoN, which has reportedly been prepared only as a thin film to date.5 These new sharp peaks are perfectly indexed to the compound having orthorhombic symmetry with the following lattice parameters: a = 3.7964(6) Å, b = 4.6131(5) Å, and c = 2.7017(6) Å. Highpressure experiments at pressures of 31.9 and 50.2 GPa also resulted in successful synthesis of the orthorhombic phase with almost the same lattice parameters, as shown in Table S2. Thus, this new orthorhombic phase can be synthesized above a pressure of at least 31.9 GPa. SEM−EDS analyses of the ambient sample recovered from the experiments at 50.2 GPa revealed two characteristic textures on the sample surface; most of the surface was covered with platelike texture having a large amount of nitrogen (N/Co = 2.3 ± 0.4), whereas fine particles with a small amount of nitrogen (N/Co = 1.0 ± 0.1) were also observed (Figure 2d−f). These textural analyses, in combination with the XRD measurements, demonstrate that the fine grains and platelike texture correspond to ZnS-type CoN and a new nitrogen-rich cobalt nitride (N/Co = 2.3 ± 0.4) crystallized with orthorhombic crystal symmetry, respectively. The broad diffraction peaks of ZnS-type CoN are quite consistent with particles having a grain size of approximately 100 nm and a N/Co chemical composition of 1.0 ± 0.1. A search for the model structure suggests that marcasite-type structure is a candidate for the structure of the newly synthesized cobalt nitride with a N/Co chemical composition of 2.3 ± 0.4, because the Miller indices are consistent with space group Pnnm, and the axial ratio is very close to that of RhN2.52 The experimental XRD profile is consistent with the simulated diffraction profile of marcasite-type CoN2. The addition of other elements such as oxygen or carbon often affects the phase stability of nitrides. Our EDS measurements detected carbon and oxygen at similar ratios in all parts of the

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RESULTS AND DISCUSSION High-Pressure Synthesis and Characterization. Laser heating of the transition metal foil loaded in a diamond anvil cell with solid molecular nitrogen changed the metallic luster to a black color (see Figure S1). This demonstrates that the transition metal foil reacted with molecular nitrogen when it was heated by the infrared laser. Figure 1a shows the XRD profile of the sample recovered after the synthesis experiment using Fe and N2 at 35.0 GPa. The intense diffraction peaks labeled ZS were assigned to ZnS-type FeN (F43̅ m), which has reportedly been prepared only as a thin film to date.4,11,16,17,26 In addition to those of ZnS-type FeN, several sharp peaks were also observed. Peak-indexing analysis using dedicated software found that this newly recovered compound crystallizes with hexagonal symmetry with the following lattice parameters: a = 2.7940(5) Å, and c = 4.996(2) Å. Although two different textures were observed in another Fe−N2 experiment at 30.7 GPa, SEM−EDS analyses of the recovered sample showed a uniform N/Fe chemical composition of ∼1 (Figure 2a−c). Therefore, these additional diffraction peaks are derived from FeN phases other than the ZnS-type phase. Accordingly, NiAstype structure (P63/mmc) is suggested as the most plausible candidate for this new FeN. The simulated XRD profile of NiAs-type FeN is consistent with the experimental profile. The lattice parameters of the NiAs-type FeN are listed in Table S2, 6412


Article

Inorganic Chemistry Table 1. Lattice Parameters and Bulk Moduli of Marcasite-Type Transition Metal Pernitrides CoN2 RuN253 RhN252 OsN249

PSynth (GPa)

a (Å)

b (Å)

c (Å)

K0 (GPa)

K0′

39.9 32.0 43.2 43

3.7964(6) 4.037(1) 3.982(1) 4.102(3)

4.6131(5) 4.888(1) 4.858(1) 4.910(5)

2.7017(6) 2.707(1) 2.834(1) 2.714(2)

216(18) 330(5) 235(13) 358(6)

6.0(1.0) 4.1(0.3) 5.9(1.8) 4.67

sample (the total molar ratio of carbon and oxygen is βb > βa and K0 = 216(18) GPa 6413


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Inorganic Chemistry

Figure 5. (a) Pressure−volume relationship for iron and cobalt mononitrides. Filled and empty symbols represent the P−V data for FeN and CoN, respectively. Circles and diamonds correspond to NiAs- and ZnS-type structure, respectively. (b) Pressure dependence of unit cell volume and lattice parameters of marcasite-type CoN2 synthesized at 39.9 GPa.

Figure 6. DOS of (a) marcasite-type CoN2, (b) NiAs-type FeN, and (c) NiAs-type CoN based on a first-principles band calculation with spin polarization.

[K0′ = 6(1)], respectively, which are comparable to those of RhN2 (Figure 5b).52 Electronic Structure of Highly Coordinated Transition Metal Nitrides. Highly coordinated iron and cobalt nitrides with NiAs- and marcasite-type structure were successfully synthesized in this study. However, because of experimental difficulties, low-nitrogen-content phases such as FexN and CoN coexisted with the nitrogen-rich phases. The technical difficulties of synthesizing a single phase and the very tiny sample in the LHDAC experiment make it difficult to characterize the physical and chemical properties of the new nitrides using conventional experimental characterization methods. Thus, a first-principles calculation was performed to evaluate the electronic structure of these highly coordinated iron and cobalt nitrides. Figure 6a shows the spin-polarized density of states (DOS) of marcasite-type CoN2 based on the electronic band calculation. Zero energy corresponds to the Fermi energy (EF). The DOS can be distinguished with respect to the orbital hybridization energy level between Co and N. The N2s* orbital lies at an energy below 10 eV, whereas the DOS band with respect to the binding energy between 5 and 10 eV is derived from the bonding orbital interaction between N 2p and Co 3d, in which the N 2p orbital contributes greatly to the DOS. On the other hand, the Co 3d orbital contributes greatly to the DOS near EF. The antibonding interaction between Co 3d and N 2p is identified at the DOS below EF.

The DOS at EF demonstrates the metallic nature of marcasitetype CoN2, which is consistent with the experimental lack of detection of a Raman signal. According to the spin-polarized band calculation, marcasite-type CoN2 is expected to be ferromagnetic and have an exchange splitting energy of ∼0.85 eV at EF. The difference in the total number of electrons with majority and minority spins up to EF gives a magnetic moment per unit cell of 1.2 μB. The DOSs of NiAs-type FeN and CoN are also shown in panels b and c of Figure 6, respectively. The intense total DOS at EF predicts that NiAs-type FeN and CoN are metallic and ferromagnetic, like marcasite-type CoN2. The magnetic moments per unit cell were calculated to be 3.4 and 0.6 μB for NiAs-type FeN and CoN, respectively. Previous studies of ZnS-type FeN and CoN demonstrated that these ZnS-type mononitrides are paramagnetic down to temperatures of a few kelvin,5,16,17 which is consistent with the result of the theoretical calculation.31,32,36,37,39,41 On the other hand, the theoretical calculation studies also predicted that the NaCl-type structure would exhibit magnetism stronger than that of the ZnS-type structure,31,32,36,37,39 as in the measurements of antiferromagnetism for NaCl-type CoN.22 However, no theoretical investigation to date has focused deeply on the stability and physical properties of NiAs-type FeN and CoN. NiAs-type structure consists of a hexagonal layer of transition metal atoms stacked along the c axis. The anisotropic arrangement of the transition metal atoms in the structure is 6414


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Inorganic Chemistry Table 2. Crystallographic Parameters of Iron and Cobalt Mononitrides structure

lattice parameters (Å)

dTM−Na (Å)

dTM−TMb (Å)

FeN PSynth = 35.0 GPa

ZnS NiAs

1.8607(1) 2.0401(4)

CoN PSynth = 39.9 GPa

ZnS NiAs

a = 4.2971(4) a = 2.7940(5) c = 4.996(2) a = 4.285(5) ac = 2.804 cc = 4.804

3.0385(2) 2.498(1) 2.7940(5) 3.030(3) 2.402 2.804

1.855(1) 2.157

magnetic moment (μB) 3.4

0.6

a dTM−N is the distance between the nitrogen and the nearest transition metal atom. bdTM−TM is the distance between the nearest and second-nearest transition metal atoms. The distance between the second-nearest neighboring transition metal atoms is also shown for NiAs-type structure. cValues extrapolated from high-pressure data.

formed by stacking of hexagonal closely packed X layers in ABCABC... and ABAB... orders, respectively. Transition atom M occupies the octahedral sites of these different types of layers to form each structure (see Figure 3 for the NiAs-type structure). Thus, the shear stress on the NaCl-type structure causes the layers to slide and the NiAs-type structure to form eventually with no large-scale atomic rearrangement.72,73 On the other hand, it could be recognized that the direct transformation from the NiAs type to the ZnS type is due mainly to the atomic size of nitrogen, although the chemical bonding between transition metal and nitrogen atoms should be taken into account. The transition metal atom in both ZnSand NaCl-type nitrides (MN) forms a face-centered cubic lattice, and a nitrogen atom occupies the tetrahedral and octahedral interstitial sites. The size of the occupying atoms is geometrically constrained by the size of the interstitial sites as follows: rX = 0.225rM, and rX = 0.414rM, where rM and rX correspond to the atomic radii of M and X occupying the tetrahedral and octahedral sites, respectively, assuming the hard sphere ball model.74 The smaller atoms preferentially occupy the tetrahedral site to form the ZnS-type structure. Thus, ZnStype iron and cobalt mononitrides crystallize not in the NaCltype structure but in the ZnS-type structure via direct transformation from the NiAs-type structure during decompression. The crystal chemistry of marcasite-type pernitrides has been discussed on the basis of recent experimental results for platinum-group pernitrides together with crystallographic consideration of other pnictides.46−53 In this study, CoN2 was synthesized at pressures above approximately 30 GPa and was successfully recovered to ambient pressure, together with the mononitride or Co2N because of the experimental difficulties of synthesizing the single phase. To explore the iron pernitrides, we also performed a high-pressure experiment on the Fe−N2 system at a pressure of 59.8 GPa. The compounds synthesized in this preliminary experiment showed an XRD profile different from either that of the marcasite type or theoretically suggested profiles,75 although a much higher nitrogen content (N/Fe ∼ 2) was detected by SEM−EDS analyses. The details of the crystal structure remain unknown because of the very low chemical and mechanical stability. Despite these technical difficulties, the preliminary results revealed that high-pressure treatment of the late transition metals iron and cobalt leads to pernitride formation. On the other hand, incompressible titanium pernitride (TiN2) was successfully synthesized via recent experimental direct chemical reactions between titanium mononitride and nitrogen molecules at 73 GPa.54 To the best of our knowledge, TiN2 is the first experimentally reported 3d transition metal pernitride. TiN2 crystallizes in the CuAl2-type structure, which is different from the marcasite-type structure of

likely to be the origin of the unique magnetic properties, as was observed for NiAs-type Fe1+δSb, a compound in the same pnictogen group.59−64 Thus, further experimental investigation should reveal the details of the electronic and physical properties of these newly synthesized highly coordinated transition metal nitrides. Crystal Chemistry of Late Transition Metal Nitrides. NiAs-type MN shows 6-fold nitrogen coordination of the transition metal atom (M) in the structure. The nitrogen atomic layer is formed in the a−b plane and stacked along the c axis (see Figure 3b). The interatomic distance between transition metal atoms in the NiAs-type structure is shorter than that in the ZnS-type structure (Table 2). Except for Fe1+δSb, most iron and cobalt monopnictides MPn (M = Fe or Co; Pn = P or As) crystallize in the MnP-type structure,65 not the NiAs-type structure. However, the MnP-type and NiAstype structures are related, because some MnP-type compounds transform to NiAs-type compounds with increases in temperature at ambient pressure.66−68 High-pressure experiments have also been conducted for iron and cobalt monopnictides to explore their high-pressure phase.69,70 Lyman and Prewitt examined the crystal chemistry of CoAs and FeAs using ambient- and high-pressure experiments.69 According to their study, the MnP-type phases remained stable up to a few gigapascals, whereas the XRD spots of MnP-type CoAs changed above 7.8 GPa, suggesting the onset of the phase transition. On the other hand, a recent high-pressure experiment demonstrated that MnP-type FeP shows no phase transition after compression to 15.6 GPa and laser heating to 1800 K.70 These experimental results offer no clear evidence of the existence of NiAs-type monopnictides under the conditions used in previous studies. Besides the fact that NiAs-type structure is unlikely to be crystallized for iron and cobalt pnictides according to the previous studies, the experiments presented here demonstrate that NiAs-type FeN and CoN are formed under high pressures and are transformed directly into ZnS-type structure with no intermediate phases during decompression. The ZnS- and NiAs-type structures share common crystallographic features, although very few examples of a direct phase transition from ZnS-type to NiAs-type structure have been reported to date. ZnS has been known to be transformed to NaCl-type structure at 12 GPa with increasing pressure and to undergo the transition to the orthorhombic (Cmcm) phase under further compression.71 On the other hand, NiAs-type structure appears as a phase transition from not only MnP-type but also NaCltype structure, as reported for FeO.72,73 NaCl-type structure thus plays a key role in combining the ZnS- and NiAs-type structures, although no NaCl-type phase of FeN or CoN was observed in this study. NaCl- and NiAs-type MX species are 6415


Inorganic Chemistry

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ACKNOWLEDGMENTS Synchrotron radiation XRD measurements were performed under the approval of the Photon Factory Program Advisory Committee (Proposal 2014G528) and also conducted at Aichi Synchrotron Radiation Center (Proposals 2015N4008 and 2016N2009). The authors thank Dr. T. Kikegawa, Dr. T. Nagae, and Prof. N. Watanabe for their technical support of the high-pressure in situ synchrotron radiation XRD measurements. We are also grateful to Dr. Y. Shirako for valuable discussions. Some experiments were performed as part of a collaboration with the Institute for Solid State Physics of the University of Tokyo. This research was supported by a Grantin-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

CoN2. In addition, the synthesis pressure of TiN2 was almost twice that of CoN2, and the bulk modulus of TiN2 is much higher than that of CoN2. A comparison of TiN2 and CoN2 indicates that the chemical bonding and physical properties of CoN2 are different from those of the other 3d transition metal pernitrides, probably because of the difference in the electronic configuration. The bulk modulus of K0 = 216(18) GPa [K0′ = 6(1)] for CoN2 was found to be close to that of RhN2.52 Advanced theoretical calculations showed that RhN2 and RuN2 had bulk moduli lower than those of the other platinum-group pernitrides because of weak orbital interaction between the transition metal and nitrogen atoms, which results in the short N−N bond distance (a quasi-molecule) in the structure.52,53 Cobalt belongs to the same group as rhodium; thus, the low bulk modulus of CoN2 is likely to be due to a short-bond nitrogen dimer (N−N) in the structure, as in RhN2. Further advanced analyses should offer direct information about many of its chemical and physical properties.

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SUMMARY

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ASSOCIATED CONTENT

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REFERENCES

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Highly coordinated iron and cobalt nitrides were successfully synthesized via direct chemical reaction between a transition metal and molecular nitrogen at pressures above 30 GPa. The synthesized novel nitrides were found to crystallize in the NiAstype and marcasite-type structures and to be quenchable to ambient pressure. In contrast to the ZnS-type mononitrides reported to date, the transition atom coordinates to six nitrogen atoms in the structure. The marcasite-type CoN2 shows a bulk modulus of 216(18) GPa, which is comparable to that of RhN2. This indicates that the atomic distance of the N−N dimer is short because of weak orbital interaction between cobalt and nitrogen. A first-principles calculation demonstrated that NiAstype FeN and CoN and marcasite-type CoN2 are metallic and have magnetic moments of 3.4, 0.6, and 1.2 μB, respectively. These quenchable highly coordinated 3d transition metal nitrides offer new insight into the fundamental properties and possible applications of transition metal nitrides.

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00516. Specifications of synchrotron radiation experiments at PF-AR, KEK, and AichiSR, examples of optical photographs of the sample chamber before and after laser heating at high pressures, lattice parameters of synthesized iron and cobalt nitrides as a result of the different experimental conditions, and XRD profiles of Fe−N2 experiments during decompression (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ken Niwa: 0000-0003-1037-675X Notes

The authors declare no competing financial interest. 6416


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