Rocksalt Structure Research Articles

Over-Stoichiometric Metastabilization of Cation-Disordered Rock Salts.

Cation-disordered rock salts (DRXs) are well known for their potential to realize the goal of achieving scalable Ni- and Co-free high-energy-density Li-ion batteries. Unlike in most cathode materials, the disordered cation distribution may lead to more factors that control the electrochemistry of DRXs. An important variable that is not emphasized by research community is regarding whether a DRX exists in a more thermodynamically stable form or a more metastable form. Moreover, within the scope of metastable DRXs, over-stoichiometric DRXs, which allow relaxation of the site balance constraint of a rock salt structure, are particularly underexplored. In this work, these findings are reported in locating a generally applicable approach to "metastabilize" thermodynamically stable Mn-based DRXs to metastable ones by introducing Li over-stoichiometry. The over-stoichiometric metastabilization greatly stimulates more redox activities, enables better reversibility of Li deintercalation/intercalation, and changes the energy storage mechanism. The metastabilized DRXs can be transformed back to the thermodynamically stable form, which also reverts the electrochemical properties, further contrasting the two categories of DRXs. This work enriches the structural and compositional space of DRX families and adds new pathways for rationally tuning the properties of DRX cathodes.

La4NiLiO8-assistant surface reconstruction to realize in-situ regeneration of the degraded nickel-rich cathodes

The cost-effectiveness and higher energy density of nickel-rich cathodes have made them appealing for electric vehicles, generating significant interest in their advancement. Unfortunately, the cathodes' high surface activity presents a challenge in humid air conditions, leading to structural degradation. The deterioration leads to the creation of the NiO rock-salt structure and residual lithium, impeding the pathways for Li+ movement throughout the entire system. Concurrently, the reduction of unstable Ni3+ triggers the generation of reactive oxygen species, causing the emergence of oxygen vacancies. These vacancies, in turn, diminish the cathode's structural stability. Herein, to mitigate the degradation of nickel-rich cathodes following storage, a surface reconstruction technique was employed to convert residual lithium and NiO phase into a conductive La4NiLiO8 repair layer. This in-situ regeneration resulted in an impressive regenerative electrochemical capacity of 56.2 mAh/g at 1C for the 28d-1La sample. Additionally, the surface reconstruction technique effectively decreased the concentration of oxygen vacancies, resulting in improved durability of the cathode structure. Furthermore, the La4NiLiO8 repair layer effectively suppressed detrimental phase transitions and mitigated electrolyte corrosion. This study presents a straightforward and efficient regeneration strategy for degraded nickel-rich cathodes resulting from storage.

Sintering behavior, structural evolution, and dielectric properties of Li2+MgTiO4F microwave dielectric ceramics

Herein, the sintering behavior, structural evolution, microstructure, and dielectric properties of Li2+xMgTiO4Fx (0 ≤ x ≤ 5) ceramics were investigated. At x ≤ 0.75, Li2+xMgTiO4Fx ceramics formed a continuous solid solution with a cubic rock salt structure. Subsequently, a composite ceramic of Li2+xMgTiO4Fx and LiF was formed. It was found that the maximum mass percentage of LiF required to fully form a solid solution was between 11% and 13%. The Li2.75MgTiO4F0.75 exhibited the best dielectric properties: εr = 16.52, Q × f = 123,574 GHz, and τf = −18.11 ppm/°C. The substitution of F- for O2- resulted in a lower sintering temperature of 875 °C, which slightly suppressed the volatilization of Li, and thus optimized the dielectric properties. The decrease in lattice vibration damping behavior and the increase in electron cloud density resulted in lower dielectric losses. The reduction in molecular polarization rate led to a reduction in εr, and the increase in bond energy optimized τf. Good chemical compatibility with Ag electrode was demonstrated, indicating that Li2+xMgTiO4Fx ceramics have unlimited potential for LTCC applications.

Vacancy ordering in zirconium carbide with different carbon contents

Zirconium carbide (ZrCx) ceramics with different carbon contents were prepared by reactive hot-pressing. The rock-salt structure of ZrCx was the only phase detected by x-ray diffraction of the hot pressed ceramics. The relative densities of ZrCx decreased as carbon content increased, in general. The actual carbon contents were measured by completely oxidizing the ZrCx ceramics to ZrO2. For most compositions, the actual carbon contents were higher than nominal batched compositions, presumably due to carbon uptake from the graphite furnace and hot press dies. Selected area electron diffraction and neutron powder diffraction revealed the presence of carbon vacancy ordering in ZrCx for 0.6 < x < 0.75. Rietveld refinement of the neutron diffraction patterns determined that the crystal structure of the ordered phase was hexagonal, and the carbon site occupancies were higher than nominal batched carbon stoichiometry.

Phase evolution during conventional and reactive flash sintering of (Mg,Ni,Co,Cu,Zn)O via in situ X‐ray diffraction

AbstractReactive flash sintering (RFS) enables the simultaneous synthesis and sintering of ceramics and has been shown to affect the reaction pathway of different materials. Herein, in situ synchrotron X‐ray diffraction (XRD) is used to investigate the (Mg,Ni,Co,Cu,Zn)O entropy‐stabilized oxide formation during: (i) conventional heating and (ii) RFS under current rate‐controlled mode. The same reaction pathway is verified in both instances: the starting rock‐salt (RS), spinel (Co3O4), tenorite (CuO), and wurtzite (ZnO) phases transform into a single RS phase with a (1 1 1) to (2 0 0) intensity ratio of 0.67, consistent with a random distribution of the cations into the structure. Pt lattice peak shift from the XRD patterns is used as standard to monitor the sample surface temperature, revealing a strong endothermic reaction during the RS single‐phase formation (Pt peaks shift toward higher angles while increasing sample temperature/current density). In RFS, the single‐phase RS structure is formed in just 60 s at a furnace temperature of 600°C and a current rate of 220 mA mm−2/min. Therefore, RFS greatly accelerates the synthesis of (Mg,Ni,Co,Cu,Zn)O, however, it does not play a role in the reaction pathway for this material formation.

Kinetics of Li Transport in Vanadium-Based Disordered Rocksalt Structures

Kinetics of Li Transport in Vanadium-Based Disordered Rocksalt Structures

Structural properties and epitaxial relation of cubic rock salt ScxAl1−xN/ScN/Si

ScN in the rock salt structure is a well-investigated material due to its desirable properties like the high hardness or large thermal conductivity. Recent computations by Adamski et al. [Appl. Phys. Lett. 115, 232103 (2019)] showed that ScN/GaN heterostructures exhibit an outstanding polarization gradient which would be beneficial for polarization induced electron gases. The pseudobinary semiconductor ScxAl1−xN, when maintaining the cubic rock salt structure, could be beneficial for tailoring the polarization gradient using the Sc dependency of material properties. The structural properties of rs-ScxAl1−xN are not fully discovered yet, thus in this work, DC-magnetron sputtered cubic rock salt ScxAl1−xN thin films with 0.55&amp;lt;x&amp;lt;1.00 were grown and analyzed on ScN(111)/Si(111). The epitaxial relation of ScN(111) thin films on the Si(111) substrate is determined to be ScN[110] ∥ Si[100]. Furthermore, concentration dependent properties like the lattice parameter of ScxAl1−xN were measured [a(ScN) = 4.50 Å, a(Sc0.55Al0.45N) = 4.30 Å] and the stress σ within the layers was determined. The crystal quality was evaluated using ω-scans, revealing FWHM=1.14° for Sc0.95Al0.05N. The diameters of the columns were determined by atomic force microscopy and scanning electron microscopy and they are range from 34 to 59 nm for 0.55&amp;lt;x&amp;lt;1.00. At x=0.55, ScxAl1−xN columns in the hexagonal wurtzite as well as cubic rock salt structure were detected. This information about the structural specifications of ScxAl1−xN in the rock salt structure forms the basis for further investigations and experimental confirmation of the electric properties of ScN/GaN heterostructures or even a ScxAl1−xN/GaN based approach for improved structures for high-electron-mobility transistors.

Computational discovery of novel U-N-C ternary phases as promising accident-tolerant fuels

Recently, uranium carbonitride solid solution has been recognized as a promising nuclear reactor fuel due to its excellent physicochemical properties. However, due to the complexity of U-N-C ternary system, the research on the structure and properties of uranium carbonitride is still insufficient. In this work, a series of promising accident-tolerant ternary compounds in the U-N-C system were predicted through a combination of first-principles calculations with an evolutionary algorithm. Fifteen dynamically and mechanically stable novel U-N-C ternary compounds with seven chemical compositions, including U-N-C solid solutions and new intermetallic structures, were suggested to be promising for experimental synthesis. For U-N-C solid solutions with rock-salt structures, it was revealed that the lattice expansion and bond length elongation caused by the substitution of carbon atoms for nitrogen atoms can lead to a decrease in elastic moduli and melting point and an increase in toughness. Moreover, two newly identified structures P63/mcm-U3N2C and P2/m-U4NC were considered to be very promising accident-tolerant fuels due to their high mechanical strength, excellent melting point, low thermal expansion coefficient, and high thermal conductivity. The larger atomic number density of P63/mcm-U3N2C enables a higher elastic modulus and a satisfactory melting point than those of rock-salt structures. While for P2/m-U4NC, its unique shorter and stronger U-N/C and U-U bonding leads to its highest mechanical strength and appropriate melting point. Furthermore, the linear thermal expansion coefficients of P2/m-U4NC and P63/mcm-U3N2C are comparable to those of UN and UO2, respectively, and their thermal conductivities increase with temperature, much higher than that of UO2.

Barium Oxynitride Electride as Highly Enhanced Promotor for Ruthenium Catalyst in Ammonia Synthesis: Comparative Study with Barium Oxide

AbstractBarium oxide is a conventional promoter for various transition‐metal (TM) catalysts in ammonia synthesis. Ba‐promoted Ru catalysts are widely used for ammonia synthesis under mild reaction conditions. However, the promotion mechanism, including the active factor, remains unclear. In this study, the excellent promotion effect of barium oxynitride is reported, which creates anionic electrons in the lattice, forming an electride (BaOxNy:e−z) with the same rocksalt structure as BaO. The BaOxNy:e−z enhances the ammonia synthesis activity of the supported Ru catalyst by 40–100 fold compared with the BaO promotor. This study reveals that a low‐work‐function electron formed in the BaO lattice plays a pivotal role in the electronic promotion effect in catalytic ammonia synthesis, suggesting that BaOxNy:e−z formed near the surface during the ammonia synthesis reaction is an active species for the promotion effect of conventional BaO.

Nitrogen Reduction Reaction to Ammonia on Transition Metal Carbide Catalysts.

The development of a low-cost, energy-efficient, and environmentally friendly alternative to the currently utilized Haber-Bosch process to produce ammonia is of great importance. Ammonia is an essential chemical used in fertilizers and a promising high-density fuel source. The nitrogen reduction reaction (NRR) has been explored intensively as a potential avenue for ammonia production using water as proton source, but to this day a catalyst capable of producing this chemical at high Faradaic efficiency (FE) and commercial yield and rates has not been reported. Here, we investigate the activity of transition metal carbide (TMC) surfaces in the (100) facets of the rocksalt (RS) structure as potential catalysts for the NRR. In this study, we use density functional theory (DFT) to model reaction pathways, estimate stability, assess kinetic barriers, and compare adsorbate energies to determine the overall performance of each TMC surface. For pristine TMC surfaces (with no defects) we find that none of the studied TMCs possess both exergonic adsorption of nitrogen and the capability to selectively protonate nitrogen to form ammonia in the desired aqueous solution. ZrC, however, is shown to be a potential catalyst if used in a non-aqueous electrolyte. To circumvent the endergonic adsorption of nitrogen onto the surface, a carbon vacancy was introduced. This provides a well-defined high coordination active site on the surface. In the presence of a vacancy VC, NbC, and WC showed efficient nitrogen adsorption, selectivity towards ammonia, and a low overpotential (OP). NbC did, however, display an unfeasible kinetic barrier to nitrogen dissociation for ambient-condition purposes, and thus it is suggested for high tempearture/pressure ammonia synthesis. Both WC and VC in their RS (100) structure are promising materials for experimental investigations in aqueous electrolytes, and ZrC could potentially be interesting for non-aqueous electrolytic systems.

Rethinking SnSe Thermoelectrics from Computational Materials Science.

ConspectusThe growing energy crisis and the adverse environmental impacts caused by carbon-based energy consumption have spurred the exploration of green and sustainable energy. Researchers have been devoted to developing thermoelectric technology that could directly and reversibly convert heat into electricity. By virtue of zero emissions, nonmoving parts, precise temperature control, and long service life, thermoelectrics exhibit broad application in power generation and refrigeration. Nevertheless, traditional narrow-bandgap thermoelectrics exhibit high performance within a narrow temperature range, limiting the overall energy conversion. Consequently, a selection rule for exploring advanced thermoelectrics was proposed: materials with wide-bandgap, crystals form, asymmetry, and anisotropic structure. According to the rules, we conducted much research and found some promising materials.As the lead-free, cost-effective, and stable thermoelectric candidates, layered SnSe crystals with wide-bandgap and covalent bonding have gained significant attention due to their ultralow thermal conductivity resulting from strong bonding anharmonicity, via strong polar covalent bonding, because of the electronegativity difference between the Sn and Se atoms. This was proved to be the result from the unique structure of layered SnSe crystals, a distorted rock-salt structure with high and anisotropic Grüneisen parameters. In this Account, we introduce and rethink our recent advancements in developing high-performance thermoelectric SnSe crystals from computational materials science, involving p- and n-type SnSe crystals, respectively. For p-type SnSe crystals, according to the complex valence band structures, we utilized the multiband synglisis via electronic structure calculations and multiband simulations to activate valence bands to participate in electrical transport of in-plane direction, achieving an ultrahigh power factor (PF) of ∼75 μW cm-1 K-2 at room temperature and an average figure-of-merit ZTave of ∼1.9 for Sn0.91Pb0.09Se. Besides, on the basis of defect chemistry, the characteristics of p-type SnSe crystals are determined by intrinsic Sn vacancies. We thus used point-defect calculations to achieve the lattice plainification, and we fixed the lattice intrinsic defects to weaken defect scattering of carriers along the in-plane direction, facilitating further a PF > 100 μW cm-1 K-2 and a ZT of ∼1.5 at room temperature for SnCu0.001Se. For n-type SnSe crystals, inspired by the anisotropic characteristics of the layered materials, we analyzed charge density and proposed the insight of 3D charge and 2D phonon transports and calculated the deformation potential to manipulate layered phonon-electron decoupling to achieve high performance, ultimately Pb-alloyed and Cl-doped SnSe (SnSe-Cl-PbSe) reaching a ZTave of ∼1.7 from 300 to 773 K. In the end, we offer potential perspectives on high-throughput calculations (HTC) and machine learning (ML), combined with our proposed insights, which could be a promising avenue for future thermoelectrics. By virtue of our theoretical and experimental understanding of thermoelectrics, integrating these insights as rules and descriptors for HTC and ML will accelerate the research and development of thermoelectrics. We want to share our recent works and latest perspectives in SnSe thermoelectrics, and we expect to inspire enthusiasm for innovative research on advanced thermoelectric materials and devices.

Fabrication and electromagnetic wave absorbing properties of the (Hf0.25Zr0.25Nb0.25Ta0.25)C high-entropy ceramics

High-entropy engineering is an effective strategy for developing high properties of the transition-metal carbides, including their mechanical and functional performance, owing to its high-entropy effect, sluggish diffusion effect, sever lattice distortion, and cocktail effect. In this study, a single-phase high-entropy ceramic with a rock-salt crystal structure (Hf0.25Zr0.25Nb0.25Ta0.25)C was fabricated through a solid-phase reaction at 2200 °C. The as-obtained, high-entropy ceramic powder exhibited high efficiency electromagnetic-wave-absorption capability. The minimum reflection loss (RL) value reached approximately − 64.38 dB at 16 GHz with a thickness of 4.43 mm. By tuning the thickness of the sample, the total effective absorption bandwidth (RL ≤ −10 dB) was ∼ 4.46 GHz, almost covering the Ku band. The excellent microwave absorption performance was ascribed to the high-entropy effect of the strong dielectric loss of the material as well as the proper impedance matching degree. Thus, high-entropy engineering is expected to be a promising route for developing microwave absorbers with excellent absorption capability.

The doping-induced phase transition in rock salt-structured Li2Ti1−x(Mg1/3Ta2/3)xO3 (0 ≤x ≤ 0.4) ceramics revealed by EBSD and XRD refinement and its effects on the microwave dielectric properties

The microwave dielectric properties (MDPs) of Li2TiO3-based ceramics can be effectively tailored by the doping-induced monoclinic-to-cubic transition. However, the mechanism of the effects of phase transition on the MDPs is still yet to be clarified, as it is hindered by overlap of the main diffraction peaks of the two phases. To solve this problem, we report accurate analyses of the phase composition of Li2Ti1−x(Mg1/3Ta2/3)xO3 ceramics by electron back-scattered diffraction (EBSD) mapping combined with X-ray diffraction (XRD) refinement. As the x value increases, the samples undergo a monoclinic-to-cubic transition, which leads to a decrease in εr, an increase in Q×f, and a negative shift of τƒ. Moreover, the theoretical values of εr, Q×f, and τƒ of the samples with various doping concentrations are calculated based on the phase composition analysis results. The theoretical values are consistent with the experimental data. The optimal MDPs (i.e., εr = 18.4, Q×f = 74300 GHz, and τf = 0.2 ppm/°C) are obtained in the sample with x = 0.2. The study results essentially reveal the effects of the doping-induced phase transition in Li2TiO3-based ceramic materials with a rock salt structure on the MDPs.

Optical properties of ScN layers grown on Al2O3(0001) by plasma-assisted molecular beam epitaxy

Accurate knowledge of optical constants (refractive index n and extinction coefficient k) of ScN is crucial for understanding optical properties of this binary nitride semiconductor as well as for its use in optoelectronic applications. Using spectroscopic ellipsometry in a spectral range from far infrared to far ultraviolet (0.045–8.5 eV), we determine n and k of ScN layers grown on Al2O3(0001) substrates by plasma-assisted molecular beam epitaxy. Fits of ellipsometry data return the energies of four oscillators representing critical points in the band structure of ScN, namely, 2.03, 3.89, 5.33, and 6.95 eV. As the infrared range is dominated by free carriers, the vibrational properties of the layers are examined by Raman spectroscopy. Despite the rock salt structure of ScN, several first-order phonon modes are observed, suggesting a high density of point defects consistent with the high electron density deduced from Hall measurements. Finally, photoluminescence measurements reveal an emission band slightly above the lowest direct bandgap. We attribute the redshift of the peak emission energy from 2.3 to 2.2 eV with increasing layer thickness to a reduction in the O concentration in the layers.

Lattice modification of ZrO2-δ and formation of rocksalt structure ZrO and Zr(O,N) after DC electrical loading of 3YSZ

It is widely acknowledged that electrochemical reduction occurs during DC flash sintering (FS) of YSZ. In situ experiments have shown the emergence of new phases during FS that disappear again when the current is switched off. In addition, it has recently been reported that YSZ flash sintered in the absence of oxygen has a high electrical conductivity at room temperature. In this investigation electrical loading of YSZ was conducted in Ar and N2 and maintained as the furnace cooled down such that on removing the current, the sample was rapidly quenched, avoiding reoxidation or other diffusion-limited phase transformations. XRD showed that the tetragonality of the ZrO2-δ phase was diminished and the volume of the unit cell increased, the effect of the electrochemical reduction being similar to an increase in Y2O3 content. In addition, rocksalt structure Zr(O,N) with a lattice constant of 0.4580 nm was formed at the surface and retained at room temperature. This phase had a metallic lustre and electrical conductivity approaching those of metals. The results enable several recent results in the literature to be reconciled and the implications for flash sintering are briefly discussed.

Epitaxial growth of oriented CoO films by radio-frequency sputtering deposition

Rock-salt CoO is a p-type semiconductor and its Néel temperature is close to room temperature. CoO-based compounds are known as promising systems for renewable energy harvest with high efficiency. CoO with catalytic and exchange bias properties can be widely used for industrial applications. In this paper, we report high-quality stable CoO(111) and (100) films epitaxially grown on c-cut (0001) and r-cut (101‾2) α-Al2O3 substrates, respectively, using radio-frequency sputtering deposition. X-ray diffraction (XRD) measurements revealed that the CoO films had a rock-salt structure (Fm3m) with lattice constants of 4.2477 Å and 4.2617 Å for film grown on (0001) and (101‾2) α-Al2O3 substrates, respectively. CoO films with the best crystal quality were grown at a substrate temperature of ∼700 °C. XRD measurements of CoO(111) films indicated a lack of structural residual strain, whereas CoO(100) films had substantial amounts of structural strain. X-ray reflectivity (XRR) and transmission electron microscopy measurements showed neither oxygen vacancy nor defects in both CoO(111) and (100) films. XRR revealed that the mean electron density of the CoO films was nearly identical to a pure CoO and that the films were considerably stable under the atmosphere.

Microstructure characterization and formation mechanism of lanthanum phosphide in FeCrAlRE alloy with ultra-low oxygen

Rare earth (RE) could be added to steels to improve their properties, but there is still controversy on its presence form. Taking 0Cr20Al6RE as the research object, the morphology, distribution, chemical composition and phase structure of RE precipitated phases were characterized by SEM, EPMA and TEM. It is found that with ultra-low oxygen (3 ppm) and RE/(O + S) = 37.1, the main existence form of rare-earth is RE-P-As in which the La-P phase is lanthanum monophosphide with a rock-salt structure, while the structure of complex inclusion is mainly RE-Al-O/RE-P-As/(Ti,Nb)(C,N). According to Gibbs free energy, precipitated phase distribution and solidification segregation calculation, it is confirmed that La-P-As is formed at the solidification front. This finding provides a technology idea for the composition design and process improvement of RE steels by avoiding the emergence of large-size RE-O-S inclusions.

A High-Entropy-Oxides-Based Memristor: Outstanding Resistive Switching Performance and Mechanisms in Atomic Structural Evolution.

The application of high-entropy oxide (HEO) has attracted significant attention in recent years owing to their unique structural characteristics, such as excellent electrochemical properties and long-term cycling stability. However, the application of resistive random-access memory (RRAM) has not been extensively studied, and the switching mechanism of HEO-based RRAM has yet to be thoroughly investigated. In this study, HEO (Cr, Mn, Fe, Co, Ni)3 O4 with a spinel structure is epitaxially grown on a Nb:STO conductive substrate, and Pt metal is deposited as the top electrode. After the resistive-switching operation, some regions of the spinel structure are transformed into a rock-salt structure and analyzed using advanced transmission electron microscopy and scanning transmission electron microscopy. From the results of X-ray photoelectron spectroscopy and electron energy loss spectroscopy, only specific elements would change their valence state, which results in excellent resistive-switching properties with a high on/off ratio on the order of 105 , outstanding endurance (>4550 cycles), long retention time (>104 s), and high stability, which suggests that HEO is a promising RRAM material.

Ab initio study of structural, mechanical and electronic properties of 3d transitional metal carbide in cubic rocksalt (rs), zincblende (zb), and cesium chloride (cc) structures by using LDA and GGA Approximation.

This study rigorously investigates three 3d transition metal carbide (TMC) structures via LDA and GGA approximations. It examines cohesive energy (Ecoh), Vickers hardness (Hv), mechanical stability, and electronic properties. Notably, most 3d TMCs exhibit higher cohesive energy than nitrides, and rs-TiC demonstrates a Vickers hardness of 25.66 GPa, outperforming its nitride counterpart. The study employs theoretical calculations to expedite research, revealing mechanical stability in CrC and MnC (GGA) and CrC (LDA in cc structure), while all 3d TMCs in rs and seven in zb structures show stability. Charge transfer and bonding analysis reveal enhanced covalency along the series, influenced by the interplay between p orbitals of carbon and d orbitals of the metal. Most 3d TMCs exhibit metallic properties, excluding zb-TiC and zb-FeC in all phases. An inverse correlation between elastic constant C44 and electronic states near the Fermi level (EF) emerges, guiding applications and design. This study efficiently uncovers 3d TMC properties, offering insights for applications and design. We employed the Vienna ab initio Simulation software (VASP) to perform computations based on density functional theory (DFT). Our approach incorporated both the projector augmented wave (PAW) and PW91 general gradient approximation (GGA) methods within the local density approximation (LDA).

Defect rocksalt structures in the La-Na-N system.

Sodium azide (NaN3) is a versatile nitrogen source that can be used for the synthesis of new nitrides under high-pressure and temperature conditions. Reactions between lanthanum nitride (LaN) and sodium azide (NaN3) at 800°C under 8 GPa pressure have led to the discovery of two defect rocksalt phases which are the first reported ternaries in the La-Na-N system. Preliminary structure assignments have been made based on fits to powder X-ray diffraction profiles. One phase is La1-xNa3xN with vacancies at octahedral La sites and interstitial tetrahedral Na cations. This phase has a tetragonally distorted rocksalt structure (space group I4[Formula: see text]mmm, a = 3.8704(2) and c = 5.2098(3) Å for nominal x = 0.10) and the distortion decreases with increasing Na content (space group I4[Formula: see text]mmm, a = 3.8060(2) Å, c = 5.2470(3) Å for nominal x = 0.14), further giving a cubic phase (a = 5.3055(2) Å) for nominal x = 0.25. This coexists with another cubic [Formula: see text] phase (a = 5.1561 (5) Å), tentatively identified as rocksalt 'NaN1/3' stabilized by a small amount of La; NaLayN(1+3y)/3 with y ≈ 1%. These initial investigations reveal that the high-pressure La-Na-N phase diagram may be rich in defect rocksalt-type materials although further work using neutron diffraction will be needed to confirm the structures. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.