Rock Salt Crystal Structure Research Articles

Thin film synthesis, structural analysis, and magnetic properties of novel ternary transition metal nitride MnCoN2

Recent high-throughput computational searches have predicted many novel ternary nitride compounds providing new opportunities for materials discovery in underexplored phase spaces. Nevertheless, there are hardly any predictions and/or syntheses that incorporate only transition metals into new ternary nitrides. Here, we report on the synthesis, structure, and properties of MnCoN2, a new ternary nitride material comprising only transition metals and N. We find that crystalline MnCoN2 can be stabilized over its competing binaries, and over a tendency of this system to become amorphous, by controlling growth temperature within a narrow window slightly above ambient condition. We find that single-phase MnCoN2 thin films form in a cation-disordered rocksalt crystal structure. X-ray photoelectron spectroscopy analysis suggests that MnCoN2 is sensitive to oxygen through various oxides and hydroxides binding to cobalt on the surface. X-ray absorption spectroscopy is used to verify that Mn3+ and Co3+ cations exist in an octahedrally coordinated environment, which is distinct from a combination of CoN and MnN binaries and in agreement with the rocksalt-based crystal structure prediction. Magnetic measurements suggest that MnCoN2 has a canted antiferromagnetic ground state below 10 K. We extract a Weiss temperature of θ=−49.7K, highlighting the antiferromagnetic correlations in MnCoN2. Published by the American Physical Society 2024

Structural electronic and thermodynamic properties of CdX(X: S, Se, and Te) cadmium chalcogenides compound

The structural and electronic properties of (CdS, CdSe, and CdTe) compounds in rock-salt, zinc-blend, and wurtzite crystal structures were calculated using ab initio calculation. In addition to these properties, the thermodynamic properties were added advantage to clarify their comportment as temperature variation. Under the context of density functional theory DFT, the calculations were carried out using the full potential linearized augmented plane wave FP-LAPW approach. The generalized gradient approximations GGA-PBE established by Perdew-Burke-Ernzerhof and the local density approximation LDA and modified Bucke Jhonson have both been employed for the exchange-correlation energy and related potential MBJ. The results show that the zinc-blend phases were the stable crystal structure for all compounds. The lowest direct band gap is found in the B3 phase for CdX, close to the experimental value. The values of band energies of CdS, CdSe, and CdTe were estimated to be 2,463 eV, 1,76 eV, and 1,532 eV, respectively. In general, this work fits well with other experimental and theoretical results. The quasiharmonic Debye theory is used to determine the impact of temperature and pressure on thermodynamic properties. This includes the calculation of pressure and temperature dependence, as well as the analysis of how heat capacity, thermal expansion, and the Debye temperature are affected by these variables.

Micropillar compression of single-crystal single-phase (Co, Cu, Mg, Ni, Zn)O

Bulk, polycrystalline (Co, Cu, Mg, Ni, Zn)O was synthesized using solid-state sintering. Micropillars were prepared and mechanically deformed along three crystallographic orientations: (001), (101), and (111). Pillars (001) and (111) cracked, while Pillar (101) remained intact. Pillars (001) and (101) exhibited activated slip systems, confirmed by a large stress drop, and the presence of slip bands, respectively. Schmid factor (SF) analysis was performed to examine the effect of grain orientations on dislocation activity and slip behavior. SF values range from 0 to 0.5, with non-zero values indicating potential for slip. Six slip systems exist in the (Co, Cu, Mg, Ni, Zn)O rock salt crystal structure: 1/2⟨110⟩11¯0. For the (001) orientation, four slip systems are potentially active (SF = 0.5). For the (101) orientation, there are four potentially active slip systems (SF = 0.25). For the (111) orientation, no potentially active slips systems exist (SF = 0). Dislocation structures, which were observed post-compression via transmission electron microscopy, demonstrated variations in size, number, and distribution across the pillar, depending on micropillar orientation. Entangled dislocations created misorientation in Pillar (001), which led to the possible formation of subgrains, while singular dislocations were observed in Pillar (101), and a lack of dislocations was observed in Pillar (111). Zener–Stroh type dislocation entanglement-mediated cracking is the proposed cause of the transgranular-type cracks in Pillar (001). The possible subgrain formation, or lack of formation, respectively, caused intergranular-type cracks to additionally form in Pillar (001), while Pillar (111) only exhibited transgranular-type brittle fracture. In combination, these findings highlight the importance of dislocation activity, without the need for elevated temperature, and grain orientation in controlling the mechanical deformation response in single-phase (Co, Cu, Mg, Ni, Zn)O.

Tailoring crystal structure of high-entropy carbides in Si-based ceramic nanocomposites through precursor engineering

High-entropy carbides with tunable crystallization and growth have been demonstrated using single-source precursor derived ceramic route. The in situ nanocrystallization of high-entropy carbide phases, (Ta0.2W0.2V0.2Mo0.2Nb0.2)SiδC and (Ta0.167W0.167V0.167Mo0.167Nb0.167Si0.167)C in amorphous Si-based ceramic matrices was achieved by using polysiloxanes and polycarbosilanes as polymer precursors respectively. The results exemplify a prominent role of the architectures of the polymeric precursors in controlling the structural features of these ceramics at various length scales. In particular, it was observed that high-entropy carbides with rock salt and zinc blende crystal structures were formed when polysiloxanes and polycarbosilanes with different backbone structure were used as polymeric precursors respectively. This is attributed to the thermodynamics of nucleation of the carbidic phases in these nanocomposites. Furthermore, the precursor architecture that dictates free carbon content, influenced nanostructural features and porosity in the material. Therefore, engineering such compositionally complex phases is feasible by selecting suitable polymeric precursors.

Unifying the size effect observed in micropillar compression experiments

ABSTRACT Micropillar compression experiments show size effect, σp/μ = A(d/b)n , where σp , is the flow stress, μ is the resolved shear modulus, d is the pillar diameter and b is Burgers’ vector. With fcc metals n ≈ –0.67 and A ≈ 0.7; however, with bcc metals there is greater variation, with n closer to zero. Here we propose a different but similar empirical relation of σp/μ = σb/μ + A’(d/b)n’, where σb is a size independent resistance stress. In which case there must be a strong correlation between the original constants, A and n. This hypothesis is found to be true for the published data from a large number of bcc metals, ionic solids that possess the rock salt crystal structure, and some covalent bonded semiconductors. This correlation is shown to predict a universal power law with the exponent in the range, −1.0 < n’ < −0.5, and with A’ close to 1. These values are very similar to the empirical relation that can be used to describe the behaviour of fcc metals tested in micropillar compression with σb = 0. This universality of the empirical relation provides strong evidence for a common mechanism for the micropillar size effect across a range of materials.

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers.

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

Anomalous mass dependence of phonon thermal transport in lanthanum monopnictides and its origin in the nature of chemical bonding

In certain compounds of binary lanthanum monopnictides exhibiting a rocksalt crystal structure, a phenomenon arises: larger average atomic mass, smaller acoustic phonon velocities, and smaller acoustic optical frequency gap do...

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.

Understanding the Degradation Mechanisms in Lithium Manganese Oxyfluoride Cathodes

The development of next-generation nickel and cobalt-free Li-ion batteries with significantly greater energy density for electric vehicles is largely contingent on the discovery of new cathode materials. A number of novel candidates with a disordered rocksalt crystal structure have recently been reported to exhibit high capacities, offering a highly promising new avenue for cathode research.1–5 However, disordered rocksalt cathode materials generally suffer from voltage and capacity fade over cycling. For example, the Mn-based archetypal oxyfluoride Li2MnO2F shows 254 mAh g-1 discharge capacity in the first cycle but fades to 104 mAh g-1 after 100 cycles. For improving these materials leading to practical devices, it is vital to develop an understanding of the fading mechanisms.Various explanations have been proposed for the gradual deterioration in performance of disordered rocksalt oxide and oxyfluoride cathodes. These include O-loss and surface densification4,6, growth of a CEI layer7, phase segregation6,8. In this study, we examine the main degradation mechanisms in Li2MnO2F over cycling and demonstrate that the capacity and voltage retention can be improved through compositional control, figure below. This understanding points the way to manganese oxyfluorides with better cycling performance. House, R. A. et al. Lithium manganese oxyfluoride as a new cathode material exhibiting oxygen redox. Energy Environ. Sci. 11, 926–932 (2018).Lee, J. et al. Reversible Mn2+/Mn4+ double redox in lithium-excess cathode materials. Nature 556, 185–190 (2018).Yabuuchi, N. et al. Origin of stabilization and destabilization in solid-state redox reaction of oxide ions for lithium-ion batteries. Nat. Commun. 7, 1–10 (2016).Li, L. et al. Fluorination‐Enhanced Surface Stability of Cation‐Disordered Rocksalt Cathodes for Li‐Ion Batteries. Adv. Funct. Mater. 2101888, 2101888 (2021).Chen, R. et al. Disordered lithium-rich oxyfluoride as a stable host for enhanced Li+ intercalation storage. Adv. Energy Mater. 5, (2015).Chen, D., Kan, W. H. & Chen, G. Understanding Performance Degradation in Cation-Disordered Rock-Salt Oxide Cathodes. Adv. Energy Mater. 9, 1–15 (2019).Källquist, I. et al. Degradation Mechanisms in Li2VO2F Li-Rich Disordered Rock-Salt Cathodes. Chem. Mater. 31, 6084–6096 (2019).Chen, D., Ahn, J., Self, E., Nanda, J. & Chen, G. Understanding cation-disordered rocksalt oxyfluoride cathodes. J. Mater. Chem. A 2, 7826–7837 (2021). Figure 1

&lt;i&gt;In Situ&lt;/i&gt; Synchrotron High-Pressure X-ray Analysis for ZnO with Rocksalt Structure

Zinc oxide (ZnO) with a rocksalt crystal structure is attractive because of the bandgap which lies in the range of visible light absorption (1.2-2.6 eV). However, the rocksalt structure is not stable at ambient pressure and temperature according to an equilibrium phase diagram. Nevertheless, this study demonstrates, for the first time, that it is possible to realize a 100% fraction of the rocksalt structure at ambient pressure and temperature. ZnO powder is initially processed by severe plastic deformation under high pressure through a technique of high-pressure torsion (HPT). The HPT-processed ZnO is then examined using a high-pressure application system available at BL04B1 of SPring-8 and in situ X-ray diffraction (XRD) analysis is conducted under high pressures at elevated temperatures. It is shown that the initial presence of the rocksalt structure produced by the HPT process is effective to attain a 100% fraction of the rocksalt structure.

Local structure analysis of DyN–ZrN solid solutions

We performed various synchrotron X-ray measurements to extract local and average structures of DyN–ZrN solid solutions. ZrN and AlN have typical phase separation systems, undergoing chemical segregation into ZrN-rich and AlN-rich domains. However, the phase separation of DyN–ZrN has not been investigated. We performed the nanoscale structural analysis to clarify the phase separation in DyN–ZrN by combining X-ray absorption fine structure and high-energy X-ray diffraction. Consequently, discontinuities indicating phase separation were observed in the average and local structures. The results showed that it is differs from the conventional phase separation mechanism caused by the difference in the crystal structure. The DyN–ZrN solid solution has a rock-salt type cubic crystal structure, and there are instabilities such as the chemical order of the metal site and the distribution of the bond length of the nitrogen site. A phase separation has occurred to reduce these structural instabilities.

Synthesis and Photothermal Properties of UV-Plasmonic Group IV Transition Metal Carbide Nanoparticles

Refractory nanostructures can be low-cost and chemically and thermally robust alternatives to metal-based plasmonic materials. While transition metal nitrides have received much attention recently, there has been less emphasis on their closely related non-layered carbide counterparts. In this work, plasmonic group IV transition metal carbide (TiC, ZrC, and HfC) nanostructures were prepared using a facile magnesiothermic reduction method, which yielded a phase pure product. TiC, ZrC, and HfC with rock salt crystal structures and an average particle size of 24, 31, and 42 nm, respectively, were obtained by reacting corresponding metal oxide, magnesium, and biochar in the solid state. Calculations performed using a finite element method predicted these group IV carbide nanostructures to have localized surface plasmon resonance in the UV region between 150 and 175 nm. The photothermal transduction efficiency of each carbide was explored to further verify the plasmonic behavior. HfC was found to have the highest photothermal transduction efficiency of 73%, followed by ZrC (69%), and then TiC (60%) at 365 nm.

On the synthesis and characterization of bimagnetic CoO/NiFe2O4 heterostructured nanoparticles

Bimagnetic nanoparticles show promise for applications in energy efficient magnetic storage media and magnetic device applications. The magnetic properties, including the exchange bias of nanostructured materials can be tuned by variation of the size, composition, and morphology of the core vs overlayer of the nanoparticles (NPs). The purpose of this study is to investigate the optimal synthesis routes, structure and magnetic properties of novel CoO/NiFe2O4 heterostructured nanocrystals (HNCs). In this work, we aim to examine how the size impacts the exchange bias, coercivity and other magnetic properties of the CoO/NiFe2O4 HNCs. The nanoparticles with sizes ranging from 10 nm to 24 nm were formed by synthesis of an antiferromagnetic (AFM) CoO core and deposition of a ferrimagnetic (FiM) NiFe2O4 overlayer. A highly crystalline magnetic phase is more likely to occur when the morphology of the core-overgrowth is present, which enhances the coupling at the AFM-FiM interface. The CoO core NPs are prepared using thermal decomposition of Co(OH)2 at 600 °C for 2 hours in a pure argon atmosphere, whereas the HNCs are obtained first using thermal evaporation followed by hydrothermal synthesis. The structural and morphological characterization made using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and scanning electron microscopy (SEM) techniques verifies that the HNCs are comprised of a CoO core and a NiFe2O4 overgrowth phase. Rietveld refinement of the XRD data shows that the CoO core has the rocksalt (Fd3 m) crystal structure and the NiFe2O4 overgrowth has the spinel (C12/m1) crystal structure. SEM-EDS data indicates the presence and uniform distribution of Co, Ni and Fe in the HNCs. The results from PPMS magnetization measurements of the CoO/NiFe2O4 HNCs are discussed herein.

Analysis of phase stability, elastic, electronic, thermal, and optical properties of Sc1-xYxN via ab initio methods.

Understanding the physical properties of a material is crucial to know its applicability for practical applications. In this study, we investigate the phase stability, elastic, electronic, thermal, and optical properties of the ternary alloying of the scandium and yttrium nitrides (Sc1-xYxN) for different compositions. To do so, we apply a "density functional theory (DFT)" based scheme of calculations named as "full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo) method" realized in the WIEN2k computational package. At first, the phase stability of the investigated compositions of the mentioned alloy is determined. The analysis of our calculations shows that Sc1-xYxN alloy is stable in rock salt crystal structure for all investigated compositions. Next to that, the elastic properties of the rock-salt phase of the studied ternary alloy Sc1-xYxN at all above said compositions were done at the level of "Wu-Cohen generalized gradient approximation (Wu-GGA)" within DFT. However, Trans-Blaha (TB) approximation of the "modified Becke-Johson (mBJ)" potential is also used in combination with Wu-GGA where the thermal properties are calculated at the level of the "quasi-harmonic Debye model." The obtained results for the absorption coefficients, and optical bandgap, represent that the title alloy may be a suitable candidate for the applications in optoelectronic devices.

Time-reversal symmetry breaking in the superconducting state of ScS

We have studied the electronic properties of ScS, a transition-metal monochalcogenide with a rocksalt crystal structure, using magnetization, specific heat, transport, and muon spin rotation/relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements. All measurements confirm the bulk superconductivity in ScS with a transition temperature of ${T}_{C}=5.1(5)$ K. Specific heat together with transverse-field $\ensuremath{\mu}\mathrm{SR}$ measurements indicate a full gap, while our zero-field $\ensuremath{\mu}\mathrm{SR}$ study reveals the presence of spontaneous static or quasistatic magnetic fields emerging when entering the superconducting state. We discuss various possible microscopic origins of the observed time-reversal symmetry breaking. As none of them can be readily reconciled with a conventional pairing mechanism, this introduces ScS as a candidate material for unconventional superconductivity.

Non-stoichiometry of (TiZrHfVNbTa)Cx and its significance to the microstructure and mechanical properties

(TiZrHfVNbTa)Cx with variable stoichiometry are fabricated by pressureless sintering utilizing self-synthesized carbide powders via carbothermal reduction reaction. The densification behavior and microstructure evolution coupled with corresponding adjustable mechanical properties are investigated. The single-phase rock-salt crystal structure is retained despite the carbon stoichiometry approaching 0.6, indicating (TiZrHfVNbTa)Cx can maintain structural stability even containing high carbon vacancy. The carbon vacancy is beneficial for promoting densification procedure. The relative density of (TiZrHfVNbTa)C0.6 sintered at 2150 °C can reach 97.9 %, while the similar value for (TiZrHfVNbTa)C1.0 is obtained even at 2400 °C. While, remarkable grain growth accompanied by decline in relative density also occurs for lower carbon stoichiometry. With the variation of carbon content, the concentration of carbon-metal bonds changes gradually, leading to the adjustable mechanical properties. This work provides a potential approach to synthesize non-stoichiometric high-entropy carbides with high carbon vacancy via low-temperature pressureless sintering.

Schmid factor analysis for chip flow induced plastic deformation of textured cubic carbonitride coatings

In high-speed metal machining, cutting tools in the form of cemented carbide inserts coated with thin wear-resistant coatings are commonly used. These coatings are often made of metal carbonitrides with cubic rock salt crystal structure and different growth textures. However, the influence of the crystallographic texture of the coatings on their wear by plastic deformation due to the chip flow during machining needs to be revealed further. In this work, in order to analyse the ability of polycrystalline fibre-textured coatings with a rock salt structure to undergo plastic deformation, a method was developed for calculating Schmid factors of such textured coatings as a function of the loading angle of an external force. The Schmid factors were calculated for coatings with 100 and 211 growth textures, and {100} <110>, {110}<110> and {111}<110> as possible slip systems. For the {111}<110> slip systems, the Schmid factors are not much influenced by the force angle and coating texture, which is contrary to the {100}<110> and {110}<110> slip systems. The simulations were compared to wear on the rake face of two textured Ti(C,N) coatings after short longitudinal turning tests. The variation of the degree of plastic deformation of Ti(C,N) coatings with growth texture and external force angle indicates that the dominant activated slip systems are {110}<110> using the machining conditions applied in this work.

Toward machine learning for microscopic mechanisms: A formula search for crystal structure stability based on atomic properties

Machine-learning techniques are revolutionizing the way to perform efficient materials modeling. We here propose a combinatorial machine-learning approach to obtain physical formulas based on simple and easily accessible ingredients, such as atomic properties. The latter are used to build materials features that are finally employed, through linear regression, to predict the energetic stability of semiconducting binary compounds with respect to zinc blende and rocksalt crystal structures. The adopted models are trained using a dataset built from first-principles calculations. Our results show that already one-dimensional (1D) formulas well describe the energetics; a simple grid-search optimization of the automatically obtained 1D-formulas enhances the prediction performance at a very small computational cost. In addition, our approach allows one to highlight the role of the different atomic properties involved in the formulas. The computed formulas clearly indicate that “spatial” atomic properties (i.e., radii indicating maximum probability densities for s,p,d electronic shells) drive the stabilization of one crystal structure with respect to the other, suggesting the major relevance of the radius associated with the p-shell of the cation species.

Synthesis of nonstoichiometric high entropy Nb-added carbides

A novel class of nonstoichiometric high-entropy carbide (HECx) materials, namely, Nb/TiC/TaC, Nb/TiC/TaC/VC and Nb/TiC/TaC/VC/WC, were produced by mechanically milled and spark plasma sintering (SPS) from Nb and carbides. XRD, SEM-EDS and S/TEM-EDS were used to characterize the phase constitution, microstructure and compositional distribution of samples, respectively. HECx exhibits a single-phase rock-salt crystal structure with a relatively uniform elemental distribution. Among the three different HECx materials, Nb/TiC/TaC/VC/WC with an average grain size of 2.15 μm sintered at 1600 °C shows an enhanced fracture toughness of 5.1 ± 0.1 MPa m1/2 compared with transition metal carbides. The mechanically mixed and low sintering temperature lead to the formation of finer grains. The higher fracture toughness can be attributed to atomic relaxation resulting from carbon vacancies and solid solution strengthening.

Plasma-enhanced atomic layer deposition of titanium molybdenum nitride: Influence of RF bias and substrate structure

In this work, TiMoN thin films were deposited by plasma-enhanced atomic layer deposition with an equal number of Ti and Mo precursor exposures at a substrate temperature of 250 °C. Tetrakis(dimethylamido) titanium and bis(tert-butylimido)bis(dimethylamido) molybdenum were used as sources for Ti and Mo, respectively. N2 and N2/H2 plasma were used, respectively, for TiN and MoN cycles as a source for N. Negative RF substrate bias voltage of magnitude, |Vbias|, of 0, 31, 62, 125, and 188 V were applied during the plasma half cycle. Nanocrystalline rock salt crystal structures were found by x-ray diffraction for films deposited on single-crystal Si and Si-thermal oxide substrates. Applying |Vbias| generated voids by the bombardment of high-energy ions, lowering the density. Further increase of |Vbias| caused the annihilation of voids and a slight increase in density. Four-point probe measurement showed increased electrical resistivity due to a reduction in grain size caused by continuous renucleation during growth. High-energy ions at high |Vbias| sputtered away the films resulting in low growth rates. Stripe test revealed inferior wear rates and coefficients of friction at higher |Vbias| due to low-density porous films. Epitaxial films deposited on c-plane sapphire had (111) orientation and considerable mosaicity with twinned domains rotated at 60° to each other.