Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Synthesis”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Magnesium diboride (MgB2): An effective and novel precursor for the synthesis of vertically aligned BNNTs

Highlights: • Discovered Magnesium diboride (MgB{sub 2}) as an effective and novel precursor for the synthesis of BNNTs. • Synthesized vertically aligned BNNTs directly on SiO{sub 2} substrate at 1000{sup °}C. • Magnesium (Mg) from MgB{sub 2} in partially melted form diffuses on SiO{sub 2} substrate. • The adsorbed Boron with Mg reacts with Nitrogen from decomposed ammonia and synthesized vertically aligned BNNTs. - Abstract: Vertically aligned Boron nitride nanotubes (BNNTs) have exceptional electrical, mechanical and thermal properties suitable for its potential applications without any further purification. However, the synthesis of aligned BNNTs via previously reported techniques is not only complicated, lengthy and misleading but also result in useless impurities in the final product. Here, we report Magnesium diboride (MgB{sub 2}) as an effective and novel precursor for the synthesis of vertically aligned BNNTs directly on SiO{sub 2} substrate at 1000 {sup °}C. Magnesium (Mg) from MgB{sub 2} in partially melted form diffuses on SiO{sub 2} substrate whereas the adsorbed Boron with Mg reacts with Nitrogen from decomposed ammonia and synthesized vertically aligned BNNTs. The morphology, alignment, structure and compositions of the as-synthesized BNNTs are studied via field emission scanning electron microscope, high resolution transmission electron microscope, energy dispersive x-ray spectroscopy, x-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Facile room temperature CTAB-assisted synthesis of mesoporous nano-cobalt ferrites for enhanced magnetic behaviour

Highlights: • Synthesis of mesoporous nano-cobalt ferrites are carried out CTAB medium. • Crystalline cobalt ferrite phase was formed below CMC of CTAB. • Bilayer arrangement of CTA-OH-Fe-Co growing units leads to inter-particle pores. • Enhanced magnetic properties (M{sub s} and H{sub c}) were obtained in synthesized cobalt ferrites. - Abstract: We report a facile, room temperature synthesis of nanostructured mesoporous cobalt ferrites using the cationic surfactant, cetyltrimethylammonium bromide (CTAB). The synthesis was carried out at various concentrations of CTAB ranging from its pre- to post-micellar concentrations. The pristine and calcined samples exhibit pure cobalt ferrite phase which are confirmed by XRD studies. The morphology of all uncalcined samples was quasi-spherical as shown by TEM images. Nitrogen adsorption – desorption study on pristine samples indicates the presence of mesopores in them. The magnetic properties of the uncalcined and calcined samples were studied by vibrating sample magnetometry. Coercivity and saturation magnetization were found to vary with the concentration of the CTAB employed. Also, the pristine samples were soft magnets, whereas the calcined samples tended towards exhibiting hard magnetism. We have proposed a mechanism to explain the mesoporosity of nanostructured ferrite based the role of CTAB in the present synthetic method.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

In-situ microwave-assisted heating synthesis of a high-performance g-C3N4/carbon nanotubes composite photocatalyst with good contact interfaces

Highlights: • One-pot microwave-assisted heating synthesis method prepared g-C{sub 3}N{sub 4} based CNTs composite photocatalyst. • Closely contact interfaces between g-C{sub 3}N{sub 4} and CNTs were prepared and observed. • WCN/CNTs exhibits a photocatalytic H{sub 2} evolution rate of 45.1 μmol/h, showing 10.02 folds of that for bulk g-C{sub 3}N{sub 4}. • WCN/CNTs exhibits a photocatalytic O{sub 2} evolution rate of 7.14 μmol/h, showing 4.61 folds of that for bulk g-C{sub 3}N{sub 4}. - Abstract: Herein, a one-pot microwave-assisted heating synthesis route was explored to prepare a g-C{sub 3}N{sub 4} based composite photocatalyst, which involved just treating of a mixture consisting of dicyandiamide and multi-walled carbon nanotubes (CNTs) using a microwave oven. The composite photocatalyst prepared by this route exhibits closely contact interfaces between g-C{sub 3}N{sub 4} and CNTs, as compared with the two ones obtained from the two-step and one-step methods previously reported, which lead to the reduced photoluminescence emission and longer lifetime of the photogenerated carriers, and the increased photocurrent response. As a result, the hydrogen evolution and oxygen evolution rates of the WCN/CNTs composite are up to 45.1 μmol/h and 7.14 μmol/h, 10.02 and 4.61 times that of BCN, respectively, which are higher than those of the other two ones prepared by the previously reported methods. This one-pot microwave-assisted heating synthesis route is suitable for preparing the g-C{sub 3}N{sub 4} based composite photocatalysts.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Solution combustion synthesis of LaxSm1−xMn2O5 nanoparticles and their electrocatalytic performances for Al-air batteries

Highlights: • Pure-phase La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} were firstly achieved through one step calcined solution combustion synthesis with high yield. • The main impact of La/Sm is the amount of surface adsorbed oxygen and surface Mn{sup 4+} ions as revealed by XPS results. • The La{sub 0.1}Sm{sub 0.9}Mn{sub 2}O{sub 5} exhibited the highest activity, which has an appropriate ratio between oxygen vacancies and Mn{sup 3+}. • The cell produced with La{sub 0.1}Sm{sub 0.9}Mn{sub 2}O{sub 5} exhibits flat discharge curves in 40 h above 1.5 V. - Abstract: Compared the most reported synthesis methods, a series of La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} (x = 0, 0.1, 0.3, 0.5) catalysts were first synthesized through sol-gel solution combustion synthesis with a short cycle and high yield. The main impact of different La/Sm molar ratios is the amount of surface adsorbed oxygen (O{sub ads}) and surface Mn{sup 4+} ions as revealed by XPS results. Electrochemical properties are characterized by rotating disk electrode (RDE) and the full dischargeable Al-air battery with 4 M NaOH electrolyte. The measurements of RDE reveal that the electron transfer number of La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} (x = 0, 0.1, 0.3, 0.5) are all closed to 4, and the sample prepared with x = 0.1 possesses the most excellent electrocatalytic activity for oxygen reduction reaction (ORR) and good discharge performance in alkaline medium. All of the above results indicate that the La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} (x = 0, 0.1, 0.3, 0.5) are promising catalysts with a high catalytic activity toward ORR.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Metal-organic framework-derived nitrogen-doped highly disordered carbon for electrochemical ammonia synthesis using N 2 and H 2 O in alkaline electrolytes

Ammonia (NH 3 ) is considered an important chemical for both agriculture fertilizer and renewable energy. The conventional Haber-Bosh process to produce NH 3 is energy intensive and leads to significant CO 2 emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) by using renewable electricity has recently attracted significant attention. Herein, we report a metal-organic framework-derived nitrogen-doped nanoporous carbon as an electrocatalyst for the NRR. It exhibits a remarkable production rate of NH 3 up to 3.4 ×10 –6 mol cm –2 h –1 with a Faradaic efficiency (FE) of 10.2% at –0.3 V vs . RHE under room temperature and ambient pressure using aqueous 0.1 M KOH electrolyte. Increasing the temperature to 60 °C further improves production rates to 7.3 × 10 –6 mol cm –2 h –1 . The stability of the nitrogen-doped carbon electrocatalyst was demonstrated during an 18-h continuous test with constant production rates. First principles calculations were used to elucidate the possible active sites and reaction pathway. The moiety, which consists of three pyridinic N atoms (N 3 ) adjacent with one carbon vacancy embedded in a carbon layer, is able to strongly adsorb N 2 and further realize N≡N triple bond dissociation for the subsequent protonation process. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of N 2 molecule. Increasing overpotentials is favorable for the protonation process during NH 3 generation. Further doping Fe into the nitrogen-doped carbon likely blocks the N 3 active sites and facilitates the hydrogen evolution reaction, a strong competitor to the NRR, thus yielding negative effect on ammonia production. Furthermore, this work provides a new insight into the rational design and synthesis of nitrogen-doped and defect-rich carbon as efficient NRR catalysts for NH 3 synthesis at ambient conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Controlled Dy-doping to nickel-rich cathode materials in high temperature aerosol synthesis

Layered nickel-rich materials are promising next-generation cathode materials for lithium ion batteries due to their high capacity and low cost. However, the poor thermal stability and longtime cycling performance hinders the commercial applications of high nickel materials. Doping with heteroatoms has been an effective approach for improving electrochemical performance of cathode materials. Controlling doping concentration and geometrical distribution is desired for optimal electrochemical performance, but it is challenging in traditional co-precipitation methods. In this work, controlled dysprosium (Dy) doping to NCM811 was studied in an aerosol synthesis method by controlling the precursor concentrations and heating parameters. The obtained materials were characterized by SEM, XRD, and XPS, and their electrochemical properties and thermal stability were evaluated. By controlling the doping concentration (1.5%), Dy-doped NCM811 was improved simultaneously in long-term cycling and high-rate performance. Here, the thermal-chemical stability of the Dy-doped cathode materials was examined in a microflow reactor with a mass spectrometer. The results showed that Dy-doping shifted the O 2 onset temperature to a higher temperature and reduced O 2 release by 80%, thus dramatically increasing the thermal-chemical stability and improving the fire safety of cathode materials. Since high temperature aerosol synthesis is a low-cost and scalable method, the findings in this work have broad implications for commercial synthesis of novel materials with controlled doping modification to achieve high electrochemical performance and safety in lithium ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Laser synthesis and processing of atomically thin 2D materials

Recent advances in laser synthesis and processing of 2D materials are described that address key issues of scalable synthesis, precise heterogeneity control, and transformative manufacturing. Here, laser spectroscopy is used to remotely characterize and optimize the structure and functionality of 2D materials, enabling their in-situ diagnostic-based synthesis and processing.

2D materials↗
DOE OSTI2013

The importance of becoming double-stranded: Innate immunity and the kinetic model of HIV-1 central plus strand synthesis

Central initiation of plus strand synthesis is a conserved feature of lentiviruses and certain other retroelements. This complication of the standard reverse transcription mechanism produces a transient “central DNA flap” in the viral cDNA, which has been proposed to mediate its subsequent nuclear import. This model has assumed that the important feature is the flapped DNA structure itself rather than the process that produces it. Recently, an alternative kinetic model was proposed. It posits that central plus strand synthesis functions to accelerate conversion to the double-stranded state, thereby helping HIV-1 to evade single-strand DNA-targeting antiviral restrictions such as APOBEC3 proteins, and perhaps to avoid innate immune sensor mechanisms. The model is consistent with evidence that lentiviruses must often synthesize their cDNAs when dNTP concentrations are limiting and with data linking reverse transcription and uncoating. There may be additional kinetic advantages for the artificial genomes of lentiviral gene therapy vectors. - Highlights: • Two main functional models for HIV central plus strand synthesis have been proposed. • In one, a transient central DNA flap in the viral cDNA mediates HIV-1 nuclear import. • In the other, multiple kinetic consequences are emphasized. • One is defense against APOBEC3G, which deaminates single-stranded DNA. • Future questions pertain to antiviral restriction, uncoating and nuclear import.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Energetic Insights into the Role of Quaternary Ammonium Cations in Zeolite Synthesis

The thermodynamics of partitioning of an organic structure-directing agent (OSDA) between water and an organic solvent such as chloroform or trichloroethane serve as a proxy for energetic interactions during zeolite synthesis. Using several newly synthesized OSDAs, we have extended our earlier calorimetric and partitioning studies of the thermodynamics of transfer to separate effects of charge (C/N + ratio) and structure in a series of structurally related OSDAs. The Gibbs free energies of transfer are close to zero, resulting from a balance of strongly exothermic and relatively similar enthalpies and strongly negative and relatively similar entropies of transfer. There is no obvious correlation between the thermodynamics of transfer and the efficacy of a given OSDA in the zeolite synthesis. Finally, one must conclude that with bulk energetics of transfer being similar in most cases studied, the critical factors in OSDA function in zeolite synthesis are kinetically rather than thermodynamically controlled and arise from differences in activation energies related to details of OSDA structure and interactions during nucleation of possible zeolite precursors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Simultaneous Process and Heat Exchanger Network Synthesis Using a Discrete Temperature Grid

We present mixed-integer linear programming models for utility targeting and heat exchanger network synthesis that account for variable stream temperatures and flow rates as well as unclassified streams and thus can be combined with process synthesis optimization models. By projecting temperature information onto a fixed discrete temperature grid, the model remains linear even under variable temperatures and flow rates, leading to a more tractable optimization model. The proposed model is well suited to address problems in the area of process intensification where the close interaction between different phenomena naturally leads to process synthesis problems with unclassified process streams. Several extensions are presented, including nonisothermal mixing as well as phase changes. Moreover, we show how a nonuniform grid can be adopted to reduce the complexity of the model for medium and large-size problems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Air-Stable Calcium Cyanamide-Supported Ruthenium Catalyst for Ammonia Synthesis and Decomposition

Efficient ammonia synthesis and decomposition processes under mild conditions are important to meet the expanding demand in major applications of ammonia as the energy carrier and to provide feedstock for chemical industry. In this study, we report that air-stable calcium cyanamide-supported ruthenium (Ru/CaCN 2 ) works as an efficient and stable catalyst for ammonia synthesis and decomposition. Ru/CaCN 2 exhibits greater catalytic performances for both reactions than Ru/Ca 2 N electride and Ru–Cs/MgO. The kinetic analysis for ammonia synthesis suggests that Ru/CaCN 2 exhibits low apparent activation energy and high resistance to hydrogen poisoning, which has characteristics similar to the kinetic parameters of Ru-supported electride catalyst. H 2 -temperature programmed reaction and temperature programmed desorption revealed that Ru promoted the formation of CN 2 vacancies on the CaCN 2 surface which in turn capture hydrogen as H – ions during the reaction. Density functional theory calculations provide insights into how the formation of CN 2 vacancies is promoted by Ru, which leads to the decrease in the work function of the CaCN 2 surface and the hydrogen capture at the Ru-support interface. These results suggest that the high catalytic performance of Ru/CaCN 2 can be attributed to the formation of a quasi-electride structure at the Ru–CaCN 2 interface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Wafer-Scale Synthesis of 2D Materials by an Amorphous Phase-Mediated Crystallization Approach

The interest in the wafer-scale growth of two-dimensional (2D) materials, including transition metal dichalcogenides (TMDCs), has been rising for transitioning from lab-scale devices to commercial-scale systems. Among various synthesis techniques, physical vapor deposition, such as pulsed laser deposition (PLD), has shown promise for the wafer-scale growth of 2D materials. However, due to the high volatility of chalcogen atoms (e.g., S and Se), films deposited by PLD usually suffer from a lack of stoichiometry and chalcogen deficiency. To mitigate this issue, excess chalcogen is necessary during the deposition, which results in problems like uniformity or not being repeatable. This study demonstrates a condensed-phase or amorphous phase-mediated crystallization (APMC) approach for the wafer-scale synthesis of 2D materials. This method uses a room-temperature PLD process for the deposition and formation of amorphous precursors with controlled thicknesses, followed by a post-deposition crystallization process to convert the amorphous materials to crystalline structures. This approach maintains the stoichiometry of the deposited materials throughout the deposition and crystallization process and enables the large-scale synthesis of crystalline 2D materials (e.g., MoS 2 and WSe 2 ) on Si/SiO 2 substrates, which is critical for future wafer-scale electronics. We show that the thickness of the layers can be digitally controlled by the number of laser pulses during the PLD phase. Optical spectroscopy is used to monitor the crystallization dynamics of amorphous layers as a function of annealing temperature. The crystalline quality, domain sizes, and the number of layers were explored using nanoscale and atomistic characterization (e.g., AFM, STEM, and EDS) along with electrical characterization to explore process–structure–performance relationships. Finally, this growth technique is a promising method that could potentially be adopted in conventional semiconductor industries for wafer-scale manufacturing of next-generation electronic and optoelectronic devices.

2D electronics↗
DOE OSTI2015

Surface-Bound Intermediates in Low-Temperature Methanol Synthesis on Copper. Participants and Spectators

The reactivity of surface adsorbed species present on copper catalysts during methanol synthesis at low temperatures was studied by simultaneous infrared spectroscopy (IR) and mass spectroscopy (MS) measurements during “titration” (transient surface reaction) experiments with isotopic tracing. The results show that adsorbed formate is a major bystander species present on the surface under steady-state methanol synthesis reaction conditions, but it cannot be converted to methanol by reaction with pure H 2 , nor with H 2 plus added water. Formate-containing surface adlayers for these experiments were produced during steady state catalysis in (a) H 2 :CO 2 (with substantial formate coverage) and (b) moist H 2 :CO (with no IR visible formate species). Both these reaction conditions produce methanol at steady state with relatively high rates. Adlayers containing formate were also produced by (c) formic acid adsorption. Various "titration" gases were used to probe these adlayers at modest temperatures (T = 410-450K) and 6 bar total pressure. Methanol gas (up to ~1% monolayer equivalent) was produced in "titration" from the H 2 :CO 2 catalytic adlayers by H 2 plus water, but not by dry hydrogen. The decay in the formate IR features accelerated in the presence of added water vapor. The H 2 :CO:H 2 O catalytic adlayer produced similar methanol titration yields in H 2 plus water but showed no surface formate features in IR (less than 0.2% monolayer coverage). Finally, formate from formic acid chemisorption produced no methanol under any titration conditions. Even under (H 2 :CO 2 ) catalytic reaction conditions, isotope tracing showed that pre-adsorbed formate from formic acid did not contribute to the methanol produced. Although non-formate intermediates exist during low temperature methanol synthesis on copper which can be converted to methanol gas by titration with pure H 2 plus water in sufficient quantities for that intermediate to be observable by IR, formate itself is only a "spectator" in this reaction and gives no observable methanol upon any titration we performed with H 2 or H 2 plus water.

copper catalyst↗
DOE OSTI2018

Computational Design of Active Site Structures with Improved Transition-State Scaling for Ammonia Synthesis

Here, the Haber–Bosch process for the reduction of atmospheric nitrogen to ammonia is one of the most optimized heterogeneous catalytic reactions, but there are aspects of the industrial process that remain less than ideal. It has been shown that the activity of metal catalysts is limited by a Brønsted–Evans–Polanyi (BEP) scaling relationship between the reaction and transition-state energies for N 2 dissociation, leading to a negligible production rate at ambient conditions and a modest rate under harsh conditions. In this study, we use density functional theory (DFT) calculations in conjunction with mean-field microkinetic modeling to study the rate of NH 3 synthesis on model active sites that require the singly coordinated dissociative adsorption of N atoms onto transition metal atoms. Our results demonstrate that this ”on-top” binding of nitrogen exhibits significantly improved scaling behavior, which can be rationalized in terms of transition-state geometries and leads to considerably higher predicted activity. While synthesis of these model systems is likely challenging, the stabilization of such an active site could enable thermochemical ammonia synthesis under more benign conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Revisiting the Polyol Synthesis of Silver Nanostructures: Role of Chloride in Nanocube Formation

Chloride (Cl – ) is normally used together with polyvinylpyrrolidone (PVP) in the polyol synthesis of Ag nanocubes. In the literature, shape control is attributed predominantly to the preferential binding of PVP to Ag(100) facets compared to Ag(111) facets, whereas the role of Cl – has not been well studied. Several hypotheses have been proposed regarding the role of Cl – ; however, there is still no consensus regarding the exact influence of Cl – in the shape-controlled synthesis of Ag nanocubes. To examine the influence of Cl – , we undertook a joint theoretical–experimental study. Experimentally, we examined the influence of Cl – concentration on the shape of Ag nanoparticles (NPs) at constant H + concentration. In the presence of H + , in situ formed HNO3 etches the initially formed Ag seeds and slows down the overall reduction of Ag + , which promotes the formation of monodisperse Ag NPs. Ex situ experiments probed the evolution of Cl – during the growth of Ag nanocubes, which involves the initial formation of AgCl nanocubes, and their subsequent dissolution to release Cl – , which adsorbs onto the surfaces of single crystal seeds to impact shape evolution through apparent thermodynamic control. The formation of cubes is independent of the source of AgCl, indicating temporal control of the Cl – chemical potential in solution leads to high-yield synthesis of Ag nanocubes. Increasing the concentration of Cl – alone leads to a progression in shape from truncated octahedra, to cuboctahedra, truncated cubes, and ultimately cubes, directly demonstrating the importance of Cl – in Ag NP shape control. Here, we used ab initio thermodynamics calculations based on density functional theory to probe the role of Cl – in directing shape control. With increasing Cl chemical potential (surface coverage), calculated surface energies γ of Ag facets transition from γ 111 < γ 100 to γ 100 < γ 111 and predict Wulff shapes terminated with an increasing (100) contribution, consistent with experimental observations. The combination of theory and experiment is beneficial for advancing the understanding of nanocrystal formation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Active Oxygen Vacancy Site for Methanol Synthesis from CO2 Hydrogenation on In2O3(110): A DFT Study

Methanol synthesis from CO2 hydrogenation on the defective In2O3(110) surface with surface oxygen vacancies has been investigated using periodic density functional theory calculations. The relative stabilities of six possible surface oxygen vacancies numbered from Ov1 to Ov6 on the perfect In2O3(110) surface were examined. The calculated oxygen vacancy formation energies show that the D1 surface with the Ov1 defective site is the most thermodynamically favorable while the D4 surface with the Ov4 defective site is the least stable. Two different methanol synthesis routes from CO2 hydrogenation over both D1 and D4 surfaces were studied and the D4 surface was found to be more favorable for CO2 activation and hydrogenation. On the D4 surface, one of the O atoms of the CO2 molecule fills in the Ov4 site upon adsorption. Hydrogenation of CO2 to HCOO on the D4 surface is both thermodynamically and kinetically favorable. Further hydrogenation of HCOO involves both forming the C-H bond and breaking the C-O bond, resulting in H2CO and hydroxyl. The HCOO hydrogenation is slightly endothermic with an activation barrier of 0.57 eV. A high barrier of 1.14 eV for the hydrogenation of H2CO to H3CO indicates that this step is the rate-limiting step in the methanol synthesis on the defective In2O3(110) surface. We gratefully acknowledge the supports from the National Natural Science Foundation of China (#20990223) and from US Department of Energy, Basic Energy Science program (DE-FG02-05ER46231). D. Mei was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The computations were performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory in Richland, Washington. PNNL is a multiprogram national laboratory operated for DOE by Battelle.

Catalytic CO2 hydrogenation↗
DOE OSTI2024

Mechanistically Guided Materials Chemistry: Synthesis of Ternary Nitrides, CaZrN 2 and CaHfN 2

Recent computational studies have predicted many new ternary nitrides, revealing synthetic opportunities in this underexplored phase space. However, synthesizing new ternary nitrides is difficult, in part because intermediate and product phases often have high cohesive energies that inhibit diffusion. Here, we report the synthesis of two new phases, calcium zirconium nitride (CaZrN 2 ) and calcium hafnium nitride (CaHfN 2 ), by solid state metathesis reactions between Ca 3 N2 and MCl 4 (M = Zr, Hf). Although the reaction nominally proceeds to the target phases in a 1:1 ratio of the precursors via Ca 3 N 2 + MCl4 → CaMN 2 + 2 CaCl 2 , reactions prepared this way result in Ca-poor materials (Ca x M 2–x N2, x < 1). A small excess of Ca 3 N 2 (ca. 20 mol %) is needed to yield stoichiometric CaMN 2 , as confirmed by high-resolution synchrotron powder X-ray diffraction. In situ synchrotron X-ray diffraction studies reveal that nominally stoichiometric reactions produce Zr 3+ intermediates early in the reaction pathway, and the excess Ca 3 N 2 is needed to reoxidize Zr 3+ intermediates back to the Zr 4+ oxidation state of CaZrN 2 . Analysis of computationally derived chemical potential diagrams rationalizes this synthetic approach and its contrast from the synthesis of MgZrN 2 . These findings additionally highlight the utility of in situ diffraction studies and computational thermochemistry to provide mechanistic guidance for synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Field-tailoring quantum materials via magneto-synthesis: metastable metallic and magnetically suppressed phases in a trimer iridate

We demonstrate that applying modest magnetic fields (< 0.1 T) during high-temperature crystal growth can profoundly alter the structure and ground state of a spin-orbit-coupled, antiferromagnetic trimer lattice. Using BaIrO₃ as a model system, whose ground state is intricately dictated by the trimer lattice, we show that magneto-synthesis , a field-assisted synthesis approach, stabilizes a structurally compressed, metastable metallic and magnetically suppressed phases inaccessible via conventional methods. These effects include a 0.85% reduction in unit cell, 4-order-of-magnitude decrease in resistivity, a 10-fold enhancement of the Sommerfeld coefficient, and the collapse of long-range magnetic order -- all intrinsic and bulk in origin. First-principles calculations confirm that the field-stabilized structure lies substantially above the ground state in energy, highlighting its metastable character. These large, coherent and correlated changes across multiple bulk properties, unlike those caused by dilute impurities, defects or off-stoichiometry, point to an intrinsic field-induced mechanism. The findings establish magneto-synthesis as a powerful new pathway for accessing non-equilibrium quantum phases in strongly correlated materials.

magneto-synthesis↗