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Zaikina, Julia V.

Publications and source records attributed to Zaikina, Julia V..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Venturing into Unexplored Phase Space: Synthesis, Structure, and Properties of MgCo 3 B 2 Featuring a Rumpled Kagomé Network

MgCo 3 B 2 , a novel ternary boride in a previously unexplored phase space, was synthesized using the hydride route. In situ powder X-ray diffraction and DFT calculations aided in the discovery of this compound, whose structure was then determined by single-crystal X-ray diffraction. Like the closely related CeCo 3 B 2 , MgCo 3 B 2 crystallizes in centrosymmetric space group P6/mmm (a = 4.883(2) Å, c = 2.926(2) Å at 210 K, Z = 1). Unlike CeCo 3 B 2 , however, it adopts a disordered structure that features a rumpled Kagomé network of Co atoms, and Mg atoms fill the channels of a Co–B framework. Although the structural disorder leads to motifs that are similar to those observed in MgNi 3 B 2 and other related ternary borides, no evidence of an ordered superstructure was found by single-crystal X-ray diffraction or high-resolution powder X-ray diffraction. In the case of CeCo 3 B 2 , boron atoms occupy the center of regular Co 6 trigonal prisms; in MgCo 3 B 2 , boron atoms are shifted from the center of the prism to form B–B dimers with roughly the same length as those found in MgNi 3 B 2 . Magnetic susceptibility data exhibit an unusual temperature dependence that cannot be convincingly modeled by the modified Curie–Weiss equation, consistent with DFT calculations predicting a nonmagnetic ground state. Intrinsic susceptibility at 300 K is 1.42 × 10 –3 emu/mol Oe, which is comparable to that of paramagnetic YCo 3 B 2 and CeCo 3 B 2 with a similar structure and composition. Here, this study showcases the efficacy of combining several methodologies to discover new solids in unexplored phase spaces. This approach includes in situ PXRD data to monitor reactions of precursors upon heating, a diffusion-enhanced synthesis method, and DFT assessment of compound stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

When van der Waals Met Kagome: A 2D Antimonide with a Vanadium-Kagome Network

2D materials showcase unconventional properties emerging from quantum confinement effects. In this work, a “soft chemical” route allows for the deintercalation of K + from the layered antimonide KV 6 Sb 6 , resulting in the discovery of a new metastable 2D-Kagome antimonide K 0.1(1) V 6 Sb 6 with a van der Waals gap of 3.2 Å. The structure of K 0.1(1) V 6 Sb 6 was determined via the synergistic techniques, including X-ray pair distribution function analysis, advanced transmission electron microscopy, and density functional theory calculations. The K 0.1(1) V 6 Sb 6 compound crystallizes in the monoclinic space group C2/m (a = 9.57(2) Å, b = 5.502(8) Å, c = 10.23(2) Å, β = 97.6(2)°, Z = 2). The [V 6 Sb 6 ] layers in K 0.1(1) V 6 Sb 6 are retained upon deintercalation and closely resemble the layers in the parent compound, yet deintercalation results in a relative shift of the adjacent [V 6 Sb 6 ] layers. The magnetic properties of the K 0.1(1) V 6 Sb 6 phase in the 2–300 K range are comparable to those of KV 6 Sb 6 and another Kagome antimonide KV 3 Sb 5 , consistent with nearly temperature-independent paramagnetism. Electronic band structure calculation suggests a nontrivial band topology with flat bands and opening of band crossing afforded by deintercalation. Transport property measurements reveal a metallic nature for K 0.1(1) V 6 Sb 6 and a low thermal conductivity of 0.6 W K –1 m –1 at 300 K. Additionally, ion exchange in KV 6 Sb 6 via a solvothermal route leads to a successful partial exchange of K + with A + (A = Na, Rb, and Cs). Here, this study highlights the tunability of the layered structure of the KV 6 Sb 6 compound, providing a rich playground for the realization of new 2D materials.

2D↗
DOE OSTI2023

Breaking New Ground: MB ene Route toward Selective Vinyl Double Bond Hydrogenation in Nitroarenes

Doping, or incremental substitution of one element for another, is an effective way to tailor a compound’s structure as well as its physical and chemical properties. Herein, we replaced up to 30% of Ni with Co in members of the family of layered LiNiB compounds, stabilizing the high-temperature polymorph of LiNiB while the room-temperature polymorph does not form. By studying this layered boride with in situ high-temperature powder diffraction, we obtained a distorted variant of LiNi 0.7 Co 0.3 B featuring a perfect interlayer placement of [Ni 0.7 Co 0.3 B] layers on top of each other–a structural motif not seen before in other borides. Because of the Co doping, LiNi 0.7 Co 0.3 B can undergo a nearly complete topochemical Li deintercalation under ambient conditions, resulting in a metastable boride with the formula Li 0.04 Ni 0.7 Co 0.3 B. Heating of Li 0.04 Ni 0.7 Co 0.3 B in anaerobic conditions led to yet another metastable boride, Li 0.01 Ni 0.7 Co 0.3 B, with a CoB-type crystal structure that cannot be obtained by simple annealing of Ni, Co, and B. No significant alterations of magnetic properties were detected upon Co-doping in the temperature-independent paramagnet LiNi 0.7 Co 0.3 B or its Li-deintercalated counterparts. Finally, Li 0.01 Ni 0.7 Co 0.3 B stands out as an exceptional catalyst for the selective hydrogenation of the vinyl C=C bond in 3-nitrostyrene, even in the presence of other competing functional groups. Finally, this research showcases an innovative approach to heterogeneous catalyst design by meticulously synthesizing metastable compounds.

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

Exploring the $A$-V-Sb landscape beyond $A$$\mathrm{V_3}$ $\mathrm{Sb_5}$: A case study on the $\mathrm{KV_6}$ $\mathrm{Sb_6}$ Kagome compound

Kagome compounds have garnered attention in the past few years for their intriguing magnetic properties arising from spin frustration dictated by the geometry of the Kagome sublattice. In this paper, we highlight the success of the unconventional hydride route for the fast and easy synthesis of the Kagome compound $\mathrm{KV_6}$ $\mathrm{Sb_6}$. Here, high-temperature in situ powder x-ray diffraction (PXRD) studies proved to be useful in hinting at the existence of $\mathrm{KV_6}$ $\mathrm{Sb_6}$, identifying its synthesis conditions, and understanding the reaction mechanism. The crystal structure for $\mathrm{KV_6}$ $\mathrm{Sb_6}$ was determined from high-resolution PXRD data. The compound has a layered structure [$R\overline{3}m, a = 5.5318$ (9) Å, $c = 34.23$ (3)Å 3 $Z = 3$] at room temperature] and features a Kagome bilayer of V atoms. $\mathrm{KV_6}$ $\mathrm{Sb_6}$ is isostructural to the previously reported $\mathrm{RbV_6}$ $\mathrm{Sb_6}$ and $\mathrm{CsV_6}$ $\mathrm{Sb_6}$ compounds. $\mathrm{KV_6}$ $\mathrm{Sb_6}$ is thermally stable in vacuum up to 1173 K, as evident from the high-temperature in situ PXRD and differential scanning calorimetric analysis. Investigation of magnetic properties for $\mathrm{KV_6}$ $\mathrm{Sb_6}$ between 2 and 300 K reveals temperature-independent paramagnetism and an absence of superconductivity, like the Rb and Cs analogs. Furthermore, we compare the magnetic properties of K V 3 Sb 5 , another ternary Kagome compound, synthesized via two different methods: the hydride route and the traditional route from elements. Low-temperature transport property measurements of $\mathrm{KV_6}$ $\mathrm{Sb_6}$ indicate metallic behavior and an intrinsically low thermal conductivity of $\mathrm{1.0 W K^-1}$ $\mathrm{m^-1}$ at 300 K. The layered structure of $\mathrm{KV_6}$ $\mathrm{Sb_6}$ makes it an attractive candidate for deintercalation and doping studies to tune both magnetic and transport properties, laying a foundation for further studies.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Interplay Between Kondo and Magnetic Interactions in Pr 0.75 Gd 0.25 ScGeH

Combined experimental and density functional theory (DFT) study of Pr 0.75 Gd 0.25 ScGe and its hydride (Pr 0.75 Gd 0.25 ScGeH) reveals intricacies of composition-structure-property relationships in those distinctly layered compounds. Hydrogenation of the intermetallic parent, crystalizing in a tetragonal CeScSi-type structure, leads to an anisotropic volume expansion, that is, a(=b) lattice parameter decreases while the lattice expands along the c direction, yielding a net increase of cell volume. DFT calculations predict an antiparallel coupling of localized Gd and Pr magnetic moments in both materials at the ground state. While experiments corroborate this for the parent compound, there is no conclusive experimental proof for the hydride, where Pr moments do not order down to 3 K. DFT results also reveal that rare-earth – hydrogen interactions reduce spin-polarization of the Pr and Gd 5d and Sc 3d states at the Fermi energy, disrupt indirect exchange interactions mediated by conduction electrons, dramatically reduce the magnetic ordering temperature, and open a pseudo-gap in the majority-spin channel. Here, both experiments and theory show evidence of Kondo-like behavior in the hydride in the absence of an applied magnetic field, whereas increasing the field promotes magnetic ordering and suppresses Kondo-like behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2023

From Layered Antiferromagnet to 3D Ferromagnet: LiMnBi-to-MnBi Magneto-Structural Transformation

Here, the intermetallic compound LiMnBi was synthesized by the two-step solid-state reaction from the elements. The synthesis temperature of 850 K was selected based on in-situ high-temperature powder X-ray diffraction data. LiMnBi crystalizes in the layered-like PbClF structure type (a = 4.3131(7) Å, c = 7.096(1) Å at 100 K, P4/nmm space group, Z = 2). LiMnBi structure is built of the alternating [MnBi] and Li layers, as determined from single-crystal X-ray diffraction data. Magnetic properties measurements and solid-state 7 Li Nuclear Magnetic Resonance data collected for polycrystalline LiMnBi samples indicate the long-range antiferromagnetic ordering of Mn sublattice at ~340 K, with no superconductivity down to 5 K detected. LiMnBi is air- and water-sensitive. In aerobic conditions, Li can be extracted from LiMnBi structure to form Li 2 O/LiOH and MnBi (NiAs structure type, P6 3 /mmc). The obtained MnBi polymorph was previously reported to be one of the strongest rare-earth-free ferromagnets, yet its bulk synthesis in powder form is cumbersome. The proposed magneto-structural transformation from ternary LiMnBi to ferromagnetic MnBi involves condensation of the MnBi4 tetrahedra upon Li deintercalation and is exclusive to LiMnBi. In contrast, ferromagnetic MnBi cannot be obtained from either isostructural NaMnBi and KMnBi, or from the structurally related CaMn 2 Bi 2 . Such a distinctive transformation in the case of LiMnBi is presumed to be due to its fitting reactivity to yield MnBi and favorable interlayer distance between [MnBi] layers, while the interlayer distance in NaMnBi and KMnBi structural analogs is unfavorably long. The studies of delithiation from the layered-like LiMnBi under different chemical environments indicate that the yield of the MnBi depends on the type of solvent used and the kinetics of the reaction. A slow rate and mild reaction media lead to a high fraction of the MnBi product. The saturation magnetization of the “as-prepared” MnBi is ~50 % of the expected value of 81.3 emu/g. Overall, this study adds a missing member to the family of ternary pnictides and illustrates how soft-chemistry methods can be used to obtain “difficult-to-synthesize” compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Microwave-Assisted Solution Synthesis of Metastable Intergrowth of AgInS2 Polymorphs

The intergrowth of stable and metastable AgInS2 polymorphs was synthesized using a microwave-assisted synthesis. The samples were synthesized in water and in a deep eutectic solvent (DES) consisting of choline chloride and thiourea. An increase in the metal precursor concentration improved the crystallinity of the synthesized samples and affected the particle size. AgInS2 cannot be synthesized from crystalline binary Ag2S or In2S3 via this route. The solution synthesis reported here results in the intergrowth of the thermodynamically stable polymorph (space group I4¯2d, chalcopyrite structure) and the high-temperature polymorph (space group Pna21, wurtzite-like structure) that is metastable at room temperature. A scanning transmission microscopy (STEM) study revealed the intergrowth of tetragonal and orthorhombic polymorphs in a single particle and unambiguously established that the long-thought hexagonal wurtzite polymorph has pseudo-hexagonal symmetry and is best described with the orthorhombic unit cell. The solution-synthesized AgInS2 polymorphs intergrowth has slightly lower bandgap values in the range of 1.73 eV–1.91 eV compared to the previously reported values for tetragonal I4¯2d (1.86 eV) and orthorhombic Pna21 (1.98 eV) polymorphs.

Adeyemi, Adedoyin N. (ORCID:0000000340096150)↗
DOE OSTI2021

The Deep Eutectic Solvent Precipitation Synthesis of Metastable Zn 4 V 2 O 9

A precipitation method involving a deep eutectic solvent (DES)–a mixture of hydrogen bond donor and acceptor–is used to synthesize a ternary metal oxide. Without toxic reagents, precipitates consisting of Zn 3 (OH) 2 V 2 O 7 ·nH 2 O and Zn 5 (OH) 6 (CO 3 ) 2 are obtained by simply introducing deionized H 2 O to the DES solution containing dissolved ZnO and V 2 O 5 . Manipulation of the synthetic conditions demonstrates high tunability in the size/morphology of the two-dimensional nanosheets precipitated during the dynamic equilibrium process. According to differential scanning calorimetry and high-temperature powder X-ray diffraction, Zn 3 V 2 O 8 and ZnO obtained by the annealing of the precipitate are intermediates in the reaction pathway toward metastable Zn 4 V 2 O 9 . Intimate mixing of the metal precursors achieved by the precipitation method allows access to the metastable zinc-rich vanadate with unusually rapid heat treatment. Furthermore, the UV–vis and surface photovoltage spectra reveal the presence of sub-band gap states, stemming from the reduced vanadium (V 4+ ) center. Photoelectrochemical measurements confirm weak photoanodic currents for water and methanol oxidation. For the first time, this work shows the synthesis of a metastable oxide with the DES-precipitation route and provides insight into the structure–property relationship of the zinc-rich vanadate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A Low-Temperature Structural Transition in Canfieldite, Ag 8 SnS 6 , Single Crystals

Canfieldite, Ag 8 SnS 6 , is a semiconducting mineral notable for its high ionic conductivity, photosensitivity, and low thermal conductivity. In this paper, we report the solution growth of large single crystals of Ag 8 SnS 6 of mass up to 1 g from a ternary Ag–Sn–S melt. On cooling from high temperature, Ag 8 SnS 6 undergoes a known cubic ($F\bar{4}3m$) to orthorhombic ($Pna2_1$) phase transition at ≈460 K. By studying the magnetization and thermal expansion between 5–300 K, we discover a second structural transition at ≈120 K. Single crystal X-ray diffraction reveals the low-temperature phase adopts a different orthorhombic structure with space group $Pmn2_1$ ($\textit{a}$ = 7.662 9(5) Å, $\textit{b}$ = 7.539 6(5) Å, $\textit{c}$ = 10.630 0(5) Å, Z = 2 at 90 K) that is isostructural to the room-temperature forms of the related Se-based compounds Ag 8 SnSe 6 and Ag 8 GeSe 6 . The 120 K transition is first-order and has a large thermal hysteresis. On the basis of the magnetization and thermal expansion data, the room-temperature polymorph can be kinetically arrested into a metastable state by rapidly cooling to temperatures below 40 K. We last compare the room- and low-temperature forms of Ag8SnS6 with its argyrodite analogues, Ag 8 TQ 6 ($\textit{T}$ = Si, Ge, Sn; $\textit{Q}$ = S, Se), and identify a trend relating the preferred structures to the unit cell volume, suggesting smaller phase volume favors the $Pna2_1$ arrangement. We support this picture by showing that the transition to the $Pmn2_1$ phase is avoided in Ge alloyed Ag 8 Sn 1–x Ge x S 6 samples as well as in pure Ag 8 GeS 6 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Topochemical Deintercalation of Li from Layered LiNiB: toward 2D MBene

The pursuit of two-dimensional (2D) borides, MBenes, has proven to be challenging, not the least because of the lack of a suitable precursor prone to the deintercalation. Here, we studied room-temperature topochemical deintercalation of lithium from the layered polymorphs of the LiNiB compound with a considerable amount of Li stored in between [NiB] layers (33 at. % Li). Deintercalation of Li leads to novel metastable borides (Li~ 0.5 NiB) with unique crystal structures. Partial removal of Li is accomplished by exposing the parent phases to air, water, or dilute HCl under ambient conditions. Scanning transmission electron microscopy and solid-state 7 Li and 11 B NMR spectroscopy, combined with X-ray pair distribution function (PDF) analysis and DFT calculations, were utilized to elucidate the novel structures of Li~ 0.5 NiB and the mechanism of Li-deintercalation. We have shown that the deintercalation of Li proceeds via a “zip-lock” mechanism, leading to the condensation of single [NiB] layers into double or triple layers bound via covalent bonds, resulting in structural fragments with Li[NiB] 2 and Li[NiB] 3 compositions. The crystal structure of Li~ 0.5 NiB is best described as an intergrowth of the ordered single [NiB], double [NiB] 2 , or triple [NiB] 3 layers alternating with single Li layers; this explains its structural complexity. Here, the formation of double or triple [NiB] layers induces a change in the magnetic behavior from temperatureindependent paramagnets in the parent LiNiB compounds to the spin-glassiness in the deintercalated Li~ 0.5 NiB counterparts. LiNiB compounds showcase the potential to access a plethora of unique materials, including 2D MBenes (NiB).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Local Structural Disorder in Metavanadates MV 2 O 6 (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies

Metavanadates MV 2 O 6–δ (M = Zn and Cu) are synthesized by using a deep eutectic solvent (DES), a mixture of hydrogen bond donor and acceptor, as a reaction medium. Dissolution of stable binary metal oxides in a DES followed by a heat treatment yields phase-pure vanadates. According to in situ powder X-ray diffraction, ternary phases (α-Zn 2 V 2 O 7 and β-Cu 2–x V 2 O 7 , x ~ 0.27) are intermediates in the reaction pathway taken. Identifying a polymorphic phase transformation temperature for CuV 2 O 6 as well as the narrow temperature range between formation and decomposition for both metavanadates allows for tackling the challenge of the synthesis of these materials. The oxygen vacancy introduced by the DES route is accompanied by the formation of reduced V 4+ and Cu + in the oxide matrix, based on X-ray photoelectron spectroscopy. These oxygen vacancies modify the vibrational modes in the corresponding Raman spectra and are also responsible for broad optical absorptions in the 1.8–1.1 eV range. The optical band gaps of the materials are found at 1.8 eV (CuV 2 O 6 ) and 2.2 eV (ZnV 2 O 6 ), approximately 0.1–0.3 eV below the values reported in the literature. The reduced band gaps and sub-band gap photon absorption are key features of the oxygen-deficient metavanadates. Surface photovoltage spectroscopy reveals that all the synthesized vanadates are n-type materials with electrons as the majority charge carriers, and photoelectrochemical measurements confirm photoanodic currents for methanol oxidation. Furthermore, these results provide insight into the synthesis and structure–property relationship of the metavanadates for their potential use as photoanodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗