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1. Lithium nickel borides: evolution of [NiB] layers driven by Li pressure

   https://doi.org/10.1039/D0QI01150A  

   Gvozdetskyi, Volodymyr; Sun, Yang; Zhao, Xin; Bhaskar, Gourab; Carnahan, Scott L.; Harmer, Colin P.; Zhang, Feng; Ribeiro, Raquel A.; Canfield, Paul C.; Rossini, Aaron J.; et al (January 2021, Inorganic Chemistry Frontiers)

   null (Ed.)

   Here we show the effect of Li chemical pressure on the structure of layered polymorphs with LiNiB composition: RT -LiNiB (room temperature polymorph) and HT -LiNiB (high temperature polymorph), resulting in stabilization of the novel RT -Li 1+x NiB ( x ∼ 0.17) and HT -Li 1+y NiB ( y ∼ 0.06) phases. Depending on the synthesis temperature and initial Li content, precisely controlled via hydride route synthesis, [NiB] layers undergo structural deformations, allowing for extra Li atoms to be accommodated between the layers. In situ variable temperature synchrotron and time-dependent laboratory powder X-ray diffraction studies suggest Li step-wise deintercalation processes: RT- Li 1+x NiB → RT- LiNiB (high temp.) → LiNi 3 B 1.8 → binary Ni borides and HT -Li 1+y NiB → HT -LiNiB (high temp.) → LiNi 3 B 1.8 → binary Ni borides. Quantum chemistry calculations and solid state 7 Li and 11 B NMR spectroscopy shed light on the complexity of real superstructures of these compounds determined from high resolution synchrotron powder diffraction data. 

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2. Exploring the A-V-Sb landscape beyond AV3Sb5: A case study on the KV6Sb6 Kagome compound

   https://doi.org/10.1103/PhysRevMaterials.7.115002  

   Mantravadi, Aishwarya; Gvozdetskyi, Volodymyr; Sarkar, Arka; Mudryk, Yaroslav; Zaikina, Julia V. (November 2023, Physical Review Materials)

   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 KV6Sb6. High-temperature in situ powder x-ray diffraction (PXRD) studies proved to be useful in hinting at the existence of KV6Sb6, identifying its synthesis conditions, and understanding the reaction mechanism. The crystal structure for KV6Sb6 was determined from high-resolution PXRD data. The compound has a layered structure [R¯3m,a=5.5318(9)Å, c=34.23(3)Å, V=907.0(8)Å3, Z=3 at room temperature] and features a Kagome bilayer of V atoms. KV6Sb6 is isostructural to the previously reported RbV6Sb6 and CsV6Sb6 compounds. KV6Sb6 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 KV6Sb6 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 KV3Sb5, another ternary Kagome compound, synthesized via two different methods: the hydride route and the traditional route from elements. Low-temperature transport property measurements of KV6Sb6 indicate metallic behavior and an intrinsically low thermal conductivity of 1.0WK−1m−1 at 300 K. The layered structure of KV6Sb6 makes it an attractive candidate for deintercalation and doping studies to tune both magnetic and transport properties, laying a foundation for further studies. 

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

   https://doi.org/10.1021/acs.chemmater.3c00140  

   Gvozdetskyi, Volodymyr; Rana, Khusboo; Ribeiro, Raquel A.; Mantravadi, Aishwarya; Adeyemi, Adedoyin N.; Wang, Renhai; Dong, Huafeng; Ho, Kai-Ming; Furukawa, Yuji; Canfield, Paul C.; et al (April 2023, Chemistry of materials)

   The intermetallic compound LiMnBi was synthesized by the two-step solid-state reaction from the elements. A 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). The LiMnBi structure is built of alternating [MnBi] and Li layers, as determined from single-crystal X-ray diffraction data. Magnetic property measurements and solid-state 7Li nuclear magnetic resonance data collected for polycrystalline LiMnBi samples indicate the long-range antiferromagnetic ordering of the Mn sublattice at ∼340 K, with no superconductivity detected down to 5 K. LiMnBi is air- and water-sensitive. Under aerobic conditions, Li can be extracted from the LiMnBi structure to form Li2O/LiOH and MnBi (NiAs structure type, P63/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 CaMn2Bi2. Such a distinctive transformation in the case of LiMnBi is presumed to be due to its fitting reactivity to yield MnBi and a favorable interlayer distance between [MnBi] layers, while the interlayer distance in NaMnBi and KMnBi structural analogues is unfavorably long. The studies of delithiation from layered-like LiMnBi under different chemical environments indicate that the yield of 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. 

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4. A three body problem: a genuine hetero tri metallic molecule vs. a mixture of two parent hetero bi metallic molecules

   https://doi.org/10.1039/c8sc00917a  

   Han, Haixiang; Wei, Zheng; Barry, Matthew C.; Carozza, Jesse C.; Alkan, Melisa; Rogachev, Andrey Yu; Filatov, Alexander S.; Abakumov, Artem M.; Dikarev, Evgeny V. (January 2018, Chemical Science)

   This work raises a fundamental question about the “real” structure of molecular compounds containing three different metals: whether they consist of genuine hetero tri metallic species or of a mixture of parent hetero bi metallic species. Heterotrimetallic complex Li 2 CoNi(tbaoac) 6 ( 1 , tbaoac = tert -butyl acetoacetate) has been designed based on the model tetranuclear structure featuring two transition metal sites in order to be utilized as a molecular precursor for the low-temperature preparation of the LiCo 0.5 Ni 0.5 O 2 battery cathode material. An investigation of the structure of 1 appeared to be very challenging, since the Co and Ni atoms have very similar atomic numbers, monoisotopic masses, and radii as well as the same oxidation state and coordination number/environment. Using a statistical analysis of heavily overlaid isotope distribution patterns of the [Li 2 MM′L 5 ] + (M/M′ = Co 2 , Ni 2 , and CoNi) ions in DART mass spectra, it was concluded that the reaction product 1 contains both heterotrimetallic and bimetallic species. A structural analogue approach has been applied to obtain Li 2 MMg(tbaoac) 6 (M = Co ( 2 ) and Ni ( 3 )) complexes that contain lighter, diamagnetic magnesium in the place of one of the 3d transition metals. X-ray crystallography, mass spectrometry, and NMR spectroscopy unambiguously confirmed the presence of three types of molecules in the reaction mixture that reaches an equilibrium, Li 2 M 2 L 6 + Li 2 Mg 2 L 6 ↔ 2Li 2 MMgL 6 , upon prolonged reflux in solution. The equilibrium mixture was shown to have a nearly statistical distribution of the three molecules, and this is fully supported by the results of theoretical calculations revealing that the stabilization energies of hetero tri metallic assemblies fall exactly in between those for the parent hetero bi metallic species. The LiCo 0.5 Ni 0.5 O 2 quaternary oxide has been obtained in its phase-pure form by thermal decomposition of heterometallic precursor 1 at temperatures as low as 450 °C. Its chemical composition, structure, morphology, and transition metal distribution have been studied by X-ray and electron diffraction techniques and compositional energy-dispersive X-ray mapping with nanometer resolution. The work clearly illustrates the advantages of heterometallic single-source precursors over the corresponding multi-source precursors. 

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5. Epitaxial stabilization versus interdiffusion: synthetic routes to metastable cubic HfO ₂ and HfV ₂ O ₇ from the core–shell arrangement of precursors

   https://doi.org/10.1039/c9nr07316g  

   Fleer, Nathan A.; Thomas, Melonie P.; Andrews, Justin L.; Waetzig, Gregory R.; Gonzalez, Oscar; Liu, Guan-Wen; Guiton, Beth S.; Banerjee, Sarbajit (November 2019, Nanoscale)

   Metastable materials that represent excursions from thermodynamic minima are characterized by distinctive structural motifs and electronic structure, which frequently underpins new function. The binary oxides of hafnium present a rich diversity of crystal structures and are of considerable technological importance given their high dielectric constants, refractory characteristics, radiation hardness, and anion conductivity; however, high-symmetry tetragonal and cubic polymorphs of HfO 2 are accessible only at substantially elevated temperatures (1720 and 2600 °C, respectively). Here, we demonstrate that the core–shell arrangement of VO 2 and amorphous HfO 2 promotes outwards oxygen diffusion along an electropositivity gradient and yields an epitaxially matched V 2 O 3 /HfO 2 interface that allows for the unprecedented stabilization of the metastable cubic polymorph of HfO 2 under ambient conditions. Free-standing cubic HfO 2 , otherwise accessible only above 2600 °C, is stabilized by acid etching of the vanadium oxide core. In contrast, interdiffusion under oxidative conditions yields the negative thermal expansion material HfV 2 O 7 . Variable temperature powder X-ray diffraction demonstrate that the prepared HfV 2 O 7 exhibits pronounced negative thermal expansion in the temperature range between 150 and 700 °C. The results demonstrate the potential of using epitaxial crystallographic relationships to facilitate preferential nucleation of otherwise inaccessible metastable compounds. 

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