Sandip Kumar Kuila

In the present work, the effect of indium substitution for tin in the ternary Ni _{1+ δ} (In/Sn) ( δ = 0.2–0.5) (Ni ₂ In(B8 ₂ )/NiAs(B8 ₁ )‐type phases) has been systematically investigated through a combination of single‐crystal X‐ray diffraction studies and composition analysis (energy‐dispersive X‐ray spectroscopy [EDS]). Ni _{1+ δ} (In/Sn) ( δ = 0.2–0.4) adopt incommensurately modulated structure and their structures can be described within the 3 + 1‐dimensional orthorhombic superspace group , where the average structure exhibits lattice parameters of , , with a unit cell volume 149 Å ³ . The structure is related to NiAs‐type arrangement Ni(1)(In1/Sn1) and additional nickel (Ni(2)) atoms partially occupying trigonal bipyramidal interstices in an ordered fashion. The modulation vector * ( = 0.41−0.47) governs the occupational modulation of the Ni(2) sites, which is successfully modeled using a Crenel function. Increasing the nickel content (60 at%) induces a structural transition from the incommensurately modulated phase to a commensurately modulated phase. The commensurate phase is related to the binary Fe _1.66 Sn structure type (). The structure of commensurately modulated Ni _1.5 (In/Sn) adopts the orthorhombic space group with lattice constants a = 7.1 Å, b = 5.2 Å, c = 8.2 Å with NiAs‐type arrangement Ni(1)(In/Sn) and additional Ni(2)/Ni(3) atoms partially occupying trigonal bipyramidal interstices, leading to the formula Ni(1)((Ni(2)/Ni(3)) _δ (In/Sn).

The synthesis of phase-pure Cu-based multinary tellurides remains challenging due to the competitive formation of stable Cu–Te binary phases, which frequently intercept the reaction pathway as secondary products. In the Cu ₄ TiTe ₄ system, rapid synthesis temperature mapping reveals the synthesis window, whereas precise compositional control suppresses secondary Cu–Te binaries to unlock non-equilibrium phase selection. We demonstrate that addition of 2 wt% excess Ti shifts the reaction chemistry toward Cu ₄ TiTe ₄ , suppressing detectable Cu–Te secondary phases and yielding phase-pure Cu ₄ TiTe ₄ over the identified 623–873 K synthesis window. Cu ₄ TiTe ₄ crystallises in a ‘stuffed sulvanite’ type structure, similar to Cu ₄ TiSe ₄ , and exhibits an order–disorder phase transition, in which partial ordering of the Cu sublattice induces structural transformation primarily governed by Cu sublattice ordering. Bulk Cu ₄ TiTe ₄ is a p-type narrow bandgap semiconductor that achieves a low lattice thermal conductivity of 0.63 to 0.68 W m ^-1 K ^-1 between 300 and 423 K. Transport calculations attribute the low observed thermal conductivity to Cu-sublattice disorder, local symmetry breaking, and localized Ti-dominated vibrations that collectively suppress phonon transport.

DFT guided unsupported intermetallics NiIn _{1− x} Sn _x ( x = 0.5, 0.8) synthesized via high temperature method. Hexagonal NiIn _0.5 Sn _0.5 has higher activity and selectivity towards ethylene for acetylene hydrogenation reaction than orthorhombic NiIn _0.2 Sn _0.8 .

The development of advanced functional electrocatalysts that couple energy storage with chemical conversion requires precise control over interfacial electronic structure and reaction energetics. Herein, we report an interfacially engineered transition-metal phosphide heterostructure composed of Ni2P and FeP, encapsulated within nitrogen-doped graphitic carbon (Ni2P/FeP@NC), which exhibits excellent activity toward bifunctional oxygen electrocatalysis, hydrogen evolution, and benzyl alcohol oxidation. The heterostructured architecture promotes interfacial charge redistribution and modulates the adsorption energies of key reaction intermediates, resulting in enhanced intrinsic activity and favorable kinetics. Electrocatalytic investigations reveal that the heterostructured catalyst (i) promotes a dominant four-electron oxygen reduction reaction (ORR) pathway, delivering a half-wave potential of 0.84 V and a limiting current density of ∼6 mA cm–2; (ii) achieves the benchmark current density for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at low overpotentials; and (iii) facilitates the selective oxidation of benzyl alcohol to benzoic acid. The narrow potential gap between ORR and OER underscores the catalyst’s suitability for rechargeable zinc–air batteries (ZABs). When employed as the air cathode, the heterostructured catalyst delivers a high peak power density of 170 mW cm–2, excellent charge–discharge rate capability, and remarkable long-term cycling stability exceeding 600 h. A solid-state ZAB fabricated using the same catalyst likewise exhibits competitive energy-storage performance. Furthermore, by exploiting the multifunctional electrocatalytic activity of the heterostructure, a ZAB-powered coupled water electrolysis system enables sustained hydrogen evolution with the selective oxidation of benzyl alcohol to benzoic acid, demonstrating a self-powered platform that seamlessly integrates electrochemical energy storage with value-added chemical production.

Intermetallic catalysts offer a unique platform for the hydrogenation reaction of acetylene, as their well-defined crystal structures and precise stoichiometry enable atomic-level control over active-site composition, geometry, and electronic structure. In ternary intermetallics, the addition of a third element in varying amounts can alter the crystal structure, thereby changing the stable crystal facet(s) and, consequently, the active-site electronic structure, demonstrating an intriguing strategy to boost product selectivity. The site-specific substitution of Sn in NiIn _{1- x} Sn _x ( x =0.5, 0.8) exhibits two distinct phases belonging to hexagonal ( x =0.5) and orthorhombic ( x =0.8) crystal systems. Density Functional Theory calculations show that (0001) and (010) facets of hexagonal and orthorhombic phases, respectively, are the most stable. Catalytic performance for the acetylene hydrogenation reaction confirms that the hexagonal NiIn _0.5 Sn _0.5 is more catalytically active and selective towards ethylene than the orthorhombic NiIn _0.2 Sn _0.8 . The Nudged Elastic Band calculations reveal a significant difference in the kinetics of the conversion reactions, making the hexagonal phase more selective than the orthorhombic phase. Thus, this study combines both experimental and theoretical approaches to understand the superior catalytic performance of the hexagonal phase over the orthorhombic phase, which mainly originates from differences in the atomic arrangement of the most stable surface, which significantly influences the reaction kinetics of acetylene hydrogenation.

Intermetallic catalysts offer a unique platform for the hydrogenation reaction of acetylene, as their well-defined crystal structures and precise stoichiometry enable atomic-level control over active-site composition, geometry, and electronic structure. In ternary intermetallics, the addition of a third element in varying amounts can alter the crystal structure, thereby changing the stable crystal facet(s) and, consequently, the active-site electronic structure, demonstrating an intriguing strategy to boost product selectivity. The site-specific substitution of Sn in NiIn _{1- x} Sn _x ( x =0.5, 0.8) exhibits two distinct phases belonging to hexagonal ( x =0.5) and orthorhombic ( x =0.8) crystal systems. Density Functional Theory calculations show that (0001) and (010) facets of hexagonal and orthorhombic phases, respectively, are the most stable. Catalytic performance for the acetylene hydrogenation reaction confirms that the hexagonal NiIn _0.5 Sn _0.5 is more catalytically active and selective towards ethylene than the orthorhombic NiIn _0.2 Sn _0.8 . The Nudged Elastic Band calculations reveal a significant difference in the kinetics of the conversion reactions, making the hexagonal phase more selective than the orthorhombic phase. Thus, this study combines both experimental and theoretical approaches to understand the superior catalytic performance of the hexagonal phase over the orthorhombic phase, which mainly originates from differences in the atomic arrangement of the most stable surface, which significantly influences the reaction kinetics of acetylene hydrogenation.

A new binary phase, Mn₁₆Ge₇, has been identified in the Mn-rich region of the Mn-Ge binary system alongside the ζ phase (ζ₁-Mn₂₃Ge₉ + ζ₂-Mn₅Ge₂) via high-temperature synthesis. Their crystal structures have been determined by single-crystal X-ray diffraction studies. The compound Mn₁₆Ge₇ crystallizes in the monoclinic crystal system with the space group C2/m (a ≈ 10.61 Å, b ≈ 7.77 Å, c ≈ 8.16 Å, and β ≈ 111.72°; Pearson code: mC46). The structure contains ten independent crystallographic sites in the unit cell in which seven are manganese and three are germanium sites. The ζ phase consists of two structurally related microsyntactic intergrowth phases (ζ₁-Mn₂₃Ge₉ and ζ₂-Mn₅Ge₂); both crystallize in the trigonal space group P3c1 (a ≈ 7.17 Å, c ≈ 39.06 Å for ζ₁-Mn₂₃Ge₉ and a ≈ 7.17 Å, c ≈ 13.00 Å for ζ₂-Mn₅Ge₂) but slightly differ in stoichiometry. Electronic structure calculations of Mn₁₆Ge₇ suggest that the most stable configuration is obtained for the model with the shortest Mn-Mn contacts with antiferromagnetic coupling, while longer Mn-Mn separations typically promote ferromagnetic alignment. The band structure shows that the compound is metallic, and bonding analysis indicates that Mn-Mn homoatomic interactions play a crucial role in the stability of the compound.

Ni_1+δSn (δ = 0.2, 0.4) and Ni_1+δ(In/Sb) (δ = 0.1-0.5) (NiAs/Ni₂In type) were synthesized, and their crystal structures were studied in this report. In Ni_1+δ(In/Sb), the excess nickel atoms (δ = 0.1-0.5) occupy the vacant trigonal bipyramidal interstitial sites in the NiAs-type structural arrangement, leading to the evolution of a fully disordered to ordered superstructure through a series of incommensurately ordered structures within the B8 phase field. In the phase field, Ni_1+δ(In/Sb) (δ = 0.15) that crystallize in the space group P6₃/mmc adopt structure having an intermediate atomic arrangement between NiAs- and Ni₂In-type structures. Phases with δ = 0.2-0.4, adopt incommensurate modulation, and the structure was modeled using (3 + 1)D superspace formalism. The structures of Ni_1+δSn (δ = 0.2, 0.4) and Ni_1+δ(In/Sb) (δ = 0.2-0.4) crystallize in the orthorhombic superspace group Cmcm(α00)0s0 (a ≈ 4.05 Å, b ≈ 7 Å, and c ≈ 5.15 Å) with a modulation vector q ≈ αa* (where α = 0.42-0.48). Ni_1+δ(In/Sb) (δ = 0.45, 0.5) that adopts the ternary variant of Ni₃Sn₂ type (Pnma with a = 7.111(3) Å, b = 5.193(3) Å, and c = 8.2113(2) Å) can alternatively be represented as a commensurately modulated structure (lock-in phase, Cmcm(α00)0s0, α = 0.5). The structural outcome in the phase field is primarily governed by the partial Ni occupancy, and the vacancy disorder in the Ni_1+δ(In/Sb) (δ = 0.15) was rationalized by density functional theory (DFT) calculations.

A series of InPd_3-xAg_x (x = 0-1) compositions were synthesized by conventional high-temperature synthesis, and as-synthesized samples were characterized by powder X-ray diffraction experiments. Up to x = 0.7, InPd_3-xAg_x adopts the ternary substitutional variant of the InPd₃ structure (TiAl₃-type), when x > 0.7, elemental Ag starts to segregate along with the main phase. Accurate structural characterization in InPd_3-xAg_x faces a critical challenge due to the narrow X-ray scattering contrast among constituents In, Pd, and Ag and nearly identical neutron scattering lengths of Pd and Ag. To overcome this "coloring problem", a combination of calculation of phase diagrams modeling (CALPHAD) and diffraction techniques (X-ray and neutron) was employed. In the compositional range 0 ≤ x ≤ 0.7, InPd_3-xAg_x presents a ternary variant of the TiAl₃-type structure, where Ag atoms selectively substitute one (the 2b Wyckoff site) of the two Pd sites in InPd₃. Notably, in contrast to the isologous InPd_3-xCu_x (x = 0-1) system, Ag substitution does not form an ordered VRh₂Sn-type structure at the limiting composition. The distinct site preference in InPd_3-xAg_x is elucidated by charge population analysis, electronic structure calculations, and orbital-resolved chemical bonding investigations, and the extent of substitution is supported by formation free energy calculations.