Partha Pratim Jana

The insufficient X-ray scattering contrast and similar neutron scattering cross-sections of Fe and Ni render the accurate determination of ‘coloring scheme’ ambiguous in the vacancy ordered 4 ³ −superstructure of CsCl-related phase Fe _1.5 Ni _1.5 Ga ₄ . Therefore, to overcome this limitation, X-ray resonance diffraction near the K-absorption edge of Fe has been utilized for the accurate site occupancy pattern of Fe and Ni in the structure of Fe _1.5 Ni _1.5 Ga ₄ . Measurements on three independently annealed samples with progressively longer annealing times revealed no evidence of atomic ordering, instead, Fe prefers to partially occupy the Ni site (48𝑔 Wyckoff site) in the structure of binary Ni ₃ Ga ₄ (𝐼𝑎3̅𝑑 space group, 𝑎 =11.52 Å). The vacancy ordering present at the 16𝑏 site drives the lattice distortion in the structure. Upon heating to ~955 K, the room-temperature (RT) structure transforms to the 2.9 Å CsCl-type structure (𝑃𝑚3̅𝑚 space group), where Fe, Ni and vacancy are randomly distributed suppressing the lattice distortions. DFT based calculations on the hypothetical ordered model predict a ferromagnetic ground state with non-magnetic and antiferromagnetic states lying very close to it in energy. This near-degeneracy points to a highly complex magnetic energy landscape with competing ferromagnetic and antiferromagnetic interactions, which explains the experimentally observed spin-glass behavior.

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.

In this study, we adopted a quasi-isostructural solid-solution strategy involving selenotitanate Cu4TiSe4 and sulvanite-type Cu3TMQ4 (TM: V, Nb, Ta; Q: S, Se). At room temperature, both systems crystallize in the cubic P4̅3m space group, where Cu4TiSe4 additionally contains positionally disordered Cu+ cations occupying two Wyckoff sites (1b and 4e) inside the sulvanite framework. The crystal structures of the solid-solution phases were determined by X-ray diffraction studies. Substituting Ti4+ for TM5+ in Cu3TMQ4 allows additional Cu+ to dissolve, maintaining the overall charge neutrality. The additional “interstitial” Cu+ ions occupy positionally disordered sites (1b and 4e) without affecting the three-dimensional (3D) sulvanite frameworks, with their occupancy controlled by the Ti4+/TM5+ ratio. Moreover, an ordering tendency of the interstitial Cu+ ions is observed within the cubic unit cell of the S-substituted solid solutions. This solid-solution formation leads to a substantial reduction in effective thermal conductivity relative to the parent sulvanite-type compounds, reaching the ultralow regime, while the optical band gaps vary systematically between 0.9 and 2.62 eV. The combination of this low thermal conductivity and tunable optical bandgap makes these materials highly attractive for diverse applications.

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 .

This investigation focuses on the high temperature synthesis and characterization using the single crystal and powder X-ray diffraction analysis of a partly disordered ternary intermetallic phase Cr _1−???? Ni ₂ Ga ₄ , 𝛿 ≈0.2 within the CsCl-related 𝑇 ₃ Ga ₄ family. With increase in annealing time during synthesis, the vacancy-disordered cubic (𝐹𝑚3̅𝑚, 𝑎 = 5.77 Å) phase transforms into a vacancy-ordered tetragonal phase (𝐼4 ₁ /𝑎𝑚𝑑, 𝑎 = 5.77 Å, 𝑐 = 11.54 Å) with three perpendicular twin domains. The superstructure reflections corresponding to vacancy ordering can be observed with both the single crystal and powder X-ray diffraction. Although the phase could not be separated in its pure form, the DFT simulations on the tetragonal model suggest the phase is suspectable to antiferromagnetic ordering. The partial occupancy of the Cr is rationalized by the antibonding populations near the fermi level. Furthermore, the variations in atomic sizes and electronegativities among the first-row transition metals provide additional insight to rationalize the structural distinctions of Co, and Fe containing analogues with the Cr-containing phase in the broader CsCl type/related 𝑇 ₃ Ga ₄ family and providing a rational pathway to discover novel intermetallic phases.

This study focuses on the binary δ-Co2.5Zn17.5 and pseudobinary δ-Co2.5–xMnxZn17.5 (x = 0–1.2) intermetallic phases, prepared via a high-temperature synthetic route. The crystal structure and atomic distribution of δ-Co2Mn0.5Zn17.5 were established using X-ray and neutron diffraction experiments. The pseudobinary δ-Co2Mn0.5Zn17.5 adopts a chiral crystal structure (P64), consistent with the binary δ-Co2.5Zn17.5. Theoretical calculations were employed to understand the site preferences of Co and Zn, as well as the overall phase stability of the binary compound. Interestingly, the substitution of Mn for Co occurs through Zn mediation (an indirect substitution). In the crystal structure, Mn occupies Zn sites at the 6c position; the displaced Zn then occupies the 3a site, ultimately maintaining the stoichiometry of Co2Mn0.5Zn17.5. The binary δ-Co2.5Zn17.5 exhibits diamagnetism, whereas Mn incorporation into the binary δ-Co2.5Zn17.5 induces cluster-glass magnetism in the pseudobinary δ-Co2Mn0.5Zn17.5, with a spin-freezing temperature of 10 K. While both compounds are structurally chiral, this chirality does not appear to influence their magnetic behavior. Instead, the cluster-glass state in the Mn-substituted phase is driven by the atomic randomness of the Mn atoms in the structural lattice. This out-of-equilibrium behavior below 10 K is further supported by the alternating-current (ac) magnetic susceptibility, thermoremanent magnetization, and the thermal memory effect.

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.

This investigation focuses on the solid-state synthesis and a detailed structural and phase analytical investigation of the CoxNi3–xGa4 series along a constant Ga compositional line within Co–Ni–Ga phase space. Combined analysis of single crystal X-ray diffraction and neutron powder diffraction of CoxNi3–xGa4, x = 1.5 reveals a random distribution of Co and Ni over a single Wyckoff site, which contrasts with previous report suggesting atomic ordering. Phase analyses via X-ray powder diffraction indicates a vacancy order–disorder transition as the Co concentration increases beyond a critical limit. DFT calculation predicted a semimetallic and nonmagnetic ground state, supported by the absence of magnetic peaks or intensity enhancement at 10 K neutron data compared to 300 K. Interestingly, Peierls-like distortions are observed within the Ga substructure in the vacancy-ordered phase, whereas such distortions are absent in the vacancy-disordered phase. These distortions result in periodic charge localization and exhibit subtle alterations between room temperature and 180 K. Magnetic measurements further reveal cluster spin-glass behavior with a high coercivity. The nontrivial spin dynamics, coupled with large coercivity, makes this phase a compelling candidate for multifunctional applications.

The insufficient X-ray scattering contrast and similar neutron scattering cross-sections of Fe and Ni render the accurate determination of ‘coloring scheme’ ambiguous in the vacancy ordered 4 ³ −superstructure of CsCl-related phase Fe _1.5 Ni _1.5 Ga ₄ . Therefore, to overcome this limitation, X-ray resonance diffraction near the K-absorption edge of Fe has been utilized for the accurate site occupancy pattern of Fe and Ni in the structure of Fe _1.5 Ni _1.5 Ga ₄ . Measurements on three independently annealed samples with progressively longer annealing times revealed no evidence of atomic ordering, instead, Fe prefers to partially occupy the Ni site (48𝑔 Wyckoff site) in the structure of binary Ni ₃ Ga ₄ (𝐼𝑎3̅𝑑 space group, 𝑎 =11.52 Å). The vacancy ordering present at the 16𝑏 site drives the lattice distortion in the structure. Upon heating to ~955 K, the room-temperature (RT) structure transforms to the 2.9 Å CsCl-type structure (𝑃𝑚3̅𝑚 space group), where Fe, Ni and vacancy are randomly distributed suppressing the lattice distortions. DFT based calculations on the hypothetical ordered model predict a ferromagnetic ground state with non-magnetic and antiferromagnetic states lying very close to it in energy. This near-degeneracy points to a highly complex magnetic energy landscape with competing ferromagnetic and antiferromagnetic interactions, which explains the experimentally observed spin-glass behavior.