The structural, thermodynamic, and magnetic properties of Na₂CrCl₄ have been investigated to provide fundamental insights into this ternary halide relevant to chloride-based molten salt reactor systems. Room-temperature powder X-ray and neutron diffraction confirm a monoclinic (P2₁/c) structure and phase purity. Neutron diffraction measurements at 4.6 K reveal additional magnetic reflections indexed with (Formula presented), indicating the onset of long-range antiferromagnetic order. Low-temperature heat capacity measurements in the range 2–300 K show a pronounced λ-type anomaly at T_N = 8.5 ± 0.5 K, with an associated magnetic entropy S_mag = 11.9 ± 0.4 J K^–1 mol ^–1 consistent with antiferromagnetic ordering of high-spin Cr²⁺ (S = 2), a second-order phase transition. The standard molar entropy at 298.15 K, S_m^°(298.15 K) = 256.8 ± 7.7 J K^–1 mol ^–1, is slightly lower than previous CALPHAD assessments of the NaCl-CrCl₂ system. Magnetic susceptibility measurements also confirm antiferromagnetic behavior, with a Curie–Weiss fit giving μ_eff = 5.57 ± 0.05 μ_B and θ_CW = −15.0 ± 1.0 K. Compared to the related ferromagnetic chlorides K₂CrCl₄, Rb₂CrCl₄, and Cs₂CrCl₄, Na₂CrCl₄ exhibits a distinctly lower ordering temperature and antiferromagnetic structure, likely due to variations in lattice geometry and exchange interactions. These results provide the first experimental thermodynamic parameters for Na₂CrCl₄, contributing to refining phase diagrams and corrosion models in chloride salt systems. ... Read more

Mg-MOF-74 is a highly efficient adsorbent for CO2. We use molecular simulations to study the effects of disorder in Mg-MOF-74 on the selective adsorption, structure, and dynamics of a CO2-CH4 mixture. Positional disorder is introduced in the adsorbent by separating individual Mg-MOF-74 crystallites via inserting intercrystalline space between them. Rotating a crystallite with respect to others by different extents provides the orientational disorder (OD). Disorder is observed to enhance the adsorption selectivity of CO2 over CH4. The additional adsorption sites available by exposing crystallite surfaces may provide added selectivity for CO2. Disorder is found to affect both the translational as well as rotational motion of CO2 in Mg-MOF-74. This behavior follows a systematic pattern dictated by the interplay of the pore geometry of Mg-MOF-74 and Mg2+ − CO2 interactions. Our results provide a guide on how to tailor Mg-MOF-74 adsorption behavior with desired properties by purposeful introduction of disorder. ... Read more

TiFe2 alloys, a C14 Laves phase system, exhibit negative or zero thermal expansion (NTE/ZTE) despite the absence of the first-order transitions that typically drive such behavior in related compounds. Across the compositional range, the magnetic ground state evolves from ferromagnetic ordering in Fe-rich alloys to antiferromagnetic ordering in Ti-rich variants, yet the thermal expansion response remains invariant. High-resolution synchrotron X-ray and neutron diffraction detect no anomalies in lattice volume or magnetic moment, and Rietveld refinements exclude significant antisite disorder. In contrast, Fe and Ti K-edge extended X-ray absorption fine structure (EXAFS) and elemental mapping via energy-dispersive X-ray spectroscopy (EDAX) reveal pronounced nanoscale compositional inhomogeneity, forming Fe-rich and Ti-rich regions. The coexistence of competing ferro- and antiferromagnetic interactions from these chemically distinct domains gives rise to an invar-like effect below a characteristic temperature, T*. These results establish local chemical disorder as a key mechanism for stabilizing NTE/ZTE behavior in intermetallic systems, independent of long-range structural or magnetic transitions. ... Read more