Ultrawide Temperature Range Super-Invar Behavior of R_{2}(Fe,Co)_{17} Materials (R = Rare Earth).

Super Invar (SIV), i.e., zero thermal expansion of metallic materials underpinned by magnetic ordering, is of great practical merit for a wide range of high precision engineering. However, the relatively narrow temperature window of SIV in most materials restricts its potential applications in many critical fields. Here, we demonstrate the controlled design of thermal expansion in a family of R_{2}(Fe,Co)_{17} materials (R=rare Earth). We find that adjusting the Fe-Co content tunes the thermal expansion behavior and its optimization leads to a record-wide SIV with good cyclic stability from 3-461 K, almost twice the range of currently known SIV. In situ neutron diffraction, Mössbauer spectra and first-principles calculations reveal the 3d bonding state transition of the Fe-sublattice favors extra lattice stress upon magnetic ordering. On the other hand, Co content induces a dramatic enhancement of the internal molecular field, which can be manipulated to achieve "ultrawide" SIV over broad temperature, composition and magnetic field windows. These findings pave the way for exploiting thermal-expansion-control engineering and related functional materials.

Differential Adsorption of l- and d-Lysine on Achiral MFI Zeolites as Determined by Synchrotron X-Ray Powder Diffraction and Thermogravimetric Analysis.

Reported here is the first crystallographic observation of stereospecific bindings of l- and d-lysine (Lys) in achiral MFI zeolites. The MFI structure offers inherent geometric and internal confinement effects for the enantiomeric difference in l- and d-Lys adsorption. Notable differences have been observed by circular dichroism (CD) spectroscopy and thermogravimetric analysis (TGA). Distinct l- and d-Lys adsorption behaviours on the H-ZSM-5 framework have been revealed by the Rietveld refinement of high-resolution synchrotron X-ray powder diffraction (SXRD) data and the density-functional theory (DFT) calculations. Despite demonstrating the approach for l- and d-Lys over MFI zeolites at an atomistic resolution, the differential adsorption study sheds light on the rational engineering of molecular interaction(s) with achiral microporous materials for chiral separation purposes.