X-ray and neutron scattering

Abstract:

The antiferromagnetic (AFM) semimetal YbMnSb2 has recently been identified as a candidate topological material, driven by time-reversal symmetry breaking. Depending on the ordered arrangement of Mn spins below the Néel temperature, TN = 345 K, the electronic bands near the Fermi energy can either have a Dirac node, a Weyl node, or a nodal line. We have investigated the ground state magnetic structure of YbMnSb2 using unpolarized and polarized single crystal neutron diffraction. We find that the Mn moments lie along the c axis of the P4/nmm space group and are arranged in a C-type AFM structure, which implies the existence of gapped Dirac nodes near the Fermi level. The results highlight how different magnetic structures can critically affect the topological nature of fermions in semimetals.

Abstract:

Hybrid glasses from melt-quenched metal-organic frameworks (MOFs) have been emerging as a new class of materials, which combine the functional properties of crystalline MOFs with the processability of glasses. However, only a handful of the crystalline MOFs are meltable. Porosity and metal-linker interaction strength have both been identified as crucial parameters in the trade-off between thermal decomposition of the organic linker and, more desirably, melting. For example, the inability of the prototypical zeolitic imidazolate framework (ZIF) ZIF-8 to melt, is ascribed to the instability of the organic linker upon dissociation from the metal center. Here, we demonstrate that the incorporation of an ionic liquid (IL) into the porous interior of ZIF-8 provides a means to reduce its melting temperature to below its thermal decomposition temperature. Our structural studies show that the prevention of decomposition, and successful melting, is due to the IL interactions stabilizing the rapidly dissociating ZIF-8 linkers upon heating. This understanding may act as a general guide for extending the range of meltable MOF materials and, hence, the chemical and structural variety of MOF-derived glasses

Abstract:

Zeolitic imidazolate frameworks (ZIFs) can be melt-quenched to form glasses. Here, we present an alternative route to glassy ZIFs via mechanically induced amorphisation.