Tuneable Short-Range Antiferromagnetic Correlation in Fe-Containing Entropy Stabilized Oxides.

To elucidate the impact of a high entropy elemental distribution of the lattice site on the magnetic properties in oxide compounds, a series of complex perovskites BaBO3 (B = Y, Fe, Ti, Zr, Hf, Nb, and Ta) with different Fe content ratios (0, 0.2, 0.3, and 0.4) have been synthesized and thoroughly characterized. In this complex oxide series, superconducting quantum interference device magnetometry reveals a gradual change of a well-defined magnetic phase transition and B-site magnetic moment, which correlates with the Fe content. More importantly, a comprehensive analysis of the sample with a 0.4-Fe content (40% on the B-site) including magnetization, heat capacity, neutron diffraction, and muon-spin rotation measurements suggests that in the low-temperature state, a short-range antiferromagnetic correlation may exist, which could result from the magnetic interaction of Fe ions and consequent redistribution of associated d-electrons.

Synthesis and Characterization of High-Entropy Dawsonite-Type Structures.

High-entropy hydroxides are an emerging subcategory of high-entropy materials (HEMs), not only because they can serve as tailorable precursors to high-entropy oxides (HEOs) but also because they can have unique high-entropy properties themselves. Many hydroxide crystal structures that are important for various applications are yet to be studied within the context of high-entropy materials, and it is unknown if they can take a high-entropy form (typically five or more incorporated cations). One such material is the dawsonite-type structure, which is a material with applications in both catalysis and ceramics. This work focuses on the adaptation of a dawsonite-type structure (NH4M(OH)2CO3) into a high-entropy material. Through a coprecipitation synthesis method, dawsonite-type materials readily took a high-entropy form with five cations that were equimolar and homogeneously distributed. The specific chemistries investigated were Al, Cr, Fe, and Ga with a fifth cation that was varied with increasing ionic radius (In, Er, Ho, Y, Eu, Ce, La). High-entropy dawsonites also exhibit the ″memory effects″ of non-high-entropy dawsonites. This work extends the field of high-entropy materials to include a structure that can serve as a material platform for the synthesis of high-entropy catalytic materials and ceramic powders.

Hydrothermal synthesis of multi-cationic high-entropy layered double hydroxides.

High-entropy materials are compositionally complex materials which often contain five or more elements. The most commonly studied materials in this field are alloys and oxides, where their composition allows for tunable materials properties. High-entropy layered double hydroxides have been recently touted as the next focus for the field of high-entropy materials to expand into. However, most previous work on multi-cationic layered double hydroxides has focused on syntheses with 5 or less cations in the structure. To bridge this gap into high-entropy materials, this work explores the range and extent of different compositional combinations for high-entropy double layered hydroxides. Specifically, pure layered double hydroxides were synthesized with different combinations of 7 cations (Mg, Co, Cu, Zn, Ni, Al, Fe, Cr) as well as one combination of 8 cations by utilizing a hydrothermal synthesis method. Furthermore, magnetic properties of the 8-cation LDH were investigated.

Cycloparaphenylene Double Nanohoop: Structure, Lamellar Packing, and Encapsulation of C60 in the Solid State.

A new member of the cycloparaphenylene double-nanohoop family was synthesized. Its π-framework features two oval cavities that display different shapes depending on the crystallization conditions. Incorporation of the peropyrene bridge within the nanoring cycles via bay-regions alleviates steric effects and thus allows 1:1 complexation with C60 in the solid state. This nanocarbon adopts a lamellar packing motif, and our results suggest that the structural adjustment of this double nanohoop could enable its use in supramolecular and semiconductive materials.

Syntheses and characterization of three new sulfides with large band gaps: acentric Ba4Ga4SnS12, centric Ba12Sn4S23 and Ba7Sn3S13.

The desirable development of infrared nonlinear optical (IR NLO) materials is to design new compounds which exhibit wide band gaps and strong second harmonic generation (SHG) responses. Herein, we report three new sulfides, Ba4Ga4SnS12 (1), Ba12Sn4S23 (2) and Ba7Sn3S13 (3), with wide band gaps of 2.90, 2.98 and 3.0 eV, respectively, which have been successfully synthesized for the first time. Significantly, compound 1 exhibited a large SHG coefficient (34 × KDP), illustrating a good balance between the band gap and the SHG response. Single crystal X-ray diffraction determined that compound 1 crystallizes in the non-centrosymmetric space group P4[combining macron]21c and it was characterized as an interesting kite-shaped linkage motif of ∞[Ga4SnS12]. Compounds 2 and 3 crystallize in the space groups of P21c and Pnma, respectively. In addition, compounds 2 and 3 were characterized as zero-dimensional (0D) structures comprising isolated SnS4 tetrahedra with Ba2+ cations and S2- anions located between them. However, compound 2 contains extra disulfide S22- anions in its isolated structure. Moreover, the theoretical calculations demonstrated that SHG responses for compound 1 could be ascribed to the transitions from S-3p and Ga-4p states to Ba-5d, Ga-4p and Sn-5p states. By analysing the relationship between the structures and properties for Pb4Ga4GeS12-type compounds, it was concluded that site disorder could be an effective way to improve optical properties.