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Title: Synthesis of (BiSe) 1+δ (Bi 2 Se 3 ) 1+γ (BiSe) 1+δ TiSe 2 by Directed Self-Assembly of a Designed Precursor
Award ID(s):
1710214
NSF-PAR ID:
10100778
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Chemistry of Materials
Volume:
31
Issue:
1
ISSN:
0897-4756
Page Range / eLocation ID:
216 to 223
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    Co‐crystallization of the spin‐crossover (SCO) cationic complex, [Fe(1‐bpp)2]2+(1‐bpp=2,6‐bis(pyrazol‐1‐yl)pyridine) with fractionally charged organic anion TCNQδ−(0<δ<1) afforded hybrid materials [Fe(1‐bpp)2](TCNQ)3.5 ⋅ 3.5MeCN (1) and [Fe(1‐bpp)2](TCNQ)4 ⋅ 4DCE (2), where TCNQ=7,7,8,8‐tetracyanoquinodimethane, MeCN=acetonitrile, and DCE=1,2‐dichloroethane. Both materials exhibit semiconducting behavior, with the room‐temperature conductivity values of 1.1×10−4 S/cm and 1.7×10−3 S/cm, respectively. The magnetic behavior of both complexes exhibits strong dependence on the content of the interstitial solvent. Complex1undergoes a gradual temperature‐driven SCO, with the midpoint temperature ofT1/2=234 K. The partial solvent loss by1leads to the increase in theT1/2value while complete desolvation renders the material high‐spin (HS) in the entire studied temperature range. In the case of2, the solvated complex shows a gradual SCO withT1/2=166 K only when covered with a mother liquid, while the facile loss of interstitial solvent, even at room temperature, leads to the HS‐only behavior.

     
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  2. Abstract

    The quinary members in the solid solution Hf2Fe1−δRu5−xIrx+δB2(x=1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness forx=1 and 3 and the highest forx=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (TN=55–70 K) found at low magnetic fields changed to ferromagnetic (TC=150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf2FeRu3Ir2B2has the highest intrinsic coercivity (Hc=74 kA/m) reported to date for Ti3Co5B2‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2FeIr5B2, indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials.

     
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  4. Combining experimental and theoretical studies, we investigate the role of R-site (R = Y, Sm, Bi) element on the phase formation and thermal stability of R 2 (Mn 1−x Fe x ) 4 O 10−δ ( x = 0, 0.5, 1) mullite-type oxides. Our results show a distinct R-site dependent phase behavior for mullite-type oxides as Fe is substituted for Mn: 100% mullite-type phase was formed in (Y, Sm, Bi) 2 Mn 4 O 10 ; 55% and 18% of (Y, Sm) 2 Mn 2 Fe 2 O 10−δ was found when R = Y and Sm, respectively, for equal Fe and Mn molar concentrations in the reactants, whereas Bi formed 54% O10- and 42% O9-mixed mullite-type phases. Furthermore, when the reactants contain 100% Fe, no mullite-type phase was formed for R = Y and Sm, but a sub-group transition to Bi 2 Fe 4 O 9 O9-phase was found for R = Bi. Thermogravimetric analysis and density functional theory (DFT) calculation results show a decreasing thermal stability in O10-type structure with increasing Fe incorporation; for example, the decomposition temperature is 1142 K for Bi 2 Mn 2 Fe 2 O 10−δ vs. 1217 K for Bi 2 Mn 4 O 10 . On the other hand, Bi 2 Fe 4 O 9 O9-type structure is found to be thermally stable up to 1227 K. These findings are explained by electronic structure calculations: (1) as Fe concentration increases, Jahn–Teller distortion results in mid band-gap empty states from unstable Fe 4+ occupied octahedra, which is responsible for the decrease in O10 structure stability; (2) the directional sp orbital hybridization unique to Bi effectively stabilizes the mullite-type structure as Fe replaces Mn. 
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