91 research outputs found
Synthesis and Properties of New Multinary Silicides R<sub>5</sub>Mg<sub>5</sub>Fe<sub>4</sub>Al<sub><i>x</i></sub>Si<sub>18–<i>x</i></sub> (R = Gd, Dy, Y, <i>x</i> ≈ 12) Grown in Mg/Al Flux
Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1
Mg/Al mixed
flux produce well-formed crystals of R<sub>5</sub>Mg<sub>5</sub>Fe<sub>4</sub>Al<sub><i>x</i></sub>Si<sub>18–<i>x</i></sub> (<i>x</i> ≈ 12). These phases have a new
structure type in tetragonal space group <i>P</i>4<i>/mmm</i> (<i>a</i> = 11.655(2) Ã…, <i>c</i> = 4.0668(8) Ã…, <i>Z</i> = 1 and <i>R</i><sub>1</sub> = 0.0155 for the Dy analogue). The structure features
two rare earth sites and one iron site; the latter is in monocapped
trigonal prismatic coordination surrounded by silicon and aluminum
atoms. Siting of Al and Si was investigated using bond length analysis
and <sup>27</sup>Al and <sup>29</sup>Si MAS NMR studies. The magnetic
properties are determined by the R elements, with the Gd and Dy analogues
exhibiting antiferromagnetic ordering at <i>T</i><sub>N</sub> = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic
behavior with varying field
Synthesis and Properties of New Multinary Silicides R<sub>5</sub>Mg<sub>5</sub>Fe<sub>4</sub>Al<sub><i>x</i></sub>Si<sub>18–<i>x</i></sub> (R = Gd, Dy, Y, <i>x</i> ≈ 12) Grown in Mg/Al Flux
Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1
Mg/Al mixed
flux produce well-formed crystals of R<sub>5</sub>Mg<sub>5</sub>Fe<sub>4</sub>Al<sub><i>x</i></sub>Si<sub>18–<i>x</i></sub> (<i>x</i> ≈ 12). These phases have a new
structure type in tetragonal space group <i>P</i>4<i>/mmm</i> (<i>a</i> = 11.655(2) Ã…, <i>c</i> = 4.0668(8) Ã…, <i>Z</i> = 1 and <i>R</i><sub>1</sub> = 0.0155 for the Dy analogue). The structure features
two rare earth sites and one iron site; the latter is in monocapped
trigonal prismatic coordination surrounded by silicon and aluminum
atoms. Siting of Al and Si was investigated using bond length analysis
and <sup>27</sup>Al and <sup>29</sup>Si MAS NMR studies. The magnetic
properties are determined by the R elements, with the Gd and Dy analogues
exhibiting antiferromagnetic ordering at <i>T</i><sub>N</sub> = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic
behavior with varying field
Flux Growth and Magnetoresistance Behavior of Rare Earth Zintl Phase EuMgSn
Reactions of europium and tin in
1:1 Mg/Al mixed flux produce large crystals of EuMgSn. This phase
crystallizes with the TiNiSi structure type in orthorhombic space
group <i>Pnma</i> (<i>a</i> = 8.0849(7) Ã…, <i>b</i> = 4.8517(4) Ã…, <i>c</i> = 8.7504(8) Ã…, <i>Z</i> = 4, <i>R</i><sub>1</sub> = 0.0137). The crystal
structure features europium cations positioned between puckered hexagonal
layers comprised of magnesium and tin atoms. Magnetic susceptibility
measurements indicate the europium in this phase is divalent, which
suggests that the compound is possibly valence-balanced as Eu<sup>2+</sup>Mg<sup>2+</sup>Sn<sup>4–</sup>. However, EuMgSn is
a metal as indicated by density of states calculations and electrical
resistivity behavior. This phase exhibits antiferromagnetic ordering
at <i>T</i><sub>N</sub> = 10.9 K at low field (100 G) and
the ordering temperature decreases when a higher magnetic field is
applied. ac magnetization and field dependence of resistivity at 4.2
K reveal that there is a spin reorientation at 2 T, in agreement with
the metamagnetic transition shown in the dc magnetization versus field
data. Temperature dependence of resistivity at 2.5 T indicates that
EuMgSn has a large magnetoresistance up to −30% near its magnetic
ordering temperature
Competing Phases, Complex Structure, and Complementary Diffraction Studies of R<sub>3‑δ</sub>FeAl<sub>4‑x</sub>Mg<sub><i>x</i></sub>Tt<sub>2</sub> Intermetallics (R = Y, Dy, Er, Yb; Tt = Si or Ge; <i>x</i> < 0.5)
Four new intermetallic phases R<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Si<sub>2</sub> (R = Yb, Dy) and R<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Ge<sub>2</sub> (R
= Er, Y) were synthesized in Mg/Al (1:1 mol ratio) molten flux. These
phases have a new structure type in tetragonal space group <i>P</i>4<i>/mbm</i> (<i>a</i> = 13.3479(9)
Ã…, <i>c</i> = 4.0996(3) Ã…, <i>Z</i> =
4, and R1 = 0.0176 for Yb<sub>2.77</sub>FeAl<sub>3.72</sub>Mg<sub>0.28</sub>Si<sub>2</sub>). The structure features iron in trigonal
prismatic coordination by aluminum atoms. The prisms share trigonal
faces to form chains running along the <i>c</i>-axis, similar
to the chains seen in several related structures, including that of
the previously reported competing phases R<sub>5</sub>Mg<sub>5</sub>Fe<sub>4</sub>Al<sub>12</sub>Si<sub>6</sub> (R = Gd, Dy, and Y).
Occupancies of Mg, Al, and Si sites in Yb<sub>2.77</sub>FeAl<sub>3.72</sub>Mg<sub>0.28</sub>Si<sub>2</sub> were determined by single crystal
X-ray and neutron diffraction, bond length analysis, and comparison
to atom positions and bond lengths in the isostructural germanides.
Electronic structure calculations indicate these phases are polar
intermetallics with pseudogaps near the Fermi level. The magnetic
properties of these phases are determined by the rare earth ions.
Y<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Ge<sub>2</sub> is Pauli paramagnetic;
the Yb<sup>3+</sup> cations in Yb<sub>2.77</sub>FeAl<sub>3.72</sub>Mg<sub>0.28</sub>Si<sub>2</sub> exhibit Curie–Weiss behavior
with no ordering in the temperature range observed. Er<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Ge<sub>2</sub> and Dy<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Si<sub>2</sub> order
antiferromagnetically at <i>T</i><sub>N</sub> = 2.8 and
4.0 K, respectively; the former undergoes a spin reorientation at
∼4400 G according to the ac field dependence of magnetization
Synthesis of α-arylalkylferrocenes through cesium fluoride-promoted coupling of arylboronic acids with <i>N</i>-tosylhydrazones
<p>A cesium fluoride-promoted reductive coupling reaction of acylferrocene tosylhydrazones with arylboronic acids has been developed, producing highly substituted α-arylalkylferrocenes in moderate to excellent yields. The reaction employs anionic fluorine to facilitate the cleavage of C–B bond. The developed methodology demonstrates a wide substrate scope and high functional groups tolerance. Moreover, the α-arylalkylferrocenes compounds were also obtained on a multi-gram scale.</p
Flux Growth and Magnetoresistance Behavior of Rare Earth Zintl Phase EuMgSn
Reactions of europium and tin in
1:1 Mg/Al mixed flux produce large crystals of EuMgSn. This phase
crystallizes with the TiNiSi structure type in orthorhombic space
group <i>Pnma</i> (<i>a</i> = 8.0849(7) Ã…, <i>b</i> = 4.8517(4) Ã…, <i>c</i> = 8.7504(8) Ã…, <i>Z</i> = 4, <i>R</i><sub>1</sub> = 0.0137). The crystal
structure features europium cations positioned between puckered hexagonal
layers comprised of magnesium and tin atoms. Magnetic susceptibility
measurements indicate the europium in this phase is divalent, which
suggests that the compound is possibly valence-balanced as Eu<sup>2+</sup>Mg<sup>2+</sup>Sn<sup>4–</sup>. However, EuMgSn is
a metal as indicated by density of states calculations and electrical
resistivity behavior. This phase exhibits antiferromagnetic ordering
at <i>T</i><sub>N</sub> = 10.9 K at low field (100 G) and
the ordering temperature decreases when a higher magnetic field is
applied. ac magnetization and field dependence of resistivity at 4.2
K reveal that there is a spin reorientation at 2 T, in agreement with
the metamagnetic transition shown in the dc magnetization versus field
data. Temperature dependence of resistivity at 2.5 T indicates that
EuMgSn has a large magnetoresistance up to −30% near its magnetic
ordering temperature
Competing Phases, Complex Structure, and Complementary Diffraction Studies of R<sub>3‑δ</sub>FeAl<sub>4‑x</sub>Mg<sub><i>x</i></sub>Tt<sub>2</sub> Intermetallics (R = Y, Dy, Er, Yb; Tt = Si or Ge; <i>x</i> < 0.5)
Four new intermetallic phases R<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Si<sub>2</sub> (R = Yb, Dy) and R<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Ge<sub>2</sub> (R
= Er, Y) were synthesized in Mg/Al (1:1 mol ratio) molten flux. These
phases have a new structure type in tetragonal space group <i>P</i>4<i>/mbm</i> (<i>a</i> = 13.3479(9)
Ã…, <i>c</i> = 4.0996(3) Ã…, <i>Z</i> =
4, and R1 = 0.0176 for Yb<sub>2.77</sub>FeAl<sub>3.72</sub>Mg<sub>0.28</sub>Si<sub>2</sub>). The structure features iron in trigonal
prismatic coordination by aluminum atoms. The prisms share trigonal
faces to form chains running along the <i>c</i>-axis, similar
to the chains seen in several related structures, including that of
the previously reported competing phases R<sub>5</sub>Mg<sub>5</sub>Fe<sub>4</sub>Al<sub>12</sub>Si<sub>6</sub> (R = Gd, Dy, and Y).
Occupancies of Mg, Al, and Si sites in Yb<sub>2.77</sub>FeAl<sub>3.72</sub>Mg<sub>0.28</sub>Si<sub>2</sub> were determined by single crystal
X-ray and neutron diffraction, bond length analysis, and comparison
to atom positions and bond lengths in the isostructural germanides.
Electronic structure calculations indicate these phases are polar
intermetallics with pseudogaps near the Fermi level. The magnetic
properties of these phases are determined by the rare earth ions.
Y<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Ge<sub>2</sub> is Pauli paramagnetic;
the Yb<sup>3+</sup> cations in Yb<sub>2.77</sub>FeAl<sub>3.72</sub>Mg<sub>0.28</sub>Si<sub>2</sub> exhibit Curie–Weiss behavior
with no ordering in the temperature range observed. Er<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Ge<sub>2</sub> and Dy<sub>3‑δ</sub>FeAl<sub>4‑<i>x</i></sub>Mg<sub><i>x</i></sub>Si<sub>2</sub> order
antiferromagnetically at <i>T</i><sub>N</sub> = 2.8 and
4.0 K, respectively; the former undergoes a spin reorientation at
∼4400 G according to the ac field dependence of magnetization
Synthesis of symmetrical terphenyl derivatives by PdCl<sub>2</sub>-catalyzed Suzuki–Miyaura reaction of dibromobenzene using 3-(diphenylphosphino)propanoic acid as a ligand
<p>A simple and efficient catalytic system for PdCl<sub>2</sub> catalyzing the Suzuki–Miyaura reaction of dibromobenzene and arylboronic acid has been developed by using 3-(diphenylphosphino)propanoic acid as a ligand in dimethylsulfoxide at 100 °C. Using this method, a series of symmetrical terphenyl derivatives were obtained with remarkably good yields, up to 93%.</p
Thermoelectric Properties of Ba<sub>1.9</sub>Ca<sub>2.4</sub>Mg<sub>9.7</sub>Si<sub>7</sub>: A New Silicide Zintl Phase with the Zr<sub>2</sub>Fe<sub>12</sub>P<sub>7</sub> Structure Type
Ba<sub>1.9</sub>Ca<sub>2.4</sub>Mg<sub>9.7</sub>Si<sub>7</sub> was
grown as large crystals from the reaction of silicon with barium and
calcium in Mg/Al flux. This compound is a charge-balanced Zintl phase
with the Zr<sub>2</sub>Fe<sub>12</sub>P<sub>7</sub> structure type
in hexagonal space group <i>P</i>6Ì… (<i>a</i> = 11.196(2) Ã…, <i>c</i> = 4.4595(9) Ã…); barium
occupies the Zr sites, the lighter alkaline earths (Mg, Ca) mix on
the Fe sites, and silicon occupies the phosphorus sites. An isostructural
germanide (Ba<sub>1.2</sub>Sr<sub>0.9</sub>Mg<sub>11.9</sub>Ge<sub>7</sub>, <i>a</i> = 11.064(1) Ã…, <i>c</i> = 4.3709(6) Ã…)) was similarly synthesized from reactions of
germanium with barium and strontium in Mg/Al flux. Density of states
calculations indicate these phases are semimetals, in agreement with
their charge-balanced nature. Measurements of electrical resistivity,
thermal conductivity, and Seebeck coefficient were carried out from
300–1000 K to investigate the thermoelectric properties of
Ba<sub>1.9</sub>Ca<sub>2.4</sub>Mg<sub>9.7</sub>Si<sub>7</sub>. This
compound is an n-type semimetal with low thermal conductivity (2 W/(m·K)),
moderate Seebeck coefficient (−200 μV/K at 900 K), and
a thermoelectric figure of merit ZT of 0.35 at 900 K
Inheritance of Crystallographic Orientation during Lithiation/Delithiation Processes of Single-Crystal α‑Fe<sub>2</sub>O<sub>3</sub> Nanocubes in Lithium-Ion Batteries
Iron oxides are very promising anode
materials based on conversion reactions for lithium-ion batteries
(LIBs). During conversion processes, the crystal structure and composition
of the electrode material are drastically changed. Surprisingly, in
our study, inheritance of a crystallographic orientation was found
during lithiation/delithiation processes of single-crystal α-Fe<sub>2</sub>O<sub>3</sub> nanocubes by ex situ transmission electron microscopy.
Single-crystal α-Fe<sub>2</sub>O<sub>3</sub> was first transformed
into numerous Fe nanograins embedded in a Li<sub>2</sub>O matrix,
and then the conversion between Fe and FeO nanograins became the main
reversible electrochemical reaction for energy storage. Interestingly,
these Fe/FeO nanograins had almost the same crystallographic orientation,
indicating that the lithiated/delithiated products can inherit the
crystallographic orientation of single-crystal α-Fe<sub>2</sub>O<sub>3</sub>. This finding is important for understanding the detailed
electrochemical conversion processes of iron oxides, and this feature
may also exist during lithiation/delithiation processes of other transition-metal
oxides
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