4 research outputs found
High‑<i>T</i><sub>c</sub> Ferromagnetism and Electron Transport in p‑Type Fe<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Sb<sub>2</sub>Se<sub>4</sub> Semiconductors
Single-phase
polycrystalline powders of Fe<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Sb<sub>2</sub>Se<sub>4</sub> (<i>x</i> = 0 and 0.13) were synthesized by a solid-state reaction
of the elements at 773 K. X-ray diffraction on Fe<sub>0.87</sub>Sn<sub>0.13</sub>Sb<sub>2</sub>Se<sub>4</sub> single-crystal and powder
samples indicates that the compound is isostructural to FeSb<sub>2</sub>Se<sub>4</sub> in the temperature range from 80 to 500 K, crystallizing
in the monoclinic space group <i>C</i>2/<i>m</i> (No. 12). Electron-transport data reveal a marginal alteration in
the resistivity, whereas the thermopower drops by ∼60%. This
suggests a decrease in the activation energy upon isoelectronic substitution
of 13% Fe by Sn. Magnetic susceptibility and magnetization measurements
from 2 to 500 K reveal that the Fe<sub>1–<i>x</i></sub>Sb<sub>2</sub>Sn<sub><i>x</i></sub>Se<sub>4</sub> phases exhibit ferromagnetic behavior up to ∼450 K (<i>x</i> = 0) and 325 K (<i>x</i> = 0.13). Magnetotransport
data for FeSb<sub>2</sub>Se<sub>4</sub> reveal large negative magnetoresistance,
suggesting spin polarization of free carriers in the sample. The high-<i>T</i><sub>c</sub> ferromagnetism in Fe<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Sb<sub>2</sub>Se<sub>4</sub> phases and the decrease in <i>T</i><sub>c</sub> of the Fe<sub>0.87</sub>Sn<sub>0.13</sub>Sb<sub>2</sub>Se<sub>4</sub> sample are rationalized by taking into account (1) the separation
between neighboring magnetic centers in the crystal structures and
(2) the formation of bound magnetic polarons, which overlap to induce
long-range ferromagnetic ordering
Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub>: A Lillianite Homologue with Promising Thermoelectric Properties
Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> crystallizes in the monoclinic space group <i>C</i>2/<i>m</i> (No. 12) with <i>a</i> = 13.991(3)
Ã…, <i>b</i> = 4.262(2) Ã…, <i>c</i> =
23.432(5) Å, and β = 98.3(3)° at 300 K. In its three-dimensional
structure, two NaCl-type layers A and B with respective thicknesses <i>N</i><sub>1</sub> = 5 and <i>N</i><sub>2</sub> = 4
[<i>N</i> = number of edge-sharing (Pb/Bi)ÂSe<sub>6</sub> octahedra along the central diagonal] are arranged along the <i>c</i> axis in such a way that the bridging monocapped trigonal
prisms, PbSe<sub>7</sub>, are located on a pseudomirror plane parallel
to (001). This complex atomic-scale structure results in a remarkably
low thermal conductivity (∼0.33 W m<sup>–1</sup> K<sup>–1</sup> at 300 K). Electronic structure calculations and
diffuse-reflectance measurements indicate that Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> is a narrow-gap semiconductor with an indirect
band gap of 0.23 eV. Multiple peaks and valleys were observed near
the band edges, suggesting that Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> is a promising compound for both n- and p-type doping. Electronic-transport
data on the as-grown material reveal an n-type degenerate semiconducting
behavior with a large thermopower (∼−160 μV K<sup>–1</sup> at 300 K) and a relatively low electrical resistivity.
The inherently low thermal conductivity of Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> and its tunable electronic properties point to a
high thermoelectric figure of merit for properly optimized samples
Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub>: A Lillianite Homologue with Promising Thermoelectric Properties
Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> crystallizes in the monoclinic space group <i>C</i>2/<i>m</i> (No. 12) with <i>a</i> = 13.991(3)
Ã…, <i>b</i> = 4.262(2) Ã…, <i>c</i> =
23.432(5) Å, and β = 98.3(3)° at 300 K. In its three-dimensional
structure, two NaCl-type layers A and B with respective thicknesses <i>N</i><sub>1</sub> = 5 and <i>N</i><sub>2</sub> = 4
[<i>N</i> = number of edge-sharing (Pb/Bi)ÂSe<sub>6</sub> octahedra along the central diagonal] are arranged along the <i>c</i> axis in such a way that the bridging monocapped trigonal
prisms, PbSe<sub>7</sub>, are located on a pseudomirror plane parallel
to (001). This complex atomic-scale structure results in a remarkably
low thermal conductivity (∼0.33 W m<sup>–1</sup> K<sup>–1</sup> at 300 K). Electronic structure calculations and
diffuse-reflectance measurements indicate that Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> is a narrow-gap semiconductor with an indirect
band gap of 0.23 eV. Multiple peaks and valleys were observed near
the band edges, suggesting that Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> is a promising compound for both n- and p-type doping. Electronic-transport
data on the as-grown material reveal an n-type degenerate semiconducting
behavior with a large thermopower (∼−160 μV K<sup>–1</sup> at 300 K) and a relatively low electrical resistivity.
The inherently low thermal conductivity of Pb<sub>7</sub>Bi<sub>4</sub>Se<sub>13</sub> and its tunable electronic properties point to a
high thermoelectric figure of merit for properly optimized samples
Indium Preferential Distribution Enables Electronic Engineering of Magnetism in FeSb<sub>2–<i>x</i></sub>In<sub><i>x</i></sub>Se<sub>4</sub> p‑Type High-Tc Ferromagnetic Semiconductors
Single-phase samples
of the solid-solution series FeSb<sub>2–<i>x</i></sub>In<sub><i>x</i></sub>Se<sub>4</sub> (0
≤ <i>x</i> ≤ 0.25) were synthesized using
solid-state reaction of the elements to probe the effect of electronic
structure engineering on the magnetic behavior of the p-type semiconductor,
FeSb<sub>2</sub>Se<sub>4</sub>. Powder X-ray diffraction data suggest
that all samples are isostructural with FeSb<sub>2</sub>Se<sub>4</sub>. Rietveld refinements of the distribution of In atoms at various
metal positions indicate a preferential substitution of Sb at the
M1Â(<i>4i</i>) position within the magnetic layer A for In
concentration up to <i>x</i> = 0.1. FeSb<sub>2–<i>x</i></sub>In<sub><i>x</i></sub>Se<sub>4</sub> compositions
with higher In content show the distribution of In atoms at all metal
positions, except for the M3Â(<i>2d</i>), which is fully
occupied by Fe atoms. Interestingly, the ordering of Fe atoms within
the crystal structure of FeSb<sub>2–<i>x</i></sub>In<sub><i>x</i></sub>Se<sub>4</sub> remains essentially
unaffected by the degree of substitution (<i>x</i> values)
and is comparable to the distribution of Fe atoms reported in FeSb<sub>2</sub>Se<sub>4</sub>. X-ray photoelectron spectroscopy confirms
the oxidation states of various metal atoms InÂ(+3), SbÂ(+3), FeÂ(+2)
in the structure. Electronic transport properties indicate p-type
semiconducting behavior for all samples. The electrical conductivity
above 300 K first increases with In content, reaches the maximum value
for <i>x</i> = 0.1, then decreases with further increase
in In content. A reverse trend is observed for the thermopower. All
samples show drastically low thermal conductivity with room temperature
values ranging from 0.45 Wm<sup>–1</sup> K<sup>–1</sup> for <i>x</i> = 0 to 0.27 Wm<sup>–1</sup> K<sup>–1</sup> for the sample with <i>x</i> = 0.25. Magnetic
susceptibility data suggest ferromagnetic-like behavior from 2–300
K for all samples. The magnitude of the magnetic susceptibility rapidly
increases with In content, reaches a maximum for <i>x</i> = 0.1, and marginally decreases with further increase in In concentration.
The observed surprising change in the magnetic and electronic behavior
of samples with high In content (<i>x</i> > 0.1) is rationalized
using the concept of antiferromagnetic scattering of charge carriers
at the interfaces between overlapping bound magnetic polarons from
adjacent layers A and B