High Entropy Alloys are inherently complex and span a vast composition space, making their research and discovery challenging. Developing quantitative predictions of their phase selection requires a ...large quantity of consistently determined experimental data. Here, we use combinatorial methods to fabricate and characterize 2478 quinary alloys based on Al and transition metals. All data are publicly available at http://materialsatlasproject.org/. Phase selection can be predicted for considered alloys when combining the content of FCC/BCC elements and the constituents’ atomic size difference. Mining our data reveals that High Entropy Alloys with increasing atomic size difference prefer BCC structure over FCC. This preference is typically overshadowed by other selection motifs, which dominate during close-to-equilibrium processing. Not suggested by the Hume-Rothery rules, this preference originates from the ability of the BCC structure to accommodate a large atomic size difference with lower strain energy penalty which can be practically only realized in High Entropy Alloys.
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The Zintl compound Eu2ZnSb2 was recently shown to have a promising thermoelectric figure of merit, zT ∼ 1 at 823 K, due to its low lattice thermal conductivity and high electronic mobility. In the ...current study, we show that further increases to the electronic mobility and simultaneous reductions to the lattice thermal conductivity can be achieved by isovalent alloying with Bi on the Sb site in the Eu2ZnSb2−xBix series (x = 0, 0.25, 1, 2). Upon alloying with Bi, the effective mass decreases and the mobility linearly increases, showing no signs of reduction due to alloy scattering. Analysis of the pair distribution functions obtained from synchrotron X-ray diffraction revealed significant local structural distortions caused by the half-occupied Zn site in this structure type. It is all the more surprising, therefore, to find that Eu2ZnBi2 possesses high electronic mobility (∼100 cm2 V−1 s−1) comparable to that of AM2X2 Zintl compounds. The enormous degree of disorder in this series gives rise to exceptionally low lattice thermal conductivity, which is further reduced by Bi substitution due to the decreased speed of sound. Increasing the Bi content was also found to decrease the band gap while increasing the carrier concentration by two orders of magnitude. Applying a single parabolic band model suggests that Bi-rich compositions of Eu2ZnSb2−xBix have the potential for significantly improved zT; however, further optimization is necessary through reduction of the carrier concentration to realize high zT.
Thermoelectric materials are a unique class of compounds that can recycle energy through conversion of heat into electrical energy. A new 21–4–18 Zintl phase has been discovered in the Yb–Mn–Sb ...system with high performance in the mid-to-high temperature regime. The efficiency of the Yb21Mn4Sb18 results mainly from its large Seebeck coefficient (∼290 μV K–1 at 650 K) and extremely low thermal conductivity (∼0.4 W m–1 K–1). The complex crystal structure has been studied through single crystal X-ray diffraction, synchrotron powder X-ray diffraction, and pair distribution function (PDF) analysis using time-of-flight neutron diffraction revealing positional disorder on several sites. Electronic structure calculations of the band structure and the partial spin-density of states reveal that states near the Fermi level are contributed mostly by the Mn and Sb atoms that participate in the Mn4Sb1022– motif of the structure. The band structure confirms the p-type semiconducting nature of this material. The optimization of the hole carrier concentration was tuned according to a single parabolic band model through Na doping on the Yb site (Yb21–x Na x Mn4Sb18, x = 0, 0.2, 0.4) showing an improvement in zT over the whole temperature range. A maximum zT ≈ 0.8 at 800 K is obtained for the x = 0.4 sample and increases the ZTavg from 0.34 to 0.49 (over the entire temperature range) compared to the undoped sample.
The Zintl compound Eu
2
ZnSb
2
was recently shown to have a promising thermoelectric figure of merit,
zT
∼ 1 at 823 K, due to its low lattice thermal conductivity and high electronic mobility. In the ...current study, we show that further increases to the electronic mobility and simultaneous reductions to the lattice thermal conductivity can be achieved by isovalent alloying with Bi on the Sb site in the Eu
2
ZnSb
2−
x
Bi
x
series (
x
= 0, 0.25, 1, 2). Upon alloying with Bi, the effective mass decreases and the mobility linearly increases, showing no signs of reduction due to alloy scattering. Analysis of the pair distribution functions obtained from synchrotron X-ray diffraction revealed significant local structural distortions caused by the half-occupied Zn site in this structure type. It is all the more surprising, therefore, to find that Eu
2
ZnBi
2
possesses high electronic mobility (∼100 cm
2
V
−1
s
−1
) comparable to that of AM
2
X
2
Zintl compounds. The enormous degree of disorder in this series gives rise to exceptionally low lattice thermal conductivity, which is further reduced by Bi substitution due to the decreased speed of sound. Increasing the Bi content was also found to decrease the band gap while increasing the carrier concentration by two orders of magnitude. Applying a single parabolic band model suggests that Bi-rich compositions of Eu
2
ZnSb
2−
x
Bi
x
have the potential for significantly improved
zT
; however, further optimization is necessary through reduction of the carrier concentration to realize high
zT
.
Alloying Eu
2
ZnSb
2
with Bi on the Sb site leads to an increase in mobility while still lowering the lattice thermal conductivity.
The Zintl compound Eu 2 ZnSb 2 was recently shown to have a promising thermoelectric figure of merit, zT ∼ 1 at 823 K, due to its low lattice thermal conductivity and high electronic mobility. In the ...current study, we show that further increases to the electronic mobility and simultaneous reductions to the lattice thermal conductivity can be achieved by isovalent alloying with Bi on the Sb site in the Eu 2 ZnSb 2−x Bi x series ( x = 0, 0.25, 1, 2). Upon alloying with Bi, the effective mass decreases and the mobility linearly increases, showing no signs of reduction due to alloy scattering. Analysis of the pair distribution functions obtained from synchrotron X-ray diffraction revealed significant local structural distortions caused by the half-occupied Zn site in this structure type. It is all the more surprising, therefore, to find that Eu 2 ZnBi 2 possesses high electronic mobility (∼100 cm 2 V −1 s −1 ) comparable to that of AM 2 X 2 Zintl compounds. The enormous degree of disorder in this series gives rise to exceptionally low lattice thermal conductivity, which is further reduced by Bi substitution due to the decreased speed of sound. Increasing the Bi content was also found to decrease the band gap while increasing the carrier concentration by two orders of magnitude. Applying a single parabolic band model suggests that Bi-rich compositions of Eu 2 ZnSb 2−x Bi x have the potential for significantly improved zT ; however, further optimization is necessary through reduction of the carrier concentration to realize high zT .
The majority of nanotechnology-related research at the CSCU-CNT at Southern Connecticut State University involves depositing thin films of controlled thicknesses using a thermal physical vapor ...deposition method. The thermal evaporative method, however, is limited to the deposition of single transition metals with low melting points. This project greatly expands the scope of available materials for deposition through the development and implementation of a pulsed-laser deposition technique. A solid state, Nd:YAG, Q-switched laser from 1989 was restored and aligned, and a 3-dimensional CAD model of the high vacuum chamber was produced to aid in the configuration of the system. The power output of the laser beam was monitored using a digital intensity readout; the beam reached a maximum power of 2 Watts. Three target elements were selected for deposition onto a Silicon substrate in order to test the efficiency of the system. Copper, Iron, and Tantalum samples were exposed to the beam under vacuum for 5 minutes. The Silicon substrates were imaged under a scanning electron microscope. The images demonstrate successful depositions. This development has greatly widened the scope of materials available for thin film deposition, subsequently impacting future research at the CSCU-CNT in the field of nanotechnology.
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