Many IV-VI semiconductors tend to be good thermoelectric materials, these include all Pb chalcogenides as well as Pb-free SnTe: all of which crystallize in a NaCl cubic structure. Another group of IV-VI compounds form layered orthorhombic structures. SnSe is one of these compounds, whose transport properties as a polycrystalline thermoelectric material have rarely been studied. Here we present our study of p-type polycrystalline SnSe doped with Ag, prepared by melting and hot pressing. SnSe has anisotropic properties with hysteresis observed in resistivity between 300 and 650 K regardless of doping. Ag is not an ideal dopant but is able to increase the carrier density significantly, as a result a peak zT of 0.6 was observed at 750 K. Transport properties of doped SnSe can be explained with a single parabolic band model, which suggests promising potential for this compound together with its challenges.

Most patients with adult intussusception in our series were men, and most intussusceptions were benign and of enteric origin. The most sensitive diagnostic modality is abdominal CT scan. Operative reduction is recommended for enteric intussusceptions but not for colonic intussusceptions. The prognosis of adult intussusception after surgery is good except for malignant intussusception.

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We report a rational method for preparation of ternary alloy (PtNiFe) nanocrystals with various shapes. PtNiFe nanocubes, polyhedrons, and octahedrons are prepared via fine-tuning the alloy compositions and surfactants, so that the crystal facet−surfactant bindings on the growth seed can be well controlled. Nanowires grow in the cylindrical template built via high concentrations of oleylamine. In the electrocatalysis examination, it appears that the oxygen reduction reaction (ORR) activities of all PtNiFe nanostructures outperform that of commercial Pt catalyst in the electrolyte of HClO 4 or H 2 SO 4 . In HClO 4 , the order of ORR activity is as follows: octahedrons ≈ nanowires > polyhedrons > nanocubes. PtNiFe nanostructures enclosed by a (111) plane, such as octahedrons and nanowires, give the highest ORR activities. Conversely, in H 2 SO 4 , the ORR activity of PtNiFe nanocubes enclosed by {100} facets is the highest among these nanostructures. The ORR activity increases in the order of nanowires ≈ octahedrons < polyhedrons, establishing a shape dependency in the ORR activity, which is valuable upon performing nanocatalysis in fuel cells.

Single-crystalline SnSe has attracted much attention because of its record high figure-of-merit ZT ≈ 2.6; however, this high ZT has been associated with the low mass density of samples which leaves the intrinsic ZT of fully dense pristine SnSe in question. To this end, we prepared high-quality fully dense SnSe single crystals and performed detailed structural, electrical, and thermal transport measurements over a wide temperature range along the major crystallographic directions. Our single crystals were fully dense and of high purity as confirmed via high statistics 119 Sn Mössbauer spectroscopy that revealed <0.35 at. % Sn(IV) in pristine SnSe. The temperature-dependent heat capacity ( C p ) provided evidence for the displacive second-order phase transition from Pnma to Cmcm phase at T c ≈ 800 K and a small but finite Sommerfeld coefficient γ 0 which implied the presence of a finite Fermi surface. Interestingly, despite its strongly temperature-dependent band gap inferred from density functional theory calculations, SnSe behaves like a low-carrier-concentration multiband metal below 600 K, above which it exhibits a semiconducting behavior. Notably, our high-quality single-crystalline SnSe exhibits a thermoelectric figure-of-merit ZT ∼1.0, ∼0.8, and ∼0.25 at 850 K along the b , c , and a directions, respectively.

The potential of exploiting the spin of the electron (in addition to its charge) in novel new electronic devices and the associated opportunities for new science has led to extensive search for viable magnetic semiconductors with room temperature ferromagnetism (RTFM). [1][2][3] Some success for ferromagnetism has been reported in dilute magnetic semiconductors (DMS) and dilute magnetic oxides (DMO) containing a few percent of transition metal ions such as (Ga,Mn)As, [4,5] (Zn,M)O [6][7][8][9] , and (Ti,M)O 2 [10][11][12] with M ¼ V,Cr, Mn, Co, Ni, and Cu. Despite the numerous reports on the successful observation of room temperature ferromagnetism (RTFM) in a number of these systems in apparent agreement with computations based on density functional theory, the issue remains unsettled and contentious for a number of reasons including lingering doubt of the possible role of undetected ferromagnetic impurities such as Fe, Co, and Ni. In some systems such as (Zn,Ni)O [13] and (Zn,Cr)Te [14] the observed RTFM has been linked to clustering of Ni and Cr nanocrystals, respectively. In this paper, we report the observation of RTFM in CdSe quantum dots (QD) capped with TOPO (tri-n-octylphosphine oxide). This RTFM is labeled as ex-nihilo since the RTFM is due to the marriage of two diamagnetic materials viz. CdSe and TOPO, possibly resulting from charge transfer from Cd d-band to the oxygen atoms of TOPO. We further show that the RTFM varies inversely with the size of the QD, in agreement with our calculations.CdSe is a II-VI semiconductor with direct band gap E g ¼ 1.74 eV at 300 K. Semiconductors nanocrystals (NCs) such as CdSe are often called quantum dots (QD) when the size of the first Bohr radius exceeds the crystallite size D, leading to quantum confinement effects such as increase in the band-gap E g with decrease in D. For the CdSe NCs, E g can be tuned to cover the whole visible range by change in D, thus making this system potentially useful for solar energy applications. [15,16] Attempts to dope CdSe with Mn to obtain a magnetic semiconductor have not been successful partly because of the limited solubility of Mn in CdSe. However, Magana et al. have reported superparamagnetism with a blocking temperature T B ' 40 K in thermally annealed Mn/CdSe QD's. [17] As the size of the nanocrystals is decreased, the fraction of atoms on the surface to the total number of atoms in NC increases as 1/D. Since the atoms on the surface experience broken symmetry and often higher anisotropy, new surface states are formed. For the CdSe QDs, a number of interesting optical properties such as band edge luminescence [18] and excitonic radiative decay [19] have been related to the surface states. Since CdSe NCs are often passivated by capping with TOPO (tri-n-octylphosphine oxide) to avoid aggregation and surface oxidation, it is important to understand the effect of TOPO on the surface atoms and on the measured properties. XPS [15] and EXAFS [20] In CdSe QDs, we report here the observation of size-dependent RTFM whose strength, wi...

PbTe is an extremely important thermoelectric (TE) material, due to its high TE conversion efficiency.

In this work, a high thermoelectric figure of merit, zT of 1.9 at 740 K is achieved in Ge 1−x Bi x Te crystals through the concurrent of Seebeck coefficient enhancement and thermal conductivity reduction with Bi dopants. The substitution of Bi for Ge not only compensates the superfluous hole carriers in pristine GeTe but also shifts the Fermi level ( E F ) to an eligible region. Experimentally, with moderate 6–10% Bi dopants, the carrier concentration is drastically decreased from 8.7 × 10 20 cm −3 to 3–5 × 10 20 cm −3 and the Seebeck coefficient is boosted three times to 75 μVK −1 . In the meantime, based on the density functional theory (DFT) calculation, the Fermi level E F starts to intersect with the pudding mold band at L point, where the band effective mass is enhanced. The enhanced Seebeck coefficient effectively compensates the decrease of electrical conductivity and thus successfully maintain the power factor as large as or even superior than that of the pristine GeTe. In addition, the Bi doping significantly reduces both thermal conductivities of carriers and lattices to an extremely low limit of 1.57 W m −1 K −1 at 740 K with 10% Bi dopants, which is an about 63% reduction as compared with that of pristine GeTe. The elevated figure of merit observed in Ge 1−x Bi x Te specimens is therefore realized by synergistically optimizing the power factor and downgrading the thermal conductivity of alloying effect and lattice anharmonicity caused by Bi doping.