Thermoelectric performance in the layered Zintl phase n-type Mg (Sb,Bi) is reported. Insertion of the excess Mg into the compounds is crucial for realizing n-type carrier transport with multivalley and isotropic character. An excellent ZT of 1.51 ± 0.06 at 716 K is achieved in the sintered polycrystals at the composition of Mg Sb Bi Te .

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A number of recent transport and magnetization studies have shown signs of ferromagnetism in the LaAlO 3 /SrTiO 3 heterostructure 1-6 , an unexpected property with no bulk analog in the constituent materials. However, no experiment thus far has provided direct information on the host of the magnetism 7-11 . Here we report spectroscopic investigations of the magnetism using element-specific techniques, including x-ray magnetic circular dichroism and x-ray absorption spectroscopy, along with corresponding model calculations. We find direct evidence for in-plane ferromagnetic order at the interface, with Ti 3+ character in the d xy orbital of the anisotropic t 2g band. These findings establish a striking example of emergent phenomena at oxide interfaces.Recent advances in the atomic-scale synthesis and characterization of perovskite oxide heterostructures have engendered significant interest in their electronic and magnetic structure. SLAC-PUB-15439Division of Materials Sciences and Engineering, under contract DE-AC02-76SF00515 and BES.Given their vast physical properties in bulk form, and their epitaxial compatibility, perovskites provide an ideal arena to explore the competition, interaction, and creation of many ground states at their interfaces 12 . The LaAlO 3 /SrTiO 3 heterostructure is a canonical example, exhibiting interface conductivity 13 , superconductivity 14 , and ferromagnetism 1-6 at the interface between two wide band-gap insulators. From a fundamental perspective, ferromagnetism is perhaps the most important property; although bulk SrTiO 3 can be doped to be metallic and superconducting, neither constituent in bulk form exhibits ferromagnetism. Hence interface ferromagnetism here could be a leading example of truly emergent phenomena. Most previous studies used bulk probes (macroscopic magnetization or torque) 3, 4 ; while scanning SQUID microscopy could localize the magnetism to the near surface region 5, 15 , the specific location where the moments reside is beyond the resolution of the probe. In principle, magnetism could arise from cation/anion defects in the LaAlO 3 or SrTiO 3 , or could be specific to the interface; theoretical scenarios have been proposed for all of these mechanisms 7-11 . Thus it is of central importance to determine the microscopic nature of the observed ferromagnetism.To address this issue, we applied element-specific techniques at the LaAlO 3 /SrTiO 3 (001) interface, namely synchrotron radiation based x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) (see Materials and Methods section). These measurements can uniquely determine whether the observed magnetization is due to a magnetic moment ( ) from one of the constituent elements, or from extrinsic impurities. All spectra were acquired by recording the total electron yield (TEY). Since the maximum probing depth of TEY is approximately 5~10 nm, these measurements are very sensitive to the interface with proper choice of LaAlO 3 thickness. Using the angle dependence of the XMCD signal, whic...

These authors contributed equally to this work.The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO 3 (LAO) and TiO 2 -terminated SrTiO 3 (STO) 1,2 . Transport and other measurements in this system display a plethora of diverse physical phenomena 3-14 . To better understand the interface conductivity, we used scanning superconducting quantum interference device (SQUID) microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in highly conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed upon thermal cycling above the STO cubic to tetragonal structural transition temperature, implying that local conductivity is strongly modified by STO tetragonal domain

In LaAlo 3 /srTio 3 heterointerfaces, charge carriers migrate from the LaAlo 3 to the interface in an electronic reconstruction. magnetism has been observed in LaAlo 3 /srTio 3 , but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlo 3 thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.

We demonstrated the metal-organic framework bearing the azide group in the organic linkers and in situ click reactions with some small alkynes. The XRPD patterns indicated that the click reaction proceeded without any decomposition of the original MOF network. Controlling the organic linkers and incorporation of the azide groups should provide the designer-made MOFs that have controlled molecular cavities with the desired steric dimensions and functionality.

The interface between the insulating oxides LaAlO 3 and SrTiO 3 exhibits a superconducting two-dimensional electron system that can be modulated by a gate voltage. While the conductivity has been probed extensively and gating of the superconducting critical temperature has been demonstrated, the question as to whether, and if so how, the gate tunes the superfluid density and superconducting order parameter needs to be answered. We present local magnetic susceptibility, related to the superfluid density, as a function of temperature, gate voltage, and location. We show that the temperature dependence of the superfluid density at different gate voltages collapses to a single curve that is characteristic of a full superconducting gap. Further, we show that the dipole moments observed in this system are not modulated by the gate voltage.

Zintl compound n-type Mg 3 (Sb,Bi) 2 was recently found to exhibit excellent thermoelectric figure of merit zT ($1.5 at around 700 K). To improve the thermoelectric performance in the whole temperature range of operation from room temperature to 720 K, we investigated how the grain size of sintered samples influences electronic and thermal transport. By increasing the average grain size from 1.0 lm to 7.8 lm, the Hall mobility below 500 K was significantly improved, possibly due to suppression of grain boundary scattering. We also confirmed that the thermal conductivity did not change by increasing the grain size. Consequently, the sample with larger grains exhibited enhanced average zT. The calculated efficiency of thermoelectric power generation reaches 14.5% (DT ¼ 420 K), which is quite high for a polycrystalline pristine material.