Solubility design leading to high figure of merit in low-cost Ce-CoSb_3 skutterudites

CoSb_3-based filled skutterudite has emerged as one of the most viable candidates for thermoelectric applications in automotive industry. However, the scale-up commercialization of such materials is still a challenge due to the scarcity and cost of constituent elements. Here we study Ce, the most earth abundant and low-cost rare earth element as a single-filling element and demonstrate that, by solubility design using a phase diagram approach, the filling fraction limit (FFL) x in Ce_xCo_4Sb_(12) can be increased more than twice the amount reported previously (x=0.09). This ultra-high FFL (x=0.20) enables the optimization of carrier concentration such that no additional filling elements are needed to produce a state of the art n-type skutterudite material with a zT value of 1.3 at 850 K before nano-structuring. The earth abundance and low cost of Ce would potentially facilitate a widespread application of skutterudites

A combinatorial approach to microstructure and thermopower of bulk thermoelectric materials: the pseudo-ternary PbTe–Ag_2Te–Sb_2Te_3 system

The microstructures and Seebeck coefficients of thermoelectric alloys in the pseudo-ternary PbTe–Ag_2Te–Sb_2Te_3 system were examined using samples that were compositionally graded by unidirectional solidification by the Bridgman method and diffusion couples. At compositions near the middle of the pseudo-binary PbTe–AgSbTe_2 line, a compositionally modulated microstructure has been found. From diffusion couple experiments, it is found that the PbTe–AgSbTe_2 system exhibits a miscibility gap at low temperatures while it forms a complete solid solution at high temperatures; the critical temperature is between 400 °C and 450 °C. The modulated microstructure originates from the decomposition of the high-temperature solid solution during cooling. Scanning Seebeck coefficient measurement on these samples covers a wide compositional space of the pseudo-ternary system. The Seebeck coefficient transitions from positive values at AgSbTe_2-rich compositions to negative values at PbTe-rich compositions on the pseudo-binary PbTe–AgSbTe_2 line. Composition-graded samples prepared by the Bridgman method are thus useful to investigate thermoelectric materials in multi-component systems

Phase diagram of In–Co–Sb system and thermoelectric properties of In-containing skutterudites

In-containing skutterudites have long attracted much attention and debate partly due to the solubility limit issue of indium in CoSb_3. The isothermal section of the equilibrium phase diagram for the In–Co–Sb system at 873 K is proposed using knowledge of the related binary phase diagrams and experimental data, which explains the debated indium solubility that depends on Sb content. In this paper, a series of In-containing skutterudite samples (In_xCo_4Sb_(12−x/3) with x varying from 0.075 to 0.6 and In_(0.3)Co_(4−y)Sb_(11.9+y) with y changing from −0.20 to 0.20) are synthesized and characterized. X-ray analysis and scanning electron microscopy images indicate that, up to x = 0.27, single-phase skutterudites are obtained with lattice constant increasing with In fraction x. A fixed-composition skutterudite In_(0.27±0.01)Co_4Sb_(11.9) was determined for the Co-rich side of In–CoSb_3 which is in coexistence with liquid InSb and CoSb_2. Indium, like Ga, is expected, from DFT calculations, to form compound defects in In-containing skutterudites. However, relatively higher carrier concentrations of In-containing skutterudites compared to Ga-containing skutterudites indicate the existence of not fully charge-compensated compound defects, which can also be explained by DFT calculations. The net n-type carrier concentration that naturally forms from the complex defects is close to the optimum for thermoelectric performance, enabling a maximum zT of 1.2 for the fixed skutterudite composition In_(0.27)Co_4Sb_(11.9) at 750 K

Charge-Compensated Compound Defects in Ga-containing Thermoelectric Skutterudites

Heavy doping changes an intrinsic semiconductor into a metallic conductor by the introduction of impurity states. However, Ga impurities in thermoelectric skutterudite CoSb_3 with lattice voids provides an example to the contrary. Because of dual-site occupancy of the single Ga impurity charge-compensated compound defects are formed. By combining first-principle calculations and experiments, we show that Ga atoms occupy both the void and Sb sites in CoSb_3 and couple with each other. The donated electrons from the void-filling Ga (GaVF) saturate the dangling bonds from the Sb-substitutional Ga (Ga_(Sb)). The stabilization of Ga impurity as a compound defect extends the region of skutterudite phase stability toward Ga_(0.15)Co_4Sb_(11.95) whereas the solid–solution region in other directions of the ternary phase diagram is much smaller. A proposed ternary phase diagram for Ga-Co-Sb is given. This compensated defect complex leads to a nearly intrinsic semiconductor with heavy Ga doping in CoSb_3 and a much reduced lattice thermal conductivity (κ_L) which can also be attributed to the effective scattering of both the low- and high-frequency lattice phonons by the dual-site occupant Ga impurities. Such a system maintains a low carrier concentration and therefore high thermopower, and the thermoelectric figure of merit quickly increases to 0.7 at a Ga doping content as low as 0.1 per Co_4Sb_(12) and low carrier concentrations on the order of 10^(19) cm^(−3)

An expert consensus for the management of chronic hepatitis B in Asian Americans.

BACKGROUND: Hepatitis B virus (HBV) infection is common with major clinical consequences. In Asian Americans, the HBsAg carrier rate ranges from 2% to 16% which approximates the rates from their countries of origin. Similarly, HBV is the most important cause of cirrhosis, hepatocellular carcinoma (HCC) and liver related deaths in HBsAg positive Asians worldwide. AIM: To generate recommendations for the management of Asian Americans infected with HBV. METHODS: These guidelines are based on relevant data derived from medical reports on HBV from Asian countries as well as from studies in the HBsAg positive Asian Americans. The guidelines herein differ from other recommendations in the treatment of both HBeAg positive and negative chronic hepatitis B (CHB), in the approach to HCC surveillance, and in the management of HBV in pregnant women. RESULTS: Asian American patients, HBeAg positive or negative, with HBV DNA levels \u3e2000 IU/mL (\u3e10 CONCLUSIONS: Application of the recommendations made based on a review of the relevant literature and the opinion of a panel of Asian American physicians with expertise in HBV treatment will inform physicians and improve patient outcomes