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To investigate the possibility of p-type doping of α-SrSi2, a promising as an eco-friendly thermoelectric material, the energy changes of substitutions of the Si site of α-SrSi2 by group 13 elements were evaluated using first-principles calculations. It is found that Ga doping was the most energetically favorable dopant while In is the most unfavorable. We examined the synthesis of Ga- and In-doped α-SrSi2 using the vertical Bridgeman method and investigated their thermoelectric properties. The Ga atoms were doped to α-SrSi2 successfully up to 1.0 at. %, while In atoms could not be doped as suggested by calculations. For experimental prepared Ga-doped samples, the carrier density was observed to increase with Ga doping, from 3.58 × 1019 cm−3 for undoped α-SrSi2 to 4.49 × 1020 cm−3 for a 1.0 at. % Ga-doped sample at 300 K. The temperature dependence of carrier concentrations was observed to change from negative to positive with increasing Ga content. In addition, the temperature dependence of the Seebeck coefficient was also observed to change from negative to positive with increasing Ga content. The results indicate that α-SrSi2 undergoes a semiconductor–metal transition with Ga doping. The power factor for the undoped sample was quite high, at 2.5 mW/mK2, while the sample with 0.3 at. % Ga had a value of 1.1 mW/mK2 at room temperature. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the clinical utility of the Gore Excluder iliac branch endoprosthesis (IBE) for Japanese patients with aortoiliac aneurysms. Materials and Methods: This was a multicenter retrospective cohort study (J-Preserve Registry). Patients undergoing endovascular aortic repair using the Gore Excluder IBE for aortoiliac aneurysms between August 2017 and June 2020 were enrolled. Data pertaining to the baseline and anatomical characteristics, technical details, and clinical outcomes were collected from each institution. The primary endpoints were technical success, IBE-related complications, and reinterventions. Secondary endpoints were mortality, aneurysm size change, and reintervention during follow-up. Technical success was defined as accurate deployment of the IBE without type Ib, Ic, or III endoleaks on the IBE sides on completion angiography. A change in aneurysm size of 5 mm or more was taken to be a significant change. Results: We included 141 patients with 151 IBE implantations. Sixty-five IBE implantations (43.0%) had at least one instruction for use violation. Twenty-two patients (15.6%) required internal iliac artery (IIA) embolization for external iliac artery extension on the contralateral side. Of 151 IBE implantations, 19 exhibited IIA branch landing zones due to IIA aneurysms. Mean maximum and proximal common iliac artery (CIA) diameters were 32.9±9.9 mm and 20.5±6.9 mm, respectively. The mean CIA length was 59.1±17.1 mm. The IIA landing diameter and length were 9.0±2.3 mm and 33.8±14.6 mm. The overall technical success rate was 96.7%. There were no significant differences in IBE-related complications (2.3% vs 5.3%, p =0.86) or IBE-related reinterventions (1.5% vs 5.3%, p =0.33) between the IIA trunk and IIA branch landing groups. The mean follow-up period was 635±341 days. The all-cause mortality rate was 5.0%. There were no aneurysm-related deaths or ruptures during the follow-up. Most patients (95.7%) had sac stability or shrinkage. Conclusion: The Gore Excluder IBE was safe and effective for Japanese patients in the midterm. Extending the IIA device into the distal branches of the IIA was acceptable, which may permit extending indications for endovascular aortic aneurysm repair of aortoiliac aneurysms to more complex lesions. Clinical Impact: This study suggests clinical benefits of the Gore Excluder IBE for Japanese patients, despite 43% of the IBE implantations having at least one IFU violation. [ABSTRACT FROM AUTHOR]

Interest in thermoelectric (TE) materials has revived in recent years because TE materials realize not only the utilization of distributed unused thermal energy, such as exhaust heat from automobiles and factories and solar heat, but also cold power generators and self-power supplies for wireless sensors. However, because the bandgap of low-temperature TE materials is relatively small, the precise calculation of its physical properties is difficult to achieve by first-principles calculations based on conventional density functional theory. The present study investigates the effects of isotropic strain and incorporation of isoelectronic impurities on the TE transport properties of extremely narrow-gap semiconducting α-SrSi2. By adopting the Gaussian–Perdew–Burke–Ernzerhof hybrid functional, the analysis clarifies the relationship between the lattice distortion and the electronic structure in α-Sr4–xAxBySi8–y (A = Mg, Ca, or Ba; B = C, Ge, Sn, or Pb) and elucidates the TE transport properties. In particular, an irregular bandgap expansion was observed in α-Sr4CSi7, suggesting that the TE performance can be maximized by appropriate tuning of the carrier concentration. [ABSTRACT FROM AUTHOR]

Thermoelectric power generation in the low temperature region has attracted considerable attention as a means of the effective use of distributed energy and for sensor applications. However, it is difficult to theoretically predict the exact thermoelectric transport properties owing to the relatively narrow bandgap of low temperature thermoelectric materials. In this study, a high-purity α-SrSi2 crystal was synthesized by the vertical Bridgman (VB) method. The carrier density of the VB-grown α-SrSi2 was investigated, and, from the temperature dependence of the carrier density, it was estimated that the bandgap was 13.1 meV. First-principles calculations using the Heyd–Scuseria–Ernzerhof screened hybrid functional for α-SrSi2 predicted the bandgap to be very close to this value (13.27 meV) when assuming the mixing parameter of the Hartree–Fock contribution to the exact exchange is 18.7%. Using the calculated electronic structure and the measured carrier concentration, the predicted temperature dependence of the Seebeck coefficient was in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]