is a potential thermoelectric (te) material that can directly convert waste heat into electricity. in this study, Mg 2 Sn single-crystal ingots are prepared by melting under an Ar atmosphere. the prepared ingots contain Mg vacancies (V Mg) as point defects, which results in the formation of two regions: an Mg 2 Sn single-crystal region without V Mg (denoted as the single-crystal region) and a region containing V Mg (denoted as the V Mg region). the V Mg region is embedded in the matrix of the single-crystal region. the interface between the V Mg region and the single-crystal region is semi-coherent, which does not prevent electron carrier conduction but does increase phonon scattering. furthermore, electron carrier concentration depends on the fraction of V Mg , reflecting the acceptor characteristics of V Mg. The maximum figure of merit zT max of 1.4(1) × 10 −2 is realised for the Mg 2 Sn single-crystal ingot by introducing V Mg. these results demonstrate that the te properties of Mg 2 Sn can be optimised via pointdefect engineering.

An electrochemical device is proposed for high-throughput electrochemical detection that consists of 32 row and 32 column electrodes on a single glass substrate. The row and column electrodes are connected to interdigitated array (IDA) electrodes to form 1024 (32 × 32) addressable sensor points in the device. Electrochemical responses from each of the 1024 sensors were successfully acquired on the device within 1 min using redox cycling at individual IDA electrodes, which ensures application of the device to comprehensive, high-throughput electrochemical detection for enzyme-linked immunosorbent assay (ELISA), reporter gene assay for monitoring gene expressions, and DNA analysis.

Mg 2 Sn is a potential thermoelectric (TE) material that exhibits environmental compatibility. In this study, we fabricated Sbdoped Mg 2 Sn (Mg 2 Sn 1−x Sb x ) single-crystal ingots and demonstrated the enhancement of TE performance via point defect engineering and Sb doping. The Mg 2 Sn 1−x Sb x single-crystal ingots exhibited considerably enhanced electrical conductivity because of the donordoping effect in addition to high carrier mobility. Moreover, the Mg 2 Sn 1−x Sb x single-crystal ingots contained Mg vacancy (V Mg ) as a point defect. The introduced V Mg and doped Sb atoms formed nanostructures, both acting as phonon-scattering centers. Consequently, lower lattice thermal conductivity was achieved for the Mg 2 Sn 1−x Sb x single-crystal ingots compared with polycrystalline counterparts. Owing to the significant enhancement in the electrical conductivity and the reduction in the lattice thermal conductivity, the maximum power factor of 5.1(4) × 10 −3 W/(K 2 m) and the maximum dimensionless figure of merit of 0.72(5) were achieved for the Mg 2 Sn 0.99 Sb 0.01 single-crystal ingot, which are higher than those of single-phase Mg 2 Sn 1−x Sb polycrystals.

Mg2Si is a potential thermoelectric (TE) material that can directly convert waste energy into electricity. In expectation of improving its TE performance by increasing electron carrier concentration, the element boron (B) is doped in Mg2Si single crystals (SCs). Their detailed crystal structures are definitely determined by using white neutron holography and single-crystal x-ray diffraction (SC-XRD) measurements. The white neutron holography measurement proves that the doped B atom successfully substitutes for the Mg site. The SC-XRD measurement confirms the B-doping site and also reveals the presence of the defect of Si vacancy (VSi) in the B-doped Mg2Si SCs. The fraction of VSi increases with increasing B-doping concentration. In the case of B-doped Mg2Si polycrystals (PCs), VSi is absent; this difference between the SCs and PCs can be attributed to different preparation temperatures. Regarding TE properties, the electrical conductivity, σ, and the Seebeck coefficient, S, decreases and increases, respectively, due to the decrease in the electron carrier concentration, contrary to the expectation. The power factor of the B-doped Mg2Si SCs evaluated from σ and S does not increase but rather decreases by the B-doping. The tendencies of these TE properties can be explained by considering that the donor effect of the B atom is canceled by the acceptor effect of VSi for the B-doped Mg2Si SCs. This study demonstrates that the preparation condition of Mg2Si should be optimized to prevent the emergence of an unexpected point defect.

Mg 2 Sn is a promising middle-temperature thermoelectric material consisting of earth-abundant, low-cost, and nontoxic elements. To obtain p-type Mg 2 Sn, a series of Mg 2 Sn 1−x Ga x (x = 0, 0.005, 0.01, 0.02, and 0.03) ingots were synthesized by melting them under an Ar atmosphere. It was found that the ingots with x ≤ 0.02 were single crystals with Mg vacancies (V Mg ) as point defects. Ga doping increased chemical pressure, leading to an increase in the V Mg fraction, and it also introduced hole carriers in Mg 2 Sn, which changed its conduction type from n-type to p-type. A maximum zT value of 0.18 at 450 K was obtained for p-type Mg 2 Sn 0.98 Ga 0.02 single crystals, which had a lower total thermal conductivity than some other p-type Mg 2 Sn-based polycrystals.