Doped BiCuSeO is one of the promising thermoelectric oxide candidates. However, the research on doping effects on the electrical transport properties of BiCuSeO, especially in crystalline samples, is still limited. Here, we studied the transport properties of doped BiCuSeO crystals, including three types of doping species (Rb, Sn, and Co) with varying concentrations. In the case of Rb-doped BiCuSeO crystals, few percentage (≤1%) Rb-doping make BiCuSeO display metallic behavior, while high one (≥2%) displays bad-metallic behavior. Both Sn- and Co-doped BiCuSeO crystals have similar electrical evolution as Rb-doped ones. The charge carriers of all these doped BiCuSeO crystals are holes, and the increased dopant concentration decreases the hole concentrations regardless of the type of dopant species. There is negative magnetoresistance (MR) in Rb- and Sn-doped BiCuSeO at low temperature (<15 K), which is due to the breakdown of weak localization by magnetic field B, but the MR behaviors in Co-doped BiCuSeO crystals are strongly correlated with their magnetic properties. The analysis of the temperature-dependent mobility of these doped BiCuSeO crystals substantiates that at low temperatures (<50 K), electron-impurity scattering dominates, while electron–phonon scattering dominates at high temperatures (>50 K). The evolution of the above-mentioned electrical/magneto-transport properties of doped BiCuSeO can be understood as follows: the dopant compensates the Bi-deficiency in pristine BiCuSeO crystals and decreases the hole concentration and leads to the metal–Anderson-insulator transition. These results may be valuable to optimize the electrical properties of layered compounds similar to BiCuSeO.
The CuCrSe2 shows attractive physical properties, such as thermoelectric and multiferroic properties, but pure-phase CuCrSe2 crystal is still quite challenging to obtain because CuCr2Se4 can be easily precipitated from a CuCrSe2 matrix. Here, taking the advantage of this precipitation reaction, we grew a series of CuCrSe2-CuCr2Se4 hetero-composites by adjusting growth parameters and explored their thermal conductivity property. Determined by electron-diffraction, the orientation relationship between these two compounds is [001] (100) CuCrSe2‖[111] (220) CuCr2Se4. The out-of-plane thermal conductivity κ of these hetero-composites was measured by a time-domain thermo-reflectance method. Fitting experimental κ by the Boltzmann-Callaway model, we verify that interface scattering plays significant role to κ in CuCrSe2-CuCr2Se4 hetero-composites, while in a CuCrSe2-dominated hetero-composite, both interface scattering and anharmonic three-phonon interaction lead to the lowest κ therein. Our results reveal the thermal conductivity evolution in CuCr2Se4-CuCrSe2 hetero-composites.
Thermoelectric materials, based on photo-thermoelectric effect (PTE), may be promising in photo-detection because of their self-power, extremely broad-band, and free of cryogenic attachments. Up to now, the performance of PTE is mainly optimized through enhancement of extrinsic absorption such as using optical metamaterials. Instead, we here improve the PTE through materials engineering, accordingly systematically investigated the PTE of both P- and N-type SnSe crystals with different carrier concentrations (1017–1019 cm−3). P-type SnSe has much better photo-thermoelectric performance than the N-type one. Among P-type SnSe, the SnSe crystal with the largest carrier concentration (∼1019 cm−3 at room temperature) demonstrates the highest photo-thermoelectric performance. Analysis by a modified two-temperature model suggests that the key parameter of enhanced PTE is the high electrical conductivity, which leads to large optical absorption and large temperature difference. Our work provides a guideline on how to engineer thermoelectric materials to enhance their photo-thermoelectric performance.
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