Study on the Targeted Improvement Mechanism of the Carrier Concentration and Mobility of BiCuSeO Ceramics

BiCuSeO has great application prospects in thermoelectric power generation and thermoelectric catalysis, but it is limited by its lower thermoelectric performance. Herein, BiCuSeO bulk materials were prepared using a solid-phase reaction method and a ball-milling method combined with spark plasma sintering, and then the thermoelectric properties were improved by synergistically increasing carrier concentration and mobility. Al was adopted to dope into the BiCuSeO matrix, aiming to adjust the carrier mobility through energy band adjustment. The results show that Al doping would widen the bandgap and enhance the carrier mobility of BiCuSeO. After Al doping, the thermoelectric properties of the material are improved in the middle- and high-temperature range. Based on Al doping, Pb is adopted as the doping element to dope BiCuSeO to modify the carrier concentration. The results show that Al/Pb dual doping in the BiCuSeO matrix can increase the carrier concentration under the premise of increasing carrier mobility. Therefore, the electrical conductivity of BiCuSeO can be improved while maintaining a large Seebeck coefficient. The power factor of Al/Pb doping reached ~7.67 μWcm-1K-2 at 873 K. At the same time, the thermal conductivity of all doped samples within the test temperature range maintained a low level (<1.2 Wm-1K-1). Finally, the ZT value of the Al/Pb-doped BiCuSeO reached ~1.14 at 873 K, which is ~2.72 times that of the pure phase, and the thermoelectric properties of the matrix were effectively improved.

Calcitic Prisms of The Giant Seashell Pinna Nobilis Form Light Guide Arrays

The shells of the Pinnidae family are based on a double layer of single-crystal-like calcitic prisms and inner aragonitic nacre, a structure known for its outstanding mechanical performance. However, on the posterior side, shells are missing the nacreous layer, which raises the question of whether there can be any functional role in giving up this mechanical performance. Here, it is demonstrated that the prismatic part of the Pinna nobilis shell exhibits unusual optical properties, whereby each prism acts as an individual optical fiber guiding the ambient light to the inner shell cavity by total internal reflection. This pixelated light channeling enhances both spatial resolution and contrast while reducing angular blurring, an apt combination for acute tracking of a moving object. These findings offer insights into the evolutionary aspects of light-sensing and imaging and demonstrate how an architectured optical system for efficient light-tracking can be based on birefringent ceramics.

Thermal Stability, Optical and Electrical Properties of Substoichiometric Molybdenum Oxide

Substoichiometric molybdenum oxide ceramics have aroused widespread interest owing to their promising optical and electrical performance. In this work, the thermal stability and decomposition mechanism of Mo₉O₂₆ and Mo₄O₁₁ at 700-1000 °C and 700-1100 °C were investigated, respectively. Based on this information, MoO_x (2 < x < 3) bulk ceramics were prepared by spark plasma sintering (SPS). The results show that Mo₉O₂₆ is stable up to 790 °C in an argon atmosphere. As the temperature rises, it decomposes into Mo₄O₁₁. Mo₄O₁₁ can exist stably at 830 °C, beyond which it will convert to MoO₂. The MoO_x ceramic bulks with four different components (MoO_2.9, MoO_2.8, MoO_2.7 and MoO_2.6) were successfully sintered by SPS, and their relative density was greater than 96.4% as measured by the Archimedes principle. The reflectivity of MoO_x ceramic bulk is low and only 6.3% when the composition is MoO_2.8. The resistivity increases from 10^-3 to 10^-1 Ωcm with the increase in the O/Mo atomic ratio x. In general, the thermal stability information provides a theoretical basis for the processing of MoO_x materials, such as the sintering of the MoO_x target. The optical and electrical properties show that MoO_x is a low-reflective conductive oxide material with great photoelectric application value.

Formation of Thick Immersion Coatings and Residual Stress Evaluation in the System ZrB2-ZrO2: Experimental and Numerical Investigation

The combination of various oxide ceramics in layered and functionally graded composites allows for the development of novel materials, including for high-temperature applications. This study demonstrates the possibility of obtaining a thick ZrO₂-based coating on a ZrB₂-SiC ceramic substrate by the immersion method. For better wettability, the porous ZrB₂-SiC substrate is treated with cold plasma without changing the structure and phase composition of the surface. Immersion of the substrate in a ZrO₂-based slurry results in the formation of a gradient transition layer due to ZrO₂ particle penetration into the pore volume. The interfacial residual microstresses are evaluated experimentally. The residual macrostresses in the samples are calculated by finite element simulation. It is shown that the thermal residual stresses in the ZrB₂-SiC substrate are compressive and do not exceed 43 MPa. In the ZrO₂ coating and transition layers of the composite, the residual stresses are tensile. Their values increase as they get closer to the outer layer of the ZrO₂ coating and reach 1525 MPa. This confirms the conclusions about the presence of tensile residual stresses made in the experimental part of the work when observing crack propagation in the surface layers during indentation.