BiCuSeO oxyselenides are promising thermoelectric materials, yet further thermoelectric figure of merit ZT improvement is largely limited by the inferior electrical transport properties. The established literature on these materials shows only one power factor maximum upon carrier concentration optimization, which is typical for most thermoelectric semiconductors. Surprisingly, we found three power factor maxima when doping Bi with Pb. Based on our first-principles calculations, numerical modeling, and experimental investigation, we attribute the three maxima to the Fermi energy optimization, band convergence, and compositing effect due to in situ formed PbSe precipitates. Consequently, three ZT peaks of 0.9, 1.1, and 1.3 at 873 K are achieved for 4, 10, and 14 at.% Pb-doped samples, respectively, revealing the significance of complex electronic structure and multiple roles of Pb in BiCuSeO. The results establish an accurate band structure characterization for BiCuSeO and identify the role of band convergence and nanoprecipitation as the driving mechanism for high ZT.
(1- x )Ba 0.5 Sr 0.5 TiO 3 - x CaAl 4 O 7 composite ceramics were prepared by solid-phase reaction method. The effects of ion diffusion and composite effects on the microwave dielectric properties of composite ceramics are analyzed in detail. The results show that as the CaAl 4 O 7 content increases, the ion diffusion intensifies, resulting in the weakening of the lattice vibration intensity of the composite ceramics and the weakening of the anharmonic vibration of Ti 4+ . Thus, the Curie peak moves toward low temperature and the tunability of the composite ceramic decreases. In addition, the difference in the influence of monoclinic structure and spinel structure on the tunability of BST ceramics is related to the degree of inhibition of BST grain growth by the two. With the continuous increase of CaAl 4 O 7 content, the composite effects became prominent, which effectively reduced the dielectric permittivity and significantly increasing the Q value of the ceramic sample. When x = 15 wt%, a composite ceramic with good microwave dielectric properties is obtained: ɛ r = 298, Q = 294 (2.953 GHz), and the tunability is 12 % (20 kV/cm).
We demonstrate the utilization of bismuth tungstate (Bi 2 WO 6 , BW) as a sintering aid and reinforcement component into neodymium-doped ceria (Nd 0.2 Ce 0.8 O 3-δ , NDC) to fabricate bismuth tungstate/neodymium-doped ceria composite electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFC). The presence of BW lowers the sintering temperature of NDC electrolyte to 1000 °C. Moreover, at 600 °C, the electrical conductivity of 5 mol.% BW-incorporated NDC (5BW-NDC) composite electrolyte is 7.12 times higher than the NDC. It is worth mentioning that the enhanced electrical conductivity of 5BW-NDC composite electrolyte does not include the contribution from electronic conductivity . Furthermore, NDC and 5BW-NDC exhibit excellent compatibility with La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3-δ cathode and NiO anode in terms of thermal expansion coefficient and chemical reactivity . The oxygen reduction reaction at 5BW-NDC composite electrolyte/cathode interface is significantly enhanced by ∼40% compared to NDC. Moreover, 5BW-NDC electrolyte-supported SOFC delivers a power density of 0.86 W cm −2 at 700 °C, which is 45.76% higher than the NDC-based SOFC. The output performance remains stable during high-temperature operation for 120 h, which indicates the stability and chemical compatibility of the as-synthesized composite electrolyte with other cell components. The results reveal that BW-NDC composite is a potential electrolyte material for stable and high-performance IT-SOFCs.
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