Tuning of dimensionless figure of merit via boundary scattering in In 2 O 3-δ

International audienceIn this paper, the dimensionless figure of merit (ZT) is optimized using the scattering in nanocrystals (NCs) of Zr-doped In2O3-δ. The effect of boundary scattering on the thermoelectric properties of the NCs was analyzed using the Boltzmann transport equation and Debye-Callaway model. A ZT map computed based on these theories determined the optimum material parameters to improve the transport properties of the NCs. A theoretically predicted enhancement in ZT of ∼40% can be reproduced experimentally, indicating that engineering of ZT using NCs is promising

Tuning of dimensionless figure of merit via boundary scattering in In 2 O 3-δ

International audienceIn this paper, the dimensionless figure of merit (ZT) is optimized using the scattering in nanocrystals (NCs) of Zr-doped In2O3-δ. The effect of boundary scattering on the thermoelectric properties of the NCs was analyzed using the Boltzmann transport equation and Debye-Callaway model. A ZT map computed based on these theories determined the optimum material parameters to improve the transport properties of the NCs. A theoretically predicted enhancement in ZT of ∼40% can be reproduced experimentally, indicating that engineering of ZT using NCs is promising

Element Strategy Using Ru-Mn Substitution in CuO-CaCu3Ru4O12 Composite Ceramics with High Electrical Conductivity

CaCu3Ru4−xMnxO12 bulks with various substitution amounts x and sintering additive CuO (20 vol.%) were prepared, and the influence of x on the electrical conductivity in a wide temperature range (8–900 K) was investigated. Microstructural observations showed an enhancement of bulk densification upon Mn substitution. Although the resistivity increased with increasing x, the resistivity was as low as a few mΩcm even in the sample with x = 2.00, where half of Ru is substituted by Mn. This high conductivity despite the loss of Ru 4d conduction following the substitution is explained by the A-site (Cu2+) conduction in CaCu3Ru4−xMnxO12. The thermopower of CaCu3Ru4−xMnxO12 was found to be influenced by the substitution, and a sign inversion was observed in the substituted samples at low temperature. The partial substitution of Ru by Mn in CaCu3Ru4O12 enables the reduction of the materials cost while maintaining good electrical conductivity for applications as a conducting device component

Peculiar effects of microwave sintering on ZnO based varistors properties

International audienc

Peculiar effects of microwave sintering on ZnO based varistors properties

International audienceNon-ohmic properties of doped zinc oxide are widely used in varistors applications. It is well established that final properties of the component are strongly correlated with reactivity of the added phases during sintering process and with final microstructure. In this paper, the specific effects of the hybrid single-mode microwave sintering process on the microstructure and electrical properties of a ZnO-based composition are investigated. Nano-sized ZnO-based powder with a proper amount of Bi2O3, Sb2O3, CoO and MnO is synthesized by a liquid route and is sintered within a short time (less than 10 min) in a conventional (CV) or by an hybrid single-mode microwave (MW) furnaces. Distinct differences can be seen in the density, reaction kinetics and dopant diffusivity: higher kinetics of MW leads to denser pellet, faster reaction among dopants and faster diffusion of cobalt and manganese into ZnO grains although grain sizes are almost identical between CV and MW. These differences in terms of chemistry and microstructure lead to sharp contrasts in electrical properties

Trial of an All-Ceramic SnO2 Gas Sensor Equipped with CaCu3Ru4O12 Heater and Electrode

We have constructed a gas sensor of SnO2 equipped with ceramic electrodes and a heater made of CaCu3Ru4O12, which demonstrated good device performance at high temperature. The CaCu3Ru4O12-based electrodes and heater were formed on Al2O3 substrates using a screen-printing process, which is cost-effective and suitable for mass-production. This all-ceramic device reached 600 °C at the lowest, and remained intact after one week of operation at 500 °C and rapid thermal cycling of 500 °C temperature changes within 10 s. We propose CaCu3Ru4O12 as a robust and reliable conducting material that can be a substitute for Pt in various devices

Co-Substitution Effect in Room-Temperature Ferromagnetic Oxide Sr3.1Y0.9Co4O10.5

We investigated the Co substitution effect for the magnetic properties in room-temperature ferromagnetic oxide Sr3.1Y0.9Co4O10.5. The substituted element (Al and Ga) and low-spin state Co3+, which was changed from a high-spin or intermediate-spin state by Al or Ga substitution, reduced the Curie temperature to even 1.5 times lower than the temperature estimated from a simple dilution effect. Al3+ preferentially substituted for intermediate-spin-state Co3+ in the ferrimagnetic CoO6 layer and deteriorated the saturation magnetization of Sr3.1Y0.9Co4O10.5. By contrast, Ga3+ substituted for high-spin-state Co3+ in the CoO6 layer and/or the antiferromagnetic CoO4.25 layer and enhanced the saturation magnetization per Co ion. These results indicate that the magnetic properties of Sr3.1Y0.9Co4O10.5 can be controlled by selectively substituting for Co3+ with different spin states