Blend Structure and n-Type Thermoelectric Performance of PA6/SAN and PA6/PMMA Blends Filled with Singlewalled Carbon Nanotubes

The present study investigates how the formation of melt-mixed immiscible blends based on PA6/SAN and PA6/PMMA filled with single walled nanotubes (SWCNTs) affects the thermoelectric (TE) properties. In addition to the detailed investigation of the blend morphology with compositions between 100/0 wt.% and 50/50 wt.%, the thermoelectric properties are investigated on blends with different SWCNT concentrations (0.25–3.0 wt.%). Both PA6 and the blend composites with the used type of SWCNTs showed negative Seebeck coefficients. It was shown that the PA6 matrix polymer, in which the SWCNTs are localized, mainly influenced the thermoelectric properties of blends with high SWCNT contents. By varying the blend composition, an increase in the absolute Seebeck coefficient, power factor (PF), and figure of merit (ZT) was achieved compared to the PA6 composite which is mainly related to the selective localization and enrichment of SWCNTs in the PA6 matrix at constant SWCNT loading. The maximum PFs achieved were 0.22 µW/m·K2 for PA6/SAN/SWCNT 70/30/3 wt.% and 0.13 µW/m·K2 for PA6/PMMA/SWCNT 60/40/3 wt.% compared to 0.09 µW/m·K2 for PA6/3 wt.% SWCNT which represent increases to 244% and 144%, respectively. At higher PMMA or SAN concentration, the change from matrix-droplet to a co-continuous morphology started, which, despite higher SWCNT enrichment in the PA6 matrix, disturbed the electrical conductivity, resulting in reduced PFs with still increasing Seebeck coefficients. At SWCNT contents between 0.5 and 3 wt.% the increase in the absolute Seebeck coefficient was compensated by lower electrical conductivity resulting in lower PF and ZT as compared to the PA6 composites.

Nanometrology: Absolute Seebeck coefficient of individual silver nanowires

Thermoelectric phenomena can be strongly modified in nanomaterials. The determination of the absolute Seebeck coefficient is a major challenge for metrology with respect to micro- and nanostructures due to the fact that the transport properties of the bulk material are no more valid. Here, we demonstrate a method to determine the absolute Seebeck coefficient S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, we show the influence of nanopatterning on S in the temperature range between 16 K and 300 K. At room temperature, a nanowire diameter below 200 nm suppresses S by 50% compared to the bulk material to less than S = 1 μVK−1, which is attributed to the reduced electron mean free path. The temperature dependence of the absolute Seebeck coefficient depends on size effects. Thermodiffusion and phonon drag are reduced with respect to the bulk material and the ratio of electron-phonon to phonon-phonon interaction is significantly increased.

Influence of Ag on the Properties of Ca0.9Yb0.1MnO3 Sintered Ceramics

In this study, Ca0.9Yb0.1MnO3 + x wt.% Ag (with x = 0, 1, 3, 5, and 10) thermoelectric materials were prepared via the classical ceramic method. In spite of the very high sintering temperature (1300 °C), no significant Ag losses were observed following this process. Moreover, Ag addition enhanced cation mobility during sintering due to the formation of a liquid phase. Microstructurally, it was found that Ag decreases porosity; this was confirmed by density measurements. Ag was also found to promote the formation of a Ca2Mn2O5 secondary phase. Despite the presence of this secondary phase, samples with Ag displayed lower electrical resistivity than Ag-free ones, without a drastic decrease in the absolute Seebeck coefficient. The highest thermoelectric performances, which were determined by power factor, were obtained in 1 wt.% Ag samples. These maximum values are slightly higher than the best of those reported in the literature for sintered materials with similar compositions, with the additional advantage of their being obtained using a much shorter sintering procedure.

Improved Thomson Coefficient Measurements Using an AC Method

ABSTRACTWe present an improved AC (Alternating Current) method for the determination of the Thomson coefficient, which can be used for obtaining the absolute Seebeck coefficient. While previous work has focused on DC (Direct Current) methods, we analyze the influence of an AC current in order to derive the Thomson coefficient of a thin wire from measurable quantities. Our expression requires five parameters including AC current, resistance, temperature gradient, and the temperature changes due to the Thomson and Joule effects. Thus, a prior determination of thermal conductivity and sample geometry is not required, unlike DC methods. In order to validate our analysis, the Thomson coefficient of a thin Pt wire has been measured at several frequencies. The results agree with those obtained from a conventional DC method.

Fabrication and Thermoelectric Properties of Al-Doped (ZnO)5In2O3 by Microwave Heating

Various (ZnO)5In2O3ceramics were fabricated by microwave heating. Density, XRD pattern and microstructure were examined and those of Al-doped (ZnO)5In2O3were almost the same as Al-free one. Highly textured (ZnO)5In2O3ceramic was also fabricated by reactive templated grain growth (RTGG) method. The electrical conductivity was not improved by Al-doping; however it was improved slightly by microwave heating compared with conventional heating and especially improved by texturing using RTGG method. On the other hand, the absolute Seebeck coefficient in microwave heating was improved about 25% by Al-doped. Maximum electric power factor of textured specimen fabricated by RTGG method along ab-plane showed 5.76×10-4WK-2m-1(at 873K), which was attributed to high electrical conductivity.

High-temperature thermoelectric properties of W-substituted CaMnO3

The thermoelectric properties of W-substituted CaMn1-xWxO3-δ (x = 0.01, 0.03; 0.05) samples, prepared by soft chemistry, were investigated from 300 K to 1000 K and compared to Nb-substituted CaMn0.98Nb0.02O3-δ. All compositions exhibit both an increase in absolute Seebeck coefficient and electrical resistivity with temperature. Moreover, compared to the Nb-substituted sample, the thermal conductivity of the W-substituted samples was strongly reduced. This reduction is attributed to the nearly two times greater mass of tungsten. Consequently, a ZT of 0.19 was found in CaMn0.97W0.03O3-δ at 1000 K, which was larger than ZT exhibited by the 2% Nb-doped sample.