Polymers beyond standard optical fibres – fabrication of microstructured polymer optical fibres

This paper reports the overall fabrication process of microstructured polymer optical fibres (mPOFs). mPOF fabrication involves a two‐step process: on the one hand, the design and creation of a preform containing a large‐scale version of the desired fibre and, on the other, the precise heating and drawing of the preform to the final fibre. The preforms are produced either by an improved drilling technique or by capillary stacking. For a correct and accurate drawing of the fibre, a controlled and precise heating unit has to be designed, an issue that will be explained in detail in this work. The quality and optical performance of the final mPOF depends strongly on key factors such as the preform annealing, the accuracy of the technique selected for the creation of the preform structure, the heating stage, as well as on the drawing parameters. All of them are analysed in detail and some drawn mPOFs of interest are reported as well. © 2018 Society of Chemical Industry     

Effect of Cu by Co substitution on Ca3Co4O9 thermoelectric ceramics

Ca₃Co_4?xCu_xO₉ polycrystalline thermoelectric ceramics with small amounts of Cu have been synthesized by the classical solid state method. X-ray diffraction data have shown that all the Cu has been incorporated into the Ca₃Co₄O₉ structure and no Cu-containing secondary phases have been produced. Apparent density measurements have shown that all samples are very similar, with densities around 75 % of the theoretical one. Electrical resistivity decreases when Cu content increases until x = 0.03 while Seebeck coefficient remains practically constant for all samples. The improvement in resistivity leads to higher power factor values than the obtained for the undoped samples.     

Thermoelectric properties in Ca3Co4−xMnxOy ceramics

Ca₃Co_4?xMn_xO_y polycrystalline thermoelectric ceramics with small amounts of Mn have been prepared by the classical solid state method. X-ray diffraction data have shown that Ca₃Co₄O₉ is the major phase, with small amounts of the Ca₃Co₂O₆ one. Moreover, they show that the Mn has been incorporated into these two phases. Electrical resistivity decreases, compared with the values for undoped samples, with Mn content until a minimum for the 0·03 doped ones, increasing for higher Mn substitution. Seebeck coefficient does not change in all the measured temperature range, independently of Mn content. The improvement in electrical resistivity leads ～30% higher power factor values for the 0·03 Mn doped samples than that obtained in the undoped ones. The maximum power factor at 800°C, ～0·28 mW K^?2 m^?1, is close to that obtained in much higher density samples, clearly indicating the good thermoelectric properties of these samples.