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This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca 3 Co 4 O 9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components, encouraged by our recent promising results obtained for similar cobalt additions. Iron and nickel were chosen because of their similarities with cobalt. The maximum power factor value of around 200 μWm -1 K -2 at 925 K was achieved for the composite with the nominal nickel content of 3% vol., processed via the two-step sintering cycle, which provides the highest densification from this work. The effectiveness of the proposed approach was shown to be strongly dependent on the processing conditions and added amounts of metallic particles. Although the conventional one-step approach results in Fe- and Ni-containing composites with the major content of the thermoelectric Ca 3 Co 4 O 9 phase, their electrical performance was found to be significantly lower than for the Co-containing analogue, due to the presence of less-conducting phases and excessive porosity. In contrast, the relatively high performance of the composite with a nominal nickel content of 3% vol. processed via a two-step approach is related to the specific microstructural features from this sample, including minimal porosity and the presence of the Ca 2 Co 2 O 5 phase, which partially compensate the complete decomposition of the Ca 3 Co 4 O 9 matrix. The obtained results demonstrate different pathways to tailor the phase composition of Ca 3 Co 4 O 9 -based materials, with a corresponding impact on the thermoelectric performance, and highlight the necessity of more controllable approaches for the phase composition tuning, including lower amounts and different morphologies of the dispersed metallic phases.

This paper reports a novel composite-based processing route for improving the electrical performance of Ca 3 Co 4 O 9 thermoelectric (TE) ceramics. The approach involves the addition of metallic Co, acting as a pore filler on oxidation, and considers two simple sintering schemes. The (1-x)Ca 3 Co 4 O 9 /xCo composites (x = 0%, 3%, 6% and 9% vol.) have been prepared through a modified Pechini method, followed by one- and two-stage sintering, to produce low-density (one-stage, 1ST) and high-density (two-stage, 2ST) ceramic samples. Their high-temperature TE properties, namely the electrical conductivity (σ), Seebeck coefficient (α) and power factor (PF), were investigated between 475 and 975 K, in air flow, and related to their respective phase composition, morphology and microstructure. For the 1ST case, the porous samples (56%-61% of ρ th ) reached maximum PF values of around 210 and 140 μWm -1 ·K -2 for the 3% and 6% vol. Co-added samples, respectively, being around two and 1.3 times higher than those of the pure Ca 3 Co 4 O 9 matrix. Although 2ST sintering resulted in rather dense samples (80% of ρ th ), the efficiency of the proposed approach, in this case, was limited by the complex phase composition of the corresponding ceramics, impeding the electronic transport and resulting in an electrical performance below that measured for the Ca 3 Co 4 O 9 matrix (224 μWm -1 ·K -2 at 975K).

This work aims at the preparation of multifunctional titania-based photocatalysts with inherent capabilities for thermal co-activation and stabilisation of anatase polymorph, by designing the phase composition and microstructure of rutile-silicon carbide mixture. The processing involved a conventional solid state route, including partial pre-reduction of rutile by SiC in inert Ar atmosphere, followed by post-oxidation in air. The impacts of processing conditions on the phase composition and photocatalytic activity were evaluated using Taguchi planning. The XRD studies confirmed the presence of rutile/anatase mixtures in the post-oxidised samples. The results emphasise that pre-reduction and post-oxidation temperatures are critical in defining the phase composition, while post-oxidation time is relevant for the photocatalytic performance. Microstructural studies revealed the formation of core-shell particles, which can suppress the photocatalytic activity. The highest apparent reaction rate of the photodegradation of methylene blue was observed for the sample pre-reduced in Ar at 1300 °C for 5 h and then calcined in air at 400 °C for 25 h. Though its performance was ~1.6-times lower than that for the same amount of nanostructured industrial P25 photocatalyst, it was achieved in the material possessing 2-3 times lower surface area and containing ~50 mol% of SiO 2 and SiC, thus demonstrating excellent prospects for further improvements.

Zinc oxide (ZnO) has being recognised as a potentially interesting thermoelectric material, allowing flexible tuning of the electrical properties by donor doping. This work focuses on the assessment of tantalum doping effects on the relevant structural, microstructural, optical and thermoelectric properties of ZnO. Processing of the samples with a nominal composition Zn 1-x Ta x O by conventional solid-state route results in limited solubility of Ta in the wurtzite structure. Electronic doping is accompanied by the formation of other defects and dislocations as a compensation mechanism and simultaneous segregation of ZnTa 2 O 6 at the grain boundaries. Highly defective structure and partial blocking of the grain boundaries suppress the electrical transport, while the evolution of Seebeck coefficient and band gap suggest that the charge carrier concentration continuously increases from x = 0 to 0.008. Thermal conductivity is almost not affected by the tantalum content. The highest ZT ~0.07 at 1175 K observed for Zn 0.998 Ta 0.002 O is mainly provided by high Seebeck coefficient (-464 V/K) along with a moderate electrical conductivity of ~13 S/cm. The results suggest that tantalum may represent a suitable dopant for thermoelectric zinc oxide, but this requires the application of specific processing methods and compositional design to enhance the solubility of Ta in wurtzite lattice., Competing Interests: The authors declare no conflicts of interest.

Activation of purinergic P2 receptors, which are expressed in neurons and microglial cells, normally induces an increase in intracellular calcium concentration ([Ca(2+)](i)) and some of the inflammatory mediators and excitatory neurotransmitters found to be implicated in neuronal cell death observed in diabetic retinas are released in response to an increase in the [Ca(2+)](i). However, it is unknown whether hyperglycemia/high glucose has an effect in the [Ca(2+)](i) changes triggered by the activation of P2 receptors in retinal cells. Using single-cell calcium imaging studies, we found that [Ca(2+)](i) changes triggered by purinergic receptors activation, both in retinal neurons and microglial cells, were potentiated in cells that had been cultured in high glucose conditions. In retinal neurons the increase in [Ca(2+)](i) was mostly due to Ca(2+) influx through voltage sensitive calcium channels, whereas in microglial cells Ca(2+) influx occurred mainly through P2X receptor channels, while there was also a smaller component of [Ca(2+)](i) rise dependent on calcium release from intracellular stores, probably due to P2Y receptor activation. In conclusion, our results show that rat retinal neural cells cultured in high glucose conditions show increased calcium responses to P2 receptors activation. This augmented calcium response might account for the increase in the release of neurotransmitters and inflammatory mediators found in diabetic retinas and, therefore, be responsible for retinal cell death observed in the early stages of diabetic retinopathy., ((c) 2009 Elsevier B.V. All rights reserved.)