The impact of charge transfer and structural disorder on the thermoelectric properties of cobalt intercalated TiS2

A family of phases, CoxTiS2 (0 ≤ x ≤ 0.75) has been prepared and characterised by powder X-ray and neutron diffraction, electrical and thermal transport property measurements, thermal analysis and SQUID magnetometry. With increasing cobalt content, the structure evolves from a disordered arrangement of cobalt ions in octahedral sites located in the van der Waals’ gap (x ≤ 0.2), through three different ordered vacancy phases, to a second disordered phase at x ≥ 0.67. Powder neutron diffraction reveals that both octahedral and tetrahedral inter-layer sites are occupied in Co0.67TiS2. Charge transfer from the cobalt guest to the TiS2 host affords a systematic tuning of the electrical and thermal transport properties. At low levels of cobalt intercalation (x < 0.1), the charge transfer increases the electrical conductivity sufficiently to offset the concomitant reduction in |S|. This, together with a reduction in the overall thermal conductivity leads to thermoelectric figures of merit that are 25 % higher than that of TiS2, ZT reaching 0.30 at 573 K for CoxTiS2 with 0.04 ≤ x ≤ 0.08. Whilst the electrical conductivity is further increased at higher cobalt contents, the reduction in |S| is more marked due to the higher charge carrier concentration. Furthermore both the charge carrier and lattice contributions to the thermal conductivity are increased in the electrically conductive ordered-vacancy phases, with the result that the thermoelectric performance is significantly degraded. These results illustrate the competition between the effects of charge transfer from guest to host and the disorder generated when cobalt cations are incorporated in the inter-layer space

Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing

No abstract available

The role of defects in microwave and conventionally synthesized LaCoO3 perovskite

In this work we investigate the magnetic, dielectric and charge transport properties of LaCoO3 (LCO) synthesized by two different techniques: microwave assisted and conventionally heated ceramic synthesis. The rapid microwave synthesis conditions are far away from thermodynamic equilibrium and are found to lead to modified crystal defect properties as compared to conventional synthesis. The thermally induced magnetic spin state transition at Ts1 ≈ 80 K is exemplified by temperature (T)-dependent dielectric spectroscopy data, which reveal the appearance of an additional dielectric contribution that is correlated to the transition. Magnetisation, M vs T, and electrical resistivity, ρ vs T, curves show that the additional dielectric phase is strongly influenced by magnetic defects and may be associated with higher spin state clusters in a magnetic spin-state coexistence scenario. We suggest that defects such as oxygen vacancies act as magnetic nucleation centres across the spin state transition Ts1 for the formation of higher spin state clusters in LCO perovskites

Structural, magnetic and dielectric properties of the novel magnetic spinel compounds ZnCoSnO4 and ZnCoTiO4

8 pags, 9 figs, 4 tabsThe transparent semiconductor ZnSnO with cubic spinel structure and the isostructural ZnTiO have been magnetically doped with Co. ZnCoSnO and ZnCoTiO exhibit ferrimagnetism below T ≈ 13 K and T ≈ 17 K. Ferrimagnetic moments are evident in M vs H curves below T by small hysteresis. Fits to strictly linear Curie-Weiss plots above T give μ ≈ 4.86 μ and ≈4.91 μ for ZnCoSnO and ZnCoTiO, above theoretical predictions. Impedance spectroscopy data from sintered ceramic can be fitted with a standard equivalent circuit model based on two RC elements for bulk and GB areas. The relative dielectric permittivity of the bulk is ≈20 and ≈30 for ZnSnO and ZnTiO. The semiconducting ZnCoSnO and ZnCoTiOceramics exhibit bulk resistivity of ≈1 10 Ω cm and ≈1 10 Ω cm at 560 K (287 °C), and bulk activation energies of E ≈ 1.2 eV and 1.1 eV.R.S. acknowledges a travel grant (Convenio Internacional) from the Universidad Complutense de Madrid to visit the USACH in Chile. JPG thanks the Spanish MINECO for granting a Juan de la Cierva fellowship. Spanish MINECO grant MAT2014-52405-C2-2-R is also acknowledged

Microwave synthesis and sintering of Sm and Ca co-doped ceria ceramics

International audienceIn this work we report on the combined use of microwave (MW) heating sources for the powder synthesis and the ceramic sintering of Sm and Ca co-doped ceria Ce0.8Sm0.18Ca0.02O1.9 polycrystalline materials for potential application as an electrolyte in intermediate-temperature solid oxide fuel cells (IT-SOFCs). We investigate the crystal structure, ceramic microstructure and the oxygen ion conductivity in detail and compare the latter to conventionally sintered ceramics. MW sintering of ceramic pellets leads to only slightly increased resistivity as compared to conventional sintering, but offers massive energy and time savings for potential industrial production processes. Exceptionally high oxygen ion conductivity without any significant electronic contribution was found in MW synthesized and MW sintered pellets, where the total resistivity, composed of grain boundary and bulk contributions, was found to be in the range of 0.5-1 kΩ at 500 °C. Sm- and Ca co-doped ceria may be well-suited for electrolyte materials in IT-SOFCs. © 2015 Hydrogen Energy Publications, LLC

The impact of charge transfer and structural disorder on the thermoelectric properties of cobalt intercalated TiS2

International audienceA family of phases, CoxTiS2 (0 ≤ x ≤ 0.75) has been prepared and characterised by powder X-ray and neutron diffraction, electrical and thermal transport property measurements, thermal analysis and SQUID magnetometry. With increasing cobalt content, the structure evolves from a disordered arrangement of cobalt ions in octahedral sites located in the van der Waals' gap (x ≤ 0.2), through three different ordered vacancy phases, to a second disordered phase at x ≥ 0.67. Powder neutron diffraction reveals that both octahedral and tetrahedral inter-layer sites are occupied in Co0.67TiS2. Charge transfer from the cobalt guest to the TiS2 host affords a systematic tuning of the electrical and thermal transport properties. At low levels of cobalt intercalation (x andlt; 0.1), the charge transfer increases the electrical conductivity sufficiently to offset the concomitant reduction in |S|. This, together with a reduction in the overall thermal conductivity leads to thermoelectric figures of merit that are 25% higher than that of TiS2, ZT reaching 0.30 at 573 K for CoxTiS2 with 0.04 ≤ x ≤ 0.08. Whilst the electrical conductivity is further increased at higher cobalt contents, the reduction in |S| is more marked due to the higher charge carrier concentration. Furthermore both the charge carrier and lattice contributions to the thermal conductivity are increased in the electrically conductive ordered-vacancy phases, with the result that the thermoelectric performance is significantly degraded. These results illustrate the competition between the effects of charge transfer from guest to host and the disorder generated when cobalt cations are incorporated in the inter-layer space. © The Royal Society of Chemistry 2016

I riflessi soggettivi delle specificit\ue0 di regolazione della sicurezza sul lavoro: il rappresentante del datore di lavoro committente.

Una delle tecniche di tutela perseguite dal legislatore della sicurezza sul lavoro consiste nella previsione di specifici soggetti dell'obbligo di sicurezza, a fronte di particolarit\ue0 regolative settoriali.Negli ambienti confinati, in particolare, il decreto n. 177 del 2011 ha introdotto la figura del rappresentante di lavoro. Tra le varie questioni che la materia pone, assume un ruolo interpretativo rilevante quella relativa alla compatibilit\ue0 delle regole generali relative al contratto di appalto, con le funzioni di controllo e di ingerenza statuite dal decreto n. 177 del 2011 a carico del rappresentante del datore di lavoro committente