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With the recent advances in thermoelectric (TE) technology, there is an increasing demand to develop thick films that would enable large-scale TE devices. Assembly of TE-films from size and morphology-controlled nano particles has been a challenging issue that can be addressed by the use of electrophoretic deposition (EPD) technique. In this work, morphology-controlled Sb2Te3 nanoparticles were synthesized through microwave assisted thermolysis, which were subsequently used for EPD of TE films on specially developed glass substrates. The electronic transport properties were measured in the temp-range of 22-45 degrees C. The as-made EPD films showed a high initial resistance, ascribed to high porosity and the presence of surface oxide/passivating layers. The impact of two types of small organic molecules-as hexanedithiol and dodecanethiol, on the electronic transport was investigated, resulting in a significant improvement in the electrical conductivity of the films. The XPS analysis suggests that the thiols bind to the surface of nanoparticles through formation of sulfides. Seebeck coefficient in the range of + 160 to + 190 & mu;V/K was measured, revealing the p-type transport through the deposited films. Finally, a power factor of about 2.5 & mu;W/K2.m was estimated the first time for p-type EPD films, revealing the potential of the developed nanoparticles and substrate, the small molecule additives and the EPD process presented in this work., QC 20231122

Despite the numerous advantages of lanthanide based luminescent thermometers, a major limitation is the limited brightness associated with the low absorption cross section of the 4f–4f transitions. In this paper, co-doping with Cr3+/4+ is proposed as a strategy to enhance the near-infrared luminescence emission of Nd3+/Er3+-based luminescent thermometers, as well as to modulate the temperature sensitivity of the ratio of Nd3+ to Er3+ in YAG microcrystals. It was found that an increase in the Cr3+ concentration leads to the enhancement of the YAG:Nd3+,Er3+ emission intensity via the Cr3+ → Ln3+ sensitization process. The quantitative analysis of the absolute brightness indicates the 30-fold enhancement of their near infrared emission upon broad white light excitation for 20% Cr3+ with respect to the non co-doped with the Cr3+ counterpart. In addition, the phonon-assisted nature of the simultaneously occurring Cr3+ → Ln3+ and Nd3+ → Cr4+ → Er3+ energy transfers leads to a 7-fold increase of the relative temperature sensitivity of the ratio of Nd3+ to Er3+ emission. In conclusion, co-doping with transition metals can enhance simultaneously the luminescence brightness and the temperature sensitivity of NIR luminescent thermometers, holding promise for sensitive and robust remote temperature sensing at physiological temperatures.

The solution synthesis route as a scalable bottom-up synthetic method possesses significant advantages for synthesizing nanostructured bulk thermoelectric (TE) materials with improved performance. Tuning the composition of the materials directly in the solution, without needing any further processing, is important for adjusting the dominant carrier type. Here, we report a very rapid (2 min) and high yield (>8 g/batch) synthetic method using microwave-assisted heating, for the controlled growth of Bi2-xSbxTe3 (x: 0-2) nanoplatelets. Resultant materials exhibit a high crystallinity and phase purity, as characterized by XRD, and platelet morphology, as revealed by SEM. Surface chemistry of as-made materials showed a mixture of metallic and oxide phases, as evidenced by XPS. Zeta-potential analysis exhibited a systematic change of isoelectric point as a function of the material composition. As-made materials were directly sintered into pellets by using spark plasma sintering process. TE performance of Bi2-xSbxTe3 pellets were studied, where the highest ZT values of 1.04 (at 440 K) for Bi2Te3 and 1.37 (at 523 K) for Sb2Te3 were obtained, as n- and p-type TE materials. The presented microwave-assisted synthesis method is energy effective, a truly scalable and reproducible method, paving the way for large scale production and implementation of towards large-area TE applications., QC 20200611

The behavior of transition metal oxalates in vacuum, under X-ray irradiation and low-energy Ar+ ion bombardment was studied. A comparative mass-spectrometric analysis was carried out of gas evolution from the surface of Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation. The rates of H2O and CO2 liberation from the oxalates were found to be in an inverse correlation with the temperatures of dehydration and decomposition, respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the X-ray induced damage in NiC2O4 and CuC2O4 by measuring the various XP spectral characteristics and surface composition of the oxalates as a function of time of exposure to X-rays. It was shown that Cu oxalate underwent a significantly faster degradation than Ni oxalate and demonstrated a high degree of X-ray induced reduction from the Cu2+ to the Cu1+ chemical state. 500 eV Ar+ sputter cleaning of CoC2O4 for 10 min was found to cause a strong transformation of the oxalate structure which manifested itself in an appreciable alteration of the XP core-level and valence band spectra. The analysis of changes in stoichiometry and comparison of XP spectra of bombarded oxalate with respective spectra of a reference carbonate CoCO3 implied that the bombardment-induced decomposition of CoC2O4 gave rise to the formation of CoO-like and disordered CoCO3-like phases., SCOPUS: ar.j, info:eu-repo/semantics/published

X-ray photoelectron spectroscopy (XPS) was employed to study the changes in the surface composition and electronic structure of a TiO2-promoted Pd/SiO2 catalyst following methane oxidation under lean-burn conditions (up to 600 C) and SO2 treatment at 350 C. Overnight exposure of the activated catalyst to SO2 was found to cause the formation of a layer of palladium sulfate and sulfate/sulfite species on the support surface, leading to its deactivation. A single cycle of methane combustion over the SO2-treated catalyst gave rise to its reactivation due to the effective decomposition of Pd sulfate and desorption of SO2 at relatively low temperatures. In the stabilized and restored states, the catalyst exhibited a high and stable activity, had the largest proportion of metallic versus oxidic palladium species, a high density of Pd 4d states near the Fermi level, and the smallest extent of surface hydroxylation. The catalytic reaction over an as-prepared or SO2-treated catalyst was revealed to cause a partial and reversible 'encapsulation' of Pd particles by TiOx suboxide moieties from the mixed oxide support. The encapsulation resulting from strong metal-support interaction was enhanced by the SO2 treatment of the Pd/(SiO2 + 10 wt% TiO 2) catalyst. © 2014 Elsevier Inc. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Non-stoichiometric Mn-oxides (MnO x and MnO y) were prepared by temperature-programmed oxidation (TPO) of Mn-oxalates, MnC 2O 4·3H 2O and MnC 2O 4·2H 2O. Both oxides provide high specific surface areas (525 m 2 g -1 and 385 m 2 g -1, respectively) and identical CO oxidation reaction rates of 10 -2 molecules nm -2 s -1 (0.017 μmol CO m -2 s -1) at 298 K. A "spinodal" transformation of oxalates into oxides was observed by transmission electron microscopy (TEM). The quantitative evaluation of TPO and temperature-programmed reduction with CO allowed x-values of 1.61, ⋯, 1.67 to be determined for MnO x. The Mn oxidation state in MnO x was found to be 3.4 ± 0.1 by X-ray absorption near-edge structure analysis and X-ray photoelectron spectroscopy. In accordance with the high specific surface area and mixed-type I/IV adsorption isotherms of MnO x, high resolution TEM demonstrated the occurrence of nested micro-rod features along with nanocrystalline particles in the endings of the rods. After CO oxidation MnO and Mn 3O 4 phases were able to be identified in the regions between rods. © 2011 Elsevier Inc. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Bismuth telluride-Bi2Te3 is a promising material for harvesting thermal energyfor applications near room temperature, where large-area applications requirenew methods of depositing pre-made particulate materials. Electrophoretic deposition(EPD) technique has the promise of enabling the formation of thickfilms using colloidally stabilized suspensions of pre-made nanoparticles. It isvery important to understand the thermoelectric (TE) materials’ performancein relation to the synthetic process, to enable promising and scalable materialstechnologies. EPD films allow to study the effect of surface chemistry, stronglylinked to the synthetic route, on the material’s physico-chemical and transportproperties. Here we report on the synthesis of Bi2Te3 through wet-chemicalreactions performed in two different media as water (hydrothermal-Hydro) andoil (thermolysis-Thermo). Synthesized materials possess platelet morphology,which were then used to fabricated EPD films on specially developed glass substrates. Characterization of the materials and films reveal significant differencesbetween the surface chemistry of the EPD films of Hydro- and Thermo-Bi2Te3samples, where a higher content of metal oxide phases are observed in the Hydro-Bi2Te3 sample. This has a big impact the electronic transport properties, asrevealed by about nine times higher resistance, confirmed by significantly higheractivation energy, of the Hydro-Bi2Te3 film as compared to the Thermo-Bi2Te3film. Slight difference in the Seebeck coefficient (S) was explained by the effectivemedium theory, revealing that the magnitude of S is linearly correlatedwith the surface oxide content. Based on the findings, TE materials synthesizedthrough thermolysis route is recommended for future studies focusing on EPD of TE materials., QC 20230825