David Berardan

Room temperature lithium superionic conductivity in high entropy oxides

Impedance spectroscopy measurements evidence superionic Li+ mobility (>10−3 S cm−1) at room temperature and fast ionic mobility for Na+ (5 × 10−6 S cm−1) in high entropy oxides, a new family of oxide-based materials with the general formula (MgCoNiCuZn)1−x−yGayAxO (with A = Li, Na, K). Structural investigations indicate that the conduction path probably involves oxygen vacancies.

Invited Article: A round robin test of the uncertainty on the measurement of the thermoelectric dimensionless figure of merit of Co0.97Ni0.03Sb3

A round robin test aiming at measuring the high-temperature thermoelectric properties was carried out by a group of European (mainly French) laboratories (labs). Polycrystalline skutterudite Co0.97Ni0.03Sb3 was characterized by Seebeck coefficient (8 labs), electrical resistivity (9 labs), thermal diffusivity (6 labs), mass volume density (6 labs), and specific heat (6 labs) measurements. These data were statistically processed to determine the uncertainty on all these measured quantities as a function of temperature and combined to obtain an overall uncertainty on the thermal conductivity (product of thermal diffusivity by density and by specific heat) and on the thermoelectric figure of merit ZT. An increase with temperature of all these uncertainties is observed, in agreement with growing difficulties to measure these quantities when temperature increases. The uncertainties on the electrical resistivity and thermal diffusivity are most likely dominated by the uncertainty on the sample dimensions. The temperature-averaged (300-700 K) relative standard uncertainties at the confidence level of 68% amount to 6%, 8%, 11%, and 19% for the Seebeck coefficient, electrical resistivity, thermal conductivity, and figure of merit ZT, respectively. Thermal conductivity measurements appear as the least accurate. The moderate value of the temperature-averaged relative expanded (confidence level of 95%) uncertainty of 17% on the mean of ZT is essential in establishing Co0.97Ni0.03Sb3 as a high temperature standard n-type thermoelectric material.

Influence of structural isomerism of amino acid on the crystal growth of ZnO nanoparticles synthetized by polyol methods

Zinc oxide nanoparticles were synthesized by using a polyol method and several isomers of aminobenzoic acid as surfactant. Our results show that nanoparticle morphology and size are closely linked with the structural isomerism of the surfactant: spherical nanoparticle for ortho-aminobenzoic acid, twin rod for meta-aminobenzoic acid, and oriented mesosphere of triangular nanoparticles were obtained. We have shown that the morphology is governed on the first step by the reaction of carboxylate functionxa0with zinc precursor and in a second step by amine group interactions with the particle surface. Moreover, in the case of para-aminobenzoic acid, the agglomeration of triangular nanoparticles originates from the mutual alignment of crystal faces due to interparticular force to formxa0oriented mesospheres. This agglomeration can be avoided by the use of basic conditions for the synthesis of the nanoparticles.Graphical Abstract