Unconventional aspects of electronic transport in delafossite oxides

The electronic transport properties of the delafossite oxides ABO$_2$ are usually understood in terms of two well separated entities, namely, the triangular A$^+$ and (BO$_2$)$^-$ layers. Here we review several cases among this extensive family of materials where the transport depends on the interlayer coupling and displays unconventional properties. We review the doped thermoelectrics based on CuRhO$_2$ and CuCrO$_2$, which show a high-temperature recovery of Fermi-liquid transport exponents, as well as the highly anisotropic metals PdCoO$_2$, PtCoO$_2$ and PdCrO$_2$ where the sheer simplicity of the Fermi surface leads to unconventional transport. We present some of the theoretical tools that have been used to investigate these transport properties and review what can and cannot be learned from the extensive set of electronic structure calculations that have been performed.Comment: 35 pages, 19 figure

Intrinsic effects of substitution and intercalation on thermal transport in two-dimensional TiS2_2 single crystals

The promising thermoelectric material TiS$_2$ can be easily chemically doped and intercalated. We present here studies of single crystals that are intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the intrinsic impact of these dopants on the thermal transport in the absence of grain boundary scattering. We show that Ta doping has the greatest impact on the thermal scattering rate per ion added, leading to a five-fold reduction in the lattice thermal conductivity as compared to stoichiometric single crystals.Comment: 5 pages, 2 figure

Concevoir une stratégie d’intégration des attitudes professionnelles en Techniques de tourisme au Collège Montmorency

La raison d’être de ce projet d’innovation est de mettre en place une stratégie d’accompagnement pour les professeurs en Techniques de tourisme au Collège Montmorency, dans le but de leur permettre d’enseigner les attitudes professionnelles (AP) aux étudiants inscrits au programme à partir de la session d’automne 2018. L’approche Scolarship of Teaching and Learning (SoTL), qui favorise le développement professionnel lié à une problématique d’apprentissage des étudiants, nous a guidée vers une réflexion sur la manière d’être ou d’agir chez plusieurs étudiants. La recension d’écrits sur les AP et l’accompagnement nous permettent de soutenir la conception d’une stratégie d’intégration des attitudes professionnelles au programme. Le projet est mis en œuvre au rythme du cycle de révision de programmes établi par le Collège. Le plan de formation (plan-cadre) lié au programme actualisé fait maintenant état de six AP enseignées en Techniques de tourisme au Collège Montmorency depuis l’automne 2018 : ouverture aux autres, organisation, polyvalence, engagement, communication et autonomie. Pour soutenir les professeurs dans l’enseignement des AP et favoriser le développement des AP chez les étudiants, nous avons conçu un guide de référence et orchestré un atelier de formation pour les professeurs. Une expérience qui serait facilement transférable à d’autres programmes et des projets de mobilité étudiante

Large anisotropic thermal conductivity of intrinsically two-dimensional metallic oxide PdCoO2_2

The highly conductive layered metallic oxide \pdcoo{} is a near-perfect analogue to an alkali metal in two dimensions. It is distinguished from other two-dimensional electron systems where the Fermi surface does not reach the Brillouin zone boundary by a high planar electron density exceeding $10^{15}$ cm$^{-2}$. The simple single-band quasi-2D electronic structure results in strongly anisotropic transport properties and limits the effectiveness of electron-phonon scattering. Measurements on single crystals in the temperature range from 10-300K show that the thermal conductivity is much more weakly anisotropic than the electrical resistivity, as a result of significant phonon heat transport. The in-plane thermoelectric power is linear in temperature at 300\,K and displays a purity-dependent peak around 50K. Given the extreme simplicity of the band-structure, it is possible to identify this peak with phonon drag driven by normal electron-phonon scattering processes.Comment: 3 figure

La prévention des problèmes sociaux : réalité québécoise

Les modèles de prévention actuels et leurs stratégies d'action contribuent-ils à une diminution importante et durable des problèmes sociaux? La réponse à cette question suppose qu'on examine la représentation des problèmes sociaux, les cibles et les contextes de prévention, la dimension de précocité de l'action ainsi que les stratégies privilégiées. Les développements théoriques actuels permettent d'acquérir une vision liant la résolution de problèmes individuels et celle de problèmes sociaux. Les auteurs dégagent enfin une première esquisse de la prévention sociale. La conjoncture actuelle nous laisse croire à une évolution intéressante de ce secteur dans la prochaine décennie

Mg substitution in CuCrO2 delafossite compounds

A detailed investigation of the series CuCr(1-x)MgxO2 (x = 0.0 - 0.05) has been performed by making high-temperature resistivity and thermopower measurements, and by performing a theoretical analysis of the latter. Microstructure characterization has been carried out as well. Upon Mg2+ for Cr3+ substitution, a concomitant decrease in the electrical resistivity and thermopower values is found, up to x ~ 0.02 - 0.03, indicating a low solubility limit of Mg in the structure. This result is corroborated by scanning electron microscopy observations, showing the presence of MgCr2O4 spinels as soon as x = 0.005. The thermopower is discussed in the temperature-independent correlation functions ratio approximation as based on the Kubo formalism, and the dependence of the effective charge carrier density on the nominal Mg substitution rate is addressed. This leads to a solubility limit of 1.1% Mg in the delafossite, confirmed by energy dispersive X-ray spectroscopy analysis.Comment: 6 pages, 5 figure

Dual electronic states in thermoelectric cobalt oxide

We investigate the low temperature magnetic field dependence of the resistivity in the thermoelectric misfit cobalt oxide [Bi1.7Ca2O4]0.59CoO2 from 60 K down to 3 K. The scaling of the negative magnetoresistance demonstrates a spin dependent transport mechanism due to a strong Hund's coupling. The inferred microscopic description implies dual electronic states which explain the coexistence between localized and itinerant electrons both contributing to the thermopower. By shedding a new light on the electronic states which lead to a high thermopower, this result likely provides a new potential way to optimize the thermoelectric properties

Anisotropic Seebeck coefficient of Sr2RuO4\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4 in the incoherent regime

Intuitive entropic interpretations of the thermoelectric effect in metals predict an isotropic Seebeck coefficient at high temperatures in the incoherent regime even in anisotropic metals since entropy is not directional. $\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$ is an enigmatic material known for a well characterised anisotropic normal state and unconventional superconductivity. Recent ab-initio transport calculations of $\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$ that include the effect of strong electronic correlations predicted an enhanced high-temperature anisotropy of the Seebeck coefficient at temperatures above 300 K, but experimental evidence is missing. From measurements on clean $\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$ single crystals along both crystallographic directions, we find that the Seebeck coefficient becomes increasingly isotropic upon heating towards room temperature as generally expected. Above 300 K, however, $S$ acquires a new anisotropy which rises up to the highest temperatures measured (750 K), in qualitative agreement with calculations. This is a challenge to entropic interpretations and highlights the lack of an intuitive framework to understand the anisotropy of thermopower at high temperatures.Comment: 5 pages, 2 figure