Raman and infrared spectroscopy of Sr2B′UO6 (B′ = Ni; Co) double perovskites

Temperature dependent normal modes and lattice thermal expansion of Sr 2B′UO6 (B′ = Ni, Co) double perovskites were investigated by Raman/infrared spectroscopies and synchrotron X-ray diffraction, respectively. Monoclinic crystal structures with space group P21/n were confirmed for both compounds, with no clear structural phase transition between 10 and 400 K. As predicted for this structure, the first-order Raman and infrared spectra show a plethora of active modes. In addition, the Raman spectra reveal an enhancement of the integrated area of an oxygen stretching mode, which is also observed in higher-order Raman modes, and an anomalous softening of ∼1 cm-1 upon cooling below T* ∼ 300 K. In contrast, the infrared spectra show conventional temperature dependence. The band profile phonon anomalies are possibly related to an unspecified electronic property of Sr2B′UO6 (B′ = Ni, Co).Centro de Química Inorgánic

Raman and infrared spectroscopy of Sr2B′UO6 (B′ = Ni; Co) double perovskites

Temperature dependent normal modes and lattice thermal expansion of Sr 2B′UO6 (B′ = Ni, Co) double perovskites were investigated by Raman/infrared spectroscopies and synchrotron X-ray diffraction, respectively. Monoclinic crystal structures with space group P21/n were confirmed for both compounds, with no clear structural phase transition between 10 and 400 K. As predicted for this structure, the first-order Raman and infrared spectra show a plethora of active modes. In addition, the Raman spectra reveal an enhancement of the integrated area of an oxygen stretching mode, which is also observed in higher-order Raman modes, and an anomalous softening of ∼1 cm-1 upon cooling below T* ∼ 300 K. In contrast, the infrared spectra show conventional temperature dependence. The band profile phonon anomalies are possibly related to an unspecified electronic property of Sr2B′UO6 (B′ = Ni, Co).Centro de Química Inorgánic

PSEUDOSYMMETRY AND INFRARED ACTIVITY IN THE INCOMMENSURATE PHASE OF A2BX4 COMPOUNDS

30106039604

Thickness and Roughness Effect of Pr2NiO4+δ Coating on the Normal Spectral Emittance

International audiencePr2 NiO(4+δ) coatings of rare earth nickelate oxide were prepared through RF magnetron co-sputtering, combined with an appropriate heat treatment. The study focused on optimizing the growth conditions to enhance the thermal emittance of the coatings, taking into account the influence of thickness and roughness. The research findings revealed interesting insights. Firstly, by analyzing room temperature infrared reflectivity and studying the temperature dependence of the normal spectral emittance in the range of 500 cm-1 to 5500 cm-1, it was observed that the total emittance increased as the coating thickness increased. However, this increase tended to approach a saturation value at higher thicknesses. Additionally, the study demonstrated that a coating thickness of 2.8 μm was sufficient to effectively shield the substrate's infrared thermal response. This suggests the potential application of these coatings for thermal management purposes. Furthermore, the influence of roughness on the emittance was predominantly observed in the spectral range of 1200 cm-1 to 3600 cm-1. This finding highlights the importance of considering surface roughness when designing coatings for optimal thermal properties. In summary, the research provided valuable insights into the growth conditions and the impact of thickness and roughness on the thermal emittance of Pr2NiO(4+δ) coatings. These findings contribute to the development of improved materials for thermal management and related applications

Black body coating by spray pyrolysis

For the first time, a rough and thick film of doped praseodymium nickel oxide (Pr2NiO4+δ) has been obtained by combining spray pyrolysis deposition technique with Rapid Thermal Annealing (RTA) process. The precursors are nitrate solutions, the thermal decomposition of which has been studied. Spectral emissivity measurements in the far and mid infrared range at T=1000 K demonstrate the strong blackbody character of the film. This feature suits very well to operate a ceramic infrared radiant plate with high thermal efficiency. The applications would be apply for the heat-treatments of organic compounds such as paint, thermo-plastic, food, paper..

Modeling of time-resolved coupled radiative and conductive heat transfer in multilayer semitransparent materials up to very high temperatures

International audienceThis paper presents an original modeling approach that enables the calculation of the temperature field within multilayer materials submitted to the flash method. The model takes into account the time-resolved coupled conducto-radiative heat transfer and the temperature of experiments. The compound can be subdivided into as many layers as desired, and their thicknesses and relevant physical properties can be chosen arbitrarily. Unconventional experimental thermograms can be reproduced faithfully by the calculations. This model, thus, makes it possible to correctly estimate the effective thermal diffusivity of semitransparent materials, thereby providing a deeper insight into the analysis of the physical phenomena involved. V C 2011 American Institute of Physics. [doi:10.1063/1.3664408] This study is part of a larger research project and its objective is to model the heat transfer in textured materials, such as foams and porous ceramics. 1,2 Modeling of the flash method, 3,4 in order to characterize the effective thermal dif-fusivity of specific materials, has been devoted a particular interest. The experimental thermograms (i.e., temperature versus time curves) that have been obtained for certain samples clearly demonstrated that conduction is not the only mode of heat transfer that occurs in these materials. Indeed, the phenomena that appear at very short times, e.g., a non-zero slope, a sharp temperature increase, a temperature step, point to the existence of radiative heat transfer as a result of the semitransparent nature of the materials. This semitrans-parent behavior can be explained by the texture of the materials as well as by their chemical composition from the local (i.e., the mean free path of the phonons) to the macroscopic scale. Moreover, our characterization studies have been conducted at several temperature levels including high temperatures where radiation becomes dominant. A model coupling both transfer modes (conduction and radiation) and taking into account the temperature level of the experiment was developed. This paper presents the validation of the model for a few cases, and it will be shown that unconventional thermograms collected on various samples can be quite satisfactorily reproduced by our model under the assumption of a one-dimensional heat transfer. Our model solves the heat transfer problem associated to the flash experiment applied to a 1D semitransparent cylindrical sample. In the case of a porous medium, no convec-tion transfer is assumed to take place according to Rayleigh's criteria. The front surface of the sample is submitted to a pulsed energy deposition of short duration, which is assumed to be uniform over the surface. The lateral surface is presumed to be adiabatic, whereas the front face and its opposite side (the back face) are submitted to boundary conditions of emission, diffuse reflection, and heat dissipa-tion through a coupled convective-radiative exchange coefficient. All these assumptions render it possible to develop a one-dimensional heat transfer model coupling conduction and radiation, where the latter is assumed to present an azi-muthal symmetry. Four more assumptions were made: (i) the intensity field was supposed to be isotropic in each half-space, (ii) the material under study was presumed to be grey (i.e., of radiative properties independent of the wavelength)

Thermal surface modes probed through theCasimir- Polder atom-surface interaction

contribution orale 30 mn, présentée par D BlochInternational audienc

Micro-structure effect on radiative properties of thermal barrier ceramic coatings

International audienc