P. Laffez

Metal–insulator transition at room temperature and infrared properties of Nd0.7Eu0.3NiO3 thin films

Nd0.7Eu0.3NiO3 thin films are deposited by rf sputtering and subsequent oxygen pressure annealing on (100) oriented silicon substrate. We characterize the thermochromic properties of films by measuring electrical transition, infrared transmittance, and reflectance. The thermochromic effect at room temperature is observed. Resistivity measurements exhibit a sharper hysteresis loop than is usually observed in NdNiO3 thin films. Infrared properties in the 8–14 μm wavelength range spectra reveal a contrast of 30% in reflectance and 55% in transmittance.

Thermal emittance changes at the charge ordering transition of (Sm0.35Ca0.65)MnO3

The reversible charge ordering transition of (Sm1−x,Cax)MnO3 is associated with strong changes in electrical, magnetic, and infrared properties. In this work, normal spectral emissivity is calculated from infrared reflectance of bulk polished ceramics. Emissivity versus temperature shows a sharp variation at the charge ordering transition near room temperature. By comparing the apparent temperature of the sample with the absolute temperature, we show that Sm0.35Ca0.65MnO3 is a good candidate for infrared furtivity around room temperature.

Electron doped (Sm1−x,Cax)MnO3 perovskite manganite as potential infrared thermochromic switch

We have synthesized (Sm1−x,Cax)MnO3 and related compositions to show their potential use as thermochromic switch in the infrared range. Depending on temperature or composition, the single phase is stabilized using the polyacrilamide gel process. Infrared transmittance was measured on selected samples in the 1,42–25μm range. Relative contrast up to 0.773 is measured in the 8–14μm range. Full opacity in the 8–14μm range occurs at temperatures between 273 and 300K, depending on the composition. The potential application of perovskites manganites as thermochromic infrared switch or coating is discussed.

X-ray diffraction investigation of the relationship between strains and metal-insulator transition in NdNiO3 thin films

Abstract The RNiO3 perovskites (R=rare earth) are well known for their metal to insulator transition, which temperature can be modulated by changing the nature of the rare earth. It makes this family of oxides very attractive for several applications such as thermochromic coating. In this work we have studied NdNiO3 thin films, grown on (110) NdGaO3, single crystal substrate, with different thicknesses. The temperature of the metal to insulator transition varies in the range 150 –200 K. Residual stress in films was analyzed using the sin2ψ method. Each film exhibits in plane tensile stress, their magnitude depending on the synthesis conditions. A possible relationship between the metal-insulator transition temperature and residual stress is discussed.

On the optical generation and detection of high frequency ultrasounds: thermal and non‐thermal processes

We report on the results of the generation and detection by femtosecond laser pulses of the acoustic waves at frequencies of tens to hundreds GHz in semiconductors and in oxides compounds exhibiting phase transition. We focus first on the generation mechanisms involved to achieve opto‐acoustic transformations. Particular attention will be paid to the cases where classical thermal effects (thermoelastic coupling) drive the mechanism of generation of acoustic phonons and those where non‐thermal effects become significant and sometimes dominant sources of acoustic phonons field. In the latter cases, we will especially focus on the phonons generation based on photo‐induced modifications of microscopic internal electric fields (potential deformation) and also on the use of photoexcited carriers dynamics (carriers recombination) as a tuning parameter of the photo‐generated ultrasounds spectrum. Secondly, we give the examples demonstrating that the choice of optical frequency for ultrasound detection influences ...

(Sm1-x,Cax)MnO3 Ceramics with Tunable Emissivity

The reversible charge ordering transition of (Sm1-x,Cax)MnO3 is associated with strong changes in electrical, magnetic and infrared properties. In this work, normal spectral emissivity is calculated from infrared reflectance of bulk polished ceramics, measured by Fourier Transform Infrared Spectroscopy (FTIR). Emissivity versus temperature shows a sharp transition at the charge ordering transition. By comparing the apparent temperature of the sample with the absolute temperature, we show that (Sm1-x,Cax)MnO3 is a good candidate for infrared furtivity around room temperature.

Thermo-Optical Properties of Nd0.3Sm0.7NiO3 Ceramic

Nd0.3Sm0.7NiO3 ceramic has been synthesised using a sol-gel method and annealing at oxygen pressure. Nd0.3Sm0.7NiO3 exhibits a reversible metal insulator phase transition which is, in the infrared range, responsible of a thermal-optical contrast. Samples are structurally characterized by X-ray diffraction and thermogravimetric analysis. The Nd0.3Sm0.7NiO3 thermal – optical contrast is characterized in the mid-infrared range, using reflectance and thermal-optical measurements.

Growth of La_{2}Mo_{2}O_{9} films on porous Al_{2}O_{3} substrates by radio frequency magnetron sputtering

Synthesis conditions of La2Mo2O9 thin film by radio frequency (RF) sputtering technique on Al2O3 ceramic substrates are studied. It is found that the deposition temperature and oxygen partial pressure are the most important factors for obtaining pure La2Mo2O9 films. Varying both parameters, Mo-rich, stoichiometric, and Mo-deficient films are obtained. With increasing the La:Mo ratio, films become denser. A crust layer is observed on top of the Mo-rich and the Mo-deficient films. The formation of the La2Mo2O9 phase is discussed with respect to the sputtering mechanism.

Transmission electron microscopy of NdNiO_{3} thin films on silicon substrates

The microstructure of NdNiO 3 thin films deposited on Si (100) has been investigated by high resolution electron microscopy. Deposition at 250 °C and 600 °C and several annealing at high temperature under oxygen pressure were performed. Depending on the deposition temperature and annealing conditions, different texture and microstructure were observed. Relationships between microstructure and transport properties are discussed. The differences of grain boundaries are suggested to be responsible for the difference in transport properties of the films.