M. El Marssi

Characterization of pulsed laser deposited WO3 thin films for electrochromic devices

Abstract Thin films of tungsten oxide were deposited on SnO2:F coated glass using pulsed laser deposition. The structure, morphology, composition of the films and thus the electrochromic properties are strongly dependent on the conditions of deposition. Emphasis is being made on both the influence of the oxygen pressure and the temperature of deposition. Crystallized films are obtained when deposited at 400°C with an oxygen pressure of 10−1 mbar while an oxygen pressure of 10−2 mbar leads to amorphous films whatever the substrate temperature is. For the lower oxygen pressure, blue colored and conductive films are deposited whereas colorless insulator films are obtained for an oxygen pressure of 10−1 mbar at room temperature (RT). The estimated optical band gaps for the films were found to be 3.2 eV when deposited at RT and 2.8 eV when deposited on a 400°C substrate while having an oxygen pressure of 10−1 mbar. Using Raman spectroscopy, the decrease of the optical band gap was ascribed to a decrease of the WO/O–W–O ratio correlated to an increase of the cluster size of tungsten oxide with crystallinity. By IR spectroscopy, we were able to relate the better electrochromic properties of the colorless films deposited at RT in an oxygen pressure of 10−1 mbar, to the presence of water.

Ferroelectric transition in an epitaxial barium titanate thin film: Raman spectroscopy and x-ray diffraction study

We have performed x-ray diffraction and Raman spectroscopy measurements in the temperature range of 300–873 K on a single phase epitaxially oriented BaTiO3 thin film grown by pulsed laser deposition on a single crystal MgO substrate. The θ–2θ room temperature diffraction measurements and asymmetric rocking curves indicate that the film is very weakly tetragonal with the c-axis parallel to the plane of the film. X-ray diffraction measurements up to high temperature reveal only a change in slope in the perpendicular to the plane lattice parameter around 450 K (in bulk Tc=395 K) indicating that a diffuse-like of phase transition is taking place. Room temperature polarized Raman spectra show that the film is indeed tetragonal with C4v symmetry and with the a-axis perpendicular to the film plane. Monitoring of the overdamped soft mode and the 308 cm−1 mode confirms that the phase transition is taking place over a wide temperature range according to the x-ray results. The increase of the phase transition temper...

Lead-free Ba0.8Ca0.2(ZrxTi1−x)O3 ceramics with large electrocaloric effect

The electrocaloric effect was investigated in lead-free Zr doped Ba0.8Ca0.2(ZrxTi1−x)O3 (BCTZ) ceramics synthesized by a conventional sintering process. Room-temperature x-ray diffraction analysis showed that the tetragonal structure is obtained in BCTZ for x  ≤ 0.08 and a pseudo cubic phase for x > 0.08. The dielectric spectroscopy and calorimetry revealed that the Curie temperature decreases as a consequence of Zr doping and that the BCTZ exhibits a first order ferroelectric phase transition. The electrocaloric effect was determined by the calculation of the electrocaloric change of temperature (ΔT) using the Maxwell relation based on the P–E hysteresis loops measured at different temperatures. A large electrocaloric responsivity ΔT/ΔE = 0.34 × 10−6 Km/V was found for x = 0.04, which significantly exceeds of values found so far in other lead-free electrocaloric materials.

A Raman scattering study of the ferroelectric ordering in rhombohedral and tetragonal La‐modified lead zirconate titanate ceramics

A Raman study of La‐doped lead zirconate titanate ceramics with La/Zr/Ti ratios of 9/65/35 and 12/40/60 has been undertaken in order to compare the onset of ferroelectric order in these two compositions. Some features, such as a splitting of a threefold degenerate T1u mode of the cubic structure into at least two lines or an enhancement of the T2u mode, can be considered as the signature of the occurrence of some ferroelectric order below Tc≂363 K in the 12/40/60 compound. Nevertheless, the Raman spectra obtained for the two ceramics are very similar, and no significant narrowing of the lines was observed in the ferroelectric phase of 12/40/60. It is thus suggested that the onset of long range order in this compound is not developed homogeneously in every direction of space, in agreement with previous transmission electron microscopy observations. The Raman scattering was dominately second order, with the broadening of the lines reflecting a distribution of the correlation function of the quasistatic pola...

Bias-field effect on the temperature anomalies of dielectric permittivity in PbMg1/3Nb2/3O3 -PbTiO3 single crystals

In contrast to ordinary ferroelectrics where the temperature

Ferroelectric and glassy states in La-modified lead zirconate titanate ceramics: A general picture

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Translational and orientational order in lead zinc niobate: An optical and Raman study

of the permittivity maximum monotonically increases with bias field

Polarized Raman and electrical study of single crystalline titanium modified lead magnesio-niobate

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A polarized Raman study of the relaxor and ferroelectric states of La-modified lead zirconate titanate ceramics

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Electrocaloric effect and luminescence properties of lanthanide doped (Na1/2Bi1/2)TiO3 lead free materials

(1\ensuremath{-}x)\mathrm{Pb}{\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}\text{\ensuremath{-}}(x)\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}