Polycrystalline powders of (1-x)Na 0.5 Bi 0.5 TiO 3 -xCaTiO 3 ((1-x)NBT-xCT, 0 ≤ x ≤ 0.55) have been synthesized by solid state route. The effects of simultaneous substitution of Na + /Bi 3+ at A-site in NBT on structural and dielectric properties were investigated. X-ray diffraction analysis revealed the phase transition from rhombohedral structure (x = 0) to orthorhombic structure (x ≥ 0.15). A distinct behaviour in dielectric properties was obtained, where for x = 0, a normal ferroelectric behaviour was observed, whereas for x ≥ 0.15, a broad dielectric anomaly was revealed such that the maximum temperature (T m ) strongly depended on the frequency and shifted towards low temperature with CT. The dielectric dispersion indicated a relaxor behaviour revealed by the degree of diffuseness and modelled via Vogel-Fulcher relation. The study highlighted the relaxor behaviour as a function of frequency and proved the transformation from a relaxor high-frequency dependence to a paraelectric phase at temperature T s . The distinct variation of the Raman spectra at room temperature was correlated with X-ray diffraction results and proved the already mentioned transition. On heating (193-500 ℃), the Raman spectra confirmed the structural stability (Pnma) of the materials. The phonon behaviour for x = 0.15 was discussed in terms of the appearance of polar nanoregions (PNRs) into a non-polar orthorhombic matrix responsible of the relaxor behaviour. For x = 0.20, unchanged phonon behaviour confirmed the variation in dielectric behaviour where the solids transformed from a relaxor to a paraelectric state without structural phase transition.

An overview is given of the development of sorbent materials for hydrogen storage. Understanding the surface properties of the adsorbed film is crucial to optimize hydrogen storage capacities. In this work, the lattice gas model (Ono-Kondo) is used to determine the properties of the adsorbed hydrogen film from a single supercritical hydrogen isotherm at 77 K. In addition, this method does not require a conversion between gravimetric excess adsorption and absolute adsorption. The overall average binding energy of hydrogen is 4.4 kJ/mol and the binding energy at low coverage is 9.2 kJ/mol. The hydrogen film density at saturation is 0.10 g/mL corresponding to a local pressure of 1500 bar in the adsorbed phase.

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