Synthèse et Caractérisation de matériaux LN : Ho en vue de fabrication de fibres cristallines

National audienc

Synthesis and characterization of holmium doped lithium niobate powders

International audienceHolmium doped lithium niobate (LN:Ho) powders with initial concentration of holmium in the range 0–7 mol% were synthesized by the ceramic powder processing method. Niobium penta-oxide Nb2O5, lithium carboxide LiCO3 and holmium oxide Ho2O3 with a purity of 99.99% were the starting materials. The phase content and lattice parameters of powders and ceramic pellets were characterized by X-ray diffraction (XRD). To further investigate the quality of the synthesized LN:Ho powders, the scanning electron microscopy (SEM) was used to determine the particle size and the morphology. The main results of this work point out the fact that the ceramic powder processing method is a well adapt method for obtaining high quality LN:Ho ceramics in the holmium concentration range analysed as the LiNbO3 phase is lonely present in the ceramics at the end of the synthesized process and as their grain sizes are regular, with a maximum for the sample doped with 7 mol% of holmium

Le lien entre la fréquence de relaxation, la température de transition et la liaison chimique dans les céramiques dérivées de BaTiO3

International audienc

Synthesis and characterization of magnesium doped lead titanate

International audienc

DIELECTRIC MEASUREMENTS AND IMPEDANCE SPECTROSCOPY OF Ba-MODIFIED (Na 0.5Bi0.5)TiO₃ PREPARED BY THE HYDROTHERMAL METHOD

Sodium bismuth titanate (Na0.5Bi0.5)TiO₃ perovskite is presented as a lead-free concurrent for electro-ceramic engineering technologies. In this paper, (1-x)(Na0.5Bi0.5)TiO₃-xBaTiO₃ type ceramic materials were obtained by the hydrothermal process at a very low heat treatment temperature of around 200 ° C and for times up to 24 hours. The structural, microstructural, and dielectric properties of the ceramic materials were investigated. The X-ray diffraction analysis confirms the formation of the rhombohedral phase of NBT with space group R3c. Based on the Rietveld refinement, the morphotropic phase boundary (MPB) was determined for the composition x (%) = 5 and 7. The grains increase in size from 11 to 23 μm and their distribution widens with an increasing barium concentration in the morphotropic phase boundary. The dielectric constants were measured from room temperature to 600 °C for various frequencies in the range of 1 kHz - 2 MHz. From the Nyquist impedance plot, the effect of the grain and the grain boundaries on the electrical properties was studied. At high temperatures, the Uchino law modified by Echatoui et al. allows one to describe the thermal variation of the permittivity. This diffuse character is attributed to a cationic disorder due to the distribution of Na + /Bi 3+ and Ba 2+ ions in the A site