Abstract
Since the discovery of the piezoelectricity in quartz, the need of efficient materials for piezoelectric and non-linear optic technological applications has increased dramatically. Both properties have to exhibit a high thermal stability over a wide temperature range. In my thesis work, the BaXO2 quartz type structure materials (X = Zn or Co) have been studied since they crystallize in the same P3121/P3221 space group than quartz, which is still one of the most widely used minerals mainly due to its piezoelectric properties.We have started this work with the BaZnO2 compound since first-principles-based calculations predicted an electromechanical coupling, k_11=35.7%. Our combined experimental and theoretical study allowed i) to characterize the chemical and thermal stability of BaZnO2 up to 1273 K, and ii) to determine the dielectric and vibrational (IR-Raman) properties of the material. Additionally the non-linear optic responses are predicted to be one order of magnitude higher than those reported for quartz.In BaCoO2, the oxidation state of Co (+II) in a tetrahedral symmetry implies an antiferromagnetic order at room temperature ( T_N=330 K). Associated with the -quartz type structure, a piezo-magnetic coupling can be considered. BaCoO2 was structurally and vibrationally characterized up to 1273 K (as obtained results were confronted to theory) and an exceptional reversible oxygen storage capacity was pointed out in BaCoO_(2+δ )(0 < δ ≤ 1) based on thermogravimetric measurements, Raman spectroscopy and X-ray diffraction characterizations. The oxygen insertion/disinsertion mechanism is governed by a topotactic transition sequence.