POWDER X-RAY-DIFFRACTION AND MICROSTRUCTU RE IN FERROELECTRIC DOMAINS

A new way of investigation with classical powder diffraction technique s is proposed: so, using, as an example, the case of the famous ferroe lectric material, barium titanate BaTiO3, it is shown how very relevan t informations related to the ferroelectric domain microstructure of s uch a material and its evolution can be obtained At room temperature, BaTiO3 is tetragonal and ferroelectric. The single crystalline grains are divided into ferroelectric domains within the polarization vector is uniform. Two domain types are coexisting: 180 degrees domains (anti parallel polarization vectors) and 90 degrees domains (perpendicular p olarization vectors) in order to minimize the overall deformation and electrostatic energies. The polar axis is [001]. The 90 degrees domain walls are (101) and (011) planes. Therefore, the ferroelectric micros tructure and the crystallographic structure are in close relation. The originality of this work is to reveal how the ferroelectric microstru cture influences the X-ray powder diffraction (XRPD) diagram of a ferr oelectric material. Such a microstructure may change with physical fac tors as pressure, electric field or temperature. The evolution of the XRPD diagram (particularly 002-200 double lines and hhh lines) with th e two last physical factors, has been shown to be correlated to the fe rroelectric microstructure changes. So, three main features have been already detected and studied: the intensity ratio of the 002-200 doubl e lines is changing with the applied electric field and is directly re lated to the material polarization, the width of the hhh lines decreas es when heating a powder above the ferroelectric to paraelectric trans ition temperature (Tc = 120 degrees C). This decrease could not be exp lained by a classical lattice microdistorsion relaxation, wich usually occures for higher temperatures. It can be interpreted by the relaxat ion of particular lattice microdistorsion : the ferroelectric domain w alls. compared to the symmetric XRD line profiles of a non ferroelectr ic tetragonal material, the 002-200 double line profiles of BaTiO3 are very asymmetrical; this asymmetry looks like an unusual diffracted in tensity between the two lines. This particular intensity has been prov ed to be closely related to the stress state of the ferroelectric micr ostructure.