Highly textured lead-free piezoelectric polycrystals grown by the micro-pulling down freezing technique in the BaTiO3 –CaTiO3 system
Résumé
Highly textured cm-sized (Ba1−xCax)TiO3 (x = 0.05) polycrystals at off-eutectic composition were grown by the micro-pulling down freezing technique from a BaTiO3–CaTiO3 system at a high pulling velocity of about 48 mm h−1. Textured polycrystals exhibiting submillimetre-sized dendrites along the (110)pc growth direction and geometrical grains along the (100)pc direction were revealed by a complementary analysis performed by Laue diffraction and EBSD techniques. An average Ca content of about x = 0.0435 was measured throughout the whole volume of the boule and led to an effective partition coefficient of Ca of about 0.87. LIBS measurements highlighted the local segregation of Ca and major impurity contents within dendrites, grains and at the grain boundaries. Dielectric and piezoelectric measurements performed on oriented polycrystalline textured samples led to Curie temperatures up to 116 °C and d33 up to 214 pC N−1, in very good agreement with literature values. Both chemical and physical results obtained in the BCT system make the μ-PD technique a promising and alternative way to improve the piezoelectric response of lead-free solid solution-based crystals through their texturing along preferential crystallographic directions.