Tham khảo tài liệu 'ferroelectrics material aspects part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 15 Lead-Free Ferroelectric Ceramics with Perovskite Structure Rigoberto Lopez-Juarez1 Federico Gonzalez2 and María-Elena Villafuerte-Castrejon1 institute de Investigaciones en Materiales Universidad Nacional Autónoma de Mexico 2Departamento de Ingeniería de Procesos e Hidráulica Universidad Autónoma Metropolitana-Iztapalapa México 1. Introduction Ferroelectric ceramics were discovered in the 1940s in polycrystalline barium titanate von Hippel et al. 1946 Wul Goldman 1945 since then there has been a continuous succession of new materials and technology developments that have led to a significant number of industrial and commercial applications. Structurally speaking there are four types of ferroelectric ceramics 1 perovskites 2 the tungsten-bronze group 3 pyrochlores and 4 the bismuth layer-structure group. Of these the perovskites ABO3 are by far the most important category. The families with composition BaTiOs PbZr1-xTixOs PZT PZT La PLZT PbTiOs Pt Pb Mg13NI 2 O PMN and NbO3 KNN represents most of the ferroelectric ceramics manufactured in the world Haertling 1999 . In this chapter the structure of calcium titanium oxide CaTiO3 the ferroelectrics ceramics BaTiO3 NBT KBT are described as well the concept of hysteresis loop ferroelectric domains and why lead free materials are now in the top of the interest in ferroelectric and piezoelectric materials. The aim of this chapter is to present results of the synthesis characterization and piezoelectric properties of two lead free piezoelectric compounds KasNaasNbOs and . Perovskite structure The mineral perovskite is calcium titanate with chemical formula CaTiO3 its ideal structure has space group Pm-3m. Most of the commercially important ferroelectric materials have perovskite related crystal structure. The family of the perovskite oxides has generic composition ABO3 where A is 12 fold coordinated with respect to oxygen Fig. 1c and B is .
