Nanosized BaTiO3-based systems

Abstract In the context of limiting or even replacing dangerous substances such as lead (a volatile, toxic, and nonrecyclable element) in electric and electronic devices, in the last decade many efforts were devoted to identify new lead-free oxides and to improve or adjust the electrical behavior of the already known ferroelectrics, in order to obtain functional properties of higher performance, close to those of piezoelectric Pb(Zr,Ti)O 3 and relaxor Pb(Mg 1/3 Nb 2/3 )O 3 systems. A viable alternative, from this point of view, is represented by the BaTiO 3 (BT)-based systems, one of the most widely investigated classes of perovskites, due to their environmentally-friendly character along with unique and multiple useful properties, such as high permitivity, high pyro- and piezoelectric coefficients, switching properties, positive temperature coefficient of resistivity (PTCR effect), and high-voltage tunability. These properties make them suitable for many applications, in high performance ceramic capacitors, information storage devices, field effect devices, piezoelectric and ultrasonic actuators, transducers, sensors, pyroelectric detectors, and thermistors. Despite the large number of exhaustive studies and reports on elaboration and characterization of materials derived from BT, they continue to represent a challenging and “hot” topic, due to their versatile electric behavior, and being very sensitive to many factors such as dopants/solutes, stoichiometry, processing methods, among others. In the last few years, the development of several innovative preparation and sintering techniques caused a revival of the interest in BT-based systems, with controlled and highly reproducible electrical behavior. This trend become even more compelling and explicable in the context of the miniaturization and of the high integrability degree imposed by nanotechnology, which involves either preservation of ferroelectricity or development of new functionalities in highly densified, nanosized BT products with restrictive geometries. Thus, in multilayer ceramic capacitors (MLCCs), for a high volumetric capacity C v in a volume as small as possible, since C v ~ e r · n / d 2 , (where n is the number of layers, d is the thickness of a ceramic layer, and e r is the relative permittivity), the thickness of the dielectric layer should be as small as possible and the number of layers as high as possible. Nowadays, the thickness of a dielectric layer is in the submicron range and the number of dielectric layers can exceed 2000 in MLCCs.