Perovskite Pb(Zr,Ti)O3-based ceramics are used widely as piezoelectric materials owing to their superior electrical attributes. Lead oxide is a major component of these materials. Reference to the ever-rising concerns of the global environment, the inception of materials that do not contain toxic metals is critical. For this reason, lead-free piezoelectric materials have been investigated all over the world.
Barium titanate appears to be a promising candidate. Single crystals of barium titanate exhibit large electric-field-induced strain through control of designed domain configuration. Unfortunately, barium titanate-based materials have low endurance in reducing atmosphere. This causes poor insulating resistance and makes the analysis of ferroelectric as well as piezoelectric attributes challenging. The production of conductive electrons accompanied by the reduction of titanium ions in the course of the sintering process is the principle cause.
In addition, with the quest for downsizing the piezoelectric actuator devices, a multilayer technology would be very critical for realizing high displacement while lowering the working voltage. In view of the fact that noble metal electrodes are normally used in current multilayer-type electric ceramic components, the cost of the internal electrode rises. As for multilayer ceramic capacitors, to minimize the cost of electrode, establishing a co-sintering process with base metal electrodes under a low oxygen partial pressure is needed for the synthesis of multilayer piezoelectric components.
In order to make reduction-resistant barium titanate-based ceramics, the impact of manganese doping on barium titanate-based materials will be addressed in this paper for ceramics sintered in argon/hydrogen atmosphere. Dr. Wataru Sakamoto and co-workers at Nagoya University in Japan successfully fabricated non-reducible (Ba,Ca)TiO3 ceramics to obtain electrical attributes comparable to those of samples sintered in air. This was in the quest for implementing lead-free barium titanate materials for multilayer piezoelectric applications at a reasonable cost. Their research work is published in peer-reviewed journal, Ceramics International.
The research team fabricated a reduction-resistant (Ba,Ca)TiO3 ceramics with high sintered density, enhanced electrical resistivity, and homogeneous grain structure through the modification of chemical composition with excess barium and manganese doping. They stabilized the tetragonal phase of barium titanate over a rage of temperature by the formation of a solid solution with calcium titanate even in non-reducible specimens.
The authors found that manganese doping was efficient in enhancing the field-induced and ferro-electric strain attributes for the developed ceramics sintered in both air and argon flow containing 0.3% hydrogen. Electron spin resonance analysis indicated that doped manganese existed as manganese ions in the resulting ceramics sintered under low oxygen partial pressure, which was below 0.1Pa. Manganese ions would have worked as acceptors to capture conductive electrons with the valence change.
The ferro-electric as well as field induced strain attributes of 1 mol% manganese doped ceramics sintered in reducing atmosphere was similar to those of 0.2 mol% manganese-doped ceramics sintered in air. By undertaking the suitable poling treatment, the poling condition of the non-reducible ceramics was enhanced, and led to the observation of potential piezoelectric attributes. The resulting reduction-resistant (Ba,Ca)TiO3-based ceramics developed in the study by Wataru Sakamoto and co-workers are promising building blocks for lead-free ceramics for multilayer piezoelectric component applications.
Wataru Sakamoto, Kouta Noritake, Hiroki Ichikawa, Koichiro Hayashi, and Toshinobu Yogo. Fabrication and properties of non-reducible lead-free piezoelectric Mn-doped (Ba,Ca)TiO3 ceramics. Ceramics International, volume 43 (2017), pages S166–S171.Go To Ceramics International