This project is focused on the critical mechanics issues in antiferroelectric ceramics subjected to electrical and/or mechanical loads. Compared to most dielectric materials used in capacitors for electrical energy storage, special (e.g. PbZrO3-based) antiferroelectric ceramics display a much higher energy density due to the reversible antiferroelectricferroelectric phase transition, which is manifested by an abrupt development of large amounts of electrical charge and volume strain. As such, the phase transition makes these ceramics responsive to both electric fields and mechanical stresses and forms the fundamental basis for energy-storage applications. The associated volume change induces complicated internal stress states in the ceramic and thus influences the reliability of capacitors. Through an integrated experimental and theoretical approach, this project aims to rigorously establish the novel phase-transition-toughening mechanism in antiferroelectric ceramics, which will lead to highly efficient and highly reliable energy-storage devices.
The success of this project will pave the way to the large-scale usage of antiferroelectric capacitors with high power/energy density. Such capacitors are urgently needed for renewable energy sources, such as wind and solar. Their intermittent nature requires efficient energy-storage technologies to ensure around-the-clock delivery. Furthermore, this project is designed to have a broad impact on both graduate and undergraduate education. Undergraduate students, especially those from underrepresented groups, will be exposed to this research through various existing educational programs at Iowa State University. In addition, participating graduate students will spend some summer months in Germany for part of the experimental work, thus acquiring international experiences.
Intellectual Merit. The global energy crisis and the disastrous impact of carbon emission to the human habitat have been forcing scientists and engineers to acquire electricity from clean and renewable sources, such as wind and solar. The intermittent nature of these renewable sources requires efficient electrical energy storage technologies to ensure around-the-clock delivery without fluctuations. Among the leading technologies used today, electrical capacitors have an extremely high power density (can release energy very fast) but a low energy density. This project is focused on critical mechanics issues related to a special class of dielectric materials, i.e. antiferroelectric ceramics, which have the potential to increase the energy density of electrical capacitors by at least one order of magnitude. The high energy density in antiferroelectric capacitors is originated from the antiferroelectric-ferroelectric phase transition which can be triggered by multi-physics stimuli, such as mechanical stresses and electric fields. Through the support of this project, it is demonstrated that a minor chemical modification of traditional antiferroelectric ceramics can enhance the reversibility of the phase transition and hence considerably increases the energy storage efficiency. With an integrated experimental and theoretical approach, a novel self-confinement mechanism is proposed and verified to increase the energy storage density further. For the first time, it is discovered that a moderate electric field with a reversed polarity can trigger the energy release process. Most importantly, for the first time, the phase transition is experimentally demonstrated to be capable of toughening the ceramic: a 60-130% increase in fracture toughness is observed in an antiferroelectric ceramic compared to other dielectric ceramics with similar compositions. This phase transition toughening effect can be utilized to greatly enhance device reliability. Therefore, the outcome of this project will help to realize the full potential of antiferroelectric ceramics in electrical capacitors for efficient energy storage. The results from this project have generated 10 articles in prestigious technical journals, including Physical Review Letters and Advanced Functional Materials. Broader Impact. The research findings have been broadly disseminated at professional technical conferences, including the NSF-CMMI PI meetings, the Electronic Materials and Applications annual meeting, the IEEE International Symposium on the Applications of Ferroelectrics, and the Fundamental Physics of Ferroelectric Workshop. The PIs have delivered 7 invited talks and 6 contributed presentations. The broad impacts of this research project are also demonstrated by the education and training of next generation engineers and scientists. It has financially supported 3 graduate students, 2 of them have graduated with a MS degree. In addition, five undergraduate students, Ms. Alexandra Skora, Mr. Daniel Hastings, Ms. Cynthia Biggs, Ms. Alexa Oser, and Mr. Benjamin Trieu were recruited to work on the project. They worked with graduate students and made contributions to ceramic processing, structure-property characterization, as well as other research skills. The PI (Tan) also hosted and mentored two Ames High School girls in spring 2011 for their science project. In the PI’s lab, the two high school students worked together with a Ph.D. student and prepared a new ceramic with a huge dielectric constant. These two students were selected to attend the Iowa Academy of Science Annual Meeting and made a poster presentation. The PI (Tan) has also involved with the Science Olympiad team at local secondary schools through mentoring team members during their preparation of competing events. The team won the state competition and represented Iowa at the national tournament in May 2012 in Orlando, Florida. One of the events the PI mentored was ranked 14th place at the nationals among 60 participating teams from all over the country.
