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In a recent paper, researchers challenge the conventional belief that smaller domain sizes lead to greater piezoelectric properties. and infrastructure needed to facilitate this paradigm shift in materials science. The challenge is so daunting that many national and multinational “Big Data” projects are underway to develop and deploy tools needed. Planetary science holds out the prospect of expanding the synthesis and fabrication conditions well beyond those possible on Earth. As Navrotsky and Householder say, understanding the complex dynamics of other planets and moons “liberates our thinking from being bound by one geotherm and one planetary composition.” For example, the extreme temperatures and pressures of other celestial bodies extend the realm of ceramic science into regions where entirely new materials and phases can be formed. Imagine the same processes that form diamond from graphite but at more extreme scales. Navrotsky and Householder explain our current understanding of the geology, atmosphere, size, and other properties of the planets and moons in our solar system as a framework for understanding such bodies orbiting other stars. All the unknowns even within our solar system lead Navrotsky and Householder to conjecture about a range of topics, including the contri- butions of comets and the possibility of superconductivity within cryogenic planets and how that might affect the magnetic fields and, in turn, the plan- etary environments. While there are many challenges to be met—including the development of analytical methods that will enable investigation of other planets at a dis- tance—the answers we will gain about materials, the origins of our universe and terrestrial life, and the possibilities of extraterrestrial life make our research and cross-discipline collaborations so important—and exciting. The open-access paper, published in International Journal of Ceramic Engineering & Science, is “New worlds, new chem- istry, new ceramics” (DOI: 10.1002/ ces2.10104). n New model for determining piezoelectricity in ferroelectric crystals In a recent paper, researchers at The Pennsylvania State University and Xi’an Jiaotong University challenge the con- ventional belief that smaller domain sizes lead to greater piezoelectric properties. Ferroelectricity is the property of certain materials having spontaneous electric polarization that is reversible through the application of external elec- tric fields. Ferroelectric materials are a subset of piezoelectric materials, which generate an electric charge in response to an applied mechanical stress. In the 100 years since the first reported discovery of ferroelectricity in 1920, identification and use of ferro- electric materials has proliferated. These materials are now essential components in many advanced technologies, includ- ing smartphones, diagnostic ultrasound, energy harvesting and storage, and more. When designing ferroelectric materi- als, researchers have long been guided by the belief that smaller domain sizes lead to greater piezoelectric properties. This belief is based on the fact that domain walls have a strong influence on piezo- electricity. Thus, smaller domain sizes equate to a higher density of domain walls, which should give a larger piezo- electric coefficient. The researchers of the recent paper challenge this belief. They explain that the idea that smaller domains lead to higher piezoelectricity is based on very limited existing data without a solid theoretical foundation, and these stud- ies looked only at the surface of a ferro- electric crystal. So, the authors decided to theoretically examine what happens under the surface of ferroelectric crys- tals using thermodynamic analysis and phase-field simulations. They determined that the nature of the domain-size dependence of piezo- electricity is based on the propensity of polarization rotation inside the domains instead of the domain wall contribu- tions. Thus, the inverse domain-size effect—the larger the domain size, the higher the piezoelectricity—is entirely possible and can be just as common. Based on these findings, the research- ers established a new analytical model for predicting the domain-size depen- dence of piezoelectricity, which “can serve as a guiding tool for optimizing piezoelectricity of ferroelectric materials beyond the ‘nanodomain’ engineering,” they write in the paper. “We hope that this study allows peo- ple to rethink the design principles for piezoelectric materials, perhaps creating better piezoelectric materials in ways that were not thought possible before,” Penn State postdoctoral scholar Bo Wang says in a Penn State press release. “This may enable better piezoelectrics made from lower-cost materials, or from materials that are more environmentally friendly.” The paper, published in Advanced Materials, is “Inverse domain-size dependence of piezoelectricity in fer- roelectric crystals” (DOI: 10.1002/ adma.202105071). n American Ceramic Society Bulletin, Vol. 101, No. 2 | www.ceramics.org 25 Credit: ACerSPDF Image | hydrogen as an alternative fuel
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