Computers Math

Perovskites, a family of materials with unique electric properties, show promise for use in a variety fields, including next-generation solar cells. A Penn State-led team of scientists created a new process to fabricate large perovskite devices that is more cost- and time-effective than previously possible and that they said may accelerate future materials discovery.
“This method we developed allows us to easily create very large bulk samples within several minutes, rather than days or weeks using traditional methods,” said Luyao Zheng, a postdoctoral researcher in the Department of Materials Science at Penn State and lead author on the study. “And our materials are high quality — their properties can compete with single-crystal perovskites.”
The researchers used a sintering method called the electrical and mechanical field-assisted sintering technique (EM-FAST) to create the devices. Sintering is a commonly used process to compress fine powders into a solid mass of material using heat and pressure.
A typical process for making perovskites involves wet chemistry — the materials are liquefied in a solvent solution and then solidified into thin films. These materials have excellent properties, but the approach is expensive and inefficient for creating large perovskites and the solvents used may be toxic, the scientists said.
“Our technique is the best of both worlds,” said Bed Poudel, a researcher professor at Penn State and a co-author. “We get single-crystal-like properties, and we don’t have to worry about size limitations or any contamination or yield of toxic materials.”
Because it uses dry materials, the EM-FAST technique opens the door to include new dopants, ingredients added to tailor device properties, that are not compatible with the wet chemistry used to make thin films, potentially accelerating the discovery of new materials, the scientists said.

“This opens up possibilities to design and develop new classes of materials, including better thermoelectric and solar materials, as well as X- and γ-ray detectors,” said Amin Nozariasbmarz, assistant research professor at Penn State and a co-author. “Some of the applications are things we already know, but because this is a new technique to make new halide perovskite materials with controlled properties, structures, and compositions, maybe there is room in the future for new breakthroughs to come from that.”
In addition, the new process allows for layered materials — one powder underneath another — to create designer compositions. In the future, manufactures could design specific devices and then directly print them from dry powders, the scientists said.
“We anticipate this FAST perovskite would open another dimension for high throughput material synthesis, future manufacturing directly printing devices from powder and accelerating the material discovery of new perovskite compositions,” said Kai Wang, an assistant research professor at Penn State and a co-author.
EM-FAST, also known as spark plasma sintering, involves applying electric current and pressure to powders to create new materials. The process has a 100% yield — all the raw ingredients go into the final device, as opposed to 20 to 30% in solution-based processing.
The technique produced perovskite materials at .2 inch per minute, allowing scientists to create quickly create large devices that maintained high performance in laboratory tests. The team reported their findings in the journal Nature Communications.

Penn State scientists have long used EM-FAST to create thermoelectric devices. This work represents the first attempt to create perovskite materials with the technique, the scientists said.
“Because of the background we have, we were talking and thought we could change some parameters and try this with perovskites,” Nozariasbmarz said. “And it just opened a door to a new world. This paper is a link to that door — to new materials and new properties.”
Other Penn State researchers on the project were Wenjie Li and Dong Yang, assistant research professors; Ke Wang, staff scientist in the Materials Research Institute; Jungjin Yoon, Tao Ye and Yu Zhang, postdoctoral researchers; Yuchen Hou, doctoral candidate; and Shashank Priya, former associate vice president for research and director of strategic initiatives and professor of materials science and engineering.
Also contributing was Mohan Sanghadasa, U.S. Army Combat Capabilities Development Command Aviation and Missile Center.
Researchers received support from the National Science Foundation Industry-University Research Partnerships’ Center for Energy Harvesting Materials and Systems, U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy, Air Force Office of Scientific Research, and Office of Naval Research and Army Research. More

Octopus arms coordinate nearly infinite degrees of freedom to perform complex movements such as reaching, grasping, fetching, crawling, and swimming. How these animals achieve such a wide range of activities remains a source of mystery, amazement, and inspiration. Part of the challenge comes from the intricate organization and biomechanics of the internal muscles.
This problem was tackled in a multidisciplinary project led by Prashant Mehta and Mattia Gazzola, professors of mechanical science & engineering at the University of Illinois Urbana-Champaign. As reported in Proceedings of the Royal Society A, the two researchers and their groups have developed a physiologically accurate model of octopus arm muscles. “Our model, the first of its kind, not only provides insight into the biological problem, but a framework for design and control of soft robots going forward,” Mehta said.
The impressive capabilities of octopus arms have long served as an inspiration for the design and control of soft robots. Such soft robots have the potential to perform complex tasks in unstructured environments while operating safely around humans, with applications ranging from agriculture to surgery.
Graduate student Heng-Sheng Chang, the study’s lead author, explained that soft-bodied systems like octopuses’ arms present a major modeling and control challenge. “They are driven by three major internal muscle groups — longitudinal, transverse, and oblique — that cause the arm to deform in several modes — shearing, extending, bending, and twisting,” he said. “This endows the soft muscular arms with significant freedom, unlike their rigid counterparts.”
The team’s key insight was to express the arm musculature using a stored energy function, a concept borrowed from the theory of continuum mechanics. Postdoctoral scholar and corresponding author Udit Halder explained that “The arm rests at the minimum of an energy landscape. Muscle actuations modify the stored energy function, thus shifting the equilibrium position of the arm and guiding the motion.”
Interpreting the muscles using stored energy dramatically simplifies the arm’s control design. In particular, the study outlines an energy-shaping control methodology to compute the necessary muscle activations for solving manipulation tasks such as reaching and grasping. When this approach was numerically demonstrated in the software environment Elastica, This model led to remarkably life-like motion when an octopus arm was simulated in three dimensions. Moreover, according to Halder, “Our work offers mathematical guarantees of performance that are often lacking in alternative approaches, including machine learning.”
“Our work is part of a larger ecosystem of ongoing collaborations at the University of Illinois,” Mehta said. “Upstream, there are biologists who perform experiments on octopuses. Downstream, there are roboticists who are taking these mathematical ideas and applying them to real soft robots.”
Mehta’s and Gazzola’s groups collaborated with Rhanor Gillette, Illinois Professor Emeritus of molecular and integrative physiology, to incorporate observed octopus physiology into their mathematical model for this study. Future work will discuss the biological implications of energy-based control. In addition, the researchers are collaborating with Girish Krishnan, an Illinois professor of industrial & enterprise systems engineering, to incorporate their mathematical ideas into real soft robot design and control. This will not only create a systematic way of controlling soft robots, but will also provide a deeper understanding of their working mechanisms.
This work was part of the CyberOctopus project, a multidisciplinary university research initiative in the University of Illinois’ Coordinated Science Laboratory supported by the Office of Naval Research. More