Collaboration sparks new model for ceramic conductivity

Credit: CC0 Public Domain

As insulators, metal oxides—also known as ceramics—may not seem like obvious candidates for electrical conductivity. While electrons zip back and forth in regular metals, their movement in ceramic materials is sluggish and difficult to detect.

An interdisciplinary collaboration led by Richard Robinson updated the “small polaron hopping model” to reflect different pathways for conduction in ceramics. Their work will help researchers who are custom-tailoring the properties of metal oxides in technologies such as lithium ion batteries, fuel cells and electrocatalysis.

But ceramics do contain a large range of conductivities. This behavior was laid out in 1961 in the “small polaron hopping model,” which described the movement of polarons—essentially electrons coupled to a lattice distortion—from one end of a material to the other.

An interdisciplinary collaboration led by Richard Robinson, associate professor of materials science and engineering in the College of Engineering, has shown just how outdated and inaccurate that model is, especially regarding complex oxide systems. By updating the model to reflect different pathways for conduction, the team hopes its work will help researchers who are custom-tailoring the properties of metal oxides in technologies such as lithium ion batteries, fuel cells and electrocatalysis.

Their paper, “Breakdown of the Small-Polaron Hopping Model in Higher-Order Spinels,” published Oct. 21 in Advanced Materials. The lead author is doctoral student Anuj Bhargava.

“This is the most commonly-used formula in the field, but it hadn’t been touched in 60 years. That’s a big deal because, nowadays, metal oxides are used in many applications where the performance is directly impacted by the conductivity—for example, in energy systems like electrical energy storage and generation, electrocatalysis, and in new-generation materials,” Robinson said. “Many people are putting a great amount of experimental effort into oxides right now, but they haven’t carefully examined how the charge carriers move in the material, and how the composition influences that conductivity.

Radical collaboration

“If we understood how electrons are conducted and we could customize the composition to have the highest conductivity, we could optimize the energy efficiency of a lot of materials out there,” he said.

To get a detailed look at the way electrons move in metal oxides and how their occupation sites can affect the material’s conductivity, Robinson turned to Darrell Schlom, the Herbert Fisk Johnson Professor of Industrial Chemistry. Schlom and his team used the Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM) and the Cornell NanoScale Science and Technology Facility (CNF) to grow and characterize thin crystalline films of manganese-doped iron oxide (MnxFe3-xO4).

Robinson’s group then used the Cornell High Energy Synchrotron Source (CHESS) to determine the atomic locations and the charge state of the positively charged ions, called cations, and measured how the material’s conductivity changes at different temperatures.

They brought the material to Lena Kourkoutis, associate professor in applied and engineering physics, who used advanced electron microscopy to get an atomically precise view of the crystal’s substrate and compositional gradients, and confirmed the team’s findings.

Lastly, Robinson’s team

The world’s best restaurant, located in the beautiful French Riviera, was forced to close when the pandemic began. Take a look at how it has successfully reopened, including picnic-style courses eaten in a garden and ceramic bowls full of hand sanitizer.

Mauro Colagreco standing in front of a tree: Mirazur's head chef Mauro Colagreco in the restaurant's garden. Matteo Carassale

© Provided by Business Insider
Mirazur’s head chef Mauro Colagreco in the restaurant’s garden. Matteo Carassale

  • Mirazur is a three Michelin-starred restaurant located in the town of Menton, France, that was ranked as the World’s Best Restaurant in 2019.
  • After the restaurant was forced to close in March for the country’s 55-day lockdown due to the pandemic, head chef Mauro Colagreco spent time in the restaurant’s gardens to develop a new reopening menu, says head sommelier Benoît Huguenin.
  • Chef Colagreco designed a new menu called Universe Mirazur, featuring meals that focus on four different themes (roots, fruits, flowers, and leaves) and is served to align with the lunar cycle.
  • The nine-course menu starts at 320, or USD$375, and rotates every three days at most, as does the biodynamic wine list.
  • Visit Business Insider’s homepage for more stories.

In June 2019 at the age of 24, Benoît Huguenin became the head sommelier at Mirazur, crowned the World’s Best Restaurant of 2019. He was by Argentinian chef Mauro Colagreco’s side as Mirazur received the title in a glitzy ceremony in Singapore.

It topped off an incredible year for the restaurant located footsteps from the Italian border in Menton on the French Riviera: Five months earlier it had been awarded its third Michelin star. With it, Colagreco became the first non-French chef in France to receive such an honor.

a man standing next to a building: Mirazur chef Mauro Colagreco (left) and head sommelier Benoît Huguenin (right). Mauro Colagreco/Matteo Carassale/Business Insider

© Mauro Colagreco/Matteo Carassale/Business Insider
Mirazur chef Mauro Colagreco (left) and head sommelier Benoît Huguenin (right). Mauro Colagreco/Matteo Carassale/Business Insider

Fast forward to spring 2020 and the whirlwind four-day trip from the Côte d’Azur to Singapore and back again last summer seemed more like a lifetime ago.

With Mirazur shuttered to the public during France’s 55-day COVID-19 lockdown, Huguenin’s sole professional responsibility was in its kitchen, one of a team of six who had volunteered to prepare meals for local hospital workers three times a week. 

Chef Colagreco spent much of the confinement tending to his gardens that supply produce to the restaurant.

The time allowed the celebrated chef to slow down, reflect, and reconnect with nature, according to Huguenin. In late April, as the country prepared for the easing of lockdown measures, Colagreco gathered his team to discuss plans for reopening the restaurant. He also shared his observations of the last two months. 

“The chef explained that, depending on the moon’s cycle, some days the roots are different, as are the flowers, the leaves, and the fruits,” Huguenin told Business Insider. “We spoke about this for three or so hours. He joked that maybe we should create a special menu around this.”

a group of stuffed animals hanging from a tree: Mirazur's Chef Mauro Colagreco in the restaurant garden. Matteo Carassale

© Matteo Carassale
Mirazur’s Chef Mauro Colagreco in the restaurant garden. Matteo Carassale

Two days later, Colagreco made it official: Mirazur would be opening with a new menu divided into four themes: roots, fruits, flowers, and leaves. Each day’s theme would align with the lunar cycle. The intention was to bring the biodynamic principles practiced in the restaurant’s gardens into the kitchen, allowing guests to experience what nature intended, when