When materials are compressed, their atoms are forced into unusual arrangements that do not normally exist under everyday conditions. These configurations are often fleeting: when the pressure is released, the atoms typically relax back to a stable low-pressure state. Only a few very specific materials, like diamond, retain their high-pressure structure after returning to room temperature and atmospheric pressure.
But locking those atomic arrangements in place under ambient conditions could create new classes of useful materials with a wide range of potential applications. One particularly compelling example is energetic materials, which are useful for propellants and explosives.
In a study published in Nature Communications Chemistry, researchers at Lawrence Livermore National Laboratory (LLNL) identified a first-of-its-kind carbon dioxide-equivalent polymer that can be recovered from high-pressure conditions.
"A polymeric form of carbon dioxide stores far more energy than ordinary carbon dioxide because its atoms are locked into a dense, covalently bonded network," said LLNL scientist and author Stanimir Bonev. "If such a material can be recovered and stabilized, it represents a high-energy-density material - meaning it can store and potentially release large amounts of energy per unit mass or volume."
The team combined quantum molecular dynamics simulations with large-scale machine-learning models to predict pathways for forming the polymer and to understand its behavior both at high pressure and as pressure is released. Together, these methods allowed the researchers to explore a broad range of pressure and temperature conditions in a controlled and systematic way, providing a clear recipe for future experimental efforts.
The breakthrough came when the authors focused on compressing a mixture of carbon monoxide and oxygen, rather than carbon dioxide itself. Starting from a molecular mixture allows transformations to occur at lower pressures and opens up more flexible reaction pathways. This approach also favors the formation of amorphous solids, which lack the regular structure of crystals and can be more stable when pressure is released.
"We believe these amorphous structures experience less bond strain when pressure is released, which enhances their stability under ambient conditions," said Bonev. "This highlights the potential of amorphous materials - often overlooked in favor of crystals - to offer greater stability and useful properties."
With this mixture, the researchers identified a synthesis pathway that begins near 7 gigapascals of pressure - more than an order of magnitude lower than the over 100 gigapascals previously required to form polymeric carbon dioxide-based materials.
Alongside the simulations that show how to create the material, the authors also provide a physical explanation of why it works. The key lies in carbon-carbon bonds, which form readily in the mixture and contribute to a distinct and stable structure that helps the material remain intact when pressure is released.
The scientists hope this work provides a concrete target and a practical strategy for future experimental efforts. More broadly, the approach could be applied to other light-element systems involving carbon, oxygen, nitrogen or hydrogen, potentially leading to new families of recoverable energetic and functional materials.
This work was supported by the LLNL's Laboratory Directed Research and Development Program.
