Barocaloric materials function through reversible structural transitions triggered by pressure changes, making them ideal for next-generation refrigeration cycles. Among these, plastic crystals have garnered significant attention due to their pronounced barocaloric response near ambient temperatures. These materials undergo transformations between disordered (plastic crystal) and ordered crystalline phases, with the associated entropy changes dictating their thermal energy exchange capabilities. However, harnessing these caloric changes efficiently for practical applications is complicated by thermal hysteresis, which limits the reversible fraction of the entropy change achievable within operable pressures.

A multinational research effort led by institutions including the University of Glasgow and the University of Cambridge has unveiled a strategic compositional engineering approach that markedly enhances the reversible barocaloric effect in neopentyl glycol (NPG) plastic crystals. Pure NPG—renowned for its significant caloric response—has been hampered by a large thermal hysteresis, impairing its cyclic cooling reliability. By blending NPG with pentaglycerine (PG) to form a binary solution, researchers first shifted the critical transition temperature closer to room temperature, improving its pragmatic usability.

The breakthrough came with the introduction of a minute 2 mol % addition of pentaerythritol (PE), creating a ternary solid solution—NPG:PG:PE in a 60:38:2 ratio. This alteration achieved a transformative increase in barocaloric reversibility and operational temperature window at achievable pressures around 1 kbar. Specifically, the ternary material exhibited a reversible entropy change of 13.4 J kg⁻¹ K⁻¹, a sevenfold enhancement compared to pristine NPG, and broadened its effective thermal range by approximately 18 K. Consequently, the reversible refrigeration capacity soared by over seventy times, positioning this material as a highly competitive candidate for sustainable cooling technology.

Importantly, this compositional tuning does not diminish the intrinsic heat absorption capacity; the material continues to transition through the requisite ordered to disordered phases with significant thermal energy exchange. Instead, the small PE fraction subtly modifies the molecular landscape, mitigating the energy barriers responsible for hysteresis during compression and decompression cycles. This refined molecular interaction enables smoother phase transformations, vital for real-world applications demanding reliability and efficiency.

To elucidate the microscopic mechanisms underpinning these macroscopic improvements, the research team leveraged quasielastic neutron scattering (QENS) techniques at the Institut Laue-Langevin’s IN16B spectrometer. QENS is uniquely capable of capturing molecular motions on picosecond to nanosecond timescales within hydrogen-rich solids, providing a window into the dynamic rotational and translational behaviors that govern phase transitions. By deploying inelastic fixed-window scans during controlled heating and cooling, the team correlated molecular dynamics directly with calorimetric hysteresis and structural phase data from diffraction studies.

The neutron scattering data revealed striking differences in the onset and progression of molecular reorientations across the order-disorder transition. In pure NPG, molecular motions appeared abruptly and exhibited pronounced asymmetry between heating and cooling, reflecting substantial thermal hysteresis. Conversely, the ternary NPG–PG–PE material demonstrated a more gradual and extended evolution of molecular dynamics with reduced directional discrepancy. This indicates that the inclusion of PE disrupts large hydrogen-bonded clusters found in the binary and pure materials, fostering a molecular environment more conducive to reversible transformations.

This fundamental insight highlights the critical influence of hydrogen bonding networks on the phase behavior and thermo-mechanical response of plastic crystals. The attenuation of these networks by minimal PE doping translates directly to lowered hysteresis and enhanced reversibility, showcasing how precise molecular design can tailor bulk material properties. Such understanding is essential for refining barocaloric materials, bridging the gap between promising physical phenomena and technologically viable cooling solutions.

Beyond advancing the frontier of barocaloric materials, this research exemplifies the power of combining compositional tuning with cutting-edge neutron spectroscopy to unravel complex molecular phenomena. These findings not only pave the way for more reliable, efficient, and environmentally benign refrigeration technologies but also establish guiding principles for molecular engineering across functional solid-state materials. As global cooling demand escalates alongside climate concerns, innovations like this will play a pivotal role in shaping sustainable cooling infrastructures.

Furthermore, the study’s implications extend to other caloric effects and stimuli-responsive materials, suggesting broad applicability of the molecular design strategies revealed. The ability to fine-tune phase transition dynamics and hysteresis behavior at the molecular level opens new horizons for solid-state thermal management and energy conversion technologies. As research continues, integrating these insights with device engineering will be critical to translating laboratory advancements into commercial refrigeration solutions.

In sum, the enhanced reversible barocaloric effect realized through subtle compositional control in neopentyl plastic crystals demonstrates a promising path forward for solid-state cooling technologies. Through meticulous molecular engineering and sophisticated neutron-scattering investigations, researchers have unlocked a significant advancement in balancing high cooling capacity with practical operational reversibility. This paradigm shift holds promise not only for reducing the environmental footprint of cooling but also for revolutionizing the way thermal energy is managed in various sectors, from food preservation to climate control.

Credit for this transformative research belongs to the collaborative efforts of the University of Glasgow, University of Cambridge, Universitat Politècnica de Catalunya, Diamond Light Source, and the Institut Laue-Langevin. Their combined expertise and innovative use of neutron spectroscopy have been instrumental in bringing these findings to light, illustrating the profound potential of interdisciplinary research strategies in materials science.

Subject of Research: Not applicable
Article Title: Enhanced reversible barocaloric effect at low pressure in neopentyl plastic crystal solid solutions
News Publication Date: 27-Jan-2026
Web References: 10.1038/s43246-026-01084-2
Image Credits: communications materials (2026)

Keywords

Materials science, Physics, Energy transfer, Heat, Spectroscopy

The focus of this investigation was the semicore electrons in alkali metals, a group renowned for their exceptional reactivity and position in the first column of the periodic table. Using sophisticated quantum chemical simulations powered by high-performance computational facilities, the team explored how these electrons influence phase transitions in compounds formed between alkali metals and fluorine. Their work was motivated by the notorious B1-B2 structural phase transition, a pressure-induced rearrangement of atomic crystals from an octahedral to a cubic lattice structure, familiar from the classical sodium chloride to cesium chloride conversion.

Quantum chemical calculations harnessed to unravel this complexity rely on approximations designed to make the famously intractable Schrödinger equation solvable for systems involving many interacting electrons. Historically, conventional wisdom attributed the need for immense pressures—on the order of hundreds of gigapascals—to activate core electron bond participation. This study defies that notion by demonstrating electron bonding activation at pressure levels far less severe, within the range of a few gigapascals, a regime found not only deep within Earth’s crust but intriguingly close to everyday atmospheric pressures.

In a stunning discovery, the researchers uncovered that cesium, among the heaviest alkali metals, exhibits semicore electron bonding even under ambient conditions. This defies previous theories that core electron involvement was exclusive to extreme planetary interiors. By analyzing cesium chloride’s crystal structure, the team deduced that the B2 phase—characterized by a cubic lattice stabilized by semicore electron activity—exists naturally without the necessity of high-pressure environments.

The implications of such a finding extend beyond academic curiosity. If semicore electrons contribute to bonding under conditions previously considered benign, this necessitates a reappraisal of theoretical models that predict elemental behavior in the Earth’s mantle and cores of terrestrial planets. The participation of these electrons could fundamentally influence key geophysical phenomena such as a planet’s density profile, tectonic dynamics, and magnetic field generation.

The team, led by SUNY Distinguished Professor Eva Zurek and co-researcher Stefano Racioppi, utilized state-of-the-art computational models facilitated by the University at Buffalo’s Center for Computational Research. Their modeling offers a high-resolution window into electron density distributions and bonding interactions that had eluded experimental characterization thus far. This theoretical advance outlines a paradigm shift in the understanding of chemical elements under pressure, with semicore electrons playing an indispensable role previously underestimated or overlooked in chemical physics.

Even more compelling is how the study’s insights could ripple into planetary science. If electrons alter their bonding behavior as a function of pressure in ways that differ from established expectations, current models of planetary formation and evolution could be incomplete or inaccurate. For example, shifts in bonding states at lower pressures could impact material properties that control mantle convection and core dynamics right down to magnetic field intensity and stability, both crucial for planetary habitability.

While these revelations stem primarily from computational simulation, the authors are cautious yet hopeful that experimental verification is within reach. They propose targeted experiments involving X-ray diffraction under controlled pressures to validate the role of semicore electrons in the bonding transformation and the B1-B2 phase transition. Such efforts could cement the theoretical predictions, potentially reshaping textbooks and inspiring new directions in materials chemistry and geophysics.

This investigation into semicore electron activation stands as a powerful reminder of how even well-established scientific doctrines remain open to challenge with the emergence of novel technology and rigorous inquiry. By pushing the boundaries of quantum chemical modeling, the researchers at Buffalo have not only illuminated the nuanced behavior of electrons deeply embedded in atomic structures but also opened pathways to understanding the underlying chemistry that defines planetary compositions and transformations.

With the support of the U.S. National Science Foundation’s Center for Matter at Atomic Pressure, this fusion of quantum computational chemistry and geophysical relevance represents the vanguard of interdisciplinary research. It underscores how foundational electron interactions—at scales far smaller than conventional chemical bonds—can dictate macroscopic properties that influence entire planetary bodies and conditions for life.

Ultimately, this study propels a revisitation of fundamental chemical bonding theories. It compels scientists to consider that electrons formerly deemed inert within atoms may emerge as active agents under a spectrum of hitherto unexpected pressures. This evolution in understanding expands the horizon for material science, planetary geology, and the quest to decode the complexities of matter both on Earth and across the cosmos.

Subject of Research:
Quantum chemical behavior of semicore electrons in alkali metals under pressure

Article Title:
Activation of Semicore Electrons in Alkali Metals and Their Role in the B1–B2 Phase Transition under Pressure

News Publication Date:
25-Aug-2025

Web References:
https://pubs.acs.org/doi/10.1021/jacs.5c08582

Image Credits:
Eva Zurek/University at Buffalo

Keywords:
Chemical elements, Chemical structure, Covalent bonds, Molecular chemistry, Materials, Heavy metals, Geophysics, Quantum mechanics