From the discovery of vanadium to the physics of vanadium dioxide VO₂: how the metal-insulator transition works, why it can conduct electricity better than heat, and what industrial applications are realistic today.

Author: Marco Arezio. Expert in the circular economy, polymer recycling, and industrial plastics processes. Founder of the rMIX platform, dedicated to the valorization of recycled materials and the development of sustainable supply chains.

First published: April 2020

Editorial Update: April 1, 2026

Reading time: 14 minutes

Introduction: Updating VO2 Without Oversimplification

In the 2020 paper, vanadium dioxide was described as a "supermetal that conducts electricity but not heat." The intuition was sound, but today, in 2026, such a formulation needs to be clarified. VO₂ is not a metal in the chemical sense of the term: it is a vanadium oxide that, around a certain temperature, changes crystalline and electronic phase, moving from an insulating to a conductive state. It is precisely this transition, studied for decades but still full of controversial and fascinating aspects, that makes it one of the most interesting materials for condensed matter physics and for certain high-added-value industrial applications.

The reason VO₂ continues to generate interest isn't merely theoretical. Its properties allow us to imagine thermochromic coatings for smart windows, ultrafast electronic switches, photonic devices, sensors, and components for low-power neuromorphic architecture. However, there's still a significant gap between the beauty of the physical phenomenon and large-scale industrial production, due to costs, durability, a transition temperature too high for many building applications, less than ideal optical performance, and sensitivity to humidity and oxidation.

The story of vanadium: from initial error to intelligent matter

To understand VO₂, it's best to start with vanadium. The element was first identified in 1801 by Andrés Manuel del Río, working in Mexico, but initially wasn't firmly recognized as a new element. In 1830, the Swedish chemist Nils Gabriel Sefström reidentified it and named it vanadium, inspired by Vanadis, a figure in Nordic tradition associated with beauty, referring to the colors of its compounds. The production of pure metallic vanadium only came later with Henry Roscoe, in the second half of the 19th century. Compared to the 2020 text, it was therefore correct to reference del Río and Sefström, but with greater historical and terminological precision.

The focus of the article, however, is not metallic vanadium, but vanadium dioxide, VO₂, an oxide that has gained enormous scientific importance, especially after the discovery of its metal-insulator transition, described by Morin in 1959 and subsequently studied with increasingly sophisticated techniques. Today, VO₂ is often treated as a model material for understanding the relationship between crystalline structure, electronic correlations, and charge and heat transport.

What VO2 Really Is and Why It Shouldn't Just Be Called "Super Metal"

VO₂ is a transition oxide that, in its most studied form, transitions from an insulating monoclinic phase at low temperature to a conductive rutile phase at high temperature. The characteristic transition temperature for the unmodified bulk material is around 68 °C, or approximately 340 K. From a technical standpoint, this transition is accompanied by a strong change in electrical resistivity, significant optical changes, especially in the near-infrared, and a reorganization of the lattice structure.

For this reason, it is more correct to say that VO₂ is a metal-insulator transition material that can enter a metallic phase, rather than that it is "a metal" per se. This distinction is not lexical, but scientific. Its behavior does not derive from simple classical metallic conduction like that of copper or aluminum, but rather from a delicate balance between electronic correlations, V–V bonds, structural deformations, and external conditions such as temperature, voltage, strain, or doping. Even after more than sixty years of study, the profound nature of the VO₂ transition remains one of the emblematic problems of the physics of strongly correlated materials.

The Wiedemann-Franz Law and Why VO2 Has Attracted So Much Attention

In ordinary metals, electrical and thermal conductivity tend to go hand in hand. This behavior is described, to a first approximation, by the Wiedemann-Franz law, according to which the charge carriers that carry current are also responsible for a significant portion of the heat transfer. Therefore, in conventional conductors, high electrical conductivity and high thermal conductivity are often coupled.

The case of VO₂ caused a stir because a study published in Science in 2017 showed a severe violation of the Wiedemann-Franz law in the metallic phase near the transition: the electronic contribution to thermal conductivity was approximately ten times lower than expected for a conventional conductor. In other words, electrons in metallic VO₂ were able to transport charge much more efficiently than they transported heat. This isn't an absolute negation of thermal transport in the material as a whole, because some heat continues to be transported from the crystal lattice via phonons; however, it is a significant deviation from the behavior expected for a normal metal.

This is where the now-famous popular phrase comes from: VO₂ "conducts electricity but not heat." The phrase is effective, but should always be accompanied by a technical note: the point is not that the material is an absolute thermal insulator, but rather that the electronic channel for heat transport is unusually weak compared to that for charge. It is this anomaly that has prompted many researchers to study it as a platform for new forms of heat management and for devices that seek to at least partially separate electrical and thermal flow.

What happens during the metal-insulator transition of VO2

When VO₂ is heated above its critical temperature, its electrical resistance changes abruptly, often by several orders of magnitude, and the material enters a conductive phase. Recent reviews report that the phenomenon is rapid, reversible, and accompanied by thermal hysteresis, meaning the transition temperature during heating does not perfectly match the return temperature during cooling. This makes the material very attractive for switching devices, but also introduces complexity in the design of reliable and repeatable components.

On a fundamental level, the scientific debate is far from over. The VO₂ transition has long been interpreted as a combination of Mott-type electronic effects and Peierls-type structural effects. Recent studies show that, in some thin and hybrid architectures, it is possible to push the system toward more distinctly electronic transitions, reducing or separating the burden of structural rearrangement. A study published in 2025 in Nature Communications demonstrated an isostructural transition driven by photoinduced doping in an ultrathin CdS/VO₂ heterostructure, opening up prospects for faster and lower-power devices.

This is one of the most important developments compared to the 2020 picture: back then, VO₂ was of interest primarily for smart windows and for violating the Wiedemann-Franz law; today, it is also increasingly being studied as a material for adaptive and neuromorphic electronics, where response speed, reversibility, and transition control are key.

Smart Windows: The most intuitive application, but not yet perfect

The most immediate application of VO₂ remains that of thermochromic windows. The principle is simple: at low temperatures, the material allows near-infrared radiation to pass through more effectively, while at high temperatures, it reduces transmission, helping to limit solar heat gain in buildings. At the same time, good transparency in the visible light is essential, otherwise the energy benefits would be offset by a deterioration in the quality of natural light indoors.

Here, however, the first major practical limitation emerges. The transition temperature of pure VO₂, around 68°C, is too high for many common building applications. For this reason, research has been focused for years on doping and micro/nano-engineering the material to lower the critical temperature and simultaneously improve light transmittance and solar modulation capabilities. The 2024 reviews emphasize that integrating elements such as tungsten or multilayer and core-shell architectures improves performance, but also that overall performance is still limited compared to the industrial ideal.

The intrinsic limitations most often cited today are clear: high transition temperature, light transmittance often below 60%, solar modulation generally below 15% in more traditional configurations, limited stability in humid environments, and a tendency to oxidize toward less desirable phases such as V₂O₅. Furthermore, to truly reach the market, extensive, cost-effective, controllable, and long-lasting deposition processes are needed. It is precisely on these points that the most up-to-date literature emphasizes most, a sign that the bottleneck is no longer simply understanding the physics, but engineering the production cycle.

Applications beyond windows: switching, photonics, sensors, and neuromorphism

However, it would be a mistake to limit VO₂ to the sole application of window and door frames. Today, the material is being studied for electronic switches, RF devices, photonic components, and volatile memories, because the abrupt change in resistivity upon phase transition makes it an ideal candidate for switches and modulators. Recent reviews emphasize that switching can be activated not only thermally, but also electrically or optically, significantly expanding the range of applications.

The most advanced research is that of neuromorphic devices, where VO₂ is considered interesting because its transition can lead to rapid switching, controllable volatile behavior, and potential power savings compared to devices in which the state change requires slower or more dissipative structural transformations. The 2025 work on the purely electronic transition to the rutile phase should be interpreted precisely in this direction: not only to understand the material, but also to seek a faster, less energy-intensive, and more controllable VO₂ for the electronics of the future.

Regarding the idea, already mentioned in the 2020 text, of converting waste heat into electricity, the discussion needs to be more cautious. Violation of the Wiedemann-Franz law suggests that VO₂ could inspire new approaches to thermoelectric management and waste heat harvesting, but this does not automatically mean that a commercial supply chain for VO₂ as a standard thermoelectric material already exists. From an industrial perspective, we are still at a stage where scientific promise outstrips commercial maturity.

From the lab to the industry: what really slows down VO2

When a material fascinates research for twenty years or more without exploding onto the mass market, there's almost always more than one problem. In the case of VO₂, there are numerous and mutually reinforcing obstacles. There's the issue of manufacturing high-quality thin films, with precise control of stoichiometry, crystalline orientation, and defects. There's the issue of durability, because vanadium is multivalent, and VO₂ can degrade or oxidize under real-world conditions. Then there's the issue of overall optical performance, which in windows requires a difficult balance between visible transparency and infrared modulation. Finally, there's the issue of industrial cost, which includes both the deposition process and long-term operational stability.

For this reason, in 2026, the most appropriate way to describe VO₂ is not as a miracle material ready to revolutionize the industry, but as a functional platform with extremely high potential, now scientifically mature but still consolidating its applications. This is an important distinction, also from an EEAT perspective: the value of the article lies not in promising an imminent revolution, but in distinguishing between what has been proven in the lab, what is plausible in prototypes, and what is truly close to large-scale commercialization.

Vanadium, industrial supply chain and recycling: the raw material matters

Finally, there is one aspect that was almost entirely missing from the original text: the vanadium supply chain. Discussing advanced applications without considering the availability of the material is reductive today. According to the USGS, by 2025, over 90% of vanadium consumption in the United States will remain tied to metallurgical uses, primarily as an alloying element for steels, while non-metallurgical uses continue to be significant as chemical catalysts. At the same time, vanadium redox flow batteries have continued to grow in medium- and long-term stationary energy storage systems, although they remain constrained by their high initial cost and the availability of high-purity vanadium.

From a circular perspective, the most interesting finding is that a significant portion of secondary vanadium production comes from ash, residues, and spent catalysts, and that vanadium recycling is primarily associated with the reprocessing of spent catalysts. According to the USGS, production from secondary sources has grown in the United States in recent years, while the global market remains heavily influenced by the Chinese steel industry and the geographic concentration of production. This means that, if VO₂ were to find broader applications in construction or electronics, the issue of the supply chain and vanadium recovery would become even more relevant.

For those who view the topic from a circular economy perspective, this is the crucial point: smart materials aren't sustainable simply because they improve energy efficiency in use; they must also demonstrate a robust, recyclable, and less vulnerable supply chain. In the case of vanadium, the presence of recoverable secondary streams is an advantage, but competition between metallurgical, chemical, energy, and electronic uses could create market tensions if demand were to grow rapidly.

Conclusion: Why VO2 remains one of the most interesting materials of 2026

VO₂ continues to fascinate because it combines three dimensions that rarely coexist so powerfully: the physical beauty of the phenomenon, potential technological utility, and actual engineering difficulty. On the one hand, it is the material that challenges a fundamental law of transport in metals and demonstrates how charge and heat can, under certain conditions, stop traveling as expected. On the other, it is a concrete candidate for smart windows, switches, sensors, photonic components, and neuromorphic devices. In between, however, remain non-trivial industrial challenges: transition temperature, stability, durability, optical performance, manufacturing costs, and long-term reliability.

Compared to the 2020 article, the correct update is therefore this: vanadium dioxide is not a "supermetal" in the simplest sense, but a transition metal-insulator oxide that, under certain conditions, conducts electricity much more efficiently than heat than predicted by classical models. It is a material promising innovation, but still in the process of being industrially refined. This is precisely why it remains so important: because it does not represent a fulfilled promise, but one of the most vibrant projects in contemporary materials science.

FAQ

Is VO2 a metal?

No, VO₂ is a vanadium oxide. Depending on temperature and external conditions, it can electronically transition from an insulating phase to a metallic phase.

At what temperature does the VO2 transition occur?

In the unmodified bulk material, the metal-insulator transition occurs around 68°C. This temperature can be lowered with doping, strain, and multilayer architectures.

Is it true that VO2 conducts electricity but not heat?

This is a journalistic simplification. More precisely, in the metallic phase near the transition, the electronic contribution to heat transport is much lower than predicted by the Wiedemann-Franz law, while electrical conduction remains high.

What is the most promising application of VO2 today?

Smart windows remain the most intuitive and visible application, but in 2025-2026, studies on electronic switching, photonics, and neuromorphic devices will also grow significantly.

Is VO2 already a mainstream technology in buildings?

No. The prospects are interesting, but large-scale commercialization is still held back by high transition temperatures, durability, cost, and optical tradeoffs.

Can vanadium be recycled?

Yes, a significant portion of secondary vanadium comes from the recovery of spent catalysts, residues, and ash. This is important if vanadium were to become increasingly important for batteries, catalysis, and advanced materials.

Sources

Royal Society of Chemistry, factsheet on the element vanadium.

Encyclopaedia Britannica, historical and technical entries on vanadium.

Berkeley Lab, communication on the anomalous behavior of VO₂ with respect to the Wiedemann-Franz law.

S. Lee et al., Science (2017), Anomalously low electronic thermal conductivity in metallic VO₂.

J.-P. Pouget, Critical review of fundamental aspects of the metal-insulator transition in VO₂.

C. Wen et al., 2024 review on the preparation, properties, and applications of VO₂ thin films.

C. Jiang et al., Light: Science & Applications (2024), review on VO₂-based thermochromic smart windows.

S. Cheng et al., Nature Communications (2025), Purely electronic transition in rutile VO₂.

USGS, Mineral Commodity Summaries 2026: Vanadium.

DOE, projects and critical supply chain issues for critical materials, including uses of vanadium.