Phase change materials (PCMs) or thermal phase change materials have been explored in recent years for their potential applications in a wide range of cutting-edge technologies. This article will provide a brief overview of these industrial important materials and explore some of the latest knowledge of phase change materials.
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What are Phase Change Materials?
Materials display different properties in each state of matter (solid, gas, liquid, and plasma) which can be manipulated for a multitude of purposes. A phase change is a change in the state of a material’s matter, and common examples of this phenomenon are the change of water from a liquid to a vapor at its boiling point, and liquid wax solidifying.
A phase change material is defined as a material that absorbs or releases a large amount of latent heat energy when it undergoes this change in its physical state. Phase change materials have several applications.
From Water to Modern Phase Change Materials: A Brief Overview
Aside from its essential use for sustaining life, water is a phase change material that has a long history of use in industry. This material is the most well-known phase change material with an accessible latent heat capacity. The use of water in steam engines kick-started the first industrial revolution, with these engines employed in factories, ships, and trains.
Materials such as alloys, organic materials, alloys, and emerging 2D materials have now been discovered that display phase change properties.
The main early use of phase change materials was in temperature-controlled heat storage devices. Over the years, this use has extended to several other applications and today is used in research into novel applications such as memory devices, photonics, actuators, thermal management solutions, and neuromorphic calculation devices. A deeper understanding of the mechanisms behind phase change in materials has facilitated the development of innovative applications.
Today, phase-change materials are at the forefront of materials science, applied physics, and electrical engineering. Some of the current knowledge on these industrially and commercially important materials is listed below.
Vanadium Oxides
The family of vanadium oxides has been extensively researched for their phase change characteristics. They exhibit these characteristics differently depending on stoichiometry. Of this family of materials, vanadium dioxide (VO2) has a well-known near-room temperature metal to insulator transition.
Many studies have been carried out on vanadium dioxide. Lu et al. developed a spin-pairing model of the metal-to-insulator transition of the material and proposed a method to estimate this transition temperature. Additionally, they used this method to study the doping and alloying process of VO2. Devthade and Lee have developed a tutorial on the synthesis of thin films of VO2 and dimensionally oriented nanostructures.
Further studies have demonstrated that the volatile and non-volatile behavior of the metal-insulator transition of VO2 can be regulated using an annealing process to tune oxygen vacancies within the material. Controlled synthesis of VO2 produces materials with superior properties and enhances the performance of devices. Further intriguing properties have been reported in VO2 and VOx-based composite films including photochromic and thermochromic characteristics and self-regulating current sharing.
Ternary Ge-Sb-Te
Ternary Ge-Sb-Te, or GST, is a family of chalcogenide alloys that exhibit phase-change characteristics. These materials have already found widespread commercial application in devices such as Blu-Ray and DVD-RAM players. They are key components in phase change memory applications. The grain refinement in these materials lowers the power consumption and improves endurance, making them ideal for this use.
The annealing temperature plays a pivotal role in determining the crystallization process and structural evolution of these alloys. Several in situ studies utilizing x-ray diffraction, transmission electron microscopy, and optical reflectance measurements have been performed to elucidate crucial information about the crystallization process in GST alloys. Modeling and simulations have been employed to provide information on the properties and characteristics of these materials.
Beyond their use as phase change memory materials, the GST family of materials has been investigated for their use in reconfigurable photonics devices. GST-based reconfigurable metasurfaces have been explored in recent years for applications in beam steering, absorbers, nonlinear optics, polaritons, and anapole control.
Phase Change Material Heat Exchangers
More uses of phase change materials. Video Credit: NASA Video/Youtube.com
Other Uses of Phase Change Materials
Phase change materials have been widely explored for a multitude of devices. CrodaThermTM 24W is a proprietary phase change material that has the physical form of a waxy solid. It is used primarily for thermal storage and maintaining ambient temperature for applications such as HVAC systems and thermally regulated pharmaceutical packaging.
Indeed, phase change materials have been studied widely for thermoelectric and thermally conductive applications. Another use, as reported by Scott et al. is as a PCM-enhanced plaster for use in long-term eco-sustainable thermal energy storage. Another study by Biswas et al. has demonstrated a proof-of-concept oxygen sensor based on phase-change characteristics. Organic ferroelectric PCM materials have been reported and studied that enhance ferroelectric and piezoelectric responses.
The Future
From heat storage and thermal regulation devices to reconfigurable photonics, ferroelectrics, memory devices, and other novel applications, phase change materials, from the well-known vanadium oxide and GST families to novel materials, display great promise for next-generation applications. Recent research has provided valuable insight into the mechanisms behind these characteristics, informing the direction of future studies into these materials.
References and Further Reading
Liu, K & Tian, Z (2021) Advances in phase-change materials [online] Journal of Applied Physics 130 (7) Available at:
https://aip.scitation.org/doi/10.1063/5.0064189
Croda Energy Technologies (2022) CrodaThermTM 24W [online] Available at:
https://www.crodaenergytechnologies.com/en-gb/product-finder/product/1365-CrodaTherm_1_24W
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