Hybrid materials have served a variety of functions in the advancement of modern technology. Despite numerous studies on hybrid materials, the reported properties and characteristics are still insufficient. This is due to the fact that synthetic methods influence hybrid material properties and behavior, so even minor changes can have a significant impact.
Scientists discovered that at chemical compositions near the structural quantum critical point in the crystalline solid Ba1-xSrxAl2O4, a highly disordered atomic arrangement forms in the AlO4 network, resulting in both crystalline and amorphous properties. This hybrid state is easily created by uniformly mixing raw materials and heating them. These findings are expected to help with the development of hybrid materials for use in harsh environments, such as outer space, by applying the technique to a variety of materials.
If you’ve ever seen water freeze to ice, you’ve seen a “phase transition,” as physicists call it. Scientists at Osaka Metropolitan University have discovered an unprecedented phase transition in which crystals acquire amorphous properties while retaining their crystalline properties. Their findings aid in the development of hybrid materials for use in harsh environments such as space. Physical Review B published the findings.
In principle, the phenomenon revealed in this research can occur in materials exhibiting acoustic soft modes. Applying this technique to various materials may help us create hybrid materials that combine the physical properties of crystals, such as optical properties and electrical conductivity, with the low thermal conductivity of amorphous materials.
Yui Ishii
A typical crystalline solid phase transition involves a change in crystal structure. Such structural phase transitions are typically observed at fixed temperatures. Controlling the chemical composition of the crystal, on the other hand, can lower -the transition temperature to absolute zero (273°C). The structural quantum critical point is the transition point at absolute zero.
In the dielectric compound Ba1-xSrxAl2O4, the structural phase transition is driven by an acoustic soft mode, the atomic vibration pattern of which is similar to that of sound waves. The compound comprises an AlO4 tetrahedral network and Ba/Sr atoms. The research team led by Associate Professor Yui Ishii from the Graduate School of Engineering at Osaka Metropolitan University has discovered that a highly disordered atomic arrangement is formed in the AlO4 network at chemical compositions near the structural quantum critical point, resulting in both characteristics of crystalline and amorphous materials.
Ba1-xSrxAl2O4 is a crystalline solid. However, the researchers found that at higher Sr concentrations than the structural quantum critical point, Ba1-xSrxAl2O4exhibits the thermal characteristic of amorphous materials, i.e., low thermal conductivity comparable to that of glass materials (e.g., silica glass). They observed that a part of the atomic structure loses periodicity because of the incoherently stopped acoustic soft mode. As a result, a combination of a glassy Al-O network and a periodic Ba arrangement is realized.
This hybrid state, which the research team was the first to discover, can be created simply by mixing raw materials uniformly and heating them.
Professor Ishii concluded, “In principle, the phenomenon revealed in this research can occur in materials exhibiting acoustic soft modes. Applying this technique to various materials may help us create hybrid materials that combine the physical properties of crystals, such as optical properties and electrical conductivity, with the low thermal conductivity of amorphous materials.”
