People usually think that water only exists in three phases: solid ice, liquid water, and gas vapor. Little did they know that matter can exist in other phases for example ice. Ice in the sense that its atom has different ways to be arranged making its existence in more than ten phases. Also, with the help and understanding of the fundamental external forces such as pressure, temperature, or electricity, the use of piezoelectric materials like microphone becomes possible.
A new study led by MIT researchers Keith A. Nelson, Xian Li, and Edoardo Balding with their collaboration with Andrew M. Rappe and Penn graduate students Tian Qui and Jiang Zhang discovered the hidden phase of a metal oxide. The hidden phase was observed when it is activated by extremely fast pulse light. It gives the subject its new photoelectric property which gives the ability to separate positive and negative charges.
With their discovery, there is a new opportunity in creating materials which one can control the properties (turn it on or off) in just trillionth of a second opened. Because of its changing electric potential, it can be used in different applications like transforming an insulator into a metal.
"It's opening a new horizon for rapid functional material reconfiguration," said Rappe. The previous collaboration between Nelson and Rappe led in developing the theoretical basis of the new study. With Nelsons' expertise in using light to induce phase transition in solid materials and Rappes' help in developing atomic-level computer model, the study became successful after 10 years, according to Eureka Alert.
The advancement in technology and their knowledge from terahertz frequencies really helped them a lot. "Nelson is the experimentalist, and we're the theorists," said Rappe. "He can report what he thinks is happening based on spectra, but the interpretation is speculative until we provide a strong physical understanding of what happened."
The team studied strontium titanate, a paraelectric material, that is commonly used in capacitors and resistors. Since it has an asymmetric and nonpolar crystal structure, it makes it possible to create a new phase. The material can turn into a phase with a polar and tetragonal structure with a pair of oppositely charged ions along its long axis. The experiment also involves a computer-generated version of strontium titanate wherein every single atom was tracked and respond to light in the same manner with the material tested in the laboratory. The strontium titanate, when exposed to light, becomes excited and ions started to pull in different directions. Positive ions moving in one direction and the negatively charged ions on the other side.
Unlike in a pendulum, instead of the ions falling back into place, a different response was observed. Due to vibrational movement, the atoms prevent the ions from swinging back to its original place. "It's been a really awesome collaboration," shared Nelson. "And it illustrates how ideas can remove then return in full force after more than ten years."
For now, the two scientists are to collaborate with engineers to use what they have discovered in different applications like creating materials with hidden phases, create longer lasting phases with charging light-pulse protocols, and of course for nanomaterials. "It's the dream of every scientist: to hatch an idea together with a friend, to map out the consequence of that idea, then to have a chance to translate it into something in the lab, it's extremely gratifying. It makes us think we're on the right track towards the future," explained Rappe.
