Diamond and graphite, for example, are but two of the many polymorphs of carbon, meaning that both have the same chemical composition and differ only in the manner in which their atoms are connected. But what a world of difference that connectivity makes: The former goes into a ring and costs thousands of dollars, while the latter has to sit content within a humble pencil.
The inorganic compound hafnium dioxide commonly used in optical coatings likewise has several polymorphs, including a tetragonal form with highly attractive properties for computer chips and other optical elements. However, because this form is stable only at temperatures above 3100 degrees Fahrenheit — think blazing inferno — scientists have had to make do with its more limited monoclinic polymorph. Until now.
A team of researchers led by University of Kentucky chemist Beth Guiton and Texas A&M University chemist Sarbajit Banerjee in collaboration with Texas A&M materials science engineer Raymundo Arroyave has found a way to achieve this highly sought-after tetragonal phase at 1100 degrees Fahrenheit — think near-room-temperature and potential holy grail for the computing industry, along with countless other sectors and applications.
The team’s research, published today in Nature Communications, details their observation of this spectacular atom-by-atom transformation, witnessed with the help of incredibly powerful microscopes at Oak Ridge National Laboratory. After first shrinking monoclinic hafnium dioxide particles down to the size of tiny crystal nanorods, they gradually heated them, paying close attention to the barcode-like structure characterizing each nanorod and, in particular, its pair of nanoscale, fault-forming stripes that seem to function as ground zero for the transition.