CEMS researchers elucidate 50-year-old phase transition

Oct. 23, 2016 - CEMS post-doc Eric McCalla and graduate student Jeffery Walter, working with Professor Chris Leighton, have recently published a breakthrough in the understanding of a 50 year old problem in the crystal structure of oxide materials. Their work focuses on the oxide strontium titanate, or SrTiO3, which is a prototype for an important family of materials known as perovskites. This material undergoes a phase transition below room temperature from a cubic structure to a tetragonal one, achieved by a classic mechanism known as phonon mode softening. The temperature of this transition has been known for years to shift with the incorporation of other elements, but in a complex manner that has proven difficult to understand. The team developed a simple, quantitative understanding of these shifts in transition temperature, using bond valence sum calculations that are widely applied in solid state chemistry. This not only enables prediction of the transition temperatures in new compounds, but also provides additional insight into the structural properties of this foundational oxide material. The work was recently published in the journal Chemistry of Materials.

Figure: Illustration of the cubic (back) and tetragonal (front) crystal structures of the perovskite oxide compound SrTiO3. In the background is the correlation discovered between the temperature of the phase transition (Ta) and the newly developed structural parameter .

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