Jahn-Teller driven electronic instability in thermoelectric tetrahedrite

Tetrahedrite, Cu12Sb4S13, is an abundant mineral with excellent thermoelectric properties owing to its low thermal conductivity. The electronic and structural origin of the intriguing physical properties of tetrahedrite, including its metal-to-semiconductor transition, remains largely unknown. This work presents the first determination of the low-temperature structure of tetrahedrite that accounts for its unique properties. Contrary to prior conjectures, our results show that the trigonal-planar copper cations remain in planar coordination below the metal-to-semiconductor transition. The atomic displacement parameters of the trigonal-planar copper cations, which have been linked to low thermal conductivity, increase by 200% above the metal-to-semiconductor transition. The phase transition is consequence of the orbital degeneracy of the highest occupied 3d cluster orbitals of the copper clusters found inside the sodalite cages in the cubic phase. This study reveals that a Jahn-Teller electronic instability leads to the formation of “molecular-like” Cu57+ clusters and suppresses copper rattling vibrations due to the strengthening of direct copper-copper interactions. Our first-principles calculations demonstrate that the structural phase transition opens a small band gap in the electronic density of states and eliminates the unstable phonon modes. The present results provide insights on the interplay between phonon transport, electronic properties and crystal structure in mixed-valence compounds

Dream Big URI: The Common Reading Program and The Last Lecture

Dr. Donald DeHayes, Provost, and Nancy Caronia, Graduate Student Coordinator, Common Reading Program. Pancreatic cancer is the fourth deadliest cancer, killing 75% of those who contract it within a year. Only 4% survive to the fifth year. In the U. S., more than 33, 000 die from it annually. Less than 2% of the budget of the National Cancer Institute is allocated to research on pancreatic cancer. When he was diagnosed with the disease in 2006, Dr. Randy Pausch, a professor of computer science and design at Carnegie‐Mellon (PA) University, responded to a request for life lessons by delivering “The Last Lecture” before a University audience of 400 on September 18, 2007. A viral hit on YouTube, “The Last Lecture” was viewed over a million times in the first month after its delivery. The success of the lecture led to the co‐authored book in 2008. Translated into 46 languages, the book was a New York Times best‐seller for more than 85 weeks. Though Dr. Pausch died from the disease on July 25, 2008 at the age of 47, the book summarizes his philosophy of life: Dream big. Enable others to pursue their dreams. Live life positively and with enjoyment