Structural Distortion in Vanadium, Niobium, and TantalumJohn J. Neumeier, Montana State University, DMR 0907036 • We discovered that the elements vanadium, niobium, and tantalum exhibit a structural distortion below room temperature. • The data on the right show the length change along the three orthogonal <100> directions for a high-purity niobium single crystal. • Change in length illustrates that niobium is no longer cubic below 290 K. • Thermal expansion coefficient displays broad, hysteretic features characteristic of martensitic structural distortions. • These elements were previously thought to possess cubic crystal structures over this entire temperature range. • Small impurity concentrations completely suppress the structural distortion. Niobium R. K. Bollinger, B. D. White, J. J. Neumeier, H. R. Z. Sandim, Y. Suzuki, C. A. M. dos Santos, R. Avci, A. Migliori, and J. B. Betts, Phys. Rev. Lett. 107 (2011) 075503.
Structural Distortion in Vanadium, Niobium, and Tantalum John J. Neumeier, Montana State University, DMR 0907036 • This discovery: • Expands our basic understanding of three elements. • Provides the physical basis for anisotropy in the superconducting properties of these elements. • Will provide a new challenge for electronic structure calculations. • Offers a new perspective on a similar distortion that occurs in the A-15 superconductors Nb3Sn and V3Si. • Brazil – the world’s largest producer of niobium – supports a significant research effort in the study of metallic elements at USP-Lorena. There, some of the highest-quality single-crystalline niobium is made. • A collaboration between the PI at Montana State University and Carlos dos Santos at USP-Lorena led to this project. The Brazilian agency CNPq supports the international component of this collaboration. Hugo Sandim, John Neumeier (PI), and Carlos dos Santos pictured before the electron-beam furnace at Escola de Engenharia de Lorena – USP, Lorena, Brazil, 5 August 2011. R. K. Bollinger, B. D. White, J. J. Neumeier, H. R. Z. Sandim, Y. Suzuki, C. A. M. dos Santos, R. Avci, A. Migliori, and J. B. Betts, Phys. Rev. Lett. 107 (2011) 075503.