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ORAL CONTRIBUTIONS
A structural phase transition in V, Nb and Ta and the possible
importance for A15 superconductors
John J. Neumeier 1 , R. K. Bollinger 1 , B. D. White 1 , S. Francoual 2 , C. A. M. dos Santos 3 , H. R. Z.
Sandim 3 , Y. Suzuki 4 , R. Avci 1 , M. von Zimmerman 2 , A. Migliori 4 , and J. B. Betts 4
1 Physics Department, Montana State University, Box 173840, Bozeman, MT, 59717, USA.
2 HASYLAB at DESY, Notkestr. 85, D22607, Hamburg, Germany.
3 Escola de Engenharia de Lorena – USP, PO Box 116, LorenaSP, 12602810, Brazil.
4 National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM,
87545 USA.
The 5d elements V, Nb and Ta are generally thought to possess cubic crystal structures.
Recently, we observed a structural phase transition using high resolution thermal
expansion between room temperature and absolute zero in all three of these elements.
Its magnitude is small, as reflected in a relative length change along the three principal
cubic axes that differs by about 1 part in 10 3 or less. It is extremely broad and hysteretic
and sensitive to impurities. We have characterized it as martensitic, although the
low‐temperature crystal structure remains unknown and competition between the two
structures needs to be directly observed. A‐15 superconductors containing V and Nb are
also known to exhibit martensitic structural phase transitions. In A‐15 compounds, the
structural phase transitions occur near to the superconducting phase transitions, and
were thought to play an important role in superconductivity. Published work on A‐15s
will be reviewed, and discussed in the framework of our observations in the elements.
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