Structural phase transition and superlattice misfit strain of RFeAsO (R=La, Pr, Nd, Sm)

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2010-10-11
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Ricci, A.
Poccia, N.
Joseph, B.
Barba, L.
Arrighetti, G.
Clasca, G.
Yan, J.-Q.
McCallum, R.
Zhigadlo, N.
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Lograsso, Thomas
Ames Laboratory Division Director
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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The tetragonal-to-orthorhombic structural phase transition (SPT) in LaFeAsO (La-1111) and SmFeAsO (Sm-1111) single crystals measured by high-resolution x-ray diffraction is found to be sharp while the RFeAsO (R=La, Nd, Pr, Sm) polycrystalline samples show a broad continuous SPT. Comparing the polycrystalline and the single-crystal 1111 samples, the critical exponents of the SPT are found to be the same while the correlation length critical exponents are found to be very different. These results imply that the lattice fluctuations in 1111 systems change in samples with different surface to volume ratio that is assigned to the relieve of the temperature-dependent superlattice misfit strain between active iron layers and the spacer layers in 1111 systems. This phenomenon that is missing in the AFe2As2 (A=Ca, Sr, Ba) “122” systems, with the same electronic structure but different for the thickness and the elastic constant of the spacer layers, is related with the different maximum superconducting transition temperature in the 1111 (55 K) versus 122 (35 K) systems and implies the surface reconstruction in 1111 single crystals.

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This article is from Physical Review B 82 (2010): 144507, doi:10.1103/PhysRevB.82.144507.

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Fri Jan 01 00:00:00 UTC 2010
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