Flux requirements for the growth of RFeAsO (R = rare earth) superconductors

Date
2011-02-16
Authors
Yan, J.-Q.
Jensen, Brandt
Dennis, Kevin
McCallum, R.
Lograsso, Thomas
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Ames Laboratory
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Abstract

Millimeter-sized LaFeAsO single crystals have been successfully grown out of NaAs flux starting with (LaAs+1/2Fe2O3):20NaAs. The factors which allow the growth of these crystals out of NaAs but not out of many other fluxes, such as FeAs, have been investigated. X-ray powder diffraction found that NaAs synthesized for the growth ofRFeAsO superconductors has monoclinic LiAs structure. Thermal analysis confirmed that NaAs melts congruently at about 600 °C. The ability to extract RFeAsO crystals from this NaAs flux suggests that NaAs has a significant oxygen solubility, possibly due to the formation of the ternary compound NaAsO2, and enough oxygen diffusivity to transport solute to the growth front. Oxygen solubility and diffusivity are two important factors in searching for an alternative environmentally benign flux for the growth of RFeAsOsuperconductors.

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The following article appeared in Applied Physics Letters 98 (2011): 072504 and can be found at http://dx.doi.org/10.1063/1.3555632.

Keywords
Materials Science and Engineering, crystal growth from melt, crystal structure, diffusion, iron compounds, lanthanum compounds, solubility, superconducting materials, X-ray diffraction
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