Thermal Analysis of High-Entropy Rare Earth Oxides

Materials
Sergey V UshakovAlexandra Navrotsky

Abstract

Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high-temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)2O3, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900-2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)2O3 sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts fut...Continue Reading

References

Sep 30, 2015·Nature Communications·Christina M RostJon-Paul Maria
Jun 7, 2018·Scientific Reports·Elinor CastleMichael Reece
Aug 26, 2018·Nature Communications·Abhishek SarkarBen Breitung
Jul 1, 1960·Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry·R S Roth, S J Schneider

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Methods Mentioned

BETA
synchrotron diffraction
X-ray
electron microprobe
backscattered electron imaging

Software Mentioned

MDI Jade
Calc
Thermo
GSAS
II
Calphad

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