In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28-xW4+xO54+3x/2 (x=0.85)
Journal article, 2013

In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements.

Author

A. Magraso

University of Oslo

C. H. Hervoches

University of Oslo

Istaq Ahmed

Volvo Group

ISIS Facility

S. Hull

ISIS Facility

Jonas Nordström

Chalmers, Applied Physics, Condensed Matter Physics

A. W. B. Skilbred

University of Oslo

R. Haugsrud

University of Oslo

Journal of Materials Chemistry A

20507488 (ISSN) 20507496 (eISSN)

Vol. 1 11 3774-3782

Subject Categories

Chemical Sciences

DOI

10.1039/c3ta00497j

More information

Latest update

11/20/2018