The crystal structure of ten different Y, REE (REE: rare earth elements) perovskite-type aluminates, doped with chromium, has been investigated by means of synchrotron powder diffraction in order to assess the crystallog. modifications related to varying the lanthanide ions. The symmetry change from orthorhombic (Y, Yb-Sm) to rhombohedral (Nd and Pr) has been confirmed. The anomalous behavior of the unit cell parameters (in the Pnma setting, b and c contract while a expands as a function of the 'lanthanide contraction') has been clarified on the basis of changes in coordination no. of the site contg. the Y and lanthanide ion: this varies from approx. eight-fold in Yb-, Er-, Ho-, Y-, and Dy-orthoaluminates to nine-fold (or larger) in Gd-, Eu-, and Sm-orthoaluminates to twelve-fold (as in the archetypal cubic structure) in rhombohedral perovskites (Nd and Pr). The coordination no. appears about two units greater in orthoaluminates with respect to the corresponding orthoferrites and an inverse correlation between the av. bond distance of the Y, REE site and that of the octahedral Al (and Cr) hosting site has been obsd.
Structural variations of Cr-doped (YREE) AlO3 perovskites
CRUCIANI, Giuseppe;
2005
Abstract
The crystal structure of ten different Y, REE (REE: rare earth elements) perovskite-type aluminates, doped with chromium, has been investigated by means of synchrotron powder diffraction in order to assess the crystallog. modifications related to varying the lanthanide ions. The symmetry change from orthorhombic (Y, Yb-Sm) to rhombohedral (Nd and Pr) has been confirmed. The anomalous behavior of the unit cell parameters (in the Pnma setting, b and c contract while a expands as a function of the 'lanthanide contraction') has been clarified on the basis of changes in coordination no. of the site contg. the Y and lanthanide ion: this varies from approx. eight-fold in Yb-, Er-, Ho-, Y-, and Dy-orthoaluminates to nine-fold (or larger) in Gd-, Eu-, and Sm-orthoaluminates to twelve-fold (as in the archetypal cubic structure) in rhombohedral perovskites (Nd and Pr). The coordination no. appears about two units greater in orthoaluminates with respect to the corresponding orthoferrites and an inverse correlation between the av. bond distance of the Y, REE site and that of the octahedral Al (and Cr) hosting site has been obsd.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
