Rhombohedral distortion in the new disordered LaBaCo2O6 perovskite

Recently, we have synthesized a new series of ordered-oxygen-deficient pero vskites of general formula LnBaCo(2)O(5+x) (Ln = Ho,Tb,La...). We have char acterized the magnetic and nuclear structures of these compounds by neutron powder diffraction. The crystallographic structure is described with an al ternate stacking of Ln and Ba layers along one direction, and rows of CoO5 pyramids. They also present various magnetic structures depending on the ox ygen concentration and on the Ln ion. Among these perovskites-like compound s, we have obtained a stoechiometric LaBaCo2O6 (x = 1). This compound deriv es from the ordered LnBaCo(2)O(5), but it is a pure perovskite with a cubic structure and a mixed La/Ba site. At low temperature. the neutron experime nts have shown a possible rhombohedral distortion, connected to the ferroma gnetic order of Co spins which appears below 250 K. (C) 2000 Elsevier Scien ce B.V. All rights reserved.