Ba 3 (Cr 0.97(1) Te 0.03(1) ) 2 TeO 9 : in Search of Jahn-Teller Distorted Cr(II) Oxide.

A novel 6H-type hexagonal perovskite Ba3 (Cr0.97(1) Te0.03(1) )2 TeO9 was prepared at high pressure (6 GPa) and temperature (1773 K). Both transmission electron microscopy and synchrotron powder X-ray diffraction data demonstrate that Ba3 (Cr0.97(1) Te0.03(1) )2 TeO9 crystallizes in P63 /mmc with face-shared (Cr0.97(1) Te0.03(1) )O6 octahedral pairs interconnected with TeO6 octahedra via corner-sharing. Structure analysis shows a mixed Cr2+ /Cr3+ valence state with ∼10% Cr2+ . The existence of Cr2+ in Ba3 (Cr2+ 0.10(1) Cr3+ 0.87(1) Te6+ 0.03 )2 TeO9 is further evidenced by X-ray absorption near-edge spectroscopy. Magnetic properties measurements show a paramagnetic response down to 4 K and a small glassy-state curvature at low temperature. In this work, the octahedral Cr2+ O6 component is stabilized in an oxide material for the first time; the expected Jahn-Teller distortion of high-spin (d4 ) Cr2+ is not found, which is attributed to the small proportion of Cr2+ (∼10%) and the face-sharing arrangement of CrO6 octahedral pairs, which structurally disfavor axial distortion.