BaCoO 2+δ : a new highly oxygen deficient perovskite-related phase with unusual Co coordination obtained by high temperature reaction with short reaction times.

A new highly oxygen deficient metastable modification of perovskite-related BaCoO2+δ (δ ∼ 0.01-0.02) has been prepared using high temperature reactions with short heating times. This defect rich compound has at least partially square planar coordination of the Co2+ ions, a highly unusual coordination environment for Co. Low temperature neutron powder diffraction showed a G-type antiferromagnetic ordering, confirmed by SQUID magnetic measurements, which indicate a high Néel temperature of 220 K. This work shows how novel defective phases can be synthesized by exploiting short reaction times in solid state synthesis, thus offering an alternative route for new materials synthesis.