The crystal structure of BaCoO2 was determined for the first time by Spitsbergen  in 1960. Despite the absence of experimental structural data, it was reported to crystallize in the non-centrosymmetric P3121 trigonal space group (no. 152), similar to that observed for SiO2 quartz, which has potential piezoelectric properties. The screw axis of this trigonal unit cell is defined by the arrangement of corner-sharing CoO4 tetrahedra around the barium atom, which is located in a distorted 8-fold (4+2+2) oxygen atoms coordination (fig).
The 3d7 electron configuration of the tetrahedral Co2+ ion exhibits a theoretical effective magnetic moment μeff = 3.87μB. The existence of this magnetic moment associated with the P3121 space group permits potential piezo-magnetic coupling .
The BaCoO2 phase was synthesized by the solid state reaction under secondary vacuum and its structural changes as a function of temperature were studied as the function of oxygen partial pressure. BaCoO2 presents antiferromagnetic ordering at room temperature and crystallizes in the P3121 space group which confirms potential piezo-magnetic coupling. In addition, oxygen insertion/disinsertion over an extended compositional range was characterized in BaCoO2+x (0≤ x ≤1) by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and Raman spectroscopy.
Such properties could be of interest for catalysis applications, commercial air separation, solar water splitting, solar CO2 splitting, chemical looping, oxy-combustion, , etc.…