High pressure and temperature are used to synthesise perovskite related phases in the Sr–Cr(IV)–O system. The n=1, 2 and ∞ members of the Sr n +1 Cr n O 3n+1 family have been obtained. Another new member, n=3 as well as an hexagonal layered perovskite have also been observed by transmission electron microscopy and electron diffraction. The average structure of Sr 3 Cr 2 O 7 as determined by XRD has space group I4/mmm, whereas its microstructure includes a large amount of defects both in the layer stacking and within the layers. 2D magnetism and a large electrical resistance in Sr 3 Cr 2 O 7 are observed as opposed to the nonlocalized electronic behaviour of SrCrO 3 .