La3Ni2-xCuxB'O9 (x = 0.25; B’ = Sb, Ta, Nb: x = 0.5; B’ = Nb)have been synthesized and characterised by transmission electron microscopy, neutron diffraction and magnetometry. Each adopts a perovskite-like structure (space group P21/n)with two crystallographically-distinct six-coordinate sites, one occupied by a disordered arrangement of Ni2+ and Cu2+ and the other by a disordered ∼1:2 distribution of Ni2+ and B′5+, although some Cu2+ is found on the latter site when x = 0.5. Each composition undergoes a magnetic transition in the range 90 ≤ T/K ≤ 130 and shows a spontaneous magnetisation at 5 K; the transition temperature always exceeds that of the x = 0 composition by ≥ 30 K. A long-range ordered G-type ferrimagnetic structure is present in each composition, but small relaxor domains are also present. This contrasts with the pure relaxor and spin-glass behaviour of x = 0, B’ = Ta, Nb, respectively.
