Synthesis, structure and properties of the hexagonal perovskite, h-BaTi1-xHoxO3-x/2

The crystal structure of hexagonal (h)-BaTi0.85Ho 0.15O2.925 has been determined using neutron powder diffraction data. The structure is derived from that of h-BaTiO3 and contains Ho3+, the largest cation known to be accommodated by the B site in h-BaTiO3. Ti and Ho are disordered over the B1 octahedral sites and the structure may be regarded as intermediate between those of h-BaTiO3 and Ba3Sr(Nb,Ta)2O9. h-BaTi0.85Ho0.15O2.925 forms as a long-lived but metastable, intermediate phase before transforming, slowly, to the thermodynamically stable cubic polymorph of the same composition; its formation is an example of Ostwald's rule of successive reactions. It is an electrical insulator with relative permittivity of �50. © 2009 The Royal Society of Chemistry.