Dielectric properties of some MM'O sub(4) and MTiM'O sub(6) (M=Cr, Fe, Ga; M'=Nb, Ta, Sb) rutile-type oxides

We describe an investigation of the structure and dielectric properties of MM'O sub(4) and MTiM'O sub(6) rutile-type oxides for M=Cr, Fe, Ga and M'=Nb, Ta and Sb. All the oxides adopt a disordered rutile structure (P4 sub(2)/mnm) at ambient temperature. A partial ordered trirutile-type structure is confirmed for FeTaO sub(4) from the low temperature (17 K) neutron diffraction studies. While both the MM'O sub(4) oxides (CrTaO sub(4) and FeTaO sub(4)) investigated show a normal dielectric property MTiM'O sub(6) oxides for M=Fe, Cr and M'=Nb/Ta/Sb display a distinct relaxor/relaxor-like response. Significantly the corresponding gallium analogs, GaTiNbO sub(6) and GaTiTaO sub(6), do not show a relaxor response at T