Ba Fe2 Hg0.467 O8.75 Sr2 Tl1.402 Nguyen N, Groult D, Boullay P, Michel C, Raveau B Journal of Solid State Chemistry 132 (1997) 308-314 New mixed valent ferrites (Tl1.5 Hg0.5) Sr3-x Bax Fe2 O9-d (0