Crystal Structures and Expansion Anomalies of MnO, MnS, FeO, Fe3O4 Between 100 degrees K and 200 degrees K

(1) Determinations have been made of structure type and lattice constants of MnO, MnS, FeO and Fe3O4 at temperatures near those at which these substances show specific heat anomalies. (2) No major structure changes were apparent in the x-ray patterns. All structures are cubic at all investigated temperatures. Lattice constant data indicate similarity in the abnormal expansion behavior of MnS and FeO and of MnO and Fe3O4. (3) The specific heat and expansion anomalies are probably due to electron transitions within certain atoms in the crystal lattice and may be analogous to the behavior of metallic iron at 765 degrees C, or of quartz at 575 degrees C.