High-pressure synthesis, crystal structure, and electromagnetic properties of CdRh _2O _4: An analogous oxide of the postspinel mineral MgAl _2O _4

摘要

The postspinel mineral MgAl _2O _4 exists only under the severe pressure conditions in the subducted oceanic lithosphere in the Earths deep interior. Here we report that its analogous oxide CdRh _2O _4 exhibits a structural transition to a quenchable postspinel phase under a high pressure of 6 GPa at 1400 °C, which is within the general pressure range of a conventional single-stage multianvil system. In addition, the complex magnetic contributions to the lattice and metal nonstoichiometry that often complicate investigations of other analogues of MgAl _2O _4 are absent in CdRh _2O _4. X-ray crystallography revealed that this postspinel phase has an orthorhombic CaFe _2O _4 structure, thus making it a practical analogue for investigations into the geophysical role of postspinel MgAl _2O _4. Replacement of Mg ~(2+) with Cd ~(2+) appears to be effective in lowering the pressure required for transition, as was suggested for CdGeO _3. In addition, Rh ~(3+) could also contribute to this reduction, as many analogous Rh oxides of aluminous and silicic minerals have been quenched from lower-pressure conditions.