COMPOUNDS AND SOLID-SOLUTIONS OF COBALT, COPPER PHOSPHATES

Cobalt phosphates have been synthesized and their thermal behavior exa mined. The formation of compounds and solid solutions among cobalt and copper phosphates is studied by X-ray diffraction, Unlimited solubili ty exists between the pyrophosphates Co2P2O7 and Cu2P2O7, the orthopho sphates Co-3(PO4)(2) and Cu-3(PO4)(2), and Co-3(PO4)(2) and Cu2P2O7. X -ray diffraction indicates that the structures of cobalt and copper py rophosphate solid solutions vary gradually from one end member to the other, The structures of orthophosphate solid solutions vary in a more complex manner: the change is gradual from Co-3(PO4)(2) to Co2Cu(PO4) (2). At Co1.5Cu1.5(PO4)(2), a new structure (L) occurs, At 950 degrees C, CoCu2(PO4)(2) also exhibits this structure, which is similar to th at of graftonite, Fe-3(PO4)(2). CoCu2(PO4)(2) is dimorphic, changing r eversibly at 1000 degrees C to a triclinic structure (H) related to th at of Cu-3(PO4)(2). From CoCu2(PO4)(2) (H) to Cu-3(PO4)(2), the struct ure appears to vary gradually. A new phosphate, Cu+Cu2+Co3(PO4)(3), ha s also been synthesized.