CHEMICAL AND STRUCTURAL VARIATION IN SYNTHETIC LOVERINGITE, (Ca,Ti3+,Ti4+,Mn)22O38. Peterson, Ronald C., Department of Geological Sciences, Queen's University, Kingston, Canada, K7L 3N6, Grey, Ian E., Cranswick, Lachlan, C.S.I.R.O, Division of Mineral Chemistry, P. O. Box 124, Port Melbourne, Australia
The relationships of loveringite to other phases in the system Ti-Mn-Ca-O, quenched from 1100deg.C and various f(O2) have been studied. Structural variation as a function of composition has been determined by Rietveld refinement of powder X-ray data. The calculated Ti3+ content, based on 38 oxygen atoms, varies from 2.5 atoms per formula unit(apfu) when grown at an f(O2) of 10-15 to 5.5 apfu at 10-18. As an example, a loveringite grown at f(O2)=10-16.7 has the compositon Ca1.54Mn2.18 Ti3+4.55Ti4+13.73O38. The Ti4+/Ti3+ ratio of a synthetic loveringite is also dependent on the other phases present which varies with the bulk composition of the charge. Other phases which coexist with loveringite at various compositions and f(O2) are Ti3O5, Ti4O7, Ti6O11, pyrophanite, perovskite and rutile. Rutile coexists with loveringite at more oxidizing conditions while perovskite and or Ti3O5, occur at more reducing conditions. Pyrophanite coexists with loveringite at more manganese-rich bulk compositions over a wide range of f(O2).
The unit cell of this closest-packed oxide structure varies most significantly with the calcium content. The substitution of Mn2++Ti4+ for 2 Ti3+ maintains charge balance for different Ti4+/Ti3 ratios within loveringite.
Ca in excess of 1 apfu and Mn are ordered into the largest octahedral site.