The MgTiO (sub 3) -FeTiO (sub 3) join at high pressure and temperature

The phase relations at high pressure and high temperature for the FeTiO (sub 3) -MgTiO (sub 3) join were determined using several different experimental methods. Through a series of multi-anvil experiments, a phase boundary with a negative slope was observed between MgTiO (sub 3) I (ilmenite structure) and a high pressure phase with the MgTiO (sub 3) II (lithium niobate structure) after quenching. The enthalpy of transformation of MgTiO (sub 3) I to MgTiO (sub 3) II was determined through transposed-temperature-drop calorimetry to be 28.78+ or -1.45 kJ/mol. The enthalpy of transformation from ilmenite to lithium niobate structure was also determined for three intermediate compositions on the FeTiO (sub 3) -MgTiO (sub 3) join, Fe (sub 0.2) Mg (sub 0.8) TiO (sub 3) , Fe (sub 0.5) Mg (sub 0.5) TiO (sub 3) and Fe (sub 0.8) Mg (sub 0.2) TiO (sub 3) , and confirmed for FeTiO (sub 3) , and was found to be a linear function of composition. These experiments represent one of the first successful calorimetric measurements on small samples (1 to 3 mg) synthesized at high pressures (15 to 21 GPa). X-ray analysis during compression of Fe (sub 0.5) Mg (sub 0.5) TiO (sub 3) II in a diamond cell confirmed a room temperature transition at 28 GPa to Fe (sub 0.5) Mg (sub 0.5) TiO (sub 3) III (a GdFeO (sub 3) -type perovskite structure), similar to the transitions previously observed in FeTiO (sub 3) and MnTiO (sub 3) . The Fe (sub 0.5) Mg (sub 0.5) TiO (sub 3) sample was heated to 802 degrees C at 21 GPa, and it was observed that the stable high temperature, high pressure phase is perovskite, Fe (sub 0.5) Mg (sub 0.5) TiO (sub 3) III. The above data combined confirm the stability of a continuous perovskite solid solution at high pressure and temperature for the FeTiO (sub 3) -MgTiO (sub 3) join.