High-PT study of solid solutions in the system ZrO (sub 2) -TiO (sub 2) ; the stability of srilankite

The ZrO (sub 2) -TiO (sub 2) phase diagram was studied in experiments between 1200 and 1650 degrees C and 1 atm to 28 kbar, investigating the effect of pressure on the compositions of rutile, zirconia and zirconium titanate [(Zr,Ti) (sub 2) O (sub 4) ] solid solutions. All three phases became more Ti-rich with increasing pressure, in agreement with ionic radii and cell volume. The range of zirconium titanate solid solution, which is limited to X (sub Ti) < 0.58 at room pressure, is extended to X (sub Ti) 0.68 at 1500 degrees C and 28 kbar. Thus (Zr,Ti) (sub 2) O (sub 4 ) and ZrTi (sub 2) O (sub 6) (srilankite) which were previously regarded as the high- and low-temperature forms, respectively, are both stable at high temperatures (< 1200 degrees C) and are part of the same solid solution that is continuous with pressure. Srilankite formed at 1440 degrees C and 28 kbar in equilibrium with rutile. These results are consistent with the natural occurrence of srilankite in high-grade rocks such as eclogites, granulites, lamprophyres and chromitites.