Phase stability, solubility and hydrothermal crystal growth of PbTiO₃

PbTiO₃ phase stability and crystal growth were investigated under hydrothermal conditions near 500°C. Solubility of PtTiO₃ was measured from 350 to 600°C; dependence on pressure and mineralizer was also determined. The PbO-TiO₂-H₂O phase diagram in 3.2 m KF shows a narrow region of PbO fraction 45.9-53.1% (Pb/Ti ratio 0.85-1.13) in which PbTiO₃ is the only solid product as determined by powder X-ray diffraction. Regions on the PbO-rich side produce PbO plus PbTiO₃, and regions on the TiO₂-rich side yield PbTi₃O₇ plus PbTiO₃. Solubility displays a positive temperature dependence with an estimated heat of solution ΔH_sol = 50 kJ/mol (12 kcal/mol). No appreciable solubility-pressure dependence is observed in the range of 10 000-30 000 psi (69-207 MPa). The solubility increases with KF concentration, then drops somewhat between 5.6 and 7.8 m KF. Decomposition of PbTiO₃ occurs when KF molalities exceed 7.8 m. Hydrothermally grown crystals are yellow in color and are of rectangular prism habit. X-ray diffraction and EDS of grown crystals verify identity of the crystals to be PbTiO₃. Crystal size increases dramatically between 485 and 600°C, with a significant decrease in optical crystal quality as the growth temperature increases.