Phase stability, solubility and hydrothermal crystal growth of PbTiO3

PbTiO3 phase stability and crystal growth were investigated under hydrothermal conditions near 500 degrees C. Solubility of PtTiO3 was measured from 350 to 600 degrees 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 Delta H-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 degrees C, with a significant decrease in optical crystal quality as the growth temperature increases. (C) 1999 Elsevier Science B.V. All rights reserved.