OH defects in synthetic xenotime (YPO₄)

The polarized infrared spectra of hydrogen-containing xenotime (YPO₄) were measured to obtain information on its OH defects. Sample syntheses were conducted at 1.0 GPa using a piston-cylinder apparatus under water-saturated conditions. By lowering the temperature at a rate of 10°C/h from 1200 to 800 °C, xenotime single crystals up to 7∼300 mm in length were obtained. A sharp OH stretching vibrational band was observed at 3302 cm-1. Using a molar absorption coefficient of 111 217 L mol-1 cm-2, the H₂O concentration in the sample was estimated as 20 ± 10 ppm. The OH band showed strong infrared absorption perpendicular to the c-Axis and weak absorption parallel to the c-Axis. According to electrostatic considerations and assuming the presence of Y3+ or P5+ vacancy, possible orientations of the O-H bonds were estimated. We propose that the OH incorporation mechanism in synthetic xenotime is controlled by Y3+ vacancy (Y-Y i V000 Y + 3H-i ).