OH defects in synthetic xenotime (YPO (sub 4) )

The polarized infrared spectra of hydrogen-containing xenotime (YPO (sub 4) ) 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 degrees C/h from 1200 to 800 degrees C, xenotime single crystals up to approximately 300 mu m in length were obtained. A sharp OH stretching vibrational band was observed at 3302 cm (super -1) . Using a molar absorption coefficient of 111 217 L mol (super -1) cm (super -2) , the H (sub 2) O concentration in the sample was estimated as 20+ or -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 Y (super 3+) or P (super 5+) vacancy, possible orientations of the O-H bonds were estimated. We propose that the OH incorporation mechanism in synthetic xenotime is controlled by Y (super 3+) vacancy (Y (sub Y) <--> V (sub Y) = 3H (sub i) ).