THE POSSIBILITY THAT THE OPTICAL 2ND-HARMONIC GENERATION IN LEAD PHOSPHATE, PB3(PO4)2, IS RELATED TO STRUCTURAL IMPERFECTIONS

The second-harmonic generation (sHG) of nominally pure lead phosphate Pb3(PO4)2, was reinvestigated. sHG is confirmed at room temperature al beit with a large spatial variation within each sample. The signal did not disappear when the crystal was heated well above the ferroelastic transition temperature of 453 K. Chemical analysis using x-ray microp robe techniques showed a weak oxygen deficit for all samples. It is su ggested that SHG is not necessarily indicative of an intrinsic symmetr y breaking process in Pb3(PO4)2 but may be related to structural imper fections.