The possibility that the optical second-harmonic generation in lead phosphate, Pb3(PO4)2, is related to structural imperfections

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Abstract
The second-harmonic generation (SHG) of nominally pure lead phosphate Pb3(PO4)2, was reinvestigated. SHG is confirmed at room temperature albeit 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 microprobe techniques showed a weak oxygen deficit for all samples. It is suggested that SHG is not necessarily indicative of an intrinsic symmetry breaking process in Pb3(PO4)2 but may be related to structural imperfections.