Single-crystal vibrational spectra of tetragonal and orthorhombic lead monoxide

Abstract

All the fundamental modes of vibration of tetragonal PbO have been observed and all but one assigned unequivocally by single-crystal techniques: B_1g 338.7, A_1g 146.5, E_g 321.5 and 81.0, A_2u 116, and E_u 243 cm^–1. From the i.r. longitudinal and transverse optic (LO and TO) frequencies, the principal components of the dielectric tensor are estimated to be ε₁= 20.3 and ε₃= 11.9. The first complete Raman spectrum, and single-crystal i.r. reflectance data, are reported for orthorhombic (yellow) PbO. The assignment has been partially established for the Raman spectrum with the aid of the group-theoretical prediction, based on a line-group approach, that i.r. and Raman modes should be in near coincidence. The high dielectric constant of the material has been accounted for, a principal contribution coming from the single B_1u mode (normal to the plane of the PbO chains) which is of unusual breadth.