Optical properties of lead monohydrogen phosphate single crystals, PbHPO4

The birefringence and the angle φ between the principal axes of the index ellipsoid and the monoclinic axis a (both measured when viewing perpendicular to the mirror plane) have been measured at 25−50°C, i.e. in the vicinity of the 2/m ← m structure phase transition. This data was used to determine the spontaneous birefringence in the ferroic phase. The magnitude of the effective quadratic and linear electrooptic coefficients (that correspond to the transverse electrooptical effect when applying an electric field so that the resulting induced polarization is parallel to the direction of spontaneous polarization, P i ∥P s ) was estimated using our data on P s (T).