Linear electro-optical properties of zincite

Orientational, dispersion, and temperature dependences of electro-optical coefficients of Li-doped ZnO single crystals are investigated. According to the data on the orientational dependences obtained far from the electronic absorption band, the values of all linearly independent components of the Pockels tensor are specified. In the range from 2 eV to Eg, at both 100 and 300 K, the dispersion obeys a power law with m=2, which indicates a two-dimensional character of the van Hove singularity. The anomalies in the temperature dependences in the range from 15 to 700 K are explained by the competing contributions of the anharmonicities of the electron and lattice subsystems, which lead to anomalous behavior of the coefficients at both low (T < 100 K) and high (T > 100 K) temperatures. In the low-temperature range, the identified anomalies correlate with data of independent measurements of birefringence, spontaneous polarization, and dilatometry.