Dielectric and optical properties of melt-grown BaTiO3

Dielectric constant, spontaneous polarization, optical absorption, refractive index, and birefringence data are reported for melt-grown single-domain crystals of BaTiO3. The temperature dependences of the clamped and unclamped dielectric constants and the spontaneous polarization are found to be similar to results previously reported for flux-grown crystals. Differences in dielectric behavior are largely attributable to the higher transition temperatures in melt-grown crystals, i.e. the tetragonal phase is stable between 6–133†C in melt-grown crystals, and between 2–120°C in flux-grown crystals. The optical properties of melt and flux-grown crystals are, however, significantly different. Melt-grown crystals, in contrast to flux-grown crystals, exhibit an exponential Urbach absorption edge with negligible absorption (< 1 cm−1) for photon energies below approximately 3 eV. Refractive indices are somewhat higher in melt-grown crystals and the dispersion, which fits a Sellmeier relation, differs from that previously reported. The birefringence is shown to be a consequence of the quadratic electro-optic effect with the same electro-optic coefficient as measured in the paraelectric phase.