Poling-induced crystallization of tetragonal BaTiO3 and enhancement of optical second-harmonic intensity in BaO–TiO2–TeO2 glass system

Effect of poling on surface crystallization behavior of BaTiO3 in 15BaO–15TiO2–70TeO2 glass and on second-harmonic generation of the resultant glass ceramics has been examined. A direct current voltage in a range of 0.3–1 kV was applied to the original glass at around 400 °C, which is above its glass transition temperature, followed by cooling of the sample to room temperature with the voltage kept constant. X-ray diffraction patterns indicate that the poling increased the fraction of crystalline phases precipitated at the glass surface and that BaTiO3 crystallites were precipitated preferentially with (101)- or (110)-orientation. It is also observable that the x-ray diffraction line assigned to BaTiO3 shifted from the position corresponding to bulk cubic crystal to that of ferroelectric tetragonal one when the applied voltage was increased. In other words, the poling treatment stabilizes the tetragonal BaTiO3 phase, leading to a larger optical second-order nonlinear susceptibility. In fact, the second-harmonic intensity for the glass ceramic poled at 420 °C was enhanced by a factor of ten compared with the glass ceramic heat treated without an external electric field.