Second Harmonic Generation in BaTiO3 Film Crystallized on Tellurite Glass Surface

Abstract

Transparent glass-ceramics containing ferroelectric crystalline phases have been successfully prepared by many investigators [1±10]. Non-linear optical properties and electro-optical properties of those materials can be utilized for optoelectronic devices such as an optical switch, an optical shutter, frequency upconversion, and so forth. Borrelli and Layton [3] determined quadratic electro-optic coef®cients of transparent glass-ceramics containing ferroelectric crystals such as NaNbO3 and LiTaO3. They also revealed that a linear electro-optic effect, i.e., Pockels effect is observed in poled transparent glass-ceramics providing the size of the crystalline phase included is at least 0:2 im in size. Kao et al. [6] prepared transparent glass-ceramics containing â-BaB2O4 crystalline phase and revealed that the resultant materials exhibit second harmonic generation. Ding et al. [7, 8] utilized ultrasonic treatments to prepare transparent glass-ceramics where crystalline thin ®lms of â-BaB2O4 and LiNbO3 are formed on the glass surfaces. These glass-ceramic materials manifested ef®cient optical second harmonic generation. Komatsu et al. [9, 10] reported preparation of transparent tellurite glass-ceramics containing dielectric crystals such as LiNbO3 and BaTiO3. In these glass-ceramics, one can increase the crystallite size while keeping the material transparent to visible light, because the refractive index of the tellurite glass matrix is close to those of LiNbO3 and BaTiO3 crystals. Recently, we reported second harmonic generation in transparent tellurite glass-ceramic material where BaTiO3 crystalline phase is precipitated [11]. However, the origin of the second harmonic generation in this glass-ceramic still remains unclear. In the present investigation, we further examine this transparent glass-ceramic to characterize the BaTiO3 phase and to clarify the origin of second harmonic generation. Glass was prepared using reagent-grade BaCO3, TiO2 and TeO2 as starting materials. The raw materials were weighed to make 15BaO 15TiO2:70TeO2 (in mol %) composition, and mixed thoroughly. The mixture was melted in a platinum crucible at 1000 8C for 40 min in air. The melt was poured onto a stainless steel plate and cooled in air. The as-prepared glass was annealed for 30 min at around the glass transition temperature determined by means of differential thermal analysis (DTA). The annealed glass was cut into a plate of about 7 mm 3 7 mm 3 1 mm, and both sides were polished with CeO2 powders. The resultant glass specimens were heat-treated at elevated temperatures to fabricate glass-ceramics. X-ray diffraction analysis with CuKa radiation (Rigaku, RAD-C) was carried out to ascertain that the as-prepared specimen was amorphous and to identify crystalline phases in the heattreated specimens. The second harmonic intensity was measured at room temperature using the Maker fringe method [12]. The fundamental wave of a pulsed Nd:YAG laser (Spectra-Physics, GCR-11) with a wavelength of 1064 nm was used as incident light. The situation of polarization was p-excitation and p-detection. The second harmonic wave generated from the specimen was detected using a monochromator (SPEX, 270M) equipped with a photomultiplier (SPEX, 1424M). The intensity of the second harmonic wave was determined using a digital oscilloscope (Hewlett Packard, 54522A). Details of the measurements of optical second harmonic intensity were described elsewhere [13]. Fig. 1 shows X-ray diffraction patterns of the pulverized glass-ceramic specimen (lower ®gure) and the surface state of the bulk glass-ceramic specimen (upper ®gure) heat-treated at 420 8C for 5 h. These two patterns are evidently different from each other. The diffraction line at around 2e ˆ 31:48 in the lower diffraction pattern is attributable to BaTiO3.