The effect of thermal/electrical poling on surface structure and poling-induced secondharmonic generation have been examined for 15Nb 2 O 5 •85TeO 2 glass. Since the poling was carried out with the 15Nb 2 O 5 • 85TeO 2 glass sandwiched in between two commercial borosilicate glasses containing Na + , penetration of Na + into the anode-side surface of 15Nb 2 O 5 • 85TeO 2 glass took place, as revealed by x-ray photoelectron spectroscopy (XPS). XPS studies also suggest that Nb 5+ migrates from the anode-side surface into the bulk by the poling. It is thought that the migration of Na + and Nb 5+ forms an internal dc electric field, leading to the second-harmonic generation.
Crystal structure of Ba x Sr 3-x MgSi 2 O 8 has been determined by Raman spectroscopy and X-ray diffraction. The solid solution series have glaserite-type layered structures made of corner-sharing SiO 4 tetrahedra and MgO 6 octahedra. Ba 2+ and Sr 2+ ions are sandwiched in between the layers. Raman spectroscopy has found that structural symmetry changes at x = 0.5 and 2.5. Structural refinement by the Rietveld method has clarified that the symmetry changes occur among C2 (Z = 4), P 3 m1 (Z = 1), and P 3 (Z = 3). They originate in SiO 4 tilting caused by size mismatch between alkaliearth cations and their site spaces. For x ≤ 0.5, SiO 4 tilting occur every other interlayer space, whereas for x ≥ 2.5, all the SiO 4 tilt.
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