A near-surface structural phase transition on a SrTiO3 single crystal, occurring at T(*) about 45 K above the bulk cubic-to-tetragonal transition, is observed by means of optical second harmonic generation. The temperature dependence of the second harmonic field in the vicinity of T(*) is described with a phenomenological Landau-type model.

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Optical second-harmonic generation (SHG) is used as a noninvasive probe of two-dimensional (2D) ferroelectricity in Langmuir-Blodgett (LB) films of the copolymer vinylidene fluoride with trifluoroethylene. The surface 2D ferroelectric-paraelectric phase transition in the topmost layer of the LB films and a thickness-independent (almost 2D) transition in the bulk of these films are observed in temperature studies of SHG.

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