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  • 1990-1994  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Freezing of the polarization fluctuations in lead magnesium niobate relaxors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2916-2921 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric relaxation of a solid solution of 10-mol % lead titanate in lead magnesium niobate is found to be similar to the magnetic relaxation in spin-glass systems.1–3 Based on this analogy, it is proposed that the relaxor ferroelectric is a polar-glassy system which has thermally activated polarization fluctuations above a static freezing temperature. An activation energy and freezing temperature of 0.0407 eV and 291.5 K, respectively, were found by analyzing the frequency dependence of the temperature of the dielectric maximum using the Vogel–Fulcher relationship.4,5 It has also been shown that a macroscopic polarization is sustained on heating up to this freezing temperature. A coupling between nanometer scale clusters is believed to control the kinetics of the fluctuations and the development of a frustration as the system freezes into states of local equilibrium. The possibility of an orientational freezing associated with the ferroelastic nature of the nanosized polar regions in the rhombohedral relaxor families as well as a polar freezing is discussed. A diffuse phase transformation is believed to arise due to a dispersion in the fluctuation frequency of the polarization. A qualitative model for the relaxation time spectrum is also proposed in which the width of the spectrum broadens strongly near the freezing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346425
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Internal strain relaxation and the glassy behavior of La-modified lead zirconate titanate relaxors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6595-6602 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonlinear internal friction measurements have been carried out on La-modified lead zirconate titanate relaxors with a Zr/Ti ratio of 65/35. Measurements have been made as a function of La content and dc bias. The elastic softening is believed to have a ferroelastic contribution due to the tilting of the oxygen octahedra, in addition to the expected electrostrictive effects. The temperatures of the maximum softening form a plausible extension to the rhombohedral-rhombohedral phase boundary [Proc. IEEE 61, 959 (1973)]. A frequency dependence of the softening has also been found which was interpreted as the existence of fluctuations in the orientations of the tilts. These fluctuations are proposed to arise in an attempt to partially relieve an inhomogeneity in the electrostrictive strains associated with the polarization fluctuations. The results are discussed in context with previously reported transmission electron microscopy work [C. Randall, Ph. D. dissertation, University of Essex (1987)]. Dielectric measurements have also been done as a function of La content and bias, and the freezing temperature of the polarization fluctuations determined as a function of composition. A revised phase diagram has been proposed using this data base which shows different phase fields having various combinations of freezing mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348871
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A sensitive modified Mach–Zehnder interferometer for studying electro-optic properties (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2109-2112 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A modified Mach–Zehnder interferometer has been built for measuring the electro-optic properties of crystals. The system is capable of resolving an optical path length change of 5×10−3 A(ring). The electro-optic R33 coefficient of the LiNbO3 crystal has been measured; the result is in excellent agreement with the previously reported values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141376
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  • 4
    Electronic Resource
    Electronic Resource
    Local polar configurations in lead magnesium niobate relaxors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 414-419 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The field dependence of the dielectric response has been measured for lead magnesium niobate relaxors. The frequency dispersion of the temperature of the permittivity maximum, Tmax, was analyzed using the Vogel–Fulcher relationship. The field dependence of the permittivity at various temperatures was also modeled using a phenomenological expansion in the electric field. The activation energy and a softening of the dielectric response were found to be maximum under a small bias. The freezing temperature was found to be minimum near this same bias. These results are interpreted to mean that the moments of the polar clusters do not freeze in random orientations, but rather locally preferred configurations of moments are proposed to exist. Evidence is presented that the scale of these configurations is approximately 100 A(ring). At higher biases the relaxation mechanism was shut down; consequently, the nonlinear response was stiffened and Tmax increased. The nonlinear response was also found to be maximum near the freezing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347732
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison of twists in isosteric propellers: X-ray structures of tris(2,6-dimethoxyphenyl)borane, tris(2,6-dimethoxyphenyl)methyl cation and tris(2,6-dimethoxyphenyl)methyl radical (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 324-329 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768191014982
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    Paper (German National Licenses)
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