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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 414-419 
    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.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6595-6602 
    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.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2916-2921 
    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.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2109-2112 
    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.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Autonomic & autacoid pharmacology 22 (2002), S. 0 
    ISSN: 1474-8673
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Medicine
    Notes: 1 The present study was designed to investigate the secretion of catecholamines (CA) evoked by stimulation of cholinergic receptors and membrane depolarization from the isolated perfused adrenal gland of spontaneously hypertensive rats (SHR) and normotensive Wistar–Kyoto rats (WKYR) at adult age. 2 The wet weight of adrenal gland in SHR was greater than that in WKYR. The CA releasing responses evoked by acetylcholine (5.32 × 10−3 m), and high potassium (5.6 × 10−2 m), a membrane depolarizer, were significantly lower in WKYR than in SHR. 3 The secretory responses of CA evoked by DMPP (10−4 m for 2 min), a selective agonist of neuronal nicotinic receptors, and McN-A-343 (10−4 m for 2 min), a selective agonist of neuronal muscarinic receptors, were also significantly lower in WKYR than in SHR. 4 The CA release evoked by Bay-K-8644 (10−5 m), a dihydropyridine-sensitive Ca2+ channel activator, and cyclopiazonic acid (10−5 m), a selective inhibitor of Ca2+-ATPase in the endoplasmic reticulum, were also significantly greater in SHR than WKYR. 5 Taken together, these experimental results demonstrate that the CA secretion evoked by stimulation of cholinergic (nicotinic and muscarinic) receptors as well as membrane depolarization is enhanced more greatly in the perfused adrenal glands of SHR than in those of WKYR. It is suggested that the augmented CA release in SHR compared with WKYR was involved in essential hypertensive pathogenesis.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1775-1780 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical and optical properties of amphoteric Si-doped GaAs diodes prepared by a single-step liquid-phase-epitaxy technique have been studied. These diodes have a P-P0-N structure and their current-voltage characteristics exhibit a negative resistance near 77 K. Existence of a recombination barrier is confirmed near the P0-P boundary by the spatial distribution of light emission, and a typical onset voltage of the negative resistance is 3 V at a current of 30 mA at 77 K. This low value can be interpreted as due to the relatively high density of thermally generated holes contributed by the shallow acceptors with activation energy of ∼30 meV. The deep acceptor level of ∼100 meV above the valence band edge is considered to be the origin for the negative resistance.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2807-2813 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we report on a modified Mach-Zehnder interferometer which is capable of measuring the ultrashort time strain response of a sample. Using this instrument, the dispersion of piezoelectric and electrostrictive coefficients of several commonly used ferroelectrics was measured. The strain switching behavior of lead lanthanum zirconate titanate (PLZT) 9/65/35 driven by a square pulse electric field was studied. The results show that the switching rise time of the strain response for PLZT 9/65/35 can be much shorter than 5 μs at a pulse field strength near 25 kV/cm and that the fall time of the strain response is considerably shorter than the rise time in the experimental field strength range.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3331-3338 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A phenomenological thermodynamic theory of PbTiO3 was developed using a modified Devonshire form of the elastic Gibbs free energy. The spontaneous strain as a function of temperature was determined from pure sol-gel derived PbTiO3 powder and used with selected data from the literature to determine the coefficients of the energy function. The theoretical prediction of the phase stability, spontaneous polarization and strains, and dielectric and piezoelectric properties agree well with experimental data. This theory provides a way of predicting the intrinsic single domain dielectric and piezoelectric properties of PbTiO3, which have not been completely determined from experimental measurements.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6445-6451 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and the depoled states. The results indicate that a reversible domain wall excitation exists which contributes to the weak-signal response of these materials. Irreversible domain wall motion can be excited within the frequency range measured by applying a field above a threshold field, which is much smaller than the coercive field. Therefore, the weak-signal linear dielectric, piezoelectric, and elastic coefficients of these materials may not provide a suitable description of their behavior when the external applied field exceeds this threshold field. All the observed phenomena can be explained by thermally activated domain wall fluctuations and nucleations.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3173-3180 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A thermodynamic theory is presented to model the phase transitions and properties of lead zirconate. The free energy ΔG is expressed as a power series in terms of the ferroelectric polarization (Pi=Pai+Pbi) and antiferroelectric polarization (pi=Pai−Pbi) including all possible terms up to the sixth power, but only first-order cross coupling terms and couplings to elastic stress. Under the assumption that only the lowest-order coefficients of Pi and pi are linearly temperature dependent (Curie–Weiss behavior) and all other constants are temperature independent, experimental data are used to define the constants and permit calculation of ferroelectric and antiferroelectric free energies as a function of temperature. Use of the function to define the averaged dielectric permittivity at room temperature in the antiferroelectric phase gives a value of εR=120 in good agreement with recent microwave measurements. A simplified technique for modifying the function to explore solid solution with lead titanate is examined, and shown to lead to excellent agreement with the known phase diagram.
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