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The dielectric permittivity ε - i of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε vs. T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results. Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002  相似文献   
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Two weakly discontinuous structural phase transitions have been observed on single domains of KCdF3 at Tc1 = 487.5 K and at Tc2 = 472.7 K in the temperature dependence of the linear birefringence (LB). Beginning with the cubic high temperature phase the crystal becomes successively uniaxial and biaxial birefringent. Within the classical Landau approximation the LB has proved to be proportional to the square of the respective order parameter of the transformations. A relation which describes the coupling between both order parameters is discussed. In disagreement with Hidaka et al. [7] we do not observe a third phase transition near 240 K by the LB technique.  相似文献   
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The preparations of CH2SF4 and CH3CHSF4 are presented and the structures are discussed. Addition reactions of polar species give a wide range of new compounds, like Hg(CH2SF5)2, F4AsCH2SF5, cisBrSF4CH3, cisF5SeOSF4CH2Br, a.o. While CH2SF4 decomposes at room temperature slowly to CH2CH2 and SF4, at high temperatures HF and CSF2 are formed. CH3CHSF4 gives mainly CH3CHF2 at room temperature. The “saturated” compounds CH3SF5 and C2H5SF5 have been prepared. They react with SbF5 in SO2 at low temperatures to form the cations CH3SF4+ and C2H5SF4+. The CH3SF4+ ion has been investigated in detail by nmr methods at low temperatures. It decomposes to CH3 and SF4, which react further in the SO2/SbF5 system to CH3OSO+ and SF3+.  相似文献   
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By close analogy with multiferroic materials with coexisting long-range electric and magnetic orders a "multiglass" scenario of two different glassy states is observed in Sr(0.98)Mn(0.02)TiO(3) ceramics. Sr-site substituted Mn2+ ions are at the origin of both a polar and a spin glass with glass temperatures T(g) approximately equal to 38 K and < or =34 K, respectively. The structural freezing triggers that of the spins, and both glassy systems show individual memory effects. Thanks to strong spin-phonon interaction within the incipient ferroelectric host crystal SrTiO3, large higher order magnetoelectric coupling occurs between both glass systems.  相似文献   
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