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1.
Orthorhombic CsH2PO4 undergoes a ferroelectric transition at Tc = ?119.5°C, whereas the ferroelectric transition temperature in isomorphous CsD2PO4 is Tc = ?5.55°C. The transitions are of first order in both cases. The rather large isotope effect demonstrates the importance of the OHO bonds in the transition mechanism.  相似文献   

2.
It is shown by X-ray diffraction measurements that the transitions at 230 K in TlH2PO4 and at ≈ 350 K in TlD2PO4 are structurally equivalent. In both cases, on cooling through the transition, new reflections appear at points (h + 12, k + 12, l) referred to the primitive monoclinic unit cell of the high-temperature phase. In TlH2PO4 some distinct but broadened scattering remains at the (h + 12, k + 12, l) points up to 10 K, or more, above the transition temperature.  相似文献   

3.
Polarization versus electric field double hysteresis loops along the b-axis of TID2PO4 were observed. From this fact and the permittivity versus temperature characteristic, the low temperature phase of TID2PO4 was confirmed to be antiferroelectric.  相似文献   

4.
A positron annihilation study of KH2PO4 provides new evidence of a high temperature phase transition at 447 K. The results suggest the formation of a long lived positron or positronium state which could be associated with bond defects.  相似文献   

5.
The origin of the low-lying modes of KH2PO4 and KD2PO4 in the ferroelectric phase has been clarified by the z(xy)z? Raman scattering experiments. The “S-mode”, which has been usually assigned to the proton tunneling mode in KH2PO4 at T<Tc, has been found in the z(xy)z? spectrum of KD2PO4 in contrast to the x(xy)y spectrum. It has been found that the frequency of the “S-mode” of KD2PO4 is higher than that of KH2PO4. These results have shown that the “S-mode” is far from the proton tunneling mode nor the proton/deuteron mode at all. From the present Raman spectroscopy, it is concluded that the “S-mode” is assigned to the libration mode of the PO4 tertahedrons.  相似文献   

6.
The spectra of 57Fe in monoclinic Fe2TiO5 were interpreted as hyperfine patterns belonging to two nonidentical iron sites. They confirm that Fe3+ ions are distributed over 4a and 8f sites. The spectra of mosaic-like crystals indicate that all iron spins lie in the (100) plane. The temperature dependences of hf parameters gave a magnetic ordering temperature 350 K, average saturation effective field 505 kG and Debye temperature 430 K. Above 1500 K, monoclinic Fe2TiO5 transformed into the stable pseudobrookite form.  相似文献   

7.
In the compound BaLa2Fe2O7, below 235 K, spins are oriented along the diagonal of the quadratic cell in an antiferromagnetic configuration. Above this temperature we observe by neutron diffraction a continuous rotation of the magnetic moments in the base plane xyO, the configuration remaining antiferromagnetic; the magnetic symmetry goes from Ipmmm′ to P2′/m Shubnikov's group. At the transition temperature we observe a discontinuity of the thermal expansion coefficient. This phenomenon can be interpreted in agreement with Landau's theory of second order transitions.  相似文献   

8.
KH2PO4 single crystals have been studied by employing complex impedance measurements in view of the domain freezing effect. As a result, distinct behaviors of the anisotropic domain-wall dynamics in the activation energy of domain freezing and the Vogel–Fulcher temperature before and after proton irradiation have been identified in the anisotropic crystal structure.  相似文献   

9.
The influence of some impurities on the conduction properties of Cr2O3 and Fe2O3 are examined and contrasted. A mechanism is proposed to account for the effect of Ti in Cr2O3.  相似文献   

10.
Solid solutions of (CsHSO4)1 − x(CsH2PO4)x (x = 0.25-0.75) were synthesized by mechanical milling method over a wide range of compositions. Superprotonic cubic phase was confirmed for all these samples between 293 and 420 K depending on its composition. These superprotonic phases have primitive cubic structure similar to that of CsH2PO4. The kinetic stability of the supercooled cubic phase depends both on the composition x and the humidity of surrounding atmosphere. The most stable composition of the cubic phase was found around x = 0.67 and could be maintained for several days even under ambient atmosphere. The ionic conductivities of these superprotonic phases reached 10− 2–10− 3 S∙cm− 1 at 450 K. With increasing x the ionic conductivity at the superprotonic phase decreased continuously associated with the increase of the activation energy. These findings suggest that the average number of the hydrogen bonds between XO4 (X = S, P) units plays an important role on the stability of the cubic phase and also on the conductivity.  相似文献   

11.
The spectra recently published by Tominaga and Urabe are shown to be in good qualitative agreement with the current coupled-mode models of the KDP transition. The need for a careful quantitative analysis of this type of data over a broad frequency range is discussed.  相似文献   

12.
We have measured the transverse dielectric constant of KH2PO4 crystal from liquid N2 to room temperatures. Extending the Blinc-de Gennes' model in conjunction with a cluster approximation leads to a new independent determination of the Slater-Takagi parameters and improves significantly the fit of the model to the data.  相似文献   

13.
Second-harmonic scattering (SHS) of light by laminar ferroelectric domains of the orthorhombic phase of RbH2PO4 below Tc=147 K is studied in detail. CCD images of the far-field SHS pattern reveal up to six off-axis distinct intensity maxima in a plane normal to the ferroelectric axis c. These scattering maxima are interpreted on the basis of the quasi-phase matching (QPM) conditions for the three sets of polarizations allowed by the nonvanishing elements of the second-order nonlinear susceptibility tensor. On this assumption scattering angles of the three SHS modes calculated from crystal optics are shown to fit well the experimental data for any incidence of the pump beam normal to c. Scattering intensities of the two most intense modes are also measured versus the component of the wave vector perpendicular to the modulated structure. A stochastic model giving the intensity as a function of the density probability of domain widths is developed and is shown to give a good fit of the scattered intensity. Moreover, it permits the evaluation of the mean and dispersion of the ferroelectric domain widths, which are found to be, respectively, 2.6 and 0.7 μm in the crystal under study. This is consistent with the domain size of the ferroelastic counterpart revealed by polarization microscopy.  相似文献   

14.
The far-infrared and the Raman spectra of KD2PO4 were measured for B2 symmetry in the paraelectric phase and for A1 symmetry in the ferroelectric phase. The results were discussed in comparison with those of KDP.  相似文献   

15.
After showing the existence of second order M.E. effect β, in Fe5LiO8 [1], we try to verify Lee and Rado's assumptions. These authors suppose that the existence of β is connected with the rotation of magnetic domains. We compare the magnetoelectric β and the magnetization σ curves vs the magnetic field H0. The latter curve reveals the different magnetic modes, and therefore illustrates the behavior of the magnetic domains. This comparison has been made for several directions of the applied field in order to illustrate all possible cases of rotation of the domains and allows us to confirm the basic assumption.  相似文献   

16.
A comparative study concerning the electronic structure of the Mn5+ ion in the Li3PO4, Ca2PO4Cl, Sr5(PO4)3Cl host lattices has been carried out in the framework of the exchange charge model. The crystal field parameters have been evaluated using the structural data as the only input information. The 10 K absorption spectra of the investigated compounds have been measured in order to verify the correspondence between experimental and calculated energy levels. A systematic trend of the crystal field splitting of the most intense transitions has been evidenced and discussed by considering the symmetry properties of the coordination polyhedra around Mn5+.  相似文献   

17.
The effects of several parameters on the aging rate of BaSi2O5:Pb under electron bombardment have been investigated. Results showed that the aging rate increased (1) at lower beam current densities, (2) at higher electron energies, (3) with certain impurities (particularly group III-A) incorporated in the phosphor, and (4) at higher temperatures. A hypothetical mechanism involving oxygen release is proposed.  相似文献   

18.
C. Li 《Applied Surface Science》2010,256(22):6801-6804
Fe2O3/Al2O3 catalysts were prepared by solid state reaction method using α-Fe2O3 and γ-Al2O3 nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ3 and τ4 are attributed to positronium annihilation in two types of pores distributed inside Al2O3 grain and between the grains, respectively. With increasing Fe2O3 content from 3 wt% to 40 wt%, the lifetime τ3 keeps nearly unchanged, while the longest lifetime τ4 shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe2O3 content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ4 is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.  相似文献   

19.
Raman scattering was applied to study the high-temperature phase transition (near 175°C) in KH2PO4. Drastic temperature-dependent changes were observed to take place in the normal modes of B1 symmetry between 1000–3400 cm?1. The disintegration of the dominant broad feature near 2500 cm?1 when temperature rises beyond 150°C suggests that the alteration of the hydrogen-bond network is closely connected with this high-temperature phase transition.  相似文献   

20.
A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe3O4 electrodes is presented. Fe3O4/Au/Fe3O4 spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe3O4 layers. By contrast, a negative GMR effect is measured on Fe3O4/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe3O4/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.  相似文献   

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