Linear Dielectric Permittivity Research Articles

Electric-field effect on phase transitions in Pb0.995La0.005[Zr0.9 − y Sn0.1Ti y ]0.99875O3 and Pb0.9975[Zr0.895 − y Sn0.1Ti y Nb0.005]O3 solid solutions

The phase diagrams of PbZrO3-PbTiO3-PbSnO3 solid solutions doped with $$ La_{Pb^{2 + } }^{3 + } $$ and $$ Nb_{B^{4 + } }^{5 + } $$ have been constructed using the temperature dependences of their linear dimensions and relative dielectric permittivity measured during zero-field cooling and field cooling. Doping to a level as low as 0.5 at % has a significant effect on the temperature and electric field at which the tetragonal antiferroelectric phase forms. Field cooling of the antiferroelectric solid solutions close in composition to the morphotropic phase boundary consecutively stabilizes two ferroelectric phases. The ferroelectric state produced by field cooling is often inhomogeneously poled and has an asymmetric dielectric hysteresis loop.

Linear dielectric response of antiferroelectric liquid crystals

We use a phenomenological model to find theoretically the linear dielectric response at the direct smectic A * to smectic C A * transition in antiferroelectric liquid crystals. The ferroelectric soft mode is the only collective mode present in the SmA * phase. However, according to the results of theory the SmC A * phase exhibits three collective modes: the ferroelectric soft mode, antiferroelectric soft mode and antiferroelectric Goldstone mode. The temperature dependence of the linear dielectric permittivity is presented for the SmA * and SmC A * phases.

Linear and Non-linear Dielectric Pretransitional Behavior Near the Isotropic-nematic Phase Transition for 4-cyano-4-n-pentylbiphenyl (5CB)

Linear and non-linear dielectric permittivity measurements for n-pentylcyanobiphenyl 5CB are presented. By two different experimental methods the same value of the temperature discontinuity for the isotropic-nematic transition was obtained. Broadband dielectric relaxation tests showed a significant influence of the pretransitional behavior on the dynamic properties above and below the nematic clearing temperature (TI-N). The form of the loss curves is clearly non-Debye’an and can be portrayed within the Cole-Davidson approximation (CD). In the isotropic and nematic phases the CD parameter βCD drops on approaching the clearing temperature. This is connected with the broadening of the dielectric absorption width.

Dielectric and Ferroelectric Properties of BaTiO 3 /Ni Cermets Under High Electric Fields

Dielectric properties of ferroelectric-ceramic/metal exhibit extraordinary high values of effective dielectric permittivity. We have prepared BT/Ni ceramics with Ni composition from f = 0 to f = 0.3 and we have studied the dependence of its dielectric permittivity, and its ferroelectric properties under high electric fields. In these composites, the ferroelectric character of the matrix is strongly modified by the metallic particles as a consequence of the large increase of linear dielectric permittivity while the non-linear part remains nearly unchanged. In samples with low or moderate nickel content, ferroelectric switching still can be detected. Samples with Ni concentrations close to the percolation threshold which have giant linear dielectric permittivity, become paraelectric. In these latter, leakage current also plays an important role.

Dielectric and Ferroelectric Properties of BaTiO 3 /Ni Cermets Under High Electric Fields

Dielectric properties of ferroelectric-ceramic/metal exhibit extraordinary high values of effective dielectric permittivity. We have prepared BT/Ni ceramics with Ni composition from f = 0 to f = 0.3 and we have studied the dependence of its dielectric permittivity, and its ferroelectric properties under high electric fields. In these composites, the ferroelectric character of the matrix is strongly modified by the metallic particles as a consequence of the large increase of linear dielectric permittivity while the non-linear part remains nearly unchanged. In samples with low or moderate nickel content, ferroelectric switching still can be detected. Samples with Ni concentrations close to the percolation threshold which have giant linear dielectric permittivity, become paraelectric. In these latter, leakage current also plays an important role.

On the critical behavior of linear and nonlinear dielectric permittivity on approaching the critical consolute point

Results are presented of the dielectric permittivity /spl epsi/ and nonlinear dielectric effects (NDE) in binary mixtures on approaching the critical consolute point (CCP), focusing first on Piekara's findings [Phys. Rev. Vol.42, pp. 445-447, 1932, and C. R. Acad. Sci. Paris Vol. 203, pp. 1058-1059, 1936]. The presented results cover changes in temperature and pressure. For NDE particular attention is given to complex liquid features of critical mixtures appearing in /spl epsi/ and NDE tests. The latter are presented for the stationary and dynamic (time-resolved NDE) behavior. New results for NDE in nitrobenzene, hexane mixture with the lowest measurement frequency ever applied and in benzonitrile-isooctane mixture for dielectric permittivity are also included. For the latter, the first test of the relation: d/spl epsi//dT /spl alpha/ (T - T/sub C/) /sup -/spl alpha// is shown.

Phenomenological model of dynamic nonlinear response of relaxor ferroelectrics

A phenomenological model was proposed which describes frequency dispersion of nonlinear dielectric response of relaxor ferroelectrics (relaxors) as a result of dispersion of their linear dielectric permittivity. The model was applied to Pb(Mg(1/3)Nb(2/3))O3 (PMN) relaxor. It provided a good qualitative description of temperature and frequency dependence of the third harmonics of PMN. Analysis within the model yielded a frequency independent nonlinear coefficient corresponding to static nonlinear dielectric susceptibility. The model explained the recently reported for PMN data on the Vogel-Fulcher law for frequency dependence of the temperature at which the third harmonics passes a maximum.

Phase transitions from THE isotropic liquid to liquid crystalline mesophases studied by linear and nonlinear static dielectric permittivity

Results of studies of static dielectric permittivity (epsilon) and nonlinear dielectric effect (NDE) in the isotropic phase of 4-n-4'-isothiocyanatobiphenyl (nBT) homologous series from n = 2 to n = 10 exhibiting the isotropic-smectic E (I-SmE) transition, are presented. They are compared with results of similar studies in 4-cyano-4-n-alkylbiphenyls (nCB) from n = 4 to n = 12. In this homologous series isotropic-nematic (I-N) and isotropic-smectic-A (I-Sm-A) transitions take place. Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of epsilon and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5, was found. It has been shown that when the length of the alkyl chain of a compound increases the discontinuity of the transition drops in nBT and rises in nCB. The influence of pressure on the discontinuity is also discussed.

Crossover in a non-analytical behaviour of dielectric non-linearity in relaxor ferroelectric

The dielectric response of the relaxor ferroelectric (PMN) is found to be a non-analytical function of the ac field, with the absolute value of the non-linear component of the polarization given by . The dependence on the temperature, T, and frequency, , of the exponent manifests itself in the form of a crossover in from approximately 2 to 3 upon cooling, whose position depends upon the frequency of the applied ac field. From the comparison of with the linear complex dielectric permittivity, , of PMN, the following can be correlated: (i) in the regime of the quasi-static response, and starts deviating from 2 simultaneously with the onset of the frequency dispersion; and (ii) when the spectrum of relaxation times in PMN becomes flat. These findings can be understood in terms of the change in the type of the motion of the interphase boundaries of the microscopic polar regions existing in PMN, namely in the change of the scale on which the interphase boundaries can move.

Electrical Properties of Paraelectric (Pb 0.72La 0.28)TiO3 Thin Films with High Linear Dielectric Permittivity: Schottky and Ohmic Contacts

Linear, paraelectric (Pb0.72La0.28)TiO3 or PLT(28) thin films with a bandgap>3 eV were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel technique. Specific top-contact metals from two distinct groups (i.e., non-noble or M T and noble or M N; the former being oxidizable transition metals) were selected to understand the electrical nature of the interfaces in terms of electrode dependent energy band diagrams and equivalent circuit models. Using a high sensitivity high-pass filter circuit to evaluate the charging and discharging behavior coupled with results of the thickness and voltage dependence of capacitance, it was determined that M T ( Ni,Cr,Ti) and M N ( Pt,Au,Ag) metals form Ohmic and Schottky contacts, respectively. Supported by thermochemical data and calculations, the ohmic M T- PLT interfaces are envisioned to be of the form: M T-M T Ox-n+ PLT-n PLT. In contrast, the M N- PLT interfaces may be characterized by a metal work function independent Schottky diode; the surface Fermi level being pinned at the mid-gap. For example, a Schottky barrier height of 1.83 eV and a built-in voltage of 1.3 eV at the Pt-PLT interface were estimated. From low field capacitance measurements, the ratio of interfacial to bulk resistance, R i/R b, was estimated to be 23.

Ferroelectric phase transitions and domain relaxation in KTa1-xNbxO3

Abstract Linear birefringence, dielectric permittivity and second harmonic generation are measured on KTa1-xNbx with x = 0.03 in order to elucidate its sequence of para-to-ferroelectric phase transitions, which occur at about 44, 42 and 39 K. The data are compatible with cubic-tetragonal-orthorhombicrhombohedral symmetry changes as in KNbO3. Domain formation and relaxation gives rise to slow polydispersive polar dynamics as evidenced by dielectric dispersion and time-dependent SHG intensity.