Search results for "ferroelectricity"
showing 10 items of 326 documents
Influence of Electromechanical Fields on Dielectric Properties of PLZT−x/65/35 Ceramics (x = 6 and 7)
2011
High density and transparent PLZT−x/65/35 (x = 6 and 7) ceramics with the average grain size of 5–7 μm was obtained by two−stage hot−pressing technology. The measurements of temperature/frequency dependence of the permittivities of these ceramics under uniaxial pressure (0–100 MPa) applied parallel to the ac electric field have been carried out. It was found that uniaxial pressure significantly influences dielectric properties of these ceramics. With the increase of pressure the maximum intensity in ϵ(T) curve decreases, becomes more diffuse and shifts towards higher temperature, dielectric dispersion decreases and classical ferroelectric seems to change to relaxor one. It was concluded, th…
The Ba2LnFeNb4O15 “tetragonal tungsten bronze”: Towards RT composite multiferroics
2009
Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd) with the Tetragonal Tungsten Bronze (TTB) structure have been synthesised by conventional solid-state methods. The Neodymium, Samarium and Europium compounds are ferroelectric with Curie temperature ranging from 320 to 440K. The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300 K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these mat…
Point Defects, Dielectric Relaxation and Conductivity in Ferroelectric Perovskites
2000
In all ferroelectric perovskites, intentionally introduced or “unwanted” point defects do play a role in the dielectric spectra and in the conductivity.
Z+/Z− lithium niobate optical waveguide sensitivity related to pyroelectric effect
2020
Lithium niobate crystal is widely used for the design and fabrication of integrated electro-optic modulators. As a ferroelectric material, one sees its spontaneous polarization change with temperature variations. This phenomenon, known as the pyroelectric effect, induces strong waveguide transmission variations for waveguides realized on Z -cut wafers. Waveguides made by titanium in-diffusion either on the Z + or Z − side of the crystal show a significant difference in temperature behavior. Experimental data, enlightened by numerical simulations, help to show why Z − waveguides are more immune to temperature changes than Z + ones.
Pseudo-stochastic multiple-pulse excitation in dielectric spectroscopy: application to a relaxor ferroelectric
2003
The nonlinear dielectric response of a lead titanate-doped lead magnesium niobate relaxor ferroelectric was studied using pseudo-stochastic binary electrical field excitation. The polarization was recorded for various pulse spacings and electrical field amplitudes. The decay of the field-polarization cross-correlation function could be accelerated by increasing the amplitude of the pulse fields. The extension of these experiments in order to record multidimensional dielectric spectra is illustrated.
Depolarization Field in Thin Ferroelectric Films With Account of Semiconductor Electrodes
2005
Within the framework of the phenomenological Ginzburg-Landau theory influence of semiconductor electrodes on the properties of thin ferroelectric films is considered. The contribution of the semiconductor electrodes with different Debye screening length of carriers is included in the functional of free energy. The influence of highly doped semiconductor electrodes on the depolarization field and the film properties was shown to be great.
Ferroelectric plasma source as an exciting source for rare earth elements
2003
The plasma sources basing on electrical discharges near the surfaces of ferroelectric materials have been described. It was shown that the ferroelectric plasma sources are especially useful for investigations in the field of optical spectroscopy. They have been found to be especially useful for exciting the atoms and ions or rare earth elements.
The Joining of LiNbO3, Quartz, TlBr-TlI and Other Optical Materials by the Use of Thin Metal Films as Bonding Agents
2000
A method of joining ferroelectric, optical and other non-metallic materials, such as lithium niobate, quartz, TlBr-TlI, glass, etc., at room temperature under a pressure of 0.1÷0.5 MPa is described. The surfaces to be joined are prepared to optical flatness, and indium or lead coatings as bonding agents are used. To obtain clean surfaces, procedures of the coating deposition and sample joining are performed in situ in a vacuum of l0-4 Pa. The strength of the obtained joints is about 20MPa for indium coatings and about 30MPa for lead coatings. It is supposed that attractive surface forces play a decisive role in the contact formation and bonding of the wafers. The method has been applied for…
Polar metal–formate frameworks templated with 1,2-diaminoethane–water assemblies showing ferromagnetic and ferroelectric properties
2017
A set of five novel formate frameworks templated with assemblies comprising diprotonated 1,2-diaminoethane (DAE) and a water molecule of the formula: [NH3(CH2)2NH3]M2(HCOO)6·H2O, where M = Mg, Mn, Co, Ni, Zn, has been synthesized. Four compounds crystallize in the polar R3 space group and one in the chiral P6322 space group (Ni-analog) at room temperature. The polyammonium–water assemblies, mutually joined by hydrogen bonds, fill the cavities of the frameworks and are disordered in the three latter compounds. Additional disorder is found in the Ni-sample as the DAE2+–H2O couple is placed in a special position on the 63 screw axis. IR spectroscopy provides evidence of proton dynamic disorder…
<title>Optical characteristics of doped lithium niobate single crystals</title>
2003
Studing of the Raman spectra was established that an optical parameters of oxygen-polyhedral ferroelectric single crystals can be improved by increasing the degree of structural ordering of the cation sublattice along the polar axis by doping them. In this case the impurity ions with the ionic radii close to the radii of the main cations (Li+ and Nb5+) and charges intermediate between those of main cations (1<Z<5) in the area of rather low concentrations were shown to exert an ordering effect on the cation sublattice of a congruent lithium niobate single crystals. Moreover the crystal resistance to laser radiation is also observed to grow. It was determined that the effect of diminishing ph…