Search results for "Pyroelectricity"
showing 10 items of 20 documents
Depolarization Field and Properties of Thin Ferroelectric Films with Inclusion of the Electrode Effect
2005
The influence of metallic electrodes on the properties of thin ferroelectric films is considered in the framework of the Ginzburg-Landau phenomenological theory. The contribution of the electrodes with different screening lengths l s of carriers in the electrode material is included in the free-energy functional. The critical temperature T cl , the critical thickness of the film, and the critical screening length of the electrode at which the ferroelectric phase transforms into the paraelectric phase are calculated. The Euler-Lagrange equation for the polarization P is solved by the direct variational method. The results demonstrate that the film properties can be calculated by minimizing t…
Exact and Variational Treatment of Ferroelectric Thin Films with Different Materials of Electrodes
2005
We trace the influence of metallic electrodes on the properties of thin ferroelectric films. This has been done in the framework of the phenomenological Landau theory. We present both exact analytical solution of the problem in terms of Weierstrass elliptic functions and the variational solution. We calculate polarization, dielectric susceptibility, pyroelectric coefficient and depolarization field. We have shown that the ferroelectric phase of the film can be destroyed by the choice of material of electrodes with screening length exceeding some critical value. This demonstrates that we can control the physical properties of thin ferroelectric films by the proper choice of the electrode mat…
Study of the pyroelectricity in LiIns2 crystal
2002
Abstract Pyroelectric current measurements performed on a LiInS2 monodomain single crystal show a linear variation of the current between 120 and 260 K. Near room temperature, a space charge relaxation screens pyroelectricity. The pyroelectric coefficient follows a linear thermal dependence leading to an extrapolated value of 6×10−10 C K−1 cm−2 at 300 K. As for other oxide-type pyroelectric compounds, this value is shown to be proportional to the electro-optic coefficient r333 of LiInS2.
Ferroelectricity in {N(CH3)4}2ZnI4
1988
Dielectric properties of the {N(CH 3 ) 4 } 2 ZnI 4 crystal were studied between room temperature and 4.2 K. Two phase transitions were seen from dielectric constant anomalies at T 1 =254 K and T c =210 K on cooling. Ferroelectric hysteresis loops were observed along the c -direction below T c with a low frequency applied field of 0.0025 Hz. The spontaneous polarization obtained by pyroelectric charge measurement tended to be 2.5×10 -3 C/m 2 at 0 K.
Structure and properties of tris(tetramethylammonium) nonabromodiarsenate(III), [(CH3)4N]3[As2Br9]
2007
The new tetramethylammonium bromoarsenate(III) crystal [(CH3)4N]3 [As2Br9] has been synthesized and its phase behaviour established by differential scanning calorimetry and dilatometry. Three phase transitions are found: at 346/346 K , at 165/171 K and at 157/165 K on cooling/heating. Single-crystal x-ray diffraction studies of phases I (at 370 K) and II (at 298 K) have shown that the structure comprises discrete [As2Br9]3− anions and disordered [(CH3)4N]+ cations. Phase II crystallizes in the polar space group P31c; its polar nature was confirmed by pyroelectric measurements. Phase I has higher symmetry, P63mc or . Dielectric dispersion measurements revealed a relaxation process in the cry…
Electric properties of KTiOPO4and NaTiOPO4from temperature-dependent X-ray diffraction
1999
Single crystals of KTiOPO4(KTP) and NaTiOPO4(NaTP) show pronounced pyroelectric behaviour. In order to determine the origin of this property on an atomic scale, X-ray diffraction measurements have been carried out at several temperatures between 100 and 600 K. Modelling of the electron density and the evolution of the structure as a function of temperature has enabled the determination of values for the spontaneous polarization of the compounds and the pyroelectric coefficient of KTP, principally due to the alkaline-ion displacements with a value of 2.0 nC cm−2 K−1. Structure modifications, compared with NaTiOPO4, and the calculation of the electrostatic potential explain the anisotropic be…
Influence of Lithium Substitution on Structure, Electric and Pyroelectric Properties of Sodium Niobate Ceramics
2012
Li0.02Na0.98NbO3 ceramics were prepared by a conventional method. A single-phase perovskite structure was identified by an X-ray diffraction method. The SEM and EDS studies revealed that the Li0.02Na0.98NbO3 samples were perfectly sintered and chemically homogeneous. Electric measurements showed that Li0.02Na0.98NbO3 was sensitive to the frequency of the applied electric field and revealed that the ac conductivity changed with frequency according to the formula: σ(ω) = σdc +Aωn where n < 1. These results were discussed with a reference to the conduction mechanism as a type of polaron hopping.
Dielectric and Ferroelectric Properties of Lead-Free NKN and NKN-Based Ceramics
2011
Lead-free ceramics of Na0.5K0.5NbO3 (NKN), Na0.5K0.5(Nb0.94Sb0.06)O3 (NKNS6) and Na0.5K0.5(Nb0.94Sb0.06)O3 + 0.5%MnO2 (NKNS6 + 0.5%MnO2) have been prepared by a solid phase hot pressing sintering process. X-ray diffraction results show that the obtained samples possess the perovskite structure. The micrograph of the fractured surface showed a dense structure in a good agreement with that of 91–94% relative density determined by the Archimedes method. An average grain size decreases with Sb and Mn doping (from about 20 μm for NKN to about 5 and 2 μm for NKNS6 and NKNS6 + 0.5%MnO2, respectively). Low frequency (100 Hz–200 kHz) investigations revealed the diffuse phase transitions. It was foun…
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.
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…