Viscous Motion Of Domain Walls Research Articles

Magnetic, dielectric and magneto-dielectric properties of Aurivillius phase Bi4.25Nd0.75FeTi2(NbCo)0.5O15 ceramics

The structural, magnetic, dielectric and magneto-dielectric properties of Aurivillius phase Bi4.25Nd0.75FeTi2(NbCo)0.5O15 (BNFTNCO) ceramics were investigated. X-ray diffraction and Raman results suggest that Nd ions can be effectively incorporated into Bi sites. A typical four-layered Aurivillius structure is confirmed by high resolution transmission electron microscope. The double remanent magnetization 2Mr at 300 K is determined to be 0.88 emu/g, which is one order of magnitude larger than that of Bi5Fe0.5Co0.5Ti3O15 ceramic. The sample undergoes the ferromagnetic and ferroelectric transition at 642 K and 1094 K, respectively. The ferromagnetic Curie temperature is about 200 K higher than that of Bi4.2Nd0.8Fe0.5Co0.5Ti3O15 ceramic. The dielectric relaxation around 300 K with activation energy of 0.435 eV is associate with the hopping process of oxygen vacancies, while the high-temperature dielectric relaxation with a rather large activation energy of Ea= 2.43 eV may be related to the viscous motion of domain walls. More importantly, the intrinsic magneto-electric coupling effect with the magneto-dielectric constant of − 0.57% can be achieved at 300 K and 1 kHz. In addition, the optical band gap Eg of BNFTNCO is 2.50 eV.

Dynamic behavior of BiVO4 material under mechanical studies

The mechanical relaxation technique is applied to investigate the fundamental dynamic behavior of BiVO4 material. A prominent internal friction peak is observed around 430 K at 1 Hz, which is actually composed of three sub-peaks (P1, P2 and P3 from low to high temperature). And the associated modulus anomalies can also be found in any of the samples. The peak P1 with activation energy E1 ∼ 3.20 eV is probably related to the stress-induced unequal positions of Bi3+ ions; while the main P2 peak with E2 = 0.91 eV is associated with a complex mechanism, which originates from the viscous motion of domain walls and the interaction of domain walls with oxygen vacancies; and the responsive P3 peak is resulted from the ferroelastic–paraelastic phase transition, accompanied by a minimum modulus value. Based on the relaxation process and crystalline structure of BiVO4, the motion model of ferroelastic domain walls and transport mechanism of diffusion are suggested. Our results pave the way for better understanding the intrinsic dynamic and multifunctional properties of BiVO4.

Effect of Polarization on Mechanical Properties of Lead Zirconate Titanate Ceramics

This study concerns two following commercial lead zirconate titanate (PZT) materials, PZT-5H and PZT-8 piezoelectric ceramics. Young's modulus and internal friction versus temperature at different vibration frequencies were investigated by means of Dynamic Mechanical Analysis (DMA) before and after polarization. The phase transition temperatures (Tc) of PZT-5H and PZT-8 ceramics were 438 K and 550 K. PZT-8 ceramic had higher Young's modulus than PZT-5H ceramic at ferroelectric phase, which resulted from the increase of internal local stress in PZT-8 ceramic. After polarization, the Young's modulus of both PZT ceramics increased, the influence of the piezo- electric effect was investigated. A relaxation peak emerges in internal friction curve of each PZT sample. Considering the hard ceramic, this peak is a pure relaxation mechanism controlled by oxygen vacancies diffusion. Considering the soft ceramic, the relaxation peak can be related to viscous motion of domain walls and the interaction between domain walls and point defects. The activation energy of the relaxation peak increased after polarization, which resulted from the increased local internal stress and directional arranged space charges caused by polarization.

Anisotropic Ferro- and Dielectric Properties of Textured Bi4Ti3O12Ceramics Prepared by the Solid-State Reaction Based on Multiple Calcination

The grain-oriented Bi4Ti3O12(BIT) samples were prepared by the solid-state reaction method with a multicalcination process. The grain-oriented BIT samples exhibit anisotropic structural, ferroelectric, piezoelectric, and dielectric properties. The remanent polarization (2Pr) and the piezoelectric constant (d33) ofa/b- andc-direction BIT ceramics are 49.5 μC cm−2, 22.2 pC N−1and 6.7 μC cm−26.9 pC N−1, respectively. The dielectric anomalies of samples are observed around 157 K and 232 K. The dielectric anomalies at around 157 K are related to oxygen vacancies. The activation energy of the dielectric relaxation of this anomaly is estimated to be 1.36 eV. Another dielectric anomaly at around 232 K is related to polarizable domains and the viscous motion of domain walls.

Mechanical spectroscopy of Mn–Zn ferrite

The shear modulus and internal friction in polycrystalline manganese-zinc ferrite are measured as a function of temperature between 20 and 500 °C, by using a torsion inverted pendulum. Curves of modulus versus temperature show a phase transition near the Curie temperature ( T C). Three internal friction peaks R 1, R 2 and R 3 are observed on the curves of internal friction versus temperature. The peak R 1 in ferrimagnetic state is discussed in interaction of domain walls with point defects. The peak R 2 below the T C is attributed to viscous motion of domain walls. The peak R 3 could be ascribed to the exchange of cations and their vacancies, and clustering Mn 3+ ions on octahedral sites.

Dielectric loss study of oxygen vacancies and domain walls in Sr2Bi4−x/3Ti5−xVxO18 ceramics

An investigation on the ferroelectric and dielectric properties of vanadium-doped Sr2Bi4Ti5O18 ceramics was presented. The ferroelectricity of Sr2Bi4−x/3Ti5−xVxO18 samples (x=0, 0.003, 0.0048, 0.018, 0.048, and 0.096) was obviously improved by vanadium doping. The dielectric property measurement indicated that the Curie temperature was unaffected by vanadium doping, while it displayed a strong dependence of their dielectric loss on vanadium content. One dielectric loss peak around 230 °C related to oxygen vacancies was reduced with doping. Another peak which was just a few degrees below the Curie point and ascribed to viscous motion of domain walls declined drastically with the increase of vanadium content. Those results suggested that the substitution of a small amount of V5+ for Ti4+ reduced the concentration of oxygen vacancies significantly under the restriction of charge neutrality. This led to the weakening of domain pinning and the increasing of the mobility of domain walls, which would be responsible for the increase in 2Pr.

Defect Structure in Undoped and Donor-Doped Polycrystalline Sr2Bi4Ti5O18

An investigation on the ferroelectric and dielectric properties of donor-doped (vanadium, niobium) Sr2Bi4Ti5O18 ceramics was presented. Compared with the undoped ceramics all the donor-doped ceramics had obviously increased 2P r . Three obvious peaks (P1, P2, P3) on the dielectric loss curve D(T) were observed. One peak which was just a few degrees below the Curie point and ascribed to viscous motion of domain walls declined drastically with vanadium doping. And the decline may result from the increase in grain size, which resulted in a large 2P r . With niobium doping the relaxation peaks P1 and P2 related to point defects declined gradually. Therefore, the increase in 2P r of Sr2Bi4Ti5O18 upon niobium doping might relate to the significant weakening of defect pinning.

Non-Debye Domain Wall-Induced Dielectric Response in SBN :Ce

Two different non-Debye dielectric spectra are observed in a polydomain relaxor ferroelectric single crystal, Sr 0.603 Ce 0.007 Ba 0.39 Nb 2 O 6 ( SBN :Ce), in the vicinity of T c , 320 K. At very low frequencies, y < 1 s m 1, the susceptibility components vary as h ' h " y m g, g , 0.2-0.7. This behavior is due to irreversible creep-like viscous motion of domain walls with a wide distribution of thermally activated domain wall mobilities. Logarithmic dispersion with a 1/ f -like relaxational spectrum due to reversible wall segment relaxation occurs at larger frequencies, y > 1 s m 1 [3]. The crossover on the frequency scale between both kinds of dielectric response is attributed to a dynamical phase transition as predicted by Nattermann et al. [5].

Non-Debye domain-wall-induced dielectric response inSr0.61−xCexBa0.39Nb2O6

Two different non-Debye dielectric spectra are observed in a polydomain relaxor-ferroelectric ${\mathrm{Sr}}_{0.61\ensuremath{-}x}{\mathrm{Ba}}_{0.39}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}:{\mathrm{Ce}}_{x}^{3+}$ single crystal in the vicinity of its transition temperature, ${T}_{c}\ensuremath{\approx}320 \mathrm{K}.$ At infralow frequencies the susceptibility varies as ${\ensuremath{\chi}}^{*}\ensuremath{\propto}{\ensuremath{\omega}}^{\ensuremath{-}\ensuremath{\beta}},$ $\ensuremath{\beta}\ensuremath{\approx}0.2,$ and is attributed to an irreversible creep-like viscous motion of domain walls, while logarithmic dispersion due to reversible wall relaxation [T. Nattermann, Y. Shapir, and I. Vilfan, Phys. Rev. B $42,$ 8577 (1990)] occurs at larger $\ensuremath{\omega}.$

Internal friction study on oxygen vacancies and domain walls in Pb(Zr, Ti)O 3 ceramics

The internal friction of Pb(Zr 0.52Ti 0.48)O 3 ceramics was measured above room temperature at low frequencies by using an inverted torsion pendulum. Two obvious relaxation peaks were observed at 420 and 560 K, respectively, on the internal friction versus temperature curves. The activation parameters were calculated by means of the peak shift method. The activation energy of the peak around 420 K was equal to 1.04 eV, and its relaxation mechanism was attributed to the stress-induced migration of oxygen vacancies, which would make it possible to determine the concentration of oxygen vacancies by the peak height of this peak. The peak around 560 K was related to a complex mechanism including the viscous motion of domain walls and the interaction between domain walls and point defects.

Ultrasonic attenuation study of TiNi and TiNiCu single crystals

Ultrasonic attenuation peaks associated with martensitic transformation and viscous motion of domain walls were observed in TiNi and TiNiCu single crystals. A precursory increase of attenuation from temperature well above M s was reported.

Dielectric Relaxation and Internal Friction Related to the Mobility of Domain Wall in PZT Ferroelectrics

The dielectric permittivity of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) ceramics as a function of temperature was measured in the frequency range from 1 to 10 kHz. There exists a dielectric loss peak close to and below the Curie point, the height of which decreases as frequency increases. Although the peak moves towards higher temperatures with increasing frequency, the relaxation time disagrees with the Arrhenius description. In addition, the internal friction measurement at 1 Hz shows a mechanical loss peak that is of static hysteresis type. Therefore the viscous motion of domain walls in PZT is dominant in a certain frequency range of a few kHz. Dielectric loss as a function of temperature under frequencies from 1 to 10 kHz is modelled by using the dynamic equation for the viscous motion of domain walls. In the simulation, the dispersion of phase transition temperature inside the ceramics has been considered. The simulation results meet quite satisfactorily the experimental data. The two important parameters, viscous coefficient and pinning force constant, can be estimated.

Internal friction and Young’s modulus of SrBi2Ta2O9 ceramics

The internal friction (IF) and the Young’s modulus of SrBi2Ta2O9 (SBT) ceramics were measured by using the reed vibration method in the temperature range from 100 to 600 K with kilo-hertz frequencies. A high IF peak associated with a modulus defect appeared around 500 K, which was assumed to be due to the migration of oxygen vacancies with the activation energy U of about 0.95 eV. The mechanism of the IF peak was discussed in detail. At 570 K, an IF peak due to the viscous motion of domain walls near the Curie temperature was found. Below room temperature, a low IF peak with a modulus defect was found with peak temperature of 200–250 K, which varied for tens of degrees in different samples. This peak was due to the depinning process of 90° domain walls from oxygen vacancies. These results can be helpful in explaining the excellent fatigue resistance property of SBT thin films at room temperature.

Dynamics of domain walls in Ti-Ni-Cu alloy

The internal friction for Ti-Ni-Cu shape memory alloys (SMAs) was measured in the Hz and kHz range. The peak temperature in the Hz range is independent of the measuring frequencies. Only in the tens of kHz range does the peak temperature shift with the frequencies, showing a thermally activated progress with = 0e-B/Tc - T, characteristic of viscous motion of domain walls, instead of the Arrhenius relation. Taking into account the change of the density of the domain walls during the phase transformation, we modified the Q-1-formula by using a model of viscous motion of domain walls, obtaining a good result in agreement with the experimental data. Additionally, corresponding parameters, which play a key role in the shape memory effect, such as the viscosity coefficient and the effective pinning force constant, were obtained.

SIMULATION OF DIELECTRIC LOSS RELATED WITH THE MOTION OF DOMAIN WALLS

The measurement of dielectric susceptibility under various frequencies for Pb(Zr0.52Ti0.48)O3 (PZT) ceramics shows that there exists a dielectric loss peak below and close to phase transition temperature, which is relaxational characteristic but disagrees with Arrhenius relation. The peak arise from the interaction between domain walls, lattice and pinning defects. In this paper the behavior of the dielectric loss peak of PZT under various frequencies is simulated by using the dynamic equation of viscous motion of domain walls and by considering the Curie temperature dispersion in ceramics as well. The agreement between the simulatied result and experimental data is quite satisfactory. And from the parameters of simulation the viscous coefficient of the motion of domain walls and the recovering force constant of pinning defects are calculated.

Low-frequency internal friction study for SrBi 2 Ta 2 O 9 ferroelectric ceramics

Low-frequency internal friction (IF) of SrBi2Ta2O9 (SBT) ceramics has been measured at temperatures ranging from 293 to 623 K. Two IF peaks, with their locations around 393 K (P1) and 569 K (P2) (f ≈ 1.58 Hz), respectively, are observed. P1 is found to be associated with a relaxation process with activation energy of 0.97 eV and pre-exponential factor of 3.58 × 10-14 s. Peak shape analyses reveal that P1 can be well described by a broadened Debye peak with the width parameter β from 2.70 to 2.92. The mechanism responsible for P1 is proposed to be relaxation of oxygen vacancies near domain walls (DWs). P2 is considered to arise from viscous motion of DWs since it shows characteristics of static hysteresis type. Comparisons for the IF behavior between SBT and Pb(Zr, Ti)O3(PZT) suggest that in SBT oxygen vacancies are much less localized near DWs than that in PZT. This result provides a possible explanation for the weak DW pinning due to oxygen vacancies in SBT.

Dielectric and mechanical loss and mobility of domain walls

Three dielectric loss (D) and /or three mechanical loss (Q−1) peaks (P1, P2, P3) for KDP, TGS and LNPP (La1-xNdxPsO14) crystals have been investigated. P1 is attributed to the dynamic domains due to the fluctuation near Tc. P2 is related to domain walls (DWs). The Q−1 and D caused by the viscous motion of DWs are calculated, being fairly coincident with the experimental data of P2 peak in the kHz range. P3 peak drops down to zero rapidly in the low temperature side for TGS, and disappears in LATGS with mono-domain. So P3 is thought to originate from glass transition of pinned domain walls.

Mechanical and Dielectric Energy Loss Related to Viscous Motion and Freezing of Domain Walls

Three dielectric loss (D) and/or three mechanical loss (Q -1 ) peaks (P1,P2,P3) and corresponding susceptibilities for ferroelectric KDP and TGS, and ferroelastic LNPP crystal and Cu-Al-Zn-Ni alloy have been investigated in the kHz range. P 1 and P 2 almost overlap for first order phase transitions. P i , a very narrow peak, is attributed to the dynamic domains due to fluctuations near Tc. P2 is recognized to be related to domain walls (DWs). The formulas of Q -1 and D caused by the viscous motion of DWs are derived, being fairly coincident with the experimental data of P2. The viscous coefficient, pinning force constant of DW and the spontaneous shear strain have been calculated for Cu-Al-Zn-Ni. The susceptibility, e' or ΔJ/J, always shows a high plateau below Tc and drops down rapidly nearly consistent with the low temperature side of P3 peak for poly-domain TGS, KDP and Cu-Al-Zn-Ni. P3 is thought to originate from the freezing of DWs of high density due to a collective pinning of randomly distributed defects, similar to the pinned-vortex glass model suggested for high Tc superconductors.