Relaxor-like Dielectric Behavior Research Articles

Structural Characterization and Physical Properties of Double Perovskite La2FeReO6+δ Powders.

The structural, optical, dielectric, and magnetic properties of double perovskite La2FeReO6+δ (LFRO) powders synthesized by solid-state reaction method under CO reduced atmosphere are reported on in this paper. Reitveld refinements on the XRD data revealed that the LFRO powders crystallized in an orthogonal structure (Pbnm space group) with column-like morphology. The molar ratios of La, Fe, and Re elements were close to 2:1:1. XPS spectra verified the mixed chemical states of Fe and Re ions, and two oxygen species in the LFRO powders. The LFRO ceramics exhibited a relaxor-like dielectric behavior, and the associated activation energy was 0.05 eV. Possible origins of the dielectric relaxation behavior are discussed based on the hopping of electrons among the hetero-valence ions at B-site, oxygen ion hopping through the vacant oxygen sites, and the jumping of electrons trapped in the shallower level created by oxygen vacancy. The LFRO powders display room temperature ferromagnetism with Curie temperature of 746 K. A Griffiths-like phase was observed in the LFRO powders with a Griffiths temperature of 758 K. The direct optical band gap of the LFRO powders was 2.30 eV, deduced from their absorption spectra, as confirmed by their green photoluminescence spectra with a strong peak around 556 nm.

Effects of crystallization kinetics on the dielectric and electrical properties of BiFeO3films

BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.

Phase coexistence at the first-order Mott transition revealed by pressure-dependent dielectric spectroscopy of κ−(BEDT−TTF)2−Cu2(CN)3

The dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ can be tuned into a metallic and superconducting state upon applying pressure of 1.5 kbar and more. We have performed dielectric spectroscopy measurements (7 kHz to 5 MHz) on $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ single crystals as a function of temperature (down to $T=8$ K) and pressure (up to $p=4$ kbar). At ambient conditions, a relaxor-like dielectric behavior develops below 50 K that shifts toward lower temperatures as the crystal is pressurized. Interestingly, a second peak emerges in $\varepsilon_{1}(T)$ around $T=15$ K, which becomes strongly enhanced with pressure and is attributed to a small volume fraction of metallic puddles in the insulating host phase. When approaching the phase boundary, this peak diverges rapidly reaching $\varepsilon_{1} \approx 10^{5}$. Our dynamical mean-field theory calculations substantiate that the dielectric catastrophe at the Mott transition is not caused by closing the energy gap, but due to the spatial coexistence of correlated metallic and insulating regions. We discuss the percolative nature of the first-order Mott insulator-to-metal transition in all details.

Symmetry of the Underlying Lattice in (K,Na)NbO3-Based Relaxor Ferroelectrics with Large Electromechanical Response.

The piezoelectric constant (d33) and converse piezoelectric coefficient (d33*) of a piezoelectric material are critically important parameters for sensors and actuators. Here, we simultaneously achieve a high d33 of 595 ± 10 pC/N and a large d33* of ∼776 ± 20 pm/V in (K,Na)NbO3 (KNN)-based ceramics, which exceed those of PZT5H and PZT4 ceramics, presenting good potential for practical piezoelectric applications. Moreover, the ceramic exhibits a relaxor-like and diffuse dielectric behavior due to the occurrence of local heterogeneity. According to the experiments and atomic resolution polarization mapping by Z-contrast imaging, hierarchical architecture of nanodomains and even smaller polar nanoregions with multiphase coexistence caused by compositional modification is the structural origin of the enhanced piezoelectric properties in this work. This work would pave a practical way to future applications of lead-free KNN-based ceramics.

Structural characterizations and dielectric, magnetic, and optical properties of Ba2FeVO6 double perovskite ceramics

Here, we present the structural characterization and physical properties of Ba2FeVO6 (BFVO) ceramics prepared by the solid-state ceramic method, which is regarded as potential Mott multiferroics. Structural studies demonstrate that the BFVO ceramic samples crystallize in a hexagonal structure with R3c symmetry. SEM images show a spherical morphology of the ceramic grains with an average composition of Bi:Fe:V close to 2.0:1.0:1.0 determined by x-ray energy dispersive spectroscopy. Infrared spectra revealed the vibrational modes of [FeO6] and [VO6] octahedrons in the ceramics, and XPS spectra confirmed the dual chemical valence states of iron (Fe2+ and Fe3+) and vanadium (V3+ and V4+) and two states of oxygen species in the BFVO ceramics, while barium was present as Ba2+. The BFVO ceramics exhibit relaxor-like dielectric behavior with an activation energy of 0.62 eV. The antiferromagnetic (AFM) nature was confirmed in the BFVO ceramics, whereas a weak magnetism was observed at 2 K. The temperature dependence of magnetizations measured with (and without) field cooling across 2 K–300 K under external magnetic fields indicates the spin glass characteristics in the present system. A strong variation of the dielectric behavior observed close to the AFM transition temperature was due to the induced dielectric polarization via the magnetostrictive effect driven by AFM transition. The bandgaps (Eg) of the investigated ceramic samples were deduced from their UV–visible spectra. The Eg values were about 1.15 eV and 1.50 eV, which were ascribed to the d–d electronic transitions of Fe 3d t2g → Fe 3d eg and 6A1g → 4T1g, respectively.

Relaxor-like dielectric behavior and its effect on energy storage performance in P(TFE-HFP-VDF) terpolymers

Relaxor-like dielectric behavior and its effect on energy storage performance in P(TFE-HFP-VDF) terpolymers

Colossal and relaxor-like dielectric behaviors in SrCrO4 ceramics

Ceramic SrCrO4 samples were prepared via conventional solid state reaction route. Dielectric properties of SrCrO4 were systematically investigated in the frequency range of 102–106 Hz and temperature range of 5–900 K. Colossal dielectric behavior near room temperature and relaxor-like dielectric behavior around 730 K with an extremely high dielectric constant up to 1.62 × 105 were found. Dual relaxation mechanism composed of a dipolar and a Maxwell-Wagner relaxations is found to be responsible for the colossal dielectric behavior. The dipolar relaxation (R1) is related the defect dipole pair of ▪-Cr3+ caused by chemically absorbed water. The Maxwell-Wagner relaxation (R2) results from grain boundaries. The relaxor-like dielectric behavior is associated with the hopping motion of oxygen vacancies which leads to a high-temperature relaxation (R3).

Williamson–Hall analysis and the dielectric behavior of complex perovskites (BaM0.9M′0.1)0.984O3 (M=Ti, Zr; M′=Nb, Ta)

The long range average structure and local distortions of perovskite type solid solutions (BaTi0.9M′0.1)0.984O3 and (BaZr0.9M′0.1)0.984O3 (M′=Nb, Ta) were examined by high-resolution synchrotron X-ray diffraction. A Rietveld refinement indicated that all four solid solutions had simple cubic symmetry, where the lattice volume varied according to the size of the cationic constituents. As revealed by Williamson–Hall analysis and scanning electron microscopy, both (BaTi0.9M′0.1)0.984O3 had denser and enlarged grains than the parental BaTiO3, and had anisotropic microstrain that are indicative of the non-periodic atomic displacements along the [100] directions of the cubic cell. (BaTi0.9Nb0.1)0.984O3 and (BaTi0.9Ta0.1)0.984O3 exhibited relaxor-like dielectric behavior with Curie temperatures of 230K and 195K, respectively. On the other hand, (BaZr0.9Nb0.1)0.984O3 and (BaZr0.9Ta0.1)0.984O3 showed almost unchanged dielectric behavior compared to that of BaZrO3.

Dynamic off-centering of Cr3+ions and short-range magneto-electric clusters in CdCr2S4

The cubic spinel CdCr2S4 gained recently a vivid interest, given the relevance of relaxor-like dielectric behavior in its paramagnetic phase. By a singular combination of local probe techniques, namely, pair distribution function and perturbed angular correlation, we firmly establish that the Cr ion plays the central key role on this exotic phenomenon, namely, through a dynamic off-centering displacement of its coordination sphere. We further show that this off-centering of the magnetic Cr ion gives rise to a peculiar entanglement between the polar and magnetic degrees of freedom, stabilizing, in the paramagnetic phase, short-range magnetic clusters, clearly seen in ultralow-field susceptibility measurements. Moreover, the Landau theory is here used to demonstrate that a linear coupling between the magnetic and polar order parameters is sufficient to justify the appearance of magnetic cluster in the paramagnetic phase of this compound. These results open insights on the hotly debated magnetic and polar interaction, setting a step forward in the reinterpretation of the coupling of different physical degrees of freedom.

Relaxor-like Dielectric Behavior in Stoichiometric Sillenite Bi12SiO20

A combination of fixed frequency dielectric measurements (103 to 106 Hz) and impedance spectroscopy reveal evidence of (nonferroelectric) relaxor-like behavior in the temperature range ∼600–750 K for the stoichiometric sillenite phase Bi12SiO20 (space group I23, a = 10.1034(5) Å). Variable temperature Raman Spectroscopy reveals significant changes associated with the Bi–O framework vibrations, and the relaxor-type behavior is attributed to noncorrelated local dipole moments associated with the BiO5E (E = 6s2 lone pair) units in the framework. Sillenites, therefore, represent another family of Bi-based oxides to exhibit relaxor-like dielectric behavior.

Perovskite crystallization kinetics and dielectric properties of the PMN-PT films prepared by polymer-modified sol-gel processing

Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT, 43% PT) thin films have been developed by modified sol-gel processing with polyvinylpyrrolidone (PVP) as a modifier and lead nitrate as a lead source. With PVP modification, perovskite phase was directly crystallized from amorphous film matrix at a temperature as low as 430 °C, and the crystallinity was significantly enhanced. Kinetics studies show that the crystallization process is controlled by heat transfer phenomena at the annealing temperatures ≤460 °C. At higher annealing temperatures (550–700 °C), it is a diffusion-controlled reaction with an activation energy of 167.7 kJ/mol, almost two times lower than that for the films without PVP modification. The promotion mechanism of perovskite crystallization by PVP addition has been discussed accordingly. The resultant films consisted of nanocrystallines and exhibited relaxor-like dielectric behavior, although the composition of the films located in normal ferroelectrics.

Relaxor-like dielectric behavior in La 2NiMnO 6 double perovskite ceramics

The dielectric and conductive characteristics of La 2NiMnO 6 double perovskite ceramics were investigated together with the crystal structure. La 2NiMnO 6 ceramics crystallized in the monoclinic P2 1/ n structure in which the Ni 2+ and Mn 4+ ions ordered periodically. Relaxor-like dielectric behavior combined with a giant dielectric constant step was observed in the present ceramics, and these unique dielectric characteristics should be attributed to the charge ordering of Ni 2+ and Mn 4+. The dielectric relaxation was well fitted by the modified Debye equation and Arrhenius law with the activation energy of 0.17 eV. The dc conductivity of La 2NiMnO 6 could be well fitted using a variable-range hopping mechanism instead of a band conduction mechanism.

Comparative Dielectric Studies of NaNbO3–Based Lead-Free Relaxor Ceramics and Lead-Containing Relaxors

Complex dielectric permittivity ϵ* = ϵ′ -iϵ″ of lead-free (Na, Sr, Li)NbO3 ceramic composition exhibiting a relaxor-like dielectric behavior was studied in wide temperature (−180–500°C) and frequency (10 2 –10 6 Hz) range. Some features characteristic of relaxors were observed, namely fulfilment of quadratic and linear Curie-Weiss laws for ϵ ′ just above and well above the temperature T m of ϵ′ (T) peak respectively, the Vogel-Fulcher scaling of both ϵ′ (T) and ϵ” (T) peaks. However, in contrast to canonical lead-containing relaxors Curie-Weiss temperature is lower than T m and the scaling parameters differ for ϵ′ (T) and ϵ”(T) suggesting different origin of dielectric relaxation in these two groups of materials.

Some Properties of the Relaxor-Like Behavior in Sodium Niobate-Based Binary Solid Solutions

Some crystallochemical regularities of the appearance of relaxor-like dielectric behavior in binary (1-x)NaNbO 3 -(x)ABO 3 solid solutions have been revealed. The most significant frequency shift of permittivity maximum temperature T m is observed for solid solutions, where the aliovalent ion substitutions take place in both cationic sublattices of NaNbO 3 , or for solid solutions, where the difference in the valency of the dopant and host ions exceeds unity. A linear correlation between the frequency shift of T m and the parameter δ of the permittivity maximum diffusion was revealed.

Relaxorlike dielectric behavior and weak ferromagnetism in YFeO3 ceramics

Dielectric characteristics of YFeO3 antiferromagnetic ceramics were evaluated over broad temperature and frequency ranges. Two dielectric relaxations were observed at low and high temperatures, respectively, and a dielectric constant step was detected between them. The low temperature dielectric relaxation was an intrinsic thermally activated process following the Arrhenius law with the activation energy very close to that for electronic ferroelectrics, while the high temperature dielectric relaxation was related to the point defect since it could be significantly suppressed by O2 annealing. M-H hysteresis loop was detected at room temperature, and this indicated the weak ferromagnetism in YFeO3 ceramics.

Dielectric and structural studies of Ba2MTi2Nb3O15 (BMTNO15, M=Bi3+,La3+,Nd3+,Sm3+,Gd3+) tetragonal tungsten bronze-structured ceramics

The structure and dielectric properties of a new family of tetragonal tungsten bronze (TTB) ceramics with the general formula, Ba2MTi2Nb3O15 where M=Bi3+,La3+,Nd3+,Sm3+,Gd3+, have been investigated. Hereafter the compositions will be referred to by the abbreviation BMTNO15 where M=B(Bi3+), L(La3+), N(Nd3+), S(Sm3+) or G(Gd3+). BLTNO15 [permittivity maximum (Tm)∼−80°C] and BBTNO15 (Tm∼−100°C) exhibited relaxorlike dielectric behavior. In contrast, BNTNO15 (Tm∼165°C), BSTNO15 (Tm∼250°C), and BGTNO15 (Tm∼320°C) were classic ferroelectrics. Tm increased with decreasing radius of the M ion. Room temperature x-ray powder diffraction (XRD) patterns of all the compounds indexed on a prototype P4∕mbm (or P4bm) space group with lattice parameters a≈12.4Å and c≈4Å. However, electron diffraction revealed that the relaxor phases, BLTNO15 and BBTNO15, exhibited an incommensurate modulation, whereas the classic ferroelectric BNTNO15, BSTNO15, and BGTNO15 featured an orthorhombic superstructure with lattice parameters a≈b≈√2aTTB and c≈2cTTB.

Relaxorlike dielectric behavior in Ba0.7Sr0.3TiO3 thin films

We present the results of a systematic dielectric study for sputter deposited barium strontium titanate thin film planar capacitors measured over a wide temperature range of 20–575K for frequencies between 1kHz and 1MHz. Our observations of dielectric loss peaks in the temperature and frequency domains cannot be understood in the typical framework of intrinsic phonon losses. We find that the accepted phenomenological Curie–von Schweidler dielectric behavior (universal relaxation law) in our barium strontium titanate films is only applicable over a narrow temperature range. An excellent fit to the Vogel-Fulcher expression suggests relaxorlike behavior in these films. The activation energy of the observed phenomenon suggests that oxygen ion motion play a role in the apparent relaxor behavior, although further experimental work is required to test this hypothesis.

Dynamic Dielectric Nonlinearity in Epitaxial Thin-Film Relaxors and Ferroelectrics

The dynamic dielectric response of epitaxial thin-film PbMg1/3Nb2/3O3, PbSc0.5Nb0.5O3, and Ba0.4Sr0.6TiO3 was experimentally studied as a function of temperature, frequency, and amplitude of ac electric field (to 10 MV/m). In thin-film relaxors at all amplitudes, a glasslike behavior was evidenced by Vogel-Fulcher relationship, scaling of the dielectric peak, and broadening of the relaxation time spectra on cooling. Both this and the nonlinear dielectric response were consistent with reorientation of randomly interacting dipoles at presence of random fields. In thin-film ferroelectrics, a relaxorlike nonlinear dielectric behavior was found. As a reason for this, possible coexistence of polar and nonpolar regions was discussed.

Relaxor-like dielectric behavior of pulsed-laser-deposited Pb0.5Sr0.5TiO3 films

Pb0.5Sr0.5TiO3 (PST) ferroelectric films were deposited onto Pt/Ti/SiO2/Si substrates by pulsed laser deposition. The state of the films can be described as a mixed state, with both ferroelectric and relaxor-like features. The films exhibited high dielectric constant and tunability at room temperature. At 10 kHz, the dielectric constants of the 200-nm- and 400-nm-thick films are 771 and 971, with the tunability of 60.2% and 70.9%, respectively. The temperature-dependent dielectric properties were studied and the relaxor-like behavior was observed in both the thinner and thicker PST films, which can be established in terms of diffuse phase transition characteristics and Vögel–Fulcher relationship. In addition, the contribution of the film–electrode interface layer to the dielectric properties was evaluated and the true dielectric properties of the films were reconstructed. Consequently, the relaxor-like character of the PST films was mainly ascribed to the effect of the film-electrode interfaces.

Random-Site Cation Ordering and Dielectric Properties of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3

(1 − x)PbMg1/3Nb2/3O3-(x)PbSc1/2Nb1/2O3 (PMN-PSN) solid solution crystals have been grown by the flux method in the whole concentration range. X-ray supercell reflections due to B-cation ordering were observed for as-grown crystals from the 0.1 ≤ x ≤ 0.65 compositional range. Though the ordered domains are rather large (∼50 nm) the relaxor-like dielectric behavior is observed for compositions with x < 0.6. The diffusion of the dielectric permittivity maximum in as-grown crystals is the lowest at x = 0.6 and increases towards the end members of solid solution. Such behavior is explained within a Bragg-Williams approach by employing the random layer model. At x ∼ 0.6 the excitation energy determined from the Vogel-Fulcher relation exhibits a jump which we regard to changing the kind of the polar regions from PbMg1/3Nb2/3O3 to PbSc1/2Nb1/2O3 related type.