Dielectric Anomaly Research Articles

Dielectric Response Behavior and Displacement‐Type Metal‐Free Organic‐Inorganic Hybrid Phase Transition Material: trans‐(NH3C6H10NH3)[NO3]2

AbstractPhase transition compounds have been attracting interest in scientific research due to their wide applications in dielectric materials. Herein, a new displacement‐type metal‐free organic‐inorganic hybrid phase transition material trans‐(NH3C6H10NH3)[NO3]2 (1) with Tc=245 K has been successfully synthesized. The single‐crystal X‐ray diffraction elucidates that the space group of 1 turns from P in the high temperature phase to P21/c in the low temperature phase. And the reason of phase transition is related to the displacements of trans‐(NH3C6H10NH3)2+ cations and [NO3]− anions. In addition, 1 shows a dielectric anomaly around the Tc. We expect that this finding will contribute to the research of displacement‐type metal‐free phase transition materials.

A Hybrid Organic‐Inorganic Bismuth Iodine Material Showing High Phase Transition Point and Low Bandgap

AbstractRecently, hybrid organic‐inorganic lead halide materials have attracted great attention for their applications in the fields of light‐emitting diodes, photovoltaics, photodetector. However, these hybrid materials usually suffer from environmental and human health issues because of the toxic lead moieties. Herein, we report a novel lead‐free bismuth iodide phase transition material, [NH3(CH2)7NH3][BiI5] (1), which undergoes a reversible phase transition at high temperature 351.7 K and exhibits a step fashion dielectric anomaly. The structural phase transition of 1 is mainly originated from the order‐disorder transition of the 1,7‐heptanediamine cations. Besides, the solid‐state UV‐vis spectrum of 1 displays an intense adsorption at around 658 nm; which gives an indirect bandgap of 1.89 eV. Such a small bandgap value is comparable to most of the organic‐inorganic hybrid lead halide type semiconductors. We believe this study will shed light on the exploration of lead‐free organic‐inorganic hybrid metal halide semiconductors toward future device applications.

Croconic Acid Doped Triglycine Sulfate: Crystal Structure, UV-Vis, FTIR, Raman, Photoluminescence Spectroscopy, and Dielectric Properties

Triglycine sulfate (TGS) single crystals doped with croconic acid (CA) were grown by evaporation from aqueous solutions. X-ray diffraction analysis shows a slight reduction in unit cell volume in TGS:CA compared to pure TGS crystals. The polarized Raman and near-infrared absorption spectra show that the positions of most lines resulting from inter- and intramolecular vibrations are in good agreement with those in spectra of undoped TGS crystals. The inclusion of CA in TGS is confirmed by the presence of bands characteristic of CA in the infrared-Fourier transform spectra. The ultraviolet-visible absorption spectra of TGS:CA are characterized by the presence of additional absorption bands (compared to the spectra of pure TGS) located in the transparent region of pure TGS. In the photon energy region 1.6–3.6 eV, a strong “green” luminescence band is present in TGS:CA upon excitation at λ = 325 nm. The position of the emission band depends on the wavelength of the exciting light. Doping of TGS with CA causes pinning of domain walls, which is accompanied by a decrease in amplitude and frequency dispersion of the dielectric anomaly at the phase transition, a decrease in the switchable polarization and an increase in the coercive field of hysteresis loops.

Structure and relaxor ferroelectric behavior of the novel tungsten bronze type ceramic Sr5BiTi3Nb7O30

This paper reports a novel lead-free tungsten bronze type ceramic, Sr5BiTi3Nb7O30, prepared by a conventional high-temperature solid-state reaction route. The crystal structure identified using synchrotron x-ray diffraction data and Raman spectroscopy for Sr5BiTi3Nb7O30 could be described as an average structure with the centrosymmetric space group P4/mbm and a local non-centrosymmetric structure at room temperature. In the second-harmonic generation measurement, the Sr5BiTi3Nb7O30 compound exhibits second-order nonlinear optical behavior, which suggests the material is ferroelectric. Temperature dependence of the dielectric permittivity indicates that the dielectric anomaly in Sr5BiTi3Nb7O30, associated with the disorder on the A and B sites, results in strong frequency dispersion with a low phase-transition temperature. A macroscopic and phenomenological statistical model was employed to describe the temperature dependence of the dielectric responses of Sr5BiTi3Nb7O30 and Sr6Ti2Nb8O30. The calculated sizes of polar nanoregions for both compounds imply structural disorder induced by A and B sites, giving rise to a more diffuse ferroelectric transition for Sr5BiTi3Nb7O30. The smaller polar nanoregions with smaller electrical dipole moments can be activated at lower temperatures, leading to Sr5BiTi3Nb7O30 having a lower Tm (∼260 K) than other tungsten bronze type ferroelectrics. This work charts a promising feasible route to the development of improved relaxor ferroelectrics in tungsten bronze type oxides.

Phase variation of ferroelectric Li2Sr1−xCax(Nb1−xTax)2O7 by selective reinforcement in the (Nb,Ta)-O covalent bonds

A phase variation of a pseudo-Roddlesden-Popper-type ferroelectric oxide ${\mathrm{Li}}_{2}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{({\mathrm{Nb}}_{1\ensuremath{-}x}{\mathrm{Ta}}_{x})}_{2}{\mathrm{O}}_{7}$ is systematically investigated using dielectric measurements, second harmonic generation, and x-ray diffraction experiments. We find an exotic $x$-T phase diagram, including paraelectric Cmcm, antiferroelectric Pmcn, and in-plane antiferroelectric and out-of-plane ferroelectric $P{2}_{1}cn$ phases. At low $x$, we observe large and divergent dielectric anomalies associated with phase transitions from Cmcm to $P{2}_{1}cn$, whereas these become small kinks at high $x$. Structural analyses reveal an internal distortion, and the rotation of octahedra strongly depends on $x$, which is consistent with the lattice dynamics obtained by a density functional theory calculation. These results demonstrate the great tunability of dielectric properties in layered perovskite-type oxides by tuning the chemical bonding state in the octahedron.

Spin-lattice-charge coupling in quasi-one-dimensional spin-chain NiTe2O5

A high-quality ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$ single crystal was grown via the flux method and characterized using synchrotron x-ray diffraction (XRD) and electron probe microscopy techniques. The dc magnetization $(M)$ confirms the antiferromagnetic long-range ordering temperature $({T}_{\mathrm{N}})$ at 28.5 K. An apparent domelike dielectric anomaly near ${T}_{\mathrm{N}}$, with scaling of magnetodielectric (MD) coupling with magnetization $(\mathrm{MD}%\ensuremath{\propto}{M}^{2})$, signifies higher-order magnetoelectric (ME) coupling. The critical finding is that magnetoelastic coupling plays a pivotal role in bridging the electrical and magnetic dipoles, which was further confirmed by temperature-dependent XRD. In addition, the theoretical charge density difference maps indicate that the emergence of electrical dipoles between the Ni and O atoms below ${T}_{\mathrm{N}}$ originates through $p\text{\ensuremath{-}}d$ hybridization. Thus, the $p\text{\ensuremath{-}}d$ hybridization-induced magnetoelastic coupling is considered a possible mechanism for the higher-order ME effect in this quasi-one-dimensional spin-chain ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$.

Electrical transport properties of La doped BiFeO3-NaNbO3 composite

ABSTRACT The composites, (1−x)(BiFe1-yLayO3)– xNaNbO3 with x = 0.25, 0.45 and y = 0.10, 0.20, are prepared by mixed oxide method. XRD analysis shows rhombohedral (hexagonal) structure at room temperature. The properties such as dielectric loss (tanδ) and dielectric constant (ϵr ) of all the samples are studied. A significant improvement in dielectric constants has been observed with the rise of Lanthanum (La) content. A dielectric anomaly above 350°C is observed for all the studied materials. Further, it is observed that ac conductivity (σ ac) spectrum obeys universal Jonscher’s power law. The variation of σ ac with inverse of temperature for all the samples is found to obey the Arrhenius equation. The formation of loop in polarisation verses electric field curve establishes the ferroelectric (FE) nature of all the studied samples. Current (I)-Electric Field (E) loops is studied to show the behaviour of domain switching.

Effect of B-site Zr and Hf substitution on ferroelectric polar order for tetragonal tungsten bronze ceramic

ABSTRACT Lead free ferroelectric ceramic Ba4Sm2Hf4Nb6O30(BSHN) with tungsten bronze structure was synthesized and characterized. The effect of B-site cation electron configuration (Hf and Zr) on origin of ferroelectricity and polarization reversal was also studied in detail. The X-ray diffraction (XRD) pattern was indexed with tetragonal tungsten bronze in P4bm space group for BSHN. Obvious dielectric anomaly was observed in the temperature dependent permittivity curve, and quite large thermal hysteresis was obtained from the differential scanning calorimetry (DSC) result. While at lower temperature (<T C), there are two distinct dielectric relaxations for BSHN, respectively related to the activation of frozen polar region and activation of the fully free reversal for the polarization. Compared with Ba4Sm2Zr4Nb6O30(BSZN), Hf substitution in B site makes it harder to activate the frozen polar nanoregion but easier to realize free polarization reversal. This could be further confirmed by the measured polarization-electric field (P-E) curve. Meanwhile, the Raman modes intensity showed gradual change rather than abrupt one for BSHN when the temperature increased through the Curie point, which was quite different from the Zr based compounds. The difference in BO6 octahedral tilting, B-site cation’s electron configuration and B-O bond character are the main cause of these distinct dielectric and ferroelectric property.

Pure PZT95/5 Ceramics and Its Phase Transition Behavior Under External Fields

Background: Compositionally modified Pb(Zr0.95Ti0.05)O3 (PZT 95/5) ferroelectric materials have been extensively investigated in past decades for many important applications. However, few study on pure PZT95/5 ceramics have been reported. Objective: Herein, pure PZT95/5 ceramics were successfully prepared, and their microstructure and phase transition behaviors under external fields were studied. Methods: The pure PZT95/5 ceramics were prepared by the conventional solid state reaction using a mixed oxide route. The microstructure and its properties under different external fields were measured. Results: The X-ray diffraction patterns indicated that the virgin pure PZT95/5 ceramics exhibit an orthorhombic antiferroelectric phase, which has also been evidenced by the superlattice reflections in the SAED pattern. While a rhombohedral ferroelectric symmetry crystal structure was observed in the poled samples suggesting that an electric field induced antiferroelectric to ferroelectric phase transition takes place. Pure PZT95/5 ceramics exhibit a quenched ferroelectric hysteresis loop with a remnant polarization of ~8μC/cm2 under 3.5kV/mm. Temperature dependence dielectric response indicated that the orthorhombic antiferroelectric to cubic paraelectric phase transition occurs at 225°C, corresponding to its Curie temperature. A shard depolarization behavior and dielectric anomalies were observed under ~240 MPa hydrostatic pressure. Conclusions: The depolarization mechanism of pure PZT95/5 ceramics under hydrostatic pressure is attributed to the hydrostatic pressure-induced FE-AFE phase transition. These results will offer fundamental insights into PZT95/5 ceramics for pulsed power supply applications.

Characterization of dielectric relaxation, electrical conductivity and impedance spectroscopy of lead-free Li0.5Bi0.5Ti0.8Zr0.2O3 ceramic

This article focuses on dielectric, electrical, and impedance spectroscopy analysis of lead-free ceramic Zr modified Lithium Bismuth Titanate (Li0.5Bi0.5Ti0.8Zr0.2O3), possessing orthorhombic structure prepared by high-temperature mixed oxide method. The room temperature X-ray diffraction study confirms the formation of a single-phase orthorhombic compound. SEM micrograph shows the homogenous and non-uniform distribution of the grains with grain size 4.9 μm. The dielectric, electrical, and impedance properties of the compound are investigated in a broad frequency (103−106 Hz) and temperature (33 °C–500 °C) range. Dielectric anomaly is observed at 112 °C showing phase transition from ferroelectric to paraelectric state and the maximum value of the dielectric constant is nearly 225 at 10 kHz. Fitted Nyquist plots show the involvement of both bulk and bulk interface to the relaxation processes. The temperature-dependent ac conductivity informs the nature of the variation of conductivity and activation energy in various zones. The impedance loss spectra show the fall in resistance with a rise in temperature which confirms the negative temperature coefficient of resistance (NTCR) nature of the compound. Complex modulus Cole-Cole plots suggest that the presence of a non-Debye type relaxation process which is poly dispersive and in nature.

Tailoring the chemical heterogeneity of Mn-modified 0.75BiFeO3-0.25BaTiO3 ceramics for piezoelectric sensor applications

The Mn-modified 0.75BiFeO3-0.25BaTiO3 (75BFBTMn) piezoelectric ceramic possesses a high depolarization temperature of 500 °C and a large piezoelectric coefficient of 110 pC/N, showing the potential for high temperature piezoelectric sensors. However, 75BFBTMn ceramic usually suffers dielectric degradation and abrupt drop of piezoelectric coefficient in the range of 300 °C to 500 °C. Combined the high-energy synchrotron X-ray diffraction analysis with Backscatter-SEM results, it is demonstrated that the electrical thermal instability is owing to the existence of chemical inhomogeneity. The Air-annealing treatment is able to decrease the volume fraction of pseudo-cubic phase and the lattice distortion, removes the chemical inhomogeneity in the grain and free Bi2O3 at grain boundary, and then eliminates dielectric anomalies and piezoelectric degradation with temperature. These results indicate that air-annealing is a simple but effective method to eliminate the chemical inhomogeneity in 75BFBTMn ceramics, thereby improving the property thermal stability for high temperature piezoelectric sensor applications.

Dielectric anomalies and structure evolution of annealed (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 ceramics

The (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 [(1-x)PST-xPIN] (x = 0.2, 0.4, 0.6, and 0.8) solid-solution ceramics were synthesized by conventional solid-state reaction method. The phase structure, microstructure, and dielectric properties were analysed. In order to obtain various ordering degrees, annealing treatment at 700 °C for 10 h, 20 h, 40 h, and 120 h was conducted on (1-x)PST-xPIN ceramics. The degree of ordering increased significantly with the extension of annealing time in 0.8PST-0.2PIN composition. However, for other compositions, no any superlattice peak was observed at all times of annealing process, which was related to the presence of more pyrochlore phase. In addition to the low-temperature relaxation peaks associated with the disordered arrangement of B-site ions, two new dielectric anomalies were found in the temperature dependence of dielectric constant of annealed (1-x)PST-xPIN solid solution. For annealed 0.8PST-0.2PIN composition, the middle-temperature and high-temperature dielectric anomalies were attributed to the ordered PST region and the incommensurate structure induced by the competition between ordered PST and disordered PST, respectively. The high-temperature dielectric anomalies in 0.6PST-0.4PIN and 0.4PST-0.6PIN compositions originated from the contribution of the ordered PIN region in solid solution. Furthermore, the relatively weak superlattice diffraction spots of (111) were found in selected-area electron diffraction patterns of annealed 0.8PST-0.2PIN ceramic, indicating that the existence of alternately ordering arrangement of B-site ions. Combined with the analysis of element mapping, it was concluded that the annealed (1-x)PST-xPIN solid solution was composed of the ordered PST region, the ordered PIN region, and the disordered region constituted by PST and/or PIN.

The antiferromagnetic ordering and metamagnetic transition induced magnetodielectric effect in Dy2Cu2O5

Ferroelectricity and magnetism seldom coexist due to mutual exclusiveness. Recent attempts have been made to achieve the coexistence of ferroelectricity and magnetism in polar magnets. In this paper, we investigated the magnetic properties, dielectric relaxation, and magnetodielectric (MD) effect of polar Dy2Cu2O5 ceramic. At the antiferromagnetic ordering temperature, the dielectric constant (ɛ) curves exhibit a spontaneous change in slope, indicating strongly coupled charge and spin degrees of freedom. With increase in the magnetic field intensity, the simultaneous suppression of the dielectric anomaly and the antiferromagnetic transformation demonstrates the existence of the MD effect. It is important to note that ɛ varies nonmonotonically with the magnetic field. Below the magnetic ordering temperature, ɛ increases continuously before the metamagnetic transition and then decreases after that. The results are discussed in terms of the magnetic field-induced change of spin configuration and spin–phonon coupling. Moreover, two dielectric relaxation-related steps are observed, which are correlated with the electrons hopping within and among the zigzag chains of Cu2+, respectively. This work helps understand the dielectric behavior and the MD effect in materials with complicated spin structures.

Observation of magnetoelectric effect in the S = 1/2 spin chain compound CoSe2O5 single crystal

The antiferromagnetic structure in the S = 1/2 zigzag spin chain compound CoSe2O5 was recently revealed by neutron scattering. Herein, we provide clear evidence for the linear ME coupling through systematic investigations on magnetic, dielectric, and ferroelectric properties. The simultaneous responses of the b-axis electric polarization (Pb) and dielectric anomaly (εb) against magnetic stimuli along the c-axis are revealed. In addition, both the ferroelectric transition and dielectric anomaly shift from the magnetic Néel temperature TN ∼ 8.5 K toward the low temperature under increasing H applied along the c-axis, providing clear evidence for the magnetism-driven ferroelectricity. The observed off diagonal linear ME effect is in accordance with the prediction based on ME tensor analysis for the magnetic space group Pb′cn. Consequently, our results may allow an interesting opportunity to further exploration of intriguing phenomena and physics of ferrotoroidicity in this linear-ME compound CoSe2O5 due to the existence of the off diagonal term in the ME tensor, similar to the case for LiCoPO4.

Dynamic Behavior of Polar Nanoregions in Re‐Entrant Relaxor 0.6Bi(Mg1/2Ti1/2)O3–0.4PbTiO3

The existence of polar nanoregions (PNRs) is the most important characteristic of ferroelectric relaxors; however, the size determination and the dynamic of PNRs remain uncertain. Herein, it is revealed that a re‐entrant relaxor behavior and ferroelectric–paraelectric transition coexist in complex perovskite oxide 0.6Bi(Mg1/2Ti1/2)O3‐0.4PbTiO3. Two dielectric anomalies, 1) the low‐temperature re‐entrant relaxor transition and 2) the high‐temperature diffuse phase transition (DPT), are described by the phenomenological statistical model. The sizes of the two kinds of PNRs corresponding to two ferroelectric states were obtained. The dynamics of PNRs are analyzed using isothermal electrical modulus, which shows three critical temperatures associated with the DPT, the formation, and freezing of PNRs, respectively. The temperature evolution of the PNRs evolution depends on the stoichiometry of bismuth. The results provide new insights into the dynamic behavior of PNRs and the modification way of re‐entrant relaxor behavior.

Manipulating Selective Metal‐to‐Metal Electron Transfer to Achieve Multi‐Phase Transitions in an Asymmetric [Fe2Co]‐Assembled Mixed‐Valence Chain

AbstractManipulation of multi‐functions in molecular materials is promising for future switching and memory devices, although it is currently difficult. Herein, we assembled the asymmetric {Fe2Co} unit into a cyanide‐bridged mixed‐valence chain {[(Tp)Fe(CN)3]2Co(BIT)} ⋅ 2CH3OH (1) (Tp=hydrotris(pyrazolyl)borate and BIT=3,4‐bis‐(1H‐imidazol‐1‐yl)thiophene), which showed reversible multi‐phase transitions accompanied by photo‐switchable single‐chain magnet properties and a dielectric anomaly. Variable‐temperature X‐ray structural studies revealed thermo‐ and photo‐induced selective electron transfer (ET) between the Co and one of the Fe ions. Alternating‐current magnetic susceptibility studies revealed that 1 displayed on and off single‐chain magnet behavior by alternating 946‐nm and 532‐nm light irradiation. A substantial anomaly in the dielectric constant was discovered during the electron transfer process, which is uncommon in similar ET complexes. These findings illustrate that 1 provided a new platform for multi‐phase transitions and multi‐switches adjusted by selective metal‐to‐metal ET.

Manipulating Selective Metal-to-Metal Electron Transfer to Achieve Multi-Phase Transitions in an Asymmetric [Fe2 Co]-Assembled Mixed-Valence Chain.

Manipulation of multi-functions in molecular materials is promising for future switching and memory devices, although it is currently difficult. Herein, we assembled the asymmetric {Fe2 Co} unit into a cyanide-bridged mixed-valence chain {[(Tp)Fe(CN)3 ]2 Co(BIT)} ⋅ 2CH3 OH (1) (Tp=hydrotris(pyrazolyl)borate and BIT=3,4-bis-(1H-imidazol-1-yl)thiophene), which showed reversible multi-phase transitions accompanied by photo-switchable single-chain magnet properties and a dielectric anomaly. Variable-temperature X-ray structural studies revealed thermo- and photo-induced selective electron transfer (ET) between the Co and one of the Fe ions. Alternating-current magnetic susceptibility studies revealed that 1 displayed on and off single-chain magnet behavior by alternating 946-nm and 532-nm light irradiation. A substantial anomaly in the dielectric constant was discovered during the electron transfer process, which is uncommon in similar ET complexes. These findings illustrate that 1 provided a new platform for multi-phase transitions and multi-switches adjusted by selective metal-to-metal ET.

Two manganese chloride organic–inorganic hybrid compounds showing strong luminescence and switchable phase transition and dielectric anomaly

Two organic–inorganic hybrid manganese halide perovskite compounds [Me3NNH2]MnCl3 and [(CH3)3NCH2CH2F]2MnCl4 exhibit switchable phase transition and dielectric anomaly, and also emit strong red and green luminescence.

Structural, morphological, thermal, and oxygen-vacancy-related dielectric relaxation behaviors in EuFeO3 perovskite

Europium-ferrite perovskite EuFeO3 was synthesized basing on standard solid state reaction technique. X-ray diffraction analysis revealed the formation of single phase identified to be crystallizing in a Pbnm orthorhombic structure. X-ray peak broadening was conducted to evaluate the crystallite size and lattice strain. Scanning electron microscopy images showed an agglomerated distribution of grain with an average size ranging between 0.47 and 1.11 µm. The presence iron ions in octahedral environment is highlighted Fourier transform infrared (FT-IR) spectroscopy. Dielectric study was performed as a function of both frequencies (1 kHz–1 MHz) and temperatures (298–300 K). The frequency dependence of dielectric properties revealed a quasi-dc process behavior in the material, typical of carrier dominated systems. Two dielectric anomalies were observed, corresponding to the conduction relaxation dominated by the migration of oxygen vacancies. All observed phenomena were pointed by differential scanning calorimetry (DSC) analysis. Optical absorption studies imply the existence of a direct band gap in the sample.

Dielectric relaxation induced by oxygen vacancies in Na0.5Bi0.5TiO3 ceramics

Dielectric permittivity was studied in ceramics of relaxor ferroelectric bismuth-sodium titanate Na0.5Bi0.5TiO3. The measurements were performed on as sintered and heat treated in vacuum samples. The diffuse dielectric anomalies associated with the structural phase transitions were observed in as sintered samples. The intense peak of permittivity (εmax ∼ 104) appeared after heat treating in vacuum. The anomaly of ε(T) was contributed by slow polarization processes (f &lt; 10 kHz) and was non-stable, vanishing on heating in air up to ∼ 800 K. Temperature and frequency dependencies of ε were described by using Cole-Cole model with accounting thermally stimulated decay of the non-stable polarization. It is supposed that the dielectric anomaly is determined by space charge polarization mechanism. Oxygen vacancies VO•• and electrons localized on titanium ions Ti'Ti are assumed to be responsible for the phenomenon observed.