Temperature-dependent Dielectric Response Research Articles

Hybrid perovskite shows temperature-dependent photoluminescence and dielectric response triggered by halogen substitution

Materials exhibiting dielectric switching response and photoluminescence (PL) are promising for sensors and information storage. In previous research, we synthesized a series of materials with red or green PL and dielectric switching capabilities by incorporating luminescent metal halides into organic ammonium compounds. However, effective modification to synthesize organic-inorganic hybrid materials with dielectric switching response and orange PL continues to be a challenge in the respective fields. Orange PL materials are valuable for switching and sensors, and most orange light sources are derived from rare earth elements, making them harder to obtain. We have successfully synthesized two organic-inorganic hybrid materials ([CMPD]PbBr3 (1) and [BMPD]PbBr3 (2), CMPD = N-ClCH2-N-methylpiperidine, BMPD = N-BrCH2-N-methylpiperidine) that exhibit both orange PL and dielectric switching response. When Cl in compound 1 is substituted by Br in compound 2, the phase transition temperature of the compound is elevated by 45 K. These compounds exhibit captivating orange light emission when exposed to ultraviolet lamps. This research provides insights into exploring multifunctional materials with orange PL and dielectric switching response and provides proof for halogen substitution strategies to design materials with higher phase transition temperatures.

Magnetoelectric coupling response of novel mullite coated Ni–Zn–Cu-ferrite nanocomposite

Novel multiferroic nanocomposite fabricated by Ni–Zn–Cu-ferrite (NZCF)-mullite is reported in this article. The crystallographic phases are confirmed by X-ray diffraction. The static magnetic properties are measured for both bare NZCF and mullite encapsulated NZCF nanocomposite which show the successful retention of the magnetic behaviors of the nanocomposites even at higher annealing temperature of 1200 °C. The dielectric response is estimated and high value of dielectric constant (∼210.7 at 100 Hz) is observed for the mullite encapsulated NZCF nanocomposite due to the formation of interfacial polarization in the nanocomposite. The temperature dependent dielectric response suggests the presence of dielectric polarization in the NZCF-mullite nanocomposite. Magnetocapacitance (MC) study of the NZCF-mullite nanocomposite sample is observed at room temperature (RT). The observed MC and its variation with magnetic field confirm the presence of strong interactions between the magnetic and ferroelectric order parameters in the nanocomposite sample.

Contribution of Embedded Bromine Molecules to the Dielectric Properties of Fluorinated Graphite Intercalation Compounds

Here, we study the dielectric properties of fluorinated graphites C2Fx with different fluorine contents (x ≈ 1.05, 0.85, and 0.60) and embedded bromine molecules by impedance spectroscopy. An analysis of the results using the Maxwell-Garnett approximation made it possible to estimate the contributions of the fluorinated graphite matrix and bromine guests to the dielectric permittivity of the compound. The permittivity of the C2Fx matrix increases with decreasing fluorine content and does not depend on temperature. The change in the permittivity upon cooling/heating of the samples is provided by the polarization of bromine molecules Br2. The significant temperature-dependent dielectric response of C2F0.60 is associated with the formation of bromine and polybromide ions, such as Br2– and Br3–, in the interlayer space of the matrix. The decrease in the permittivity at low temperature is explained by the freezing of the ion mobility.

Site selective response of cationic dopants in ZnO nanomaterials: Optical, dielectric and magnetic behaviors

Modulations of dielectric response and the investigation of magnetic property due to the percentage variation (3, 5 and 7 wt%) of chromium ion doping in 5 wt% yttrium doped-ZnO nanomaterials are considered in this report. The rods like Cr3+ and Y3+co-doped ZnO nanomaterials with polycrystalline single phase of wurtzite lattice structure are prepared by hydrothermal synthesis route. Frequency and temperature dependent dielectric response of all the co-doped ZnO nanomaterials were investigated in this report and the observation suggests that the dielectric permittivity of these co-doped ZnO nanomaterials can be modulated based on the site selectivity of the cationic dopants like Cr3+ or Y3+in between the lattice sites and the interstitial sites inside the host ZnO lattice structure. In addition, low temperature (10 K) magnetic ordering with ‘S’ shape hysteresis loop are observed. The hysteresis curve has been fitted and contribution of each magnetic phase (paramagnetic and ferromagnetic) has been extracted. This report is not only helpful to understand the modulation of dielectric response of ZnO like semiconducting materials depending on site selectivity of the cationic dopants inside the lattice structure of ZnO but also explore the underlying physics of DMS system consisting of multiple magnetic phases. This study shows that the semiconductors based dielectric materials are more effective for tailor made applications in various dielectric devices.

Optimization of dielectric and magnetoresistive response in Nd2-xLaxCe2O7 (0 ≤ x ≤ 2.0) for efficient energy storage applications

Magnetoresistive and temperature-dependent dielectric response of La-substituted Nd2Ce2O7 pyrochlores is comprehensively presented in this work. The samples were synthesized using a facile chemical route. Structural investigations confirmed that La-substitution resulted in a slight increase in lattice parameters without any phase transformation of cubic fluorite structure. The credibility of structural information is further affirmed via Rietveld's refined parameters. The spherical-shaped particles with increased agglomeration were revealed in morphological analysis. The elemental purity of all the compositions was verified via energy-dispersive X-ray spectroscopy. The dielectric constant increased significantly by rising temperature from 300 to 500 K. The maximum value of the dielectric constant was noted as 5213 at 500 K for x = 0.8, which highlighted the potential of this composition for energy storage devices, operating at elevated temperatures. When 40% Nd was substituted at La-site, the sample exhibited maximum dispersion in magnetoresistive coupling which revealed the potential of these compositions for magnetoresistive devices.

Temperature-dependent dielectric anomalies in powder aerosol deposited ferroelectric ceramic films

Room-temperature fabrication of functional ceramic films using powder aerosol deposition (AD) is important for practical applications. However, the as-processed ferroelectric films show unusual temperature-dependent dielectric response, including enhanced conductivity in the as-processed state and subsequent significant increase in the permittivity following heat treatment. In this work, we investigate the influence of the residual internal stresses developed during the high-impact consolidation process on the dielectric response. Moreover, the recombination of charged defects generated during deposition is driven by the temperature and the atmospheric condition during the heat treatment as well as the carrier gas type used during deposition. Thermal treatment up to 500 °C in different atmospheres was used to tune the dielectric and ferroelectric response, highlighting that irrespective of the type of carrier gas, AD deposition process induces charged defects in polar oxide ceramics that can be reduced through heat-treatment far-below their bulk sintering temperature. Macroscopic electromechanical properties are contrasted to in-situ heating scanning transmission electron microscopy to observe possible local effects, such as crystallization, grain growth, crystal defect structure, or grain reorientation. In addition X-ray diffraction and X-ray photoelectron spectroscopy studies were conducted to gain insight into the effect of annealing on the crystal structure and local moisture adsorption.

Dielectric response of rock-salt crystals at finite temperatures from first principles

We combine ab initio simulations and Raman scattering measurements to demonstrate explicit anharmonic effects in the temperature-dependent dielectric response of a NaCl single crystal. We measure the temperature evolution of its Raman spectrum and compare it to both a quasiharmonic and anharmonic model. Results demonstrate the necessity of including anharmonic lattice dynamics to explain the dielectric response of NaCl, as it is manifested in Raman scattering. Our model fully captures the linear dielectric response of a crystal at finite temperatures and may therefore be used to calculate the temperature dependence of other material properties governed by it.

Study of structural correlations with temperature dependent dielectric response and ferroelectric behavior for (Sr, Mn) co-doped BaTiO3

Study of structural correlations with temperature dependent dielectric response and ferroelectric behavior for (Sr, Mn) co-doped BaTiO3

Studies of Optical, Dielectric, Ferroelectric, and Structural Phase Transitions in 0.9[KNbO3]-0.1 [BaNi1/2Nb1/2O3−δ

The compound 0.9[KNbO3]-0.1[(BaNi1/2Nb1/2O3−δ] (KBNNO), a robust eco-friendly (lead-free) ferroelectric perovskite, has diverse applications in electronic and photonic devices. In this work, we report the dielectric, ferroelectric, and structural phase transitions behavior in the KBNNO compound using dielectric, X-ray diffraction, and Raman studies at ambient and as a function of temperature. Analyses of X-ray diffraction (XRD) data at room temperature (rtp) revealed the orthorhombic phase (sp. Gr. Amm2) of the compound with a minor secondary NiO cubic phase (sp. Gr. Fm3m). A direct optical band gap Eg of 1.66 eV was estimated at rtp from the UV–Vis reflectance spectrum analysis. Observation of non-saturated electric polarization loops were attributed to leakage current effects pertaining to oxygen vacancies in the compound. Magnetization studies showed ferromagnetism at room temperature (300 K) in this material. XRD studies on KBNNO at elevated temperatures revealed orthorhombic-to-tetragonal and tetragonal-to-cubic phase transitions at 523 and 713 K, respectively. Temperature-dependent dielectric response, being leaky, did not reveal any phase transition. Electrical conductivity data as a function of temperature obeyed Jonscher power law and satisfied the correlated barrier-hopping model, indicating dominance of the hopping conduction mechanism. Temperature-dependent Raman spectroscopic studies over a wide range of temperature (82–673 K) inferred the rhombohedral-to-orthorhombic and orthorhombic-to-tetragonal phase transitions at ~260, and 533 K, respectively. Several Raman bands were found to disappear, while a few Raman modes such as at 225, 270, 289, and 831 cm−1 exhibited discontinuity across the phase transitions at ~260 and 533 K.

Significance of considering pellet molding pressure and dielectric experimental conditions in the [dielectric constant—temperature] response of switchable dielectric molecular materials: illustration on dabcoHBF4 polycrystals

In this study, we investigate the temperature-dependent dielectric response of dabcoHBF4 molecular switchable dielectric materials. This compound made of polycrystals has been shaped into pellets under different controlled applied pressures [0.2–1 GPa]. The dielectric analysis carried out on these samples showed that the mechanical stresses induced by this shaping pressure had a significant effect on the value of the dielectric constant in both the ferroelectric and the paraelectric phase. However, the impact of this pressure remains secondary in the AC electrical conductivity, determined for the first time in these compounds. Thus, conductivity values around 2 × 10–7 S/cm in the ferroelectric phase and 2 × 10–6 S/cm in the paraelectric phase were found. The behavior of these compounds over wide frequency ranges [1–1 MHz] and temperature ramps [0.5–10 K/min] revealed that the frequency had no effect on the transition temperature at the difference of temperature rate as expected in most ferroelectric materials. When decreasing the frequency, the dielectric constant gains in value and can reach values higher than 50 in the ferroelectric phase and 1000 in the paraelectric phase with a frequency solicitation at 10 Hz. At lower frequencies, the Curie–Weiss law is lost in the paraelectric regime and an enhanced rise of the dielectric constant with increasing temperature probably reflects an interfacial polarization mechanism. Finally, this dielectric analysis in frequency, temperature (323–403 K) and along temperature ramps allowed to extract analytical laws of behavior associating some of these parameters. For example, one of these equations will be useful in the choice of the temperature ramp to be applied to optimize the switching time between a ferroelectric and a paraelectric state according to a condition on the value of the desired dielectric constant at the low and high states in the implementation of memories.

Lead-substituted barium hexaferrite for tunable terahertz optoelectronics

Due to their outstanding dielectric and magnetic properties, hexaferrites are attracting ever-increasing attention for developing electronic components of next-generation communication systems. The complex crystal structure of hexaferrites and the critical dependences of their electric and magnetic properties on external factors, such as magnetic/electric fields, pressure, and doping, open ample opportunities for targeted tuning of these properties when designing specific devices. Here we explored the electromagnetic properties of lead-substituted barium hexaferrite, Ba1−xPbxFe12O19, a compound featuring an extremely rich set of physical phenomena that are inherent in the dielectric and magnetic subsystems and can have a significant effect on its electromagnetic response at terahertz frequencies. We performed the first detailed measurements of the temperature-dependent (5–300 K) dielectric response of single-crystalline Ba1−xPbxFe12O19 in an extremely broad spectral range of 1 Hz–240 THz. We fully analyzed numerous phenomena with a corresponding wide distribution of specific energies that can affect the terahertz properties of the material. The most important fundamental finding is the observation of a ferroelectric-like terahertz excitation with an unusual temperature behavior of its frequency and strength. We suggest microscopic models that explain the origin of the excitation and its nonstandard temperature evolution. Several narrower terahertz excitations are associated with electronic transitions between the fine-structure components of the Fe2+ ground state. The discovered radio-frequency relaxations are attributed to the response of magnetic domains. Gigahertz resonances are presumably of magnetoelectric origin. The obtained data on diverse electromagnetic properties of Ba1−xPbxFe12O19 compounds provide information that makes the entire class of hexaferrites attractive for manufacturing electronic devices for the terahertz range.

Observation of magnetodielectric properties in BTFO-LSMO composites synthesized via sol-gel precursor hybrid technique

Composite Bi5Ti3FeO15 (BTFO) and manganite-based La0.67Sr0.33MnO3 (LSMO) is prepared by the following sol-gel precursor hybrid technique in order to study the magnetodielectric (MD) properties. The coexistence of dual phases of BTFO (orthorhombic) and LSMO (rhombohedral) is confirmed from the Rietveld refinement of the X-ray diffraction (XRD) pattern. The microstructural analysis is carried out using the field-emission scanning electron microscope (FESEM), suggesting the formation of inhomogeneous distribution of both large and small grains of size 586 nm and 261 nm. In addition to the crystallite size calculation, the formation of strain is calculated using the uniform deformation model (UDM). Temperature-dependent dielectric constant and loss responses subjected to a constant magnetic field confirm the existence of the MD effect. The maximum magnitude of the MD effect at room temperature is found to be ~0.17% at a magnetic field of 1.3 T. The behavior of MD effect arises due to the presence of magnetoresistance (MR) in the core of the manganite-based composite material.

Nickel Doping Effects on the Structural and Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Perovskite Ceramics

The effects of nickel doping into Ba(Zn1/3Nb2/3)O3 (acronym: BZN) ceramics is structurally, morphologically and electrically investigated. The nickel substitution in sites of Zn which was carried out by the solid state reaction technique strongly enhanced the structural, morphological and electrical performances of the BZN. Specifically, while the lattice constant and crystallite sizes increased, the microstrain and the defect density decreased. The relative density of the BZN ceramics increased from 95.40% to 98.24% upon doping of Ni with content of x = 0.05. In addition, the Ni doping increased the values of electrical conductivity without significant changes in the dielectric constant values. It is also observed that the doping the BZN ceramics highly altered the temperature dependent variation of the relative dielectric constant. In the temperature range of 293–473 K, the x = 0.05 Ni doped BZN samples were less sensitive to temperature. The dynamics of the temperature dependent dielectric response is dominated by the coupled defects excitation mechanisms. Both of the temperatures and frequency dependent dielectric constant, dielectric loss and electrical conductivity suggests that the Ni doped Ba(Zn1/3Nb2/3)O3 ceramics is more appropriate for electronic device fabrication than the pure ones.

Probing the in-time piezoelectric responses and depolarization behaviors related to ferroelectric-relaxor transition in BiFeO3–BaTiO3 ceramics by in-situ process

Phase transition from a ferroelectric to relaxor phase at high temperature plays a crucial role on thermal depolarization process for piezoceramics. However, so far very few have been reported concerning the effect because the thermally induced depolarization was mainly based on ex-situ measuring. In this work, temperature-dependent dielectric, piezoelectric, and ferroelectric responses of BiFeO3–BaTiO3 (BF–BT) ceramics have been measured to evidence real-time depolarization behavior as well as their relationship with ferroelectric-relaxor transition. It is confirmed that in-situ temperature-dependent piezoelectric coefficient (d33) shows a considerable increase in ferroelectric phase. In particular, a sharp drop of d33 with the evidently depolarization process is directly related to the ferroelectric-relaxor transition at 200 °C. The development of the long-range ferroelectric order to the relaxor transition aiding the loss of preferred domain orientation is discussed as the origins for the depolarization behaviors, which is different from usual ex-situ measurements. In addition, d33 showed a second increase to a small extent due to the drastic improvement dielectric constant near Curie temperature Tc. The two increases and two decreases of in-time piezoelectric responses may provide a new insight to optimize the high-temperature piezoelectric performance by regulating phase transition temperature.

Temperature and frequency dependent dielectric response of C3H7NH3PbI3: A new hybrid perovskite

Propylammonium lead iodide (C3H7NH3PbI3), a promising hybrid perovskite, is successfully synthesized by a solgel technique. Structural, optical, and dielectric properties have been studied in detail. The dielectric constant, loss factor, electric modulus, and AC and DC conductivity of this hybrid perovskite exhibit strong temperature dependence over the frequency range of 10 Hz ≤ f ≤ 8 MHz. The Nyquist plot reveals the distinct contributions of grain and grain boundary to the total impedance. The dielectric constant is found to increase with temperature in the high frequency region. The modified Cole–Cole plot shows that the space charge and free charge conductivity increase with the elevation of temperature, whereas the relaxation time decreases with the rise in temperature. From the modified Kohlrausch–Williams–Watts equation, we perceived asymmetrical nature in electric modulus spectra at various temperatures, which corresponds to the non-Debye type nature of perovskite. It has also been found that, with the elevation of temperature, the imaginary part of electric modulus spectra shifts from the non-Debye type toward the Debye type nature, though failing to acquire exact Debye type response, and emerges as a semiconductor material. AC conductivity of PAPbI3 is illustrated on the basis of the correlated barrier hopping (CBH) mechanism. Activation energy estimated from both modulus spectra and DC conductivity matches well, affirming the similarity between relaxation behavior and conduction mechanism. Along with all these, PAPbI3 possesses a high dielectric constant associated with a small dielectric loss, making it a potential candidate for energy harvesting devices.

Structural, Electrical, and AC-Resistivity Studies of BNT-KN Piezoelectric Ceramics

The lead-free (1 – x) Bi0.5Na0.5TiO3 – x KNbO3 (BNT-KN; x = 0 – 0.12) composite ceramics have been synthesized by a sol-gel process. Their structure, morphology, AC conductance and dielectric response were studied systematically. The X-ray diffraction patterns of BNT-KN revealed a morphotropic phase boundary between a rhombohedral and a pseudocubic structure. The temperature-dependent dielectric response of pure BNT revealed two-phase transitions at 200 °C (TR-T or Td) and 320 °C (TC). Furthermore, the critical temperatures were found to shift to lower values with increasing KN concentration. The manifested relaxor behavior was well confirmed by a modified Curie – Weiss law. The hopping conduction mechanism in BNT-KN was characterized through AC-resistivity analysis.

Temperature dependent broadband dielectric, magnetic and electrical studies on Li1-xMg2xFe5-xO8 for microwave devices

Polycrystalline samples of Mg substituted lithium ferrites (Li1-xMg2xFe5-xO8 (LMFO) (x = 0, 0.003, 0.005, 0.007 and 0.01) have been prepared by conventional solid-state reaction. X-ray diffraction patterns revealed the formation of a single-phase cubic structure with P4132 space group. The dielectric constant of lithium ferrite increased with Mg substitution attaining a maximum value for x = 0.005 (εr = 3034, tan δ = 0.001at 1 MHz) at room temperature. Temperature-dependent dielectric response in the high frequency range (1 MHz–1 GHz) showed the relaxor behaviour of the dipoles, evident from the shift in the loss tangent with frequency. The activation energy of LMFO is found to be in the range of 1.39 - 0.35 eV. An enhanced permeability is found to be ∼29 for x = 0.007 at 1 MHz, RT. The variation in permeability is attributed to the variation in thickness of the domain walls and magneto-crystalline anisotropy. The temperature-dependent magnetization curves reveal the ferrimagnetic transition of LFO at 600 °C, which reduced with Mg substitution. Magnetic hysteresis loops showed the highest saturation magnetization (Ms = 54.6 emu/g) for x = 0.007 among all the samples. The magnetic properties are explained by considering Neel’s two sub-lattice model. Thus, LMFO samples, (especially with x = 0.005) are very promising for circulator and phase shifter applications.

Effect of oxygen partial pressure on nonlinear optical and electrical properties of BNT–KNNG composite thin films

Composite thin films of 1–x [Bi0.5Na0.5TiO3] – x [K0.5Na0.5NbO3 + 1 wt% Gd2O3] (BNT–KNNG); (x = 0.01) have been deposited at various O2 pressures from 0.1 to 10 Pa by pulsed laser deposition, and their crystal structure, surface morphology, optical, dielectric, and ferroelectric properties were investigated. X-ray diffraction analysis of thin films deposited at 0.1 Pa revealed a single phase of BNT–KNNG and further (> 0.1 Pa), film crystallinity gradually increased with a rise in O2 pressure. The improvement in the refractive index and a reduction in optical bandgap are observed with O2 pressure and are estimated to be 2.28–2.42 and 4.08–3.65 eV, respectively. The third-order nonlinear optical coefficients estimated using the Z-scan technique are found to be enhanced with O2 pressure. The film deposited at 10 Pa exhibited a higher nonlinear refractive index (n2 = 6.188 × 10− 6 cm2/W) and a strong absorption coefficient (β = 1.043 cm/W). The temperature-dependent dielectric response displayed two structural phase transitions from rhombohedral to tetragonal phase at 165 oC and tetragonal to cubic phase at 298 oC. The enhanced dielectric (er = 411, tanδ = 0.156 @ 1 kHz), Microwave dielectric (er = 317 and tanδ = 0.0074 @ 10 GHz), and ferroelectric (Pr = 25.31 µC/cm2, EC = 42.62 kV/cm @ 1 kHz) properties with low leakage current are observed for the film deposited at 10 Pa which followed a space charge limited conduction behavior. The obtained microwave and nonlinear optical properties of BNT–KNNG composite films are suitable for tunable microwave and optical photonic device applications.

Dynamic Motion of Twisted π System-Induced Temperature-Dependent Dielectric Response in the Neat Liquid State

Molecular assemblies of twisted π molecules of tetraphenylene with long alkoxy chains (1) and tetra[2,3]thienylene with long alkylamide chains (2) or long alkoxy chains (3) and their dielectric properties were investigated. Different degrees of intermolecular interaction of 1–3 afforded different molecular assemblies, including an ordered columnar structure, disordered columnar, and lamellar structures. The introduction of long alkyl chains enabled us to create thermally stable liquid crystalline or liquid states. Temperature-dependent dielectric measurement revealed that the dynamic flipping motion of the tetra[2,3]thienylene core of 3 induced a temperature- and frequency-dependent dielectric anomaly in the neat liquid phase. This flipping motion of the central tetra[2,3]thienylene π core occurred relatively easily in the liquid state with a high degree of freedom of molecular motion.

Enhanced microwave dielectric and electrical properties of Zn substituted Mg2TiO4 ceramics for RF/microwave applications

The structural, microstructural, electrical and microwave dielectric properties of Mg2Ti1−xZnxO4 (x = 0.01–0.05) ceramics prepared by solid-state reaction method have been reported. The X-ray diffraction patterns and Raman spectra have showed the presence of pure Mg2TiO4 (MMTO) along with some fraction of MgTiO3 (MTO) phase. It is observed that the cubic structure of MMTO is deformed and evaluated to become pseudo cubic structure with Zn substitution. The surface morphology of the sintered MMTO ceramics at 1350 °C exhibited uniform and dense microstructures. Temperature dependent dielectric response of Mg2Ti1−xO4Znx ceramics with x = 0.03, showed stable dielectric response in the temperature range from RT to 300 °C. The overall enhancement in dielectric response of the samples is attributed to the compositional heterogeneity due to substitution of Zn2+ in the Ti4+ site. The complex impedance spectra revealed two parallel RC combination circuit [(RgCg) (RgbCgb)] elements in series. The dispersion of AC conductivity followed Jonscher’s power law, and non-overlapping small polaron hole hopping assisted conductivity. Mg2Ti1−xZnxO4 ceramics with x = 0.03, exhibited best structural, dielectric and microwave dielectric property with uniform and dense microstructure, moderate dielectric constant (er) ~ 23 and quality factor (Q × fo) ~ 165 THz at 8.89 GHz. A voltage independent capacitance for the sample at all the measured frequencies have observed. The obtained properties of the ceramics are promising for dielectric resonator, microwave integrated circuit and type-I capacitor applications.