Temperature-dependent Relaxation Process Research Articles

Investigation on structural, optical and electrical properties of BiFeO3:ZnO nano–micro particles–matrix composite

A new class of materials called matrix-nano composites has the ability to meet the needs of modern advanced applications and technology. To prepare the BiFeO3:ZnO composite, BiFeO3 nanoparticles were prepared using a low–cost sol–gel method, to which ZnO in its micron-sized form was added in varying concentrations of 5%, 10%, and 15%. The structural, morphological, and optical properties of the pure and composite materials were characterized using XRD, FESEM, EDAX, PL spectra, and UV-Visible spectroscopy. The dielectric properties of the pristine and composites were investigated at room temperature. The a.c. conductivity fit with Jonscher's power law and CBH model described the charge conduction behaviour in all pure and composite materials. The temperature-dependent dielectric and loss measurements showed a temperature dependent relaxation process. UV–vis and PL characterization show that the composite materials exhibited improved charge separation efficiency and wider band gaps with increasing BFO content.

Investigations of structural, optical, dielectric and antimicrobial properties of Zirconia-Vanadia nanocomposite

Zirconia-Vanadia nanocomposite synthesized by coprecipitation-calcination technique was prepared. XRD plots confirmed the presence of both materials in the composite. SEM and TEM pictures showed the formation of spherical and needle shaped structures. EDX spectrum confirms the presence of both elements. A.C conductivity plots show a linear variation with frequency. Impedance analysis suggested a decrease in impedance with increase in temperature. Modulus analysis showed a temperature dependent relaxation process. The material has a high dielectric constant of about 2500, making it suitable for use as a gate dielectric. Antimicrobial activity analysis suggested the efficacy of the composite against three types of bacteria.

Dielectric Behaviour and Electrical Conductivity of α-BiNbO4 and β-BiNbO4 Ceramics

In this work, orthorhombic (α-BiNbO4) and triclinic bismuth niobate (β-BiNbO4) ceramics were prepared by a wet chemical route. The structure of the obtained powders was characterised by X-ray diffraction and the morphology by scanning electron microscopy. The dielectric measurements were performed in the radiofrequency region, at different temperatures, using the impedance spectroscopy technique. The α-BiNbO4 sample presented a temperature-dependent relaxation process, with the corresponding activation energy being calculated through the Arrhenius equation. The AC conductivity dependence on the frequency was in agreement with Jonscher’s universal power. The conduction mechanism in the α-BiNbO4 compound is governed by two processes, which can be ascribed to a hopping transport mechanism. The correlated barrier hopping model until 280 K and the non-overlapping small polaron tunnelling model above 280 K are the most suitable models to describe the conductivity of this sample. In the β-BiNbO4 compound, the motion of mobile charge carriers involves localised hopping between neighbouring sites.

Structural, dielectric, and electrical study of bismuth ferrite-lithium vanadate

The composite, BiFeO3-LiVO3 was synthesized through a solid-state reaction technique. The X-ray diffraction (XRD) confirmed the formation of the tetragonal structure at room temperature. The dielectric constant and dielectric loss increased with the rise in temperature. The Nyquist plot projected the contribution of bulk effect and a slight indication of grain boundary effect. The presence of a temperature-dependent relaxation process occurred in the material. Electrical modulus confirmed the non-Debye type relaxation and indicated the asymmetric peak broadening for the spread of relaxation time. The activation energies were calculated from the ac conductivity by linear fitting. The fitted Jonscher power law was very close which implied a similar type of charge carrier which exists in the conduction mechanism for the system. Thermistor parameters were evaluated using the grain resistance for different temperatures.

Novel pyrochlore-structured bismuth iron antimonates: Structural, impedance and electrochemical studies

A moderate pyrochlore solid solution range of 0.00 ≤ x ≤ 0.64 was observed in the Bi3.36Fe2.08+xSb2.56-xO14.56-x (BFS) system prepared by solid-state reaction at 925 °C for 2 days. The overall charge compensation required a one-to-one cationic replacement and oxygen vacancies, i.e. Sb5+ ↔Fe3+ - O2–. BFS cubic pyrochlores showed their refined lattice parameters varying linearly in the range of 10.4284 (8)-10.4513(8), thus obeying the Vegard's rule. The measured crystallite sizes by both Scherrer and Williamson-Hall methods were found to be in the range of 46–67 nm; whilst, the larger grain sizes in the range of 0.2–2.9 μm were calculated using scanning electron microscopy (SEM) analysis. The AC impedance analysis also verified a few electrical responses of BFS pyrochlores: (i) BFS pyrochlores had moderate dielectric constants in the range of 24–35 and dielectric losses in the order of 10−1 at room temperature and 1 MHz, (ii) BFS pyrochlores were not electrically homogeneous with bulk capacitances in the order of 10−12 Fcm−1, (iii) a non-Debye type and temperature-dependent relaxation process were discernible and (iv) the movement of charge carrier were either in the long-range or short-range migration subjected to time availability. In addition, BFS pyrochlore thin films had a good capacitive behaviour and electrochemical reversibility, according to the cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analyses. All these excellent properties rendered BFS pyrochlores to be a suitable material for Class 1 ceramic capacitors.

Effect of Structural Features on Ionic Conductivity and Dielectric Response of PVA Proton Conductor-Based Solid Polymer Electrolytes

In this study, the effect of structure on the ionic conductivity and dielectric response of polyvinyl alcohol solid polymer electrolyte films doped with ammonium nitrate (NH4NO3) was investigated. Structural studies show that the solid polymer electrolytes in a suitable salt ratio enhance the amorphous fraction of the host matrix and facilitate the fast movement of H-ions, resulting in the enhancement of electrical conductivity. The highest ionic conductivity at room temperature (5.17 × 10−5 S/cm) was achieved by incorporating 30 wt.% of NH4NO3, which shows the maximum ion dissociation in the host matrix due to ion–polymer interaction. The reduction in the ionic conductivity at higher salt concentrations (above 30 wt.%) is the consequence of a decrease in the carrier concentration and its movement, respectively, due to the formation of ion pairs and a reduction in the amorphous fraction of the system. A broad asymmetric peak of the imaginary part of the electrical modulus suggests a temperature-dependent non-Debye relaxation process for the present system.

Temperature dependence of the longitudinal spin relaxation time T1 of single nitrogen-vacancy centers in nanodiamonds

We report the experimental study of the temperature-dependence of the longitudinal spin relaxation time $T_1$ of single Nitrogen-Vacancy (NV) centers hosted in nanodiamonds. To determine the relaxation mechanisms at stake, measurements of the $T_1$ relaxation time are performed for a set of individual NV centers both at room and cryogenic temperatures. The results are consistant with a temperature-dependent relaxation process which is attributed to a thermally-activated magnetic noise produced by paramagnetic impurities lying on the nanodiamond surface. These results confirm the existence of surface-induced spin relaxation processes occurring in nanodiamonds, which are relevant for future developments of sensitive nanoscale NV-based quantum sensors.

Size dependent dielectric, magnetic, transport and magnetodielectric properties of BiFe0.98Co0.02O3 nanoparticles

Nanostructured polycrystalline samples of BiFe0.98Co0.02O3 (BFCO) with various sizes were prepared using acetate precursor based modified sol–gel method. Rhombohedral phase of nanoparticles has been confirmed by X–ray diffraction (XRD) measurement. The electrical and magnetic properties of samples were investigated for different sized nanoparticles (47.25–93.30 nm). The effect of sintering temperature on the structural, microstructural and dielectric properties has been discussed in the context of crystallite size and oxygen vacancy concentration. The temperature dependent impedance study confirms that the temperature dependent relaxation process is non Debye type and dominated by the short–range movement of oxygen vacancies. The value of magnetization is found to increase with decreasing particle size. Large magnetodielectric (MD) effect has been observed for BFCO nanoparticles with size less than ∼ 62 nm. Complex impedance spectroscopy analysis has been used to ensure intrinsic MD effect.

Temperature-dependent AC conductivity and dielectric and impedance properties of ternary In–Te–Se nanocomposite thin films

The temperature- and frequency-dependent AC conductivity and dielectric and impedance properties of thermally evaporated ternary In–Te–Se nanocomposite thin films were measured in the temperature range from 100 to 300 K with the frequency range of 20 kHz–2 MHz. The measured dielectric constant (e′), loss tangent (tanδ), and the ac electrical conductivity (σac) values are considerably sensitive to the frequency and temperature. The variations in e′, e″ and tanδ characteristics confirm the interfacial polarization. The values of C and e′ decrease with frequency, while σac increases with both temperature and frequency. The estimated activation energy is found to decrease with increase in temperature. Further, the frequency dependence real (Z′) and imaginary parts (Z″) of the impedance spectra of the sample depend on the dielectric relaxation process. The Nyquist plot shows that the radius of the semicircular arc decreases with temperature and reveals a temperature-dependent relaxation process. The mechanism responsible for thermally assisted AC conduction can be due to the electronic hopping of charge carriers.

PCH1 and PCHL promote photomorphogenesis in plants by controlling phytochrome B dark reversion

Phytochrome B (phyB) is the primary red light photoreceptor in plants, and regulates both growth and development. The relative levels of phyB in the active state are determined by the light conditions, such as direct sunlight or shade, but are also affected by light-independent dark reversion. Dark reversion is a temperature-dependent thermal relaxation process, by which phyB reverts from the active to the inactive state. Here, we show that the homologous phyB-binding proteins PCH1 and PCHL suppress phyB dark reversion, resulting in plants with dramatically enhanced light sensitivity. Moreover, far-red and blue light upregulate the expression of PCH1 and PCHL in a phyB independent manner, thereby increasing the response to red light perceived by phyB. PCH1 and PCHL therefore provide a node for the molecular integration of different light qualities by regulation of phyB dark reversion, allowing plants to adapt growth and development to the ambient environment.

Temperature and frequency dependence of AC electrical properties of Zn and Ni doped CoFe2O4 nanocrystals

We have investigated the structure and the electrical properties of CoFe2O4, Ni0.5Co0.5Fe2O4 and Zn0.5Co0.5Fe2O4 nanoparticles, prepared through a chemical pyrophoric reaction technique. The study of the dielectric constant reveals evidence of Rabinkin and Novikova polarisation in the system. The increased value of the dielectric constant at low frequency is attributed to the presence of interfacial and dipolar polarisation in the system. The impedance for Zn0.5Co0.5Fe2O4 nanoparticles is found to decrease with increase in temperature, indicating the presence of a temperature-dependent electrical relaxation process in the system. Nyquist plots have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for the relaxation and the conduction processes in the system. Ac conductivity curves follow a double power law, as proposed by Jonscher. The conduction mechanism with temperature is mainly due to the large polaronic hopping in the system.

Dielectric, electrical and magnetic properties of La doped BiFeO3–PbZrO3 composites

The composites of 0.5(BiLayFe1−yO3)–0.5(PbZrO3) [y = 0.05, 0.10, 0.15 and 0.20] were synthesized through solid-state reaction technique. The X-ray diffraction data confirms the rhombohedral structure of the above systems at room temperature. From the SEM, it is shown that the grains were inhomogeneously distributed over the surface of the composites. The dielectric constant and loss of the composites increased with rise in temperature. The low remanent polarization (0.005, 0.006, 0.008, and 0.004 μC/cm2) for 0.5(BiLayFe1−yO3)–0.5(PbZrO3) [y = 0.05, 0.10, 0.15 and 0.20] respectively shows the weak ferroelectric nature. The Nyquist plot showed the contribution of bulk effect and slight indication of grain boundary effect. The presence of temperature dependent relaxation process occurs in the material. The activation energies calculated from the ac conductivity using least square fitting. The dc and ac conductivity increases with rise in temperature. The ac conductivity spectrum obeyed Johnscher universal power law. The low remanent magnetization was found to be 0.010, 0.009, 0.008 and 0.005 emu/gm for 0.5(BiLayFe1−yO3)–0.5(PbZrO3) [y = 0.05, 0.10, 0.15 and 0.20] respectively.

Dielectric and impedance spectroscopic studies of 0.8BaTiO3–0.2Bi0.5K0.5TiO3lead-free ceramics

0.8 BaTiO3–0.2 Bi0.5K0.5TiO3(BT–BKT20) lead-free ceramics were prepared by conventional solid state reaction method followed by high energy ball milling. The formation of a single phase tetragonal structure in the material was confirmed by X-ray diffraction. Frequency and temperature-dependent dielectric studies show relaxor behavior in the BT–BKT20 which was found to obey modified Curie–Weiss law with degree of diffuseness 1.573. Complex impedance and electric modulus spectroscopy studies reveal temperature-dependent relaxation process in the material. The Cole–Cole plots were measured at high temperatures at which grain effect was observed. Impedance and electric modulus spectroscopy studies show non-Debye kind of conductivity relaxation process in the present material. Activation energies were calculated from impedance and electric modulus spectroscopy and the values of activation energy indicated that the conduction is ionic in nature. AC and DC conductivity have been measured and studied at different temperatures.

Impedance spectroscopy study of Na2SmV5O15 ceramics

The polycrystalline Na2SmV5O15 (NSV), a new member of the tungsten bronze (TB) family, was prepared by a mixed-oxide technique. The room-temperature X-ray diffraction (XRD) confirmed the formation of single phase compound with orthorhombic crystal structure. The scanning electron microscopy (SEM) analysis indicated that the compound has homogeneous micrograph with a uniform distribution of small grains over the entire surface of the sample. The analysis of impedance spectra of NSV in a low-temperature range (−100 °C to 100 °C) at different frequencies exhibited interesting electrical properties like the contribution of bulk effect in conduction process. The study of imaginary part of the impedance at different temperatures showed existence of relaxation peak with its shift towards higher frequency on increasing temperature. This suggested the presence of frequency and temperature dependent relaxation process in the material. The loss peak spectra were found to abide by Arrhenius law with small activation energy of 0.12 eV. The temperature dependence of AC and DC electrical conductivity (σAC and σDC) was also obtained.

Electrical conductivity of Gd doped BiFeO3-PbZrO3 composite

The composite, 0.5(BiGd0.15Fe0.85O3)-0.5(PbZrO3), was synthesized using the solid-state reaction technique. The formation of the compound was confirmed by XRD with an orthorhombic structure at room temperature. The impedance parameters were studied using an impedance analyzer in a wide range of frequency (102–106 Hz) at different temperatures. The Nyquist plot suggests the contribution of bulk effect and a slight indication of grain boundary effect and the bulk resistance decreases with a rise in temperature. The presence of temperature-dependent relaxation process occurs in the material. Electrical modulus reveals the presence of the hopping mechanism in the materials. The value of exponent n, pre-factor A and σ dc were obtained by fitting ac conductivity data with Jonscher’s universal power law. The activation energies calculated from the ac conductivity were found to be 0.50, 0.46, 0.44, 0.43, 0.42 and 0.38 eV at 1, 10, 50, 100, 500 kHz and 1 MHz respectively in the temperature region of 110°C–350°C. The dc conductivity was found to increase with the rise in temperature. The activation energy calculated from complex impedance plot and from the fitted Jonscher’s power law are very close, which results similar type of charge carrier exist in conduction mechanism of the material.

Synthesis, characterization and dielectric properties of [Ru(SO3)(bpy)2(TCNX)] complexes

Na[Ru(SO3)(TCNQ)(bpy)2] and [Ru(SO3)(bpy)2(TCNE)] complexes were synthesized and characterized by means of electrochemical techniques and electronic, vibrational and electron paramagnetic resonance (EPR) spectroscopies. Vibrational data indicated a metallocyclopropane configuration for TCNE while TCNQ ligand is coordinated through the nitrile fragment. EPR data indicated the reduced state for the metal centers and for the TCNQ ligand (TCNQ−). The values of the potentials assigned to the redox processes associated to the TCNX ligands indicated a decrease in the electron transfer barrier. Data of dielectric measurements hinted that TCNQ containing complex is more polarized than the TCNE containing compound. Impedance spectroscopy measurements indicated a temperature-dependent relaxation process for both the complexes. However, for TCNQ containing complex, the results suggested the transition from long-range to short-range mobility. In addition, two values of activation energy (2.0 and 0.6eV) were calculated for this complex suggesting a phase transition process.

MORPHOTROPIC PHASE BOUNDARY AND DIELECTRIC RELAXATION STUDY OF (Bi0.5Na0.5)TiO3–BaTiO3 LEAD-FREE CERAMIC

We report the temperature and frequency dependence impedance spectroscopy of (1 - x) ( Bi 0.5 Na 0.5) TiO 3-x BaTiO 3 (abbreviated as BNT–BT) ceramics with 0 ≤ x ≤ 0.07 prepared by conventional solid-state route. X-ray diffraction analysis indicated that a solid solution is formed when BaTiO3 diffuses into the (Bi0.5Na0.5)TiO3 lattice and a morphotropic phase boundary between rhombohedral and tetragonal locates at x = 0.07. The microstructure indicated that the grain size reduces and the shape changes from rectangular to quasi-spherical with increase in BaTiO3 content. Complex Impedance Spectroscopy analysis suggested the presence of temperature-dependent relaxation process in the materials. The modulus mechanism indicated the non-Debye type of conductivity relaxation in the materials, which is supported by impedance data. The activation energies have been calculated from impedance, electric modulus studies and dc conductivity which suggests that the conductions are ionic in nature. The activation energy increases with increase of BT content up to x = 0.05 and decreases at x = 0.07 which also indicates the presence of morphotropic phase boundary at x = 0.07.

Impedance and AC Conductivity Study of (Bi0.5Na0.5)TiO3 –Ba(Zr0.25Ti0.75)O3 Lead-Free Ceramics

The polycrystalline (1-x)(Bi0.5Na0.5)TiO3-xBa(Zr0.25Ti0.75)O3 (x = 0.01, 0.03, 0.05 & 0.07) (abbreviated as BNT-BZT) ceramics have been synthesized by conventional solid state sintering technique. X-ray diffraction analysis indicated that a solid solution is formed when Ba(Zr0.25Ti0.75)O3 diffuses into the (Bi0.5Na0.5)TiO3 lattice and a morphotropic phase boundary (MPB) co-existing between rhombohedral and tetragonal region at x = 0.05. The microstructure indicated that the grain size reduces and the shape changes from rectangular to quasispherical with increasing in Ba(Zr0.25Ti0.75)O3 content. Complex Impedance Spectroscopy analysis suggested the presence of temperature-dependent relaxation process in the materials. The modulus mechanism indicated the non-Debye type of conductivity relaxation in the materials, which is supported by impedance data. The ac conductivity was found to obey the universal power law. The activation energies have been calculated from impedance, electric modulus studies and dc conductivity which suggests that the conductions are ionic in nature. The activation energy increases with increasing of BZT content up to x = 0.03 and then decreases which also indicates the presence of morphotropic phase boundary at x = 0.05.

Impedance spectroscopy study of BNKLT polycrystalline ceramic

Complex impedance analysis of perovskite structured polycrystalline, [Bi0.5(Na1−x−yKxLiy)0.5]TiO3, at x=0.2, y=0.1 ceramic was synthesized by a mixed oxide method. The formation of single-phase material was confirmed by X-ray studies, and it was found to be rhombohedral structure at room temperature. Under scanning electron microscope, grains separated by well-defined boundaries are visible, which is in good agreement with impedance analysis. The BNKLT ceramic shows excellent piezoelectric properties and the optimum properties measured are: d33=251 pC/N, g33=24×10−3 mV/N, kp=30.5% and kt=28.1%. A complex impedance spectroscopy (CIS) study has been carried out to investigate the electrical properties. Impedance and modulus plots helped to separate the grain and grain boundary to the overall polarization or electrical behavior. CIS analysis suggests the presence of temperature-dependent relaxation process in the material. A possible hopping mechanism for electrical transport processes in the studied material is evident from the modulus analysis. The modulus mechanism indicates the non-Debye type of conductivity relaxation in the materials, which is supported by impedance data. The activation energies have been calculated from impedance (Eτ=0.58 eV) and electric modulus (Eτ=0.40 eV) studies, which suggests that the conduction is ionic in nature. The variation in width of the curves, \(M''/M''_{\max}\) and \(Z''/Z''_{\max}\) at FWHM, allows to conform that the relaxation process involved is of non-Debye type.

Direct melt neutralization and nano-structure of polyethylene ionomer-based nano-composites

The highly neutralized ionomer-based nano-composite materials were prepared via direct melt processing using zinc oxide (as a neutralizating agent) and organically modified clay. The nano-structure was characterized using wide-angle X-ray diffraction analyses, transmission electron microscopy observations and rheometry. The dispersed organo-clay acted as catalytic sites for the neutralization. From TEM analyses, the nano-sized ionic aggregates with a domain size of approximately 2 nm were randomly arranged in the ionomer matrix. The calculated aggregates density for the nano-composite was 0.08–0.15 nm−2. The temperature-dependent relaxation process observed in the viscoelastic measurements was somehow affected by the presence of the silicate layers, whereas it was strongly affected by the specific interaction via ionic aggregated domains.