Frequency Dependent Dielectric Measurements Research Articles

Effect of Sr substitution on the structural, dielectric and ferroelectric property of BaTiO3

We have performed a comprehensive study to explore the effect of Sr substitution on the structural and ferroelectric properties of BaTiO3(BTO) with compositions Ba1-xSrxTiO3for 0 ⩽x⩽ 1. The room temperature structural investigation inferred that the samples with compositionsx> 0.30 has cubic phase instead of tetragonal as for pristine BTO. The temperature dependent dielectric studies illustrate that all well-known three structural phase transitions of BTO are coming closer to each other and the cubic phase is shifted towards lower temperature with increasing Sr content. The frequency dependent dielectric measurements show that there exists the mesoscopic subdomain, whose relaxation time decreases with increasing Sr concentration. The Sr substitution enhanced the ferroelectric properties and maximum remnant polarization at room temperature is observed for 20% Sr substituted sample. The frequency dependent dielectric measurements illustrate the relaxation which could be due to the mesoscopic subdomain, and its relaxation time decreases with increasing Sr concentration. The frequency dependentP-Emeasurements at room temperature infer that for 30% Sr substituted sample, the ferroelectric domain switching is dominated by the rate of nucleation whereas in other compositions forx< 0.3, it is governed by the domain wall speed. The Raman measurements infer the rearrangement of the domain configuration with Sr substitution. Modification in the intensity of the E(TO4) and A(TO3) Raman modes with electric field is also observed for 30% Sr substituted sample and the origin of this is also discussed.

Multiple relaxation mechanisms in SrBi2Nb2O9 ceramic tweaked by tin and samarium incorporation in assistance with single-step microwave sintering

Non-stoichiometric lead free polycrystalline Sr0.8Sn0.2Bi1.75Sm0.25Nb2O9 (SSBSN) ferroelectric ceramics were synthesized through conventional solid step route method by incorporating ball milling and microwave sintering method. X-ray diffraction along with the Rietveld refinement technique confirms the single-phase orthorhombic structure with A21 crystal symmetry. Additionally, the short-range ordering was confirmed by Raman spectroscopy. Doping induced crystallite size and strain were further calculated from the Williamson-Hall plot, which comes around 150 nm and 1.48 × 10–3 respectively. A plate like morphology with an average grain size of 0.41 μm was confirmed by scanning electron microscopy (SEM). A diffuse type ferroelectric to paraelectric phase transition was recorded at 395 °C, mostly arising due to structural heterogeneity at the inter-ferroelectric phase boundary. The temperature and frequency-dependent dielectric measurement of SSBSN ceramic reveal a Maxwell–Wagner relaxation, with prominent dielectric loss in a low frequency regime perhaps due to the generation of leakage current in the SSBSN system. Frequency dependent ac conductivity indicates the polaron assisted hopping mechanism in SSBSN, which further obeys Jonscher’s formulation. The intra and intergranular contributions to impedance in SSBSN ceramics were probed by the complex impedance spectroscopy (CIS) technique. A non-Debye type relaxation mechanism in SSBSN ceramics was indicated by the Cole–Cole plot, whereas the conduction mechanism and transport properties were briefly studied using modulus spectroscopy.

Universal Dielectric Response in Electronically Correlated Functional Oxides CaCu3Ti4O12, LaFeO3, YFe0.5Cr0.5O3 and their Nanocomposites: A Comparative Study

AbstractCaCu3Ti4O12 (CCTO), LaFeO3 (LFO) and YFe0.5Cr0.5O3 (YFCO) were synthesized via conventional sol–gel auto–combustion method using citric acid as gelling agent. The X‐ray diffraction analysis revealed the phase purity of the samples. The energy dispersive X‐ray (EDX) analysis confirms the stoichiometry of the pristine phases. The average particle size obtained from the field emission Scanning electron microscopy (FE−SEM) images revealed that CaCu3Ti4O12 exhibits a broad range of particle size starting from a couple of hundreds of nanometer to micrometer, whereas that for LaFeO3 and YFe0.5Cr0.5O3 are about 110 nm and 50 nm, respectively. We have fabricated the new composites: CCTO–LFO, CCTO–YFCO and LFO–YFCO. The grain sizes of the composite phases are consistent with the pristine phases as they are prepared by at lower sintering temperatures and duration. The dielectric properties of these ceramic composites were compared to those of the pristine phases. The temperature and frequency dependent dielectric measurements reveal a wide range of dielectric constant with moderate tan δ values. The temperature dependent dielectric constant of the investigated samples varies from 100 to 1500 at room temperature and the data have been analyzed using universal dielectric response (UDR) model.

Effect of excess Bi2O3/PbO on the structural and electrical properties of ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 ceramics

The ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3:x(Bi2O3/PbO) [x = 0, 1, and 2 wt%] ceramics were synthesized via solid-state sintering technique. The impact of excess addition on structural and electrical properties was investigated. PXRD results confirmed the diffusion of excess addition in the 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 (BNPZT) lattice, exhibiting the perovskite structure with major rhombohedral (R3c) and minor tetragonal (P4mm) phases. The microstructure of the samples exhibits average grain size distribution (<8 μm). The temperature and frequency-dependent dielectric measurement revealed the relaxor-like ferroelectric behaviour and curie temperature (Tc∼290 °C) observed in BNPZT:1 Pb ceramics. The improved remnant polarization (Pr∼23.47 μC/cm2) and coercive field (Ec∼16.13 kV/cm) were obtained in BNPZT:2 Pb ceramics. The enhanced piezoelectric charge coefficient (d33∼ 496 pC/N) and maximum strain (Smax∼0.12 %) were obtained for BNPZT. The least asymmetric factor (γs) illustrates the lower concentration of inherent defects in BNPZT:1(Bi/Pb) ceramics. This study provides insight into microstructural and electrical properties tuning and paves the way for designing piezoelectric materials.

A facile one-step microwave-assisted synthesis of bismuth oxytelluride nanosheets for optoelectronic and dielectric application: An experimental & computational approach

In the recent developments of research on various 2D materials, a new type of semiconducting material, bismuth oxychalcogenides (Bi2O2X, X = S, Se, Te), has gained tremendous attention among the scientific community. Compared to other Bi2O2X, Bi2O2Te has not acquired significant attention due to the difficulty of synthesizing stable composition. Here in this report, we have used "microwave-assisted synthesis method" to prepare bismuth oxytelluride samples with varying synthesis conditions. A few sharp and well-defined diffraction peaks were observed from crystallographic studies, along with several binary phases. Nanosheet-like morphology was observed for different as-prepared samples. The elemental mapping confirms the presence of Bi, O, and Te in the synthesized samples. In the UV-Vis absorption spectra, a redshift with the variation of synthesis conditions was observed, suggesting the presence of more acceptor states. The calculated bandgap energies display the wide bandgap nature of the samples. A broad photoluminescence emission spectrum with peaks centered around orange-red regions was observed for individual nanosheet cases, making them useful for various optoelectronic applications. The temperature and frequency-dependent dielectric measurements were carried out for the possible application in energy storage. The obtained conductivity of the samples is suitable for different electrical applications. The computational analysis using the DFT method was carried out to provide some necessary information about the structure and physical properties of the prepared materials.

Free standing organometallic dimethylammonium zinc formate perovskite for photonic and antimicrobial applications

In this study, we have focused on the synthesis and analysis of a photoactive perovskite polymer composite film consisting of dimethylammonium zinc formate perovskite (DMAZF) as a crucial member of the metal-organic frameworks family, templated by polycarbonate. The characterization of DMAZF involved a comprehensive analysis using various techniques, including UV-VIS absorption spectra, Raman spectra, Fourier-transform infrared spectra, Z Scan, thermal analysis, frequency-dependent dielectric measurements, and nuclear magnetic resonance. The results of the characterizations revealed that the DMAZF composite film exhibits excellent crystallinity, promising thermodynamic capability for water splitting, desirable dielectric properties, nonlinear effects, and a remarkable surface response to adhering microorganisms, particularly against E. coli and S. aureus. The antibacterial activity was evaluated using the well diffusion method, confirming the material's potential as an antimicrobial agent. Moreover, Z scan studies have unveiled exciting technological applications of DMAZF, further enhancing its appeal as an emerging class of nanomaterial in nanotechnology.

Impacts of annealing temperature on microstructure, optical and electromagnetic properties of zinc ferrites nanoparticles synthesized by polymer assisted sol-gel method

Nanocrystalline zinc ferrite (NZF) were successfully synthesized at different calcination temperature via sol-gel method from the precursor salt solutions using tartaric acid and PVA solution as a chelating agent and binder respectively. The characterization of NZF and their properties had been investigated using sophisticated techniques viz. X-ray diffraction, Fourier transform infra-red spectroscopy, Scanning electron microscopy, Transmission electron microscopy, Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV–Vis-NIR spectroscopy, Vibrating sample magnetometer and Impedance analyzer. X-ray peak profile analysis through Debye Scherer and Wilson method, Halder-Wagner method has been used to estimate the structural parameters. The crystallite size and particle size of ZnFe2O4 samples were found to increases with increasing annealing temperature while lattice parameters and lattice strain decreases. Dynamic light scattering and zeta potential measurements were used to evaluate the particle size distribution and stability of these systems. The room temperature magnetic properties measurement showed that the net magnetic moment is observed for NZF due to cation distribution although the bulk ZnFe2O4 is non-magnetic. Direct optical band gaps of the prepared NZF samples has been investigated by UV–Vis NIR spectroscopy using Tauc formula and found that energy band gaps (Eg) values are in a narrow range of 1.19–1.86 eV. The frequency dependent dielectric properties, impedance and modulus spectroscopy measurement has been investigated in the frequency range of 100 Hz to 20 MHz. The synthesized NZF particles will be applied for Gas sensor, humidity sensor and photocatalyst.

Dielectric Characterization of Electromagnetic Mixing Model Assisted Optimization Derived Heterogeneous Composites for Stealth Technology

In this contribution, the numerical and experimental dielectric characterization of electromagnetic (EM) mixing model-assisted optimization-derived heterogeneous stealth composites was carried out. First, a shuffled frog leaping algorithm (SFLA) fused with the EM mixing model was introduced for the optimal design of the composite under certain constraints. Based on the optimal solutions provided by the analytical model, the heterogeneous composites, constituted multiwalled carbon nanotube (MWCNT) and titanium-di-oxide (TiO2), were developed and characterized. The frequency-dependent dielectric measurements of composites are executed in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band (i.e., 8.2–12.4 GHz) using a waveguide-based microwave measurement technique. At 8.2 GHz, the maximum components of measured complex dielectric permittivity (i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime }$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime \prime }$ </tex-math></inline-formula> ) are 16.2 and 6, respectively. The dielectric loss tangent (tan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta _{\varepsilon }$ </tex-math></inline-formula> ) of the composite has a maximum value of 0.3 in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band. The measured outcomes are compared afterward with the Maxwell Garnett (MG) effective medium model. The Bruggeman (BG) effective medium theory and Landau–Lifshitz–Looyenga (LLL) formulation are included for validation of the adopted MG model. The measured dielectric permittivity and effective medium responses strongly agree with each other. Further, the effect of the quarter-wavelength thickness ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /4), and normalized impedance are studied to better understand the composite’s EM behavior. The effect of different inclusions (i.e., spherical, cylindrical, disks, and ellipsoidal) on the dielectric properties was also studied. The composite with cylindrical inclusions provided the best dielectric and stealth response. The measured and theoretical findings are in strong correlation and reflect the potential of the proposed model in the realization of efficient stealth composites.

The role of Pr3+, Pr3+-Y3+ and Pr3+-Y3+-Dy3+ ions substitutions on the electrical and dielectric properties of NiCo nanospinel ferrites

This study investigated the electrical and dielectric features for NiCo (Ni0.5Co0.5Fe2O4) NSFs, Pr-NiCo (Ni0.5Co0.5Pr0.1Fe1.9O4) NSFs, PrY-NiCo (Ni0.5Co0.5Pr0.1Y0.1Fe1.8O4) NSFs and PrYDy-NiCo (Ni0.5Co0.5Pr0.1Y0.1Dy0.1Fe1.7O4) NSFs have been synthesized hydrothermally. The microstructure of all compositions was characterized thru XRD, SEM, EDX, TEM and HR-TEM. XRD analyses proved the formation of cubic structure and the absence of any impurity. The cubic morphologies of all products have been confirmed by HR-TEM and SEM measurements. The chemical composition presented by EDX was matched with the predicted chemical composition. Temperature (T) and frequency (f) dependent electrical and dielectric measurements were made to evaluate ac/dc conductivities, dielectric constant/losses, and dissipation factor as well as Cole-Cole plots of impedance functions for all NiCo NSFs substituted with Pr3+, Pr3+Y3+ and Pr3+Y3+Dy3+-ions. The ac conductivity measurements confirmed that it obeyed power law rules, largely dependent on the ion substitutions in the host NiCo NSFs. The dielectric constant of NiCo NSFs leads to the usual dielectric distribution, which is strongly influenced by substituted Pr3+, Pr3+-Y3+ and Pr3+-Y3+-Dy3+ ions. Impedance analysis indicated that the conduction mechanisms in all samples were mainly due to grain-to-grain boundaries. The variation in dispersion factors with frequency, like Koop's phenomenological model, is generally attributable to the conduction mechanism in ferrites.

Synthesis, structure and electrical properties of Ti4+ and Zr4+ doped MoO3 transition metal oxide

Hereby, we report synthesis, structural and electrical properties of transition metal oxides of the type Mo0.99Ti0.01-xZrxO3 [x = 0.0, 0.01]. The materials synthesized by solid state route were double calcined before characterizations. We employed a reliable X-ray diffraction characterization technique to confirm the crystal structure acquired by these samples. We used room temperature frequency dependent dielectric measurements to investigate the electric behaviour of these transition oxide materials. Both transition metal ion substituted molybdenum oxides on analysis of XRD data reveals their crystallization into the orthorhombic phase with space group Pbnm. The analysis of frequency dependent room temperature dielectric characteristics of these samples inferred these samples to be better dielectric materials. These transition metal oxides were found to have lower values of dielectric permittivity and dielectric dissipation thereby makes them ideal for high-frequency applications. Comparatively, the dielectric constant and the dielectric loss for Zr-doping are rather low. However, the Ti doped MoO3 displays more smooth behaviour. Furthermore, this piece of work throws light on electrical properties viz. ac conductivity, electric impedance and electric modulus of the as synthesized transition metal oxides.

Effect of DC Bias on Dielectric Properties of NdFeO3

The solid-state synthesis method was used to prepare polycrystalline samples of NdFeO3. The effect of dc bias was observed on the dielectric properties of prepared NdFeO3 samples. Impedance was found to be comprised of three contributions corresponding to grains, grain boundaries, and sample-electrode contact. Temperature and frequency-dependent dielectric measurements revealed that the sample electrode contact and grain boundary responses get modified, while grain response remains unaltered under dc bias. Large dielectric permittivity (of the order of ∼103) in the entire studied temperature range (100 K–450 K) and at high frequencies (∼5 MHz) was found to remain unaffected under dc bias, suggesting that the large dielectric constant is an intrinsic property of NdFeO3.

Temperature and frequency dependent dielectric and conductivity properties of Sr doped LiFe5O8

We report on enhanced dielectric constant and reduction in dielectric loss with Sr doping in LiFe5O8 bulk material. LiSrxFe5-xO8 (x = 0, 0.025, 0.05) samples are seen to crystallize in ordered α- LiFe5O8 phase. Dielectric constant is observed to increase from 2 × 104 to 3 × 106 and loss decreases with the doping of Sr at Fe site. Temperature dependent DC conductivity follows the Arrhenius relationship and the activation energy associated with the conduction process is seen to be 0.42, 0.41 and 0.52 eV for the LiSrxFe5-xO8 (x = 0, 0.025, 0.05) samples. Temperature and wide frequency dependent dielectric measurements indicate that the Sr doped LiFe5O8 samples exhibit relaxation behavior and can be employed for high frequency applications.

Structural, Dielectric and Electric Modulus Studies of MnFe2O4/(MWCNTs)x Nanocomposites

Nanocomposites of multi-walled carbon nanotubes (MWCNTs) and manganese ferrites (MnFe2O4) nanoparticles (i.e., MnFe2O4/(MWCNTs)x; x = 0 ~ 20 wt.% nanocomposites) were synthesized using two-step synthesis process. Initially, MnFe2O4 nanoparticles were prepared by co-precipitation method and, at second stage, different weight percentages (wt.%) of MWCNTs were added and mixed by ultra-sonication assisted method to get the desired MnFe2O4/(MWCNTs)x nanocomposites. X-ray diffraction (XRD) technique was used to investigate the crystal structure and phase purity of MnFe2O4/(MWCNTs)x nanocomposites. The accumulation of MnFe2O4 nanoparticles on the surface of MWCNTs was examined via scanning electron microscopy (SEM). The elemental composition of these nanocomposites was determined with the aid of energy-dispersive x-ray (EDX) spectroscopy, and Fourier transform infrared spectroscopy (FTIR) was employed for the estimation of different vibrational modes. The frequency-dependent dielectric measurements were conducted at room temperature with the help of LCR meter. The improved dielectric and modulus properties of MnFe2O4 nanoparticles with increasing MWCNTs contents signified the importance of these MnFe2O4/(MWCNTs)x nanocomposites for different energy storage applications.

Dipolar order in an amphidynamic crystalline metal-organic framework through reorienting linkers.

Amphidynamic crystals, which possess crystallinity and support dynamic behaviours, are very well suited to the exploration of emergent phenomena that result from the coupling on the dynamic moieties. Here, dipolar rotors have been embedded in a crystalline metal-organic framework. The material consists of Zn(II) nodes and two types of ditopic bicyclo[2.2.2]octane-based linkers-one that coordinates to the Zn clusters through two 1,4-aza moieties, and a difluoro-functionalized derivative (the dipolar rotor) that coordinates through linked 1,4-dicarboxylate groups instead. Upon cooling, these linkers collectively order as a result of correlated dipole-dipole interactions. Variable-temperature, frequency-dependent dielectric measurements revealed a transition temperature Tc = 100 K, when a rapidly rotating, dipole-disordered, paraelectric phase transformed into an ordered, antiferroelectric one in which the dipole moments of the rotating linkers largely cancelled each other. Monte Carlo simulations on a two-dimensional rotary lattice showed a ground state with an Ising symmetry and the effects of dipole-lattice and dipole-dipole interactions.

Structural, morphological, dielectric and optical properties of double perovskites RBaFeTiO6 (R = La, Eu).

Double perovskites RBaFeTiO6 (R = La, Eu) were successfully synthesized using a solid state reaction route. Structural refinement analysis has been performed to investigate the details of the crystalline structure which was found to be a cubic double perovskite structure at room temperature (space group Pm3̄m, No. 221). Crystallite size, lattice strain, density, and porosity parameters were also calculated. The morphology and the elemental composition were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and elemental mapping. FTIR and Raman scattering spectroscopy have been performed in order to study the vibrational modes and the various bond formations of the synthesized samples. The optical properties investigated by means of the optical absorbance measurements highlight that both materials present large band gap energies, and are thus potential candidates for various technological applications. The electrical behavior of these double perovskites was also studied by frequency-dependent dielectric measurements and impedance spectroscopy. The electrical conduction follows Jonscher's power law and the conduction mechanisms are identified.

Insight Into the Anomalous Electrical Behavior, Dielectric and Magnetic Study of Ag-Doped CoFe2O4 Synthesised by Okra Extract-Assisted Green Synthesis

The effect of substitution of silver (Ag) on the structural, electric, dielectric and magnetic properties of nano-CoFe2O4 synthesized via green synthesis using okra plant extract is investigated. The lattice parameters and inverse spinel structure of Ag-substituted CoFe2O4 is confirmed from Rietveld refinement of the x-ray diffraction measurements, Fourier transform infrared (FT-IR) and Raman spectra. A lattice expansion is observed due to the incorporation of larger Ag ions into the CoFe2O4 lattice. Field emission scanning electron micrography analyses elucidate the formation of poly-faceted surfaces with reduction in particle size on Ag doping. The temperature dependent impedance and modulus study reveals the presence of relaxation phenomenon which is dependent on frequency and temperature. Frequency dependent dielectric measurements with increasing temperature obey the modified Debye model. Dielectric loss in the negative region for Ag-doped CoFe2O4 signifies the change of polarization direction due to an increase of Co2+/Fe2+ ratio for the substitution of Ag ions in the B site. Magnetic hysteresis curves exhibit a low field hysteresis loop at room temperature indicating the long-range ferromagnetic ordering nature of the samples. Low loss and high dielectric values make these materials a promising candidate for high frequency devices.

Enhanced Rotation by Ground State Destabilization in Amphidynamic Crystals of a Dipolar 2,3-Difluorophenylene Rotator as Established by Solid State 2H NMR and Dielectric Spectroscopy

We report the synthesis and rotational dynamics of the pillared metal–organic framework Zn2(F2BDC)2(DABCO) where F2BDC = 2,3-difluorobenzene-1,4-dicarboxylate acts as a rotating dipolar linker and DABCO = 1,4-diazabicyclo[2.2.2]octane acts as a spacer (F2MOF 1). The pillared structure of F2MOF 1 was confirmed by X-ray diffraction and CP-MAS 13C NMR analyses. Using variable temperature solid state 2H NMR and broadband dielectric spectroscopy, we characterized the rotational dynamics of the dipolar F2BDC linker in the solid state. Variable temperature (VT) quadrupolar echo 2H NMR measurements revealed a rotational activation energy of Ea = 6.8 ± 0.1 kcal/mol, which agreed well with temperature- and frequency-dependent dielectric measurements, indicating a barrier of Ea = 7.1 ± 0.5 kcal/mol. Structural data from single crystal X-ray diffraction and quantum mechanical calculations (DFT) suggest that the rotational potential is determined by steric interactions between the dipolar rotator and the stator linkers such that fluorine atoms in the F2BDC linker reduce the activation energy by destabilization of the coplanar BDC ground state.

Unravelling the effect of Ni doping on the structural, optical and dielectric properties of nanocrystalline SnO2

Nanocrystalline pristine and Ni doped (x= 0.05, 0.10 and 0.15) SnO2 samples are synthesized via sol-gel process. An extensive microstructure, optical and dielectric studies are performed through several analytical techniques. Analysis of the x-ray diffraction (XRD) data through Rietveld refinement confirms tetragonal crystal structure with P42/mnm space group for all the samples without any impurity or secondary phase. Scanning electron microscopy (SEM) images exhibit smooth surface morphology with agglomeration of the particles and energy dispersive x-ray spectra (EDS) confirm elemental composition of the samples. The average crystallite/particles size of the samples is found to increase for 5% Ni doped SnO2 but reduces on further increase in the Ni content. Fourier transform infrared (FTIR) spectra show vibrational modes of the functional groups present in the samples. UV-visible absorption spectra indicate a red shift on Ni doping in SnO2, ascribed to the trapping of excitons by the oxygen vacancies and thereby creating extra energy states within the bandgap. The band gap is found to diminish from 3.81 eV for pristine SnO2 to 3.57 eV for the sample with 15% Ni concentration. Frequency dependent dielectric measurements at room temperature reveal higher values of the dielectric constant at lower frequencies that can be described on the basis of Maxwell-Wagner theory. The results demonstrate that the oxygen vacancies play a crucial role and concentration of Ni has strong influence on the microstructure, optical and dielectric behaviour of SnO2.

Relaxor Phase Evolution of (Bi0.5Na0.5-xKx)TiO3 Ceramics due to K Ion Substitution and Their Corresponding Electrical Properties

We synthesized lead-free piezoelectric (Bi0.5Na0.5-xKx)TiO3 (BNKT) ceramics using a conventional solid-state reaction method. We have investigated the structural and electrical properties of the materials with x = 0.05 to 0.40. The X-ray diffraction (XRD) analysis suggests that the BNKT ceramics show the transition from rhombohedral to tetragonal structure. The ratio of the tetragonal structure increased continuously in accordance with the increasing composition of x. The sample of x = 0.10 showed a similar ratio between the tetragonal and rhombohedral structures. Frequency-dependent dielectric measurements showed a sort of relaxor properties emerged with increasing x composition, this effect may be interpreted in terms of the formation of polar nano-regions (PNRs) in samples. The value of remnant polarization (Pr) decreases rapidly as x increases beyond the point of x = 0.10 from 25.3 μC/cm2 to 5.9 μC/cm2. On the contrary, as for inverse piezoelectric coefficient (d33*), a higher value of d33* (336 pm/V) at x = 0.10, was observed when compared with x = 0.05 (d33* = 51 pm/V). These results can be explained by the formation of PNRs and their variations with the external applied field. We here propose a possible mechanism showing the effects of dipolar defects, which can be resulted from the K ion substitution on (Bi,Na)TiO3 (BNT) ceramics.

High Temperature Dielectric Response and AC Conductivity Mechanism of (Nd, Ni) codoped BiFeO3

BiFeO3(BFO)and Bi0.9Nd0.1Fe0.9Ni0.1O3 (BNFNO) nanocrystalline samples have been synthesized through the sol-gel auto combustion process. Frequency and temperature dependent dielectric measurements have been performed in order to apprehend the influence of (Nd,Ni) co-doping on the conduction mechanism of pristine BFO.Thereal part of the dielectric constant is found to increase with the Nd and Ni doping, which is accredited to higher space charge polarization induced by the dopant ions.The dielectric constant measured as a function of frequency exhibits a dispersivebehaviour within low frequency region and attains a constant value at higher frequencies. A thermally activated relaxation peak is found at around 500K in the BNFNO samplewhich shifts towards lower temperatures at higher frequencies. The AC conductivity follows the Jonscher’s universal dynamic law, which has been utilized to evaluate the value of frequency exponent ‘s’. The decrease in the value of the ‘s’ parameter with the increase in temperature establishes that the conduction mechanism is governed by the correlated barrier hopping (CBH) model. The ac conductivity data has been utilized to evaluate the minimum hopping distance (Rmin) and the binding energies (Wm) of the electrons in BNFNO. Arrhenius equation has been used to fit the experimental data and activation energy has been evaluated at different temperatures. The Activation energy is found to increase with the increase in the temperatures, owing to the creation of more oxygen vacancies instigated by (Nd, Ni) co-doping.