Analysis of the dielectric characteristics for polycrystalline Ba0.65Sr0.35TiO3 (I)–frequency dependence in the paraelectric state

The frequency and d.c. field dependences of dielectric properties of Ba_0.65Sr_0.35TiO₃ (BST) with various grain sizes (0.87 μm to 5.43 μm) have been studied in the paraelectric state. The frequency response is analyzed by two approximated power laws obtained on the basis of the Cole–Cole expression. The distribution of relaxation times in BST is broader for specimens with finer grains. The d.c. field is found to affect the static permittivity ?₀ rather than the distribution of relaxation times. The effect of the d.c. field on the dielectric permittivity is suppressed for samples with smaller grains and transition broadening is presumed to cause this suppression. It is concluded that both the temperature dependence and the frequency response of the dielectric characteristics of Ba_0.65Sr_0.35TiO₃ are suppressed by the transition broadening.     

Influence of precursor molar concentration on the electrical and magnetic properties of synthesized MnS nanocrystals

MnS Nanocrystals have been synthesized with 1:1, 1:2 and 2:1 molar ratio of precursors using wet chemical method. The electrical and magnetic properties of as-synthesized MnS nanocrystals have been investigated using the impedance spectroscopy and vibrating sample magnetometer respectively. An increase in dielectric constant from 68.5 to 87.9 with increasing Mn content and decrease to 54.1 with increase in the sulfur content was observed. Both the dielectric constant and the loss factor increased with temperature due to the Maxwell–Wagner type interfacial space-charge polarization. The Cole–Cole plot confirmed that the conduction in as-synthesized samples are through the grain and grain boundaries. The resistance and capacitance of grain and grain boundaries have been calculated. The grain resistance varies from 248 to 199 Ω whereas the grain boundary resistance varies from 16 to 6.7 KΩ over the temperature ranges of 323–473 K for 1:1 sample. It endorsed the NTCR type behavior in all the samples. The electric modulus representation revealed the well-defined relaxation peaks. The relaxation time versus temperature behavior revealed that the relaxation time decreases with increase in temperature. AC-conductivity (σ_ac) increases with increasing frequency and temperature. σ_ac increases from 1.58 × 10^?5 to 1.51 × 10^?3 S cm^?1 with the increase of Mn content and then decreases to 1.22 × 10^?8 S cm^?1 with increase of sulfur content. The activation energy is found to be 0.35 eV (1:1), 0.64 eV (1:2) and 0.28 eV (2:1) at 3 kHz. The chemically modified MnS nanocrystals exhibit paramagnetic behavior. A typical saturation magnetization of 0.56, 0.38, and 0.57 emu/g and coercivity of 2.31, 8.42, and 5.57 Oe at room temperature for 1:1, 1:2 and 2:1 sample respectively.     

Structural and dielectric studies of Eu3+/Ag nanocrystallites: SiO2–TiO2 matrices

Silver nanocrystallites/Eu³⁺ doped SiO₂–TiO₂ matrices were synthesised through sol–gel route and the structural and dielectric properties of the matrices were studied. Structural characterizations were done using EDX, XRD, FTIR, AFM and TEM measurements. The TEM and XRD measurements confirm the presence of Ag and TiO₂ nanocrystals. The dielectric and electrical conductivity studies of the samples were done for a frequency range of 100 Hz–2 MHz. The conductivity variation with the Ag content in the Eu³⁺ doped SiO₂–TiO₂ system has been explained by correlating the presence of ionic contribution to the electrical conductivity process. Also, the frequency dependence of dielectric constant and conductivity were studied. The Cole–Cole parameters were calculated and the semicircles observed in the plots indicate a single relaxation process. This behaviour can be modelled by an equivalent parallel RC circuit.     

Giant dielectric permittivity and room temperature magnetodielectric study of BaTi0.2(Fe0.5Nb0.5)0.8O3 nanoceramic

BaTi_0.2(Fe_0.5Nb_0.5)_0.8O₃ [BTFN] ceramic was prepared by sol–gel method. X-ray diffraction pattern of the sample at room temperature shows a cubic phase. Microstructure analysis shows well-grown and dense grains in the sintered sample. High dielectric constant (∼15,000) with low loss (∼0.6) was found at room temperature at 1 kHz frequency. Cole–Cole plot analysis shows that the grain boundary effect (barrier layer formation) is responsible for such a high value of dielectric constant. Another interesting feature of BTFN ceramic is the appearance of room temperature high magnetodielectric response (∼8%) at 9 kOe magnetic field. Magnetodielectric effect was observed in the sample which is due to the Maxwell–Wagner polarization along with magnetoresistance.     

Structural,microstructural and dielectric properties of nanostructured mechanically alloyed polycrystalline Bismuth Ferrite (BiFeO<Subscript>3</Subscript>)

This paper reports the synthesis and characterization of polycrystalline Bismuth Ferrite (BiFeO₃) by high energy ball milling method (HEBM). Bismuth ferrite was mechanically alloyed in a hardened steel vial for 6 h and subsequent molding; the pellet samples went through multi-sample sintering, where the samples were sintered from 425 to 775?°C with 50?°C increments. The phase characterization by X-ray diffraction (XRD) revealed that all the major peaks were of rhombohedral distorted perovskite structure with R3c space group. The XRD patterns showed an improvement of crystallinity with increasing sintering temperature. The morphology of the samples was studied using FESEM showed larger grain size as the sintering temperature increased, consequently increasing the multi-domain grains. The dielectric constant and dielectric loss were observed to increase corresponded to increases in grain size and are mainly due to easier domain wall movement. The capacitance values were observed to be increased when the grain size increases due to increase in sintering temperature.     

Influence of Sr/Ba ratio on the energy storage properties and dielectric relaxation behaviors of strontium barium titanate ceramics

Sr _x Ba_1?x TiO₃ (x = 0.50–0.70) ceramics were prepared by conventional solid-state method. The effects of Sr/Ba ratio on the microstructures, energy storage properties and dielectric relaxation behaviors of ceramics were systematically investigated. Scanning electron microscopy observations revealed that the grain size was inhibited with increasing Sr molar fraction. The Sr_0.6Ba_0.4TiO₃ ceramics obtained the highest energy density of 0.3629 J/cm³ attributed to the increase of average breakdown strength resulting from the decrease of grain size and the optimizing of microstructure. In order to investigate the influence of Sr/Ba ratio on the dielectric relaxation behaviors, the activation energy has been calculated from the relaxation of dielectric loss and the complex impedance spectra by the Arrhenius relationship, respectively. The same results indicated that the decrease of grain size resulting in more grain boundaries, it was difficult for transferring charge and making an orientation under external electric field. Meanwhile, more defects existed at grain boundary and accelerated the thermally activated motions of defects, leading to the increase of activation energy.     

Effect of Ti and Zn Doping on the Structural,Electric, and Magnetic Properties of GaFeO<Subscript>3</Subscript>

Multidoped (Zn,Ti) gallium orthoferrite [GaFeO₃ and Ga_0.98Zn_0.02Fe_0.98Ti_0.02O₃] ceramic was synthesized through a solid-state reaction. X-ray analysis of the prepared material provides its basic crystal data of a single-phase orthorhombic system. The scattered crystallite size and lattice strain of the material were estimated. Analysis of the micrograph of field emission scanning electron microscope shows uniform grain distribution in the sample, suggesting the formation of good quality of sample. Founded on the magnetic measurements, it is concluded that (Zn,Ti)-modified gallium ferrite has provided a reduction in the Curie temperature (T_C); however, no significant changes in the magnetization values with Zn and Ti integration in GaFeO₃ lattice. A noteworthy effect of substitution of multiple elements at the Ga and Fe sites on dielectric constant and tangent loss of GaFeO₃ has been observed. Complete studies of temperature (180–400 K) and frequency (10–10⁷ Hz) dependence of dielectric constant and impedance have provided the effect of grains and grain boundaries on the conduction mechanism and dielectric relaxation of the material.     

Preparation of TiO2 thick film by laser chemical vapor deposition method

A TiO₂ film was prepared on Pt/Ti/SiO₂/Si substrate by a laser chemical vapor deposition method. The rutile TiO₂ film with pyramidal grains and columnar cross-section was obtained at a high deposition rate (R _dep = 11.4 μm h^?1). At 300 K and 1 MHz, the dielectric constant (ε _r) and loss (tanδ) of the TiO₂ film were about 73.0 and 0.0069, respectively. The electrical properties of TiO₂ film were investigated by ac impedance spectroscopy over ranges of temperature (300–873 K) and frequency (10²–10⁷ Hz). The Cole–Cole plots between real and imaginary parts of the impedance (Z′ and Z′′) in the above frequency and temperature range suggested the presence of two relaxation regimes that were attributed to grain and grain boundary responses. The ionic conduction in the rutile TiO₂ film was dominated by the oxygen vacancies.     

Laser ablated lead free (Na,K) NbO<Subscript>3</Subscript> thin films with excess alkali-content

Lead free (Na_0.5K_0.5) NbO₃ (NKN) being hygroscopic in nature is very difficult to be fabricated with enhanced properties in thin films. To maintain stoichiometry 0, 5 and 10% mole excess of Na on A-site were added on NKN bulk targets. The perovskite ABO₃ crystal structure incorporating 0, 5 and 10% excess alkali ions were grown on Pt/Ti/SiO2/Si substrate by pulsed laser deposition, using stoichiometric high density ceramic targets. X-ray diffraction peaks and Raman scattering spectra suggest the formation of single phase of the film in monoclinic phase. The dielectric properties and leakage current is improved with increasing amount of Na concentration. The reduction in leakage current with addition of excess Na concentration may be due to increase in grain size decrease in the connection of grain boundaries with grains. The impedance spectra of the film shows single dielectric relaxation which is non-debye type and the relaxation frequency is shifted to higher side at higher frequency.     

Structural and electrical properties of Ba(Fe<Subscript>1/3</Subscript>Nb<Subscript>1/3</Subscript>Ta<Subscript>1/3</Subscript>)O<Subscript>3</Subscript> perovskite

Ba(Fe_1/3Nb_1/3Ta_1/3)O₃ (BFNT) perovskite compound (phase purity>99%) was synthesized by conventional ceramic preparation method. XRD, microstructure, impedance spectroscopy and ac conductivity properties were analyzed in this study. BFNT compound has a cubic crystal structure, having grain size of 0.31 μm. This compound has shown normal ferroelectric behaviour but not obeying Curie-Weiss law. The impedance and electrical studies have been performed as a function of frequency and temperature. Impedance as a function of frequency revealed single relaxation process. The impedance spectroscopic plots exhibit the major response due to grains with partial contribution from the grain boundary and negligible electrode effect. Complex impedance plot showed data points lying on a single semicircle, implying the response originated from a single capacitive element corresponding to the bulk grains. Also, the centre of semicircle lies below the real axis indicating non-Debye type relaxation. Relaxation time was calculated from Z″_max of Cole–Cole plots. It is observed that conduction is due to hopping of charge carriers. Activation energies were computed from the Arrhenius plots of the sample.     

Electronic behavior and impedance analysis of microcrystalline LiFePO4

We report on the structure, DC electrical conductivity, dielectric, and impedance spectroscopic characterization of microcrystalline LiFePO₄ cathode material. Frequency variation of the dielectric constant (ε′) exhibits the dispersion that can be modeled with a modified Debye’s function, which considers the possibility of more than one ion contributing to the relaxation. At a constant frequency, the dielectric constant value increases with increasing temperature. At 100 kHz, the measured values of ε′ at 433 and 473 K are 4.6 and 5.7, respectively. The real (Z′) and imaginary part (Z″) of impedance as a function of frequency at different temperatures indicate the existence of relaxation processes and their distribution in LiFePO₄. Cole–Cole plots at different temperatures indicate that the conductivity is predominantly due to the intrinsic bulk grains. Temperature variation of DC electrical conductivity (σ _dc) (273–573 K) follows the Arrhenius relationship. Activation energy (E _a) calculated from the ln σ _dc versus 1000/T plot is 0.44 eV, which indicates the predominant electronic conduction mechanism in LiFePO₄. The AC conductivity increases with increasing frequency and temperature.     

Dielectric,humidity behavior and conductivity mechanism of Mn<Subscript>0.2</Subscript>Ni<Subscript>0.3</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrite prepared by co-precipitation method

Mn–Ni–Zn ferrite with the chemical formula of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ was prepared by co-precipitation method. The X-ray diffraction (XRD) results show that the prepared sample crystallizes in the cubic spinel structure with the space group of Fm3m. The morphological analysis of the sample was investigated by scanning electron microscopy (SEM). The dielectric properties of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ ferrite were studied in a frequency range from 20 Hz to 10 MHz and at a temperature range from 293 to 733 K. The dielectric constant decreases with the increasing frequency for all the temperature values chosen. The AC conductivity mechanism was found the small polaron type of conductivity, and in addition to that, the DC conductivity can be explained by Arrhenius type conductivity. According to the dielectric results, relaxation process fits Cole–Cole model. Finally, the effect of the relative humidity upon the impedance of the sample was discussed for a frequency range between 20 Hz and 10 MHz. It is found that the impedance values decrease almost linearly with the increasing % RH (relative humidity) values at low frequencies, while the impedance of the sample is independent of % RH at high frequencies.     

Microstructure and dielectric properties of BaTiO3-based X7R ceramics

The relationship between the microstructures and dielectric properties of BaTiO₃-based X7R ceramics has been investigated at different calcination temperatures. The XRD and SEM results show that calcinations of BaTiO₃ raw powders increase the grain size and stabilize the tetragonality (c/a ratio) of the ceramics. The grain growth caused by the calcination prevents the doped ions from diffusing into the interior of the grains, and then increases the volume fraction of the tetragonal phased core. This process greatly increases the dielectric constant by improving the ferroelectricity. As a result, the relaxation mechanism of the domain reorientation generates high loss tangent. The BaTiO₃ ceramics with X7R specifications were prepared at the calcination temperature of 1200 °C and the sintering temperature of 1240 °C, whose dielectric properties were ɛ _r ≥ 4500, Δɛ _r/ɛ _r25 ≤ ± 10%(−55∼125 °C), tanδ ≤ 0.012(25 °C), respectively.     

Effect of sintering temperature on the grain growth and electrical properties of barium zirconate titanate ferroelectric ceramics

In the present work, structural, dielectric and ferroelectric properties of barium zirconate titanate ferroelectric ceramics have been investigated. The specimens were synthesized using a solid state reaction technique. The XRD analysis reveals that the synthesized compound was formed with no secondary phases. As the sintering temperature increases from 1,200 to 1,300 °C, the average grain size is observed to increase from ~0.39 to ~6.15 μm. The dielectric measurements as a function of temperature show a decrease in Curie temperature (T_C) on increasing the sintering temperature. The decrease in Curie temperature is attributed to the substitution of Zr⁺⁴ whose ionic radius is larger than Ti⁺⁴. A large increase in the dielectric constant with the increase in grain size is observed. The remanent polarization is also observed to increase with the increase in grain size.     

Dielectric relaxation of NdMnO3 nanoparticles

The neodymium manganate (NdMnO₃) nanoparticles are synthesized by the sol–gel process. The phase formation and particle size of the sample are determined by X-ray diffraction analysis and transmission electron microscopy. The band gap of the material is obtained by UV–visible absorption spectroscopy using Tauc relation. Dielectric properties of the sample have been investigated in the frequency range from 42 Hz to 1 MHz and in the temperature range from 303 K to 573 K. The dielectric relaxation peaks are observed in the frequency dependent dielectric loss spectra. The Cole–Cole model is used to explain the dielectric relaxation mechanism of the material. The complex impedance plane plot confirms the existence of both the grain and grain-boundary contribution to the relaxation. The temperature dependence of both grain and grain-boundary resistances follow the Arrhenius law with the activation energy of 0.427 and 0.431 eV respectively. The frequency-dependent conductivity spectra follow the power law.     

Dielectric Behavior of Diamond Films

Nanostructured diamond films have been synthesized using microwave plasma enhanced chemical-vapor-deposition methods. The dielectric behavior has been investigated by using impedance spectroscopy up to 500°C. Impedance data are presented in the form of a Cole–Cole plot. It is found that: (i) The resistivity contributed from both the grain interior and the grain boundary decreases with an increase of temperature. (ii) Above 250°C, the impurities at grain boundaries are thermally activated, and thus contribute to the dielectric relaxation. (iii) The electrical conductivity of diamond films follows an Arrhenius law with an activation energy transition from 0.13 and 0.67 eV at 250°C. A similar activation energy is found for the Arrhenius plot of relaxation frequencies from 0.14 to 0.73 eV. Possible physical mechanisms responsible for the dielectric behavior are presented and discussed.     

Abnormal high dielectric constant in SmFeO3 semiconductor ceramics

The dielectric properties and impedance spectroscopy (IS) of perovskite SmFeO₃ ceramics were studied in the frequency range of 100 Hz-1 MHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant of ∼10⁴ at room temperature. The response is similar to that observed for relaxor-ferroelectrics. IS data analysis indicates the ceramic to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 20 and more resistive grain boundaries. We conclude, therefore that grain boundary effect is the primary source for the high effective dielectric constant in SmFeO₃ ceramics.     

Microstructure and dielectric properties of (La0.9Sr0.1)[(Ga1−x Crx)0.8Mg0.2]O3−δ (x = 0−0.35) oxygen-ion-conducting solid solutions

The microstructure and dielectric properties of (La_0.9Sr_0.1)[(Ga_1?x Cr_x)_0.8Mg_0.2]O_3?δ (x = 0?0.35) oxygen-ion-conducting ceramics have been studied. The dielectric relaxation observed in the ceramics has been interpreted in terms of ionic transport in the grain bulk and across grain boundaries. The grains in the ceramics have been shown to consist of nanoscale domains, which seems to be due to a correlated distribution of the chromium dopant.     

Effect of strain and grain boundaries on dielectric properties in La0.7Sr0.3MnO3 thin films

High dielectric constant and its dependence on structural strain and grain boundaries (GB) in La_0.7Sr_0.3MnO₃ (LSMO) thin films are reported. X-ray diffraction, magnetization, and magneto-transport measurements of the LSMO films, made by pulsed laser deposition on two different substrates—MgO and SrTiO₃ (STO), were compared to co-relate magnetic properties with dielectric properties. At room temperature, in the ferromagnetic phase of LSMO, a high dielectric constant (6 × 10⁴) was observed up to 100 kHz frequency for the films on MgO, with polycrystalline properties and more high-angle GB related defects, while for the films on STO, with single-crystalline properties but strained unit cells, high dielectric constant (≈10⁴) was observed until 1 MHz frequency. Also, a large dielectric relaxation time with significant broadening from the Debye single-dielectric relaxation model has been observed in samples with higher GB defects. Impedance spectroscopy further shows that large dielectric constant of the single-crystalline, strained LSMO film is intrinsic in nature while that in the polycrystalline films are mainly extrinsic due to higher amount of GBs. The presence of high dielectric constant value until high frequency range rules out the possibility of “apparent giant dielectric constant” arising from the sample-electrode interface. Coexistence of ferromagnetism and high dielectric constant can be very useful for different microelectronic applications.     

Effects of Li and Fe doping on dielectric relaxation behavior in (Li,Fe)-doped NiO ceramics

High permittivity (Li, Fe)-doped NiO (LFNO) ceramics are prepared by a simple PVA sol–gel route and their dielectric properties are investigated as functions of temperature and frequency. It is found that the concentrations of Li and Fe have strong influences on the microstructure and dielectric properties of the LFNO ceramics. Two thermally activated dielectric relaxations are observed in the Li_0.05Fe_0.10Ni_0.85O ceramic sample with the activation energies of 0.448 and 0.574 eV for the high- and low-frequency relaxations, respectively. By using a complex impedance analysis, it is believed that the high-frequency relaxation is closely related to the transport properties inside the grains, and the low-frequency relaxation might be ascribed to the interfacial polarization at the interface layers of grain boundaries and/or NiFe₂O₄ secondary phase layers.