Structural,dielectric and impedance properties of NaCa2V5O15 ceramics

Polycrystalline sample of NaCa₂V₅O₁₅ (NCV) with tungsten bronze structure was prepared by a mixed oxide method at relatively low temperature (i.e. 630 °C). Preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Microstructural study showed that the grains are uniformly and densely distributed over the surface of the sample. Detailed studies of dielectric properties showed that the compound has dielectric anomaly above the room temperature (i.e. 289 °C), and shows hysteresis in polarization study. The electrical parameters of the compound were studied using complex impedance spectroscopy technique in a wide temperature (23–500 °C) and frequency (10²–10⁶ Hz) ranges. The impedance plots showed only bulk (grain) contributions, and there is a non-Debye type of dielectric dispersion. Complex modulus spectrum confirms the grain contribution only in the compound as observed in the impedance spectrum. The activation energy, calculated from the ac conductivity of the compound, was found to be 0.20–0.30 eV. These values of activation energy suggest that the conduction process is of mixed type (i.e. ionic–polaronic).     

Finite size effect and influence of temperature on electrical properties of nanocrystalline Ni–Cd ferrites

Electrical conductivity and dielectric measurements have been investigated for four different average grain sizes ranging from 3 to 7 nm of nanocrystalline Ni_0.2Cd_0.3Fe_2.5−xAl_xO₄ (0.0 ⩽ x ⩽ 0.5) ferrites. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of the Al doped Ni–Cd ferrites. The analysis of data shows only one semi-circle corresponding to the grain boundary volume suggesting that the conduction mechanism takes place predominantly through grain boundary volume in the studied samples. The variation of impedance properties with temperature and composition has been studied in the frequency range of 120 Hz–5 MHz between the temperatures 300–473 K. The hopping of electrons between Fe³⁺ and Fe²⁺ as well as hole hopping between Ni³⁺ and Ni²⁺ ions at octahedral sites are found to be responsible for conduction mechanism. The dielectric constant and loss tangent (tan δ) are found to decrease with increasing frequency, whereas they increase with increasing temperature. The dielectric constant shows an anomalous behavior at selected frequencies, while the temperature increases, which is expected due to the generation of more electrons and holes as the temperature increases. The behavior has been explained in the light of Rezlescu model.     

Studies on structural and dielectric properties of Na1/2Dy1/2TiO3 ceramic

The polycrystalline sample of Na_1/2Dy_1/2TiO₃ ceramic was prepared by a standard high-temperature solid-state reaction technique. X-ray structural analysis confirmed the formation of single-phase (with minor secondary phase) compound in the orthorhombic (distorted tetragonal) crystal system at room temperature. Study of surface morphology by scanning electron microscope exhibits uniform distribution of rectangular/cubical grains with less voids. The elemental composition of the prepared compound was confirmed by energy dispersive X-ray spectroscopy microanalysis. Detailed studies of dielectric properties exhibit a dielectric anomaly at 94 °C suggesting a possible ferroelectric–paraelectric phase transition in the compound. The activation energy (E_a), calculated from the temperature dependence of ac conductivity plot, was found to be small (∼0.1 eV) in low temperature and large (∼0.5 eV) in high temperature region.     

Field induced modification of SmC1–SmCA1 transition temperature of a fluorinated antiferroelectric liquid crystal

The temperature and frequency dependent dielectric relaxation data and simultaneous observation of optical texture reveal co-existence of ferroelectric (SmC¹) and antiferroelectric (SmC_A¹) phases in the pre-transition regime of the antiferroelectric liquid crystal (AFLC) sample viz. (R)-4-[1-methyl-2-(2,2,3,3,3-pentafluoropropyloxy)ethyloxy)carbonyl]phenyl 4′-decyloxybiphenyl-4-caboxylate. Interestingly, this sample shows irreversible change in the antiferroelectric to ferroelectric (AFE → FE) phase transition temperature (T₀) for consecutively increasing bias field treatment in successive cycles. The lowest upper bound of the threshold field for AFE → FE transition at the boundary of the said phases is found to be ∼1 kV cm⁻¹.     

Influence of Zn–Zr ions on physical and magnetic properties of co-precipitated cobalt ferrite nanoparticles

Cobalt ferrite nanoparticles having the chemical formula CoFe_2−2xZr_xZn_xO₄ with x ranging from 0.0 to 0.4 were prepared by chemical co-precipitation method. The powder X-ray diffraction pattern confirms the spinel structure for the prepared compound. The particle size was calculated from the most intense peak (3 1 1) using Scherrer formula. The particle size of the samples was found within the range of 12–23 nm for all the compositions. The magnetic and electrical properties of these materials have been studied as a function of temperature. Activation energy and drift mobility have been calculated from the DC electrical resistivity measurements. Dielectric properties such as dielectric constant and dielectric loss tangent were measured at room temperature in the frequency range 100 Hz–1 MHz.     

Study of the temperature dependent transport properties in nanocrystalline lithium lanthanum titanate for lithium ion batteries

The nano-crystalline Li_0.5La_0.5TiO₃ (LLTO) was prepared as an electrolyte material for lithium-ion batteries by the sol–gel method. The prepared LLTO material is characterized by structural, morphological and electrical characterizations. The LLTO shows the cubic perovskite structure with superlattice formation. The uniform distribution of LLTO particles has been analyzed by the SEM and TEM analysis of the sample. Impedance measurements at various temperatures were carried out and the temperature dependent conductivity of as prepared LLTO nanopowders at different temperatures from room temperature to 448 K has been analyzed. The transport mechanism has been analyzed using the dielectric and modulus analysis of the sample. Maximum grain conductivity of the order of 10⁻³ S cm⁻¹ has been obtained for the sample at higher temperatures.     

Dielectric properties and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in Bis(4-acetylanilinium) tetrachlorocuprate(II) compound

In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420–520 K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363 k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338–413 K) and frequency range (200 Hz–5 MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358–373 K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from log σT vs 1000/T plot and are found to be E=1.27 eV (T<363 K) and E=1.09 eV (363 K<T).The frequency dependence of ac conductivity, σ_ac, has been analyzed by Jonscher's universal power law σ(ω)=σ_dc+Aω^s. The value of s is to be temperature-dependent, which has a tendency to increase with temperature and the non-overlapping small polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound.     

Studies of structural and electrical properties on four-layers Aurivillius phase BaBi4Ti4O15

BaBi₄Ti₄O₁₅ (BBT) ceramic was synthesized using mixed oxide route and the structural and electrical properties were investigated systematically. The structural studies confirmed it to be an n=4 member of the Aurivillius oxide. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel–Fulcher relation wherein f₀=8.37E+14 Hz, E_a=0.13 eV, and T_f=608.18 K. The diffuseness parameter γ established the relaxor nature and it was attributed to the A-site cationic disorder. The specimen exhibited the excellent reproducibility in the measurements of displacement current, a remnant polarization of 5.4 μC/cm², and a coercive field of 4.03 MV/m. The room temperature piezoelectric coefficient d₃₃ was found to be 23 pC/N and the field-induced strain S was about 0.018% at the 8 MV/m electric field.     

Microstructure and dielectric properties of Li2CO3 doped 0.7(Ba,Sr)TiO3–0.3MgO ceramics

Microstructure and dielectric properties of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃–0.3MgO ceramics for the low temperature sintering and microwave applications will be presented. In these days, low temperature sintering process has been widely spread out for the integrated electronic modules for the communication systems such as front-end modules, antenna modules, and switching modules. We have added Li₂CO₃ and MgO to (Ba,Sr)TiO₃ material to reduce the sintering temperature and improve dielectric properties such as loss tangent, and frequency dispersion.In this paper, we have discussed the crystalline properties, dielectric properties, and the microstructures of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃–0.3MgO ceramics. No pyro phase was observed in the X-ray diffraction method. Very weak frequency dispersion (<0.7%) of dielectric permittivity was observed from the 1 kHz to 1 MHz range. We found that the grain size of BST is around 2 μm, while the grain size of Li₂CO₃ dope 0.7BST–0.3MgO is around 4 μm from the SEM analysis.     

Synthesis and growth of sodium bitartrate monohydrate a new organometallic nonlinear optical single crystal

Sodium bitartrate monohydrate (SBTMH) a new organometallic nonlinear optical material, with molecular formula, [C₄H₅NaO₆ · H₂O] has been synthesized at ambient temperature. Spectral, thermal and optical techniques have been employed to characterize the new material. Bulk single crystals of size 13 × 4 × 4 mm³ of SBTMH have been grown by slow cooling method. The unit cell parameters of the grown crystal were determined by single crystal XRD. Functional groups present in the sample were identified by FTIR spectral analysis. Thermal stability of SBTMH was determined using TGA/DTA. The grown crystals exhibit nonlinear properties. The dielectric response of the crystal with varying frequencies was studied. The optical transparency range and the lower cut-off wavelength of the material were identified from the UV–vis–NIR absorption spectrum.     

A.c. conductivity and relaxation in LiCoVO4 ceramics

The LiCoVO₄ compound is synthesized by solution-based chemical method. X-ray diffraction analysis exhibits a single phase nature of the compound with cubic structure. The dielectric constant (ε_r), tangent loss (tanδ) and a.c. conductivity (σ_ac) have been studied as a function of frequency and temperature using complex impedance spectroscopy (CIS) technique. The variation of (ε_r and tanδ) with frequency at studied temperatures shows a dispersive behavior at low frequencies. Frequency dependence of σ_ac at different temperatures obeys Jonscher’s universal power law governed by the relation: σ_ac = σ_dc + Aωⁿ, where n is the frequency exponent in the range of 0 ⩽ n ⩽ 1 and A is a constant that depends upon temperature.     

Fast and wide-band response infrared detector using porous PZT pyroelectric thick film

Porous lead zirconate titanate (PbZr_0.3Ti_0.7O₃, PZT30/70) thick films and detectors for pyroelectric applications have been fabricated on alumina substrates by screen-printing technology. Low temperature sintering of PZT thick films have been achieved at 850 °C by using Li₂CO₃ and Bi₂O₃ sintering aids. The microstructure of PZT thick film has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dielectric properties were measured using HP 4284 at 1 kHz under 25 °C. The permittivity and loss tangent of the thick films were 94 and 0.017, respectively. Curie temperature of PZT thick film was 425 °C as revealed by dielectric constant temperature measurement. The pyroelectric coefficient was determined to be 0.9 × 10⁻⁸ Ccm⁻² K⁻¹ by dynamic current measurement. Infrared detector sensitive element of dual capacitance was fabricated by laser directly write technology. Detectivity of the detectors were measured using mechanically chopped blackbody radiation. Detectivity ranging from 1.23 × 10⁸ to 1.75 × 10⁸ (cm Hz^1/2 W⁻¹) was derived at frequency range from 175.5 Hz to 1367 Hz, and D^*’s −3 dB cut-off frequency bandwidth was 1.2 kHz. The results indicate that the infrared detectors based on porous thick films have great potential applications in fast and wide-band frequency response conditions.     

Magnetic and dielectric study of Bi2CuO4

Magnetic and dielectric properties have been investigated for Bi₂CuO₄, which has the same chemical formula as that of the parent materials of cuprate superconductors R₂CuO₄ (R: rare earths). Magnetization measurements show the antiferromagnetic transition of the Cu²⁺ spins at ～42 K, as reported previously. Dielectric measurements for the frequencies of 1 kHz to 1 MHz show that the dielectric constants are 100–500 at room temperature. The dielectric dispersion reveals that the dielectric response lacks spatial coherence, a property which indicates the possible existence of phase separation as suggested for La₂CuO₄. The imaginary part of dielectric response gives the activation energy of 0.22 eV, suggesting that the dielectric response is governed by the electron hopping between the Cu ions.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

Impedance spectroscopy and conduction mechanism of multiferroic (Bi0.6K0.4)(Fe0.6Nb0.4)O3

Polycrystalline (Bi_0.6K_0.4) (Fe_0.6Nb_0.4)O₃ material has been prepared using a mixed-oxide route at 950 °C. It was shown by XRD that at room temperature structure of the compound is of single-phase with hexagonal symmetry. Some electrical characteristics (impedance, modulus, conductivity etc.) were studied over a wide frequency (1 kHz–1 MHz) and temperature (25–500 °C) ranges. The Nyquist plot (i.e., imaginary vs real component of complex impedance) of the material exhibit the existence and magnitude of grain interior and grain boundary contributions in the complex electrical parameters of the material depending on frequency, input energy and temperature. The nature of frequency dependence of ac conductivity follows Joncher׳s power law, and dc conductivity follows the Arrhenius behavior. The appearance of P–E hysteresis loop confirms the ferroelectric properties of the material with remnant polarization (2P_r) of 1.027 µC/cm² and coercive field (2E_c) of 16.633 kV/cm. The material shows very weak ferromagnetism at room temperature with remnant magnetization (2M_r) of 0.035 emu/gm and coercive field (2H_c) of 0.211 kOe.     

Dielectric relaxation in NH4HSO4 above room temperature

The dispersion curves of the dielectric response of NH₄HSO₄ show that the corrected imaginary part of permittivity, εʺ, and its real part ε′ versus frequency reveal a dielectric relaxation around 9.1 × 10⁵ Hz at 31 °C, which shifts to higher frequencies (∼ 10⁶ Hz) as the temperatures increases. The relaxation frequency shows an activated relaxation process over the temperature range 31–83 °C with activation energy E_a = 0.14 eV, which is close to that derived from the dc conductivity. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SO₄⁻ reorientation that cause distortion and change the local lattice polarizability inducing dipoles like HSO₄⁻.     

The dc and ac properties of potassium trioxalatoferrate (III) trihydrate

The complex potassium trioxalatoferrate (III) trihydrate {K₃(Fe(C₂O₄)₃ · 3H₂O)} was synthesised and characterised by energy dispersion X-ray fluorescence (XRF) and X-ray diffraction (XRD). The electrical and dielectric properties of the complex pellet were studied by ac- and dc-techniques in room temperature and in a temperature range of 293–373 K. The data of the ac conductivity as a function of frequency in a frequency range of 1–100 kHz follow the correlated barrier hopping CBH model and the parameters of the model were determined and connecting them with the optical properties. The temperature dependence of dc conductivity shows that the semiconducting behaviour of conduction phenomenon in the complex is realised by hopping mechanism between localised states and the minimum hopping distance was determined. High relative permittivity of about 30 at 100 kHz was obtained for the complex, which can find technological applications like alternative for the SiO₂ insulator in MOS devices.     

Dielectric properties of PIN–PT ceramics under compressive stress

Lead indium niobate, Pb(In_1/2Nb_1/2)O₃ or (PIN), is an interesting ferroelectric material, because it can be changed from a disordered state to ordered state by long-time thermal annealing. However, the temperature related to the maximum dielectric constant (T_max) of PIN in relaxor phase is low (at 1 kHz, T_max = 66 °C). In this study, to increasing T_max of PIN, lead titanate, PbTiO₃(PT) was thus added to PIN with compositions (1 − x)PIN–xPT (for x = 0.1–0.5). The influence of stress on the dielectric properties of (1 − x)PIN–xPT ceramics was then investigated. The dielectric properties were measured under various uniaxial compressive stress up to 400 MPa. The results showed that the superimposed compression load reduced the dielectric constant in 0.9PIN–0.1PT. For the other compositions, the dielectric constants first increased with the compressive stress, and then decreased when the stress was further increased up to 400 MPa. The dielectric loss tangent of all composition was found to decrease with increasing compressive stress.     

High-pressure dielectric studies of a novel hydrogen-bonded ferroelectric (NH4)2H2P2O6

The hydrostatic pressure effect on the dielectric properties of (NH₄)₂H₂P₂O₆ ferroelectric crystal was studied for pressures from 0.1 MPa to 360 MPa and for temperatures from 100 to 190 K. The pressure–temperature phase diagram obtained is linear with increasing pressure. The paraelectric–ferroelectric phase transition temperature decreases with increasing pressure with the pressure coefficient dT_c/dp=?5.16×10^?2 K MPa^?1. Additionally, the pressure dependences of Curie–Weiss constants for the crystal in paraelectric (C₊) and ferroelectric (C_?) phases are evaluated and discussed. The possible mechanism of paraelectric–ferroelectric phase transition is also discussed.     

Structural and AC conductivity study of CdTe nanomaterials

Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.