Piyush R. Das

Studies of dielectric and electrical properties of a new type of complex tungsten bronze electroceramics

A polycrystalline ceramic with a new type of complex tungsten-bronze type structure, having a general formula K2Ba2Nd2Ti4Nb4W2O30 has been prepared using a high temperature solid-state reaction route after optimizing the calcinations conditions on the basis of thermal analysis results. The material has been characterized by different experimental techniques. The formation of the compound has been confirmed using X-ray diffraction analysis. Dielectric properties (εr and tanδ) of the compound as a function of temperature at different frequencies have been carried out. Temperature dependence of dielectric constant indicates the presence of ferroelectric phase transition well above the room temperature. Complex impedance spectroscopic analysis has been carried out as a function of frequency at different temperatures to establish some correlation between the microstructure and electrical properties of the material. The nature of frequency dependence of ac conductivity obeys the Jonscher’s power law. The dc conductivity calculated from the ac conductivity spectrum shows the negative temperature coefficient of resistance behavior like a semiconductor.

Erratum to: A comparative study of structural, electrical and magnetic properties rare-earth (Dy and Nd)-modified BiFeO3

The polycrystalline samples of BiFeO3 (BFO) and rare earth-modified bismuth iron oxide, Bi0.95R0.25FeO3 (R = Nd, Dy) (BNFO, BDFO) are prepared by a standard high-temperature solid-state reaction technique. A preliminary x-ray structural analysis is carried out to examine the structural deformation and stability of rare earth-modified BFO. Room temperature surface morphologies and textures of the samples are recorded by a scanning electron microscope, which reveals the uniform distribution of the plate-and rod-shaped grains. Studies of dielectric and electric properties in a wide frequency (1 kHz–1 MHz) and temperature (30–400 °C) ranges using complex impedance spectroscopic method have provided many new results. The dielectric constant is found to be increases, and the tangent loss decreases as compared to BFO. The electrical polarizations (spontaneous and remnant) is found to be enhanced on rare-earth substitutions. Studies of ac conductivity suggest that the samples obey Jonscher’s universal power law. The enhancement of magnetization was observed in rare-earth doped samples compared to pure BFO.

Dielectric and electrical properties of Na2Pb2La2W2Ti4Ta4O30 electroceramics

The polycrystalline sample of complex tungsten-bronze type compound (Na2Pb2La2W2Ti4Ta4O30) was prepared by a high-temperature solid-state reaction technique. Room temperature preliminary structural study using X-ray diffraction (XRD) data exhibits the formation of a single-phase new compound. The SEM micrograph of the compound exhibits non uniform rectangular grains distributed throughout the sample surface. Detailed studies of dielectric parameters (ɛr, tan δ) as a function of temperature and frequency, and P-E hysteresis (spontaneous polarization) confirmed the existence of ferroelectricity in the material. Complex impedance spectroscopy analysis, carried out as a function of frequency at different temperatures, established a correlation between the microstructure and electrical properties of the material. The electrical relaxation process occurring in the material is temperature dependent. The activation energy found from the Arrhenius plot that the conduction process in the material is of mixed type. The nature of frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.

Structural, Dielectric, and Electrical Properties of BiFeWO6 Ceramic

A polycrystalline sample of BiFeWO6 was synthesized using a high-temperature solid-state reaction method. The formation of the single-phase compound was checked using an x-ray diffraction technique. The surface morphology recorded by scanning electron microscopy exhibited a uniform distribution of grains of different sizes on the surface of the sample. The existence of ferroelectric properties in the material was confirmed by temperature-dependent dielectric and polarization studies. The temperature and frequency dependence of the electrical properties (impedance, modulus, and conductivity) of the compound were studied using a complex-impedance spectroscopy technique. The frequency dependence of the modulus and impedance plots confirmed the presence of dielectric and conductivity relaxation processes of non-Debye type. The frequency dependence of the alternating-current (ac) conductivity obeys Jonscher’s universal power law.

Dielectric and impedance spectroscopy of (Bi0.5Li0.5)(Fe0.5Nb0.5)O3 multiferroics

The polycrystalline sample of (Bi0.5Li0.5)(Fe0.5Nb0.5)O3 was prepared by a solid-state reaction method. Preliminary X-ray structural analysis of the sample suggests the formation of a tetragonal phase with a new unit cell configuration. Dielectric, electrical, impedance and modulus properties of the material were investigated in a wide range of temperature (25–500 °C) and frequency (1 kHz–1 MHz). Two dielectric anomalies observed at 295 °C and 400 °C clearly suggest the existence of magnetic phase transition and two relaxation processes in the system. Dielectric properties have greatly been improved on addition of LiNbO3 to BiFeO3. The appearance of a hysteresis loop at room temperature confirms the ferroelectric properties of the material. The nature of the Nyquist plot confirms the presence of both bulk and grain boundary effects in the material. The ac conductivity was found to obey Jonschers power law. The dc conductivity variation with temperature follows the Arrhenius equation. The induced voltage changes with the applied magnetic field, showing that the sample is multiferroic.

Electrical properties of Na 2 Pb 2 R 2 W 2 Ti 4 V 4 O 30 (R = Dy, Pr) ceramics

The polycrystalline samples of complex tungsten bronze (TB) Na2Pb2R2W2Ti4V4O30 (R=Dy, Pr) compounds were prepared by solid-state reaction technique. Room- temperature preliminary structural studies confirm the formation of the compounds in the orthorhombic crystal system. Detailed studies of electrical properties of the materials using complex impedance spectroscopy technique exhibit that the impedance and related parameters are strongly dependent upon temperature and microstructure (bulk, grain boundary, etc). An observation of negative temperature coefficient of resistance (NTCR) suggests the materials have semiconducting properties. The variation of AC conductivity with temperature shows a typical Arrhenius behavior of the materials. Both the samples obey Jonscher’s universal power law. The existence of hopping mechanism in the electrical transport processes in the system with non-exponential type of conductivity relaxation is confirmed by electrical modulus analysis.

Ferroelectric phase transition and conduction mechanism of Li2Pb2La2W2Ti4Ta4O30

The polycrystalline sample of Li2Pb2La2W2Ti4Ta4O30 was synthesized by a high-temperature solid-state reaction route. Room temperature X-ray structural analysis and scanning electron micrograph show the formation of single phase high density compound. Existence of ferroelectricity in the in the compound was confirmed through detailed studies of its dielectric and polarization characteristics. From the impedance and modulus analysis it has been concluded that the charge carriers of the material have both short as well as long range order. Again, the electrical transport properties in the material are due to hopping of small polarons.

Structural, dielectric and electrical properties of a new tungsten bronze ferroelectric ceramics

The polycrystalline sample of Li2Pb2Nd2W2Ti4Ta4O30 was prepared by a solid-state reaction technique. Room temperature X-ray structural analysis confirms the formation of a single phase compound. The morphology of the sintered sample recorded by scanning electron microscope exhibits a uniform grain distribution. Detailed studies of the nature of variation of dielectric constant, tangent loss and polarization with temperature and frequency confirmed the existence of ferroelectricity in the material. The temperature and frequency dependence of impedance parameters (impedance, modulus, etc.) of the material exhibits a strong correlation of its micro-structure (i.e., bulk, grain boundary, etc.). The nature of variation of pyroelectric-coefficient and current with temperature suggests that material has good pyroelectric properties useful for pyroelectric detector.

Ferroelectric Properties of Na2Pb2R2W2Ti4V4O30 (R = Dy, Pr) Ceramics

The polycrystalline samples of Na2Pb2R2W2Ti4V4O30 (R = Dy, Pr) were prepared by low-temperature, (i.e., at 650∘C) solid-state reaction technique. The preparation conditions have been optimized using thermogravimetry analysis (TGA) technique. X-ray diffraction (XRD) studies of the compounds showed the formation of a single-phase orthorhombic crystal structure at room temperature. Studies of dielectric properties (ɛr and tan δ) of the compounds at frequencies 10, 100, and 1000 kHz in a wide temperature range (room temperature–500∘C) exhibit ferroelectric phase transitions at 132∘C for NPDWTV and at 122∘C for NPPWTV of diffuse type. Ferroelectric properties of the materials are confirmed by polarization study.

Development of Multiferroism in PVDF with CoFe2O4 Nanoparticles

Thin films of some polymer-ceramic nanomultiferroic composites (in 0–3 connectivity) of compositions (1-x) PVDF-xCoFe2O4 (x = 0.05, 0.1, 0.5) have been fabricated through a solution casting route. Based on X-ray diffraction pattern and data, basic crystal structure and unit cell parameters were obtained. The surface morphology of the materials was studied using a scanning electron microscopy (SEM) technique. Structural investigation confirms the presence of a polymeric electro-active β-phase of matrix (PVDF) and nano filler spinel phase of the incorporated nano-ceramics. The observed SEM micrographs confirm that the nanoparticles are well distributed in the PVDF matrix without any agglomeration with a lesser spherulitic microstructure. The flexible nano-composites fabricated with polymer (PVDF) and CoFe2O4 provide high permittivity (relative dielectric constant) and low loss tangent. An impedance spectroscopy (IS) technique was employed to study the effect of grain and grain boundary in the resistive properties of the composite materials in terms of electric circuit. The study of AC conductivity as a function of frequency follows Jonscher’s power law. The improved conductivity and dielectric, magnetic, and measured first-order magnetoelectric coefficients suggest some promising applications in the embedded capacitors as well as in multifunctional devices.