R. Padhee

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, impedance and modulus spectroscopy of Bi2NdTiVO9 ferroelectric ceramics

Detailed studies of electrical and resistive properties of Bi2NdTiVO9 (a member of the Aurivillius family), fabricated by a method of standard high-temperature solid-state reaction, are discussed here. The compound crystallizes in the orthorhombic crystal structure. The surface morphology studies show a uniform distribution of grains. The single semicircle of the complex impedance plot and the value of the nonlinear coefficient of the J∼E graph suggest that the polarization in the material is due to grain effect only. The semiconducting nature (i.e., negative temperature coefficient of resistance) is observed in the temperature dependence of bulk resistance and J–E characteristics of the sample. The frequency dependence of impedance and electrical modulus of the material shows the existence of non Debye-type of relaxation. The activation energy obtained from the relaxation and conduction processes is found to support the activation of oxygen vacancies in the compound. An analysis of ac conductivity, based on the Jonscher’s power law, suggests that the conduction mechanism in the material can be explained using CBH model (i.e., hopping of oxygen ions between vacancies). The nature and existence of electric field dependent polarization (P–E hysteresis loop) at room temperature show that the material has ferroelectric property.

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.

Tailoring of electrical properties of BiFeO 3 by praseodymium

The polycrystalline samples of Bi1−xPrxFeO3 (x = 0 and 0.1) were prepared by a solid-state reaction technique. Preliminary X-ray structural analysis has confirmed the formation of a single-phase compound. Studies of dielectric and impedance spectroscopy of the materials, carried out in wide frequency (1 kHz-1 MHz) and temperature (25–400 °C) ranges, have provided many interesting results including significant decrement in tangent loss, structural stability, obeying Jonscher’s universal power law, etc.

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.

Phase transition in tungsten–bronze Li2Pb2Nd2W2Ti4Nb4O30 ferroelectric

The polycrystalline sample of Li2Pb2Nd2W2Ti4Nb4O30 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 at room temperature. The temperature and frequency dependence of impedance parameters (impedance, modulus, etc.) of the material exhibits a strong correlation of its microstructure (i.e., bulk, grain boundary, etc.). Furthermore, the temperature dependence of DC conductivity shows a typical Arrhenius behavior of the material. The nature of variation of pyroelectric coefficient and current with temperature suggests that material has good pyroelectric properties useful for pyroelectric detector.

Diffuse ferroelectric phase transition in Li2Pb2Dy2W2Ti4V4O30

Tungsten–bronze polycrystalline ceramic Li2Pb2Dy2W2Ti4V4O30 was prepared by mixed-oxide method. The preparation conditions were optimized by thermogravimetry analysis and repeated firing. Room-temperature structural analysis confirms the formation of the compound in single phase (orthorhombic). Studies of dielectric parameters () of the compound with temperature at different frequencies suggest the existence of phase transition in the compound. The existence of ferroelectric property (based on dielectric anomaly) of the material was confirmed by polarization study.

SYNTHESIS AND CHARACTERIZATION OF COMPLEX FERROELECTRIC OXIDE

The polycrystalline sample of Li2Pb2Pr2W2Ti4V4O30 was prepared by a solid-state reaction technique. The preparation conditions of the compound have been optimized using thermal analysis (DTA and TGA) technique. Room temperature structural analysis confirms the formation of single phase compound in orthorhombic crystal system. The surface morphology of the sample, recorded by scanning electron microscope, shows uniform grain distribution on the surface of the sample. The observation of hysteresis loop confirmed that the material has ferroelectric properties at room temperature. Electrical properties of the material were studied by complex impedance spectroscopic technique. Temperature dependence of electrical parameters (impedance, modulus, etc.) is strongly correlated to the micro-structural characteristics (bulk, grain boundary, etc.) of the sample. A typical temperature-dependent resistive characteristic of the sample (i.e., negative temperature coefficient of resistance (NTCR)) exhibits its semiconducting properties. The temperature dependence of dc conductivity shows a typical Arrhenius behavior. A signature of ionic conductivity in the system was observed in ac conductivity spectrum. The sample obeys Jonschers universal power law. The hopping mechanism for electrical transport properties of the system with nonexponential-type conductivity relaxation was suggested from the electrical modulus analysis.