Biswajit Pati

Dielectric and impedance spectroscopy of barium orthovanadate ceramics

Barium orthovanadate (Ba3V2O8), a derivative of perovskite family has been prepared using a mixed-oxide technique. The room temperature X-ray diffraction analysis has confirmed the formation of a single phase compound in trigonal crystal structure. The study of microstructure by scanning electron microscopy shows that the compound has well defined grains, distributed uniformly throughout the surface. The studies of dielectric parameters (εr and tanxa0δ) of the compound as a function of temperature at three different frequencies (100, 500, 1,000xa0kHz) exhibit that they are almost temperature independent at low and medium temperature ranges. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature. It shows that the material has negative temperature co-efficient of resistance similar to that of semiconductors. The same behaviour has also been observed in the study of I–V characteristics of the material. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.

Dielectric and impedance characteristics of Ba(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Ba(Bi0.5Nb0.5)O3 was prepared using a high-temperature mixed oxide technique using high purity ingredients. The formation of the material in monoclinic crystal structure was confirmed by an X-ray structural analysis at room temperature. The nature and texture of microstructure by scanning electron microscopy show that the compound has well defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material, carried out in the frequency range of (1xa0kHz–1xa0MHz) at different temperatures (30xa0°C to 475xa0°C), have shown many interesting properties. Dielectric study showed an existence of diffuse phase transition around 317xa0°C. The temperature dependence of impedance parameters (impedance, modulus etc.) of the material exhibits a strong correlation of its micro-structure (i.e., bulk, grain boundary, etc.) with the electrical parameters. An existence of negative temperature coefficient of resistance (NTCR) type behavior in the material similar to that of semiconductors was also observed. The complex electric modulus analysis indicates the existence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. The temperature dependent pre-exponential factor (A) shows peak and frequency exponent (n) possesses a minimum at transition temperature.

Dielectric and Impedance Spectroscopy of Barium Orthoniobate Ceramic

Barium orthoniobate (Ba3Nb2O8), a derivative of the perovskite family, was prepared using a high-temperature solid-state reaction technique (calcination temperaturexa0=xa01425°C and sintering temperaturexa0=xa01450°C for 4xa0h). Preliminary x-ray structural analysis with room-temperature x-ray diffraction data confirmed the formation of a single-phase compound with hexagonal crystal structure. Study of the microstructure of a gold-coated pellet by scanning electron microscopy (SEM) showed that the sample has well-defined grains that are distributed uniformly throughout the surface of the sample. Detailed studies showed that the dielectric parameters (εr and tanxa0δ) of the compound at three different frequencies (10xa0kHz, 100xa0kHz, and 1000xa0kHz) are almost constant in the low-temperature region (from room temperature to about 200°C). An anomaly in the relative permittivity (εr) (∼357°C) suggests the possible existence of a ferroelectric–paraelectric phase transition of diffuse type in the material. Detailed studies of impedance and related parameters show that the electrical properties of the material are strongly dependent on temperature, showing good correlation with its microstructure. The bulk resistance (evaluated from impedance studies) is found to decrease with increasing temperature. This shows that the material has negative temperature coefficient of resistance (NTCR), similar to that of semiconductors. Studies of electric modulus indicate the presence of a hopping conduction mechanism in the system with nonexponential-type conductivity relaxation. The nature of the variation of the direct-current (dc) conductivity with temperature confirms the Arrhenius and NTCR behavior in the material. The alternating-current (ac) conductivity spectra show a typical signature of an ionic conducting system and are found to obey Jonscher’s universal power law.

Development of Electronic and Electrical Materials from Indian Ilmenite

Some new complex electronic materials have been prepared by mixing bismuth oxide (Bi2O3) and ilmenite in different proportions by weight, using a mixed-oxide technique. Room-temperature x-ray diffraction analysis confirms the formation of a new compound with trigonal (rhombohedral) crystal structure with some secondary phases. Studies of dielectric parameters (εr and tanxa0δ) of these compounds as a function of temperature at different frequencies show that they are almost temperature independent in the low-temperature range. They possess high dielectric constant and relatively small tangent loss even in the high-temperature range. Detailed studies of impedance and related parameters show that the electrical properties of these materials are strongly dependent on temperature, showing good correlation with their microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to decrease with increasing temperature. Thus, these materials show negative temperature coefficient of resistance (NTCR)-type behavior similar to that of semiconductors. The same has also been observed from their I–V characteristics. Complex electric modulus analysis indicates the possibility of a hopping conduction mechanism in these systems with nonexponential-type conductivity relaxation. The nature of the variation of the direct-current (dc) conductivity with temperature confirms the Arrhenius behavior of these materials. The alternating-current (ac) conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.

Pyroelectric Response and Conduction Mechanism in Highly Crystallized Ferroelectric Sr3(VO4)2 Ceramic

We present a study on the ferroelectric phase transition, pyroelectric properties, and conduction mechanism of highly crystallized strontium orthovanadate (Sr3V2O8) ceramic, prepared by a solid-state reaction technique. X-ray diffraction studies show the formation of a single-phase compound in trigonal crystal system. Detailed studies of dielectric parameters (εr and tanxa0δ) of the compound as a function of temperature and frequency reveal their independence over a wide range of temperature and frequency. An anomaly in εr suggests the possible existence of a ferroelectric–paraelectric phase transition of diffuse type in the material, which is confirmed by electric polarization and pyroelectric studies. The low dielectric loss and moderate relative permittivity make this material (with suitable modifications) a potential candidate for use in microwave applications. The low leakage current and negative temperature coefficient of resistance (NTCR) behavior of the sample have been verified from J–E plots. The nature of the variation of the direct-current (DC) conductivity with temperature confirms the Arrhenius and NTCR behavior of the material.

Development of electronic materials from industrial waste red mud

The current research work presents the preparation and characterization of some new electronic materials using bismuth oxide (Bi2O3) and industrial waste red mud in different proportion by weight using a cost-effective mixed-oxide technique. Preliminary X-ray structural analysis exhibits the formation of compounds with structure analogous to that of BiFeO3 compound along with some impurity phases. Studies of dielectric parameters (εr and tanδ) of these compounds as a function of temperature and frequency exhibit that they are almost temperature independent in the low temperature range and possess high relative permittivity with low loss in the high temperature range. Detailed studies of impedance and related parameters exhibit that the electrical properties of these materials are strongly dependent on temperature, and bear a good correlation with their microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR)—type behavior similar to that of semiconductors. Studies of electric modulus indicate the presence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The low leakage current and NTCR behavior of the sample have been verified from I–V characteristics. The nature of variation of dc conductivity with temperature confirms the Arrhenius and NTCR behavior in the material. The ac conductivity spectra show a typical-signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.

Structural and Electrical Properties of Complex Tungsten Bronze Ferroelectrics; Li2Pb2La2W2Ti4V4O30

The polycrystalline sample of a new tungsten bronze ferroelectric vanadate, Li2Pb2La2W2Ti4V4O30, was prepared at a relatively low temperature using a mixed-oxide technique. The formation of the material under the reported conditions has been confirmed by an X-ray diffraction technique. A preliminary structural analysis exhibits orthorhombic crystal structure of the material at room temperature. Studies of dielectric properties (ϵ, tanδ) of the above compound as a function of temperature (273–600K) at frequencies 10, 100, 1000 KHz exhibits a ferroelectric phase transition of diffuse type. The electrical properties of the material have been studied using ac impedance spectroscopy technique. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructures. The temperature dependence of electrical relaxation phenomenon in the materials has been observed. The bulk resistance, evaluated from complex impedance spectra, is found to decrease with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR) –type behavior similar to that of semiconductors. A small contribution of grain boundary effect was also observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The ac conductivity spectra exhibit a typical signature of an ionic conducting system, and are found to obey Jonschers universal power law.

Studies on structural and electrical properties in highly crystallized lead-free ferroelectric Ba(Bi0.5Ta0.5)O3

ABSTRACT A lead free polycrystalline material Ba(Bi0.5Ta0.5)O3 was prepared by a standard mixed oxide method using high-purity precursor materials. A preliminary X-ray diffraction study confirmed the formation of a single-phase material, crystallized in monoclinic phase and homogeneous morphology for the sample. The dielectric properties (ϵr and tanδ) have been studied for a wide range of temperature at some selected frequencies. The temperature dependence of relative permittivity suggests that the material may exhibit ferroelectricity of diffuse type around 315°C. The frequency dependence of ac conductivity follows the Jonschers power lawreveals the material exhibit NTCR behavior similar to that of a semiconductor.

Dielectric response and pyroelectric properties of lead-free ferroelectric Ba3(VO4)2

The current paper presents results of dielectric response, pyroelectric behavior and conductivity study of lead-free ferroelectric barium orthovanadate (Ba3(VO4)2 or Ba3V2O8) ceramic, for a wide range of temperature and frequency. An X-ray diffraction study suggests the formation of a single-phase compound in trigonal crystal system. The SEM micrograph of gold-coated pellet sample shows well-defined and homogeneous morphology. Detailed studies of dielectric parameters (er and tan δ) of the compound as a function of temperature and frequency reveal their independence over a wide range of temperature and frequency. The nature of Polarization versus electric field (P–E) hysteresis loop of Ba3V2O8 at room temperature suggests its ferroelectric nature. The temperature dependence of pyroelectric coefficient and figure of merits of the sample support its dielectric response. The nature of variation of dc conductivity with temperature confirms the Arrhenius and negative temperature coefficient of resistance (NTCR) behavior of the material.