Radheshyam Rai

Investigation of dielectric and electrical properties of Mn doped sodium potassium niobate ceramic system using impedance spectroscopy

A single perovskite phase formation of polycrystalline samples of (Na0.52K0.44Li0.04) (Nb0.86-x Ta0.1Sb0.04Mnx) (where x = 0.00, 0.01, 0.03, and 0.05) here by denoted as NKNLST and Mn doped NKNLST were prepared by mixed oxide method. The preliminary structural studies were carried out by x-ray diffraction technique showing the formation of single perovskite phase with orthorhombic symmetry for all compositions. Addition of Mn in NKNLST system lowered the sintering temperature by 75 °C. Detail study of impedance parameters shows the non-Debye temperature of relaxation phenomena in the system. This analysis enables us to separate grain and grain boundary contribution of the materials. Above the ferroelectric–paraelectric phase transition temperature, the electrical conduction is governed by the thermal excitation of carriers from oxygen vacancies exhibiting Negative temperature coefficient (NTCR) behaviour.

Impedance and Modulus Spectroscopy Characterization of Tb modified Bi0.8A0.1Pb0.1Fe0.9Ti0.1O3 Ceramics

In this paper we present the impedance spectroscopy of ternary solid solutions of BiFeO3, TbFeO3 and PbTiO3, prepared by solid-state reaction method. The preliminary structural studies were carried out by x-ray diffraction technique, showing the formation of polycrystalline sample with ABO3 type of perovskite structure with hexagonal symmetry for Bi0.8Tb0.1Pb0.1Fe0.9Ti0.1O3system at room temperature. Dielectric and impedance study of this ceramic has been characterized in the temperature range 175 - 325 0C and frequency range 100 Hz - 1 MHz. The maximum ferroelectric transition temperature (Tc) of this system was in the range 210 - 225 0C with the dielectric constant having maximum value ~2480 at 1 kHz. The complex impedance graph exhibited one impedance semicircle arc at all reported temperatures, which indicates that the impedance response is a Cole-Cole type relaxation. Single semicircle indicate that the grain effect of the bulk in ceramic. The bulk resistance of the material decreases with increasing temperature showing negative temperature showing a typical semiconducting property, i.e. negative temperature coefficient of resistance (NTCR) behavior.

IMPEDANCE AND MODULUS SPECTROSCOPY CHARACTERIZATION OF SODIUM-BISMUTH TITANATE-BASED LEAD-FREE FERROELECTRIC MATERIALS

In this paper, we present impedance spectroscopy of Sodium Bismuth Titanate-based materials belonging to (1-x)Na1/2Bi1/2TiO3-xBaTiO3(x = 0.04) (NBT–BT) system. NBT–BT ceramics are prepared by high temperature solid-state reaction method. X-ray diffraction technique showed single-phase polycrystalline sample with an ABO3 perovskite structure. Dielectric behavior and the impedance relaxation were investigated in a wide range of temperature (room temperature (RT) –500°C) and frequency (1 kHz–1 MHz). A broad dielectric constant peak was observed over a wide temperature range around the phase transition temperature. The complex impedance plot exhibited one impedance semicircle identified over the frequency range of 1 kHz–1 MHz, which is explained by the grain effect of the bulk. The centers of the impedance semicircles lie below the real axis, which indicates that the impedance response is a Cole–Cole type relaxation.

Review: hydrothermal technology for smart materials

In broad terms, hydrothermal synthesis is a technology for crystallising materials (chemical compounds) directly from aqueous solution by adept control of thermodynamic variables (temperature, pressure and composition). The objective of this review is to introduce the field of hydrothermal materials synthesis and show how understanding solution thermodynamics of the aqueous medium can be used for engineering hydrothermal crystallisation processes. In this review, powder synthesis, and their applications are introduced. In Section ‘Introduction’, we will focus on the hydrothermal synthesis as a materials synthesis technology by providing history, process definitions, technological merits and comments on its current implementation in the laboratory. In Section ‘Scope of hydrothermal synthesis in future’, we will describe the development of hydrothermal technology for materials synthesis, their results and comparison with other methods.

Synthesis and physical properties of Ca- and Ta-modified (K,Na)NbO3 lead-free piezoelectric ceramics

Polycrystalline samples of lead-free Ca and Ta co-substituted potassium sodium niobate (K0.5Na0.5NbO3, KNN) ceramics have been prepared by solid state reaction technique. X-ray diffraction showed formation of a single-phase perovskite structure with orthorhombic symmetry. Substitution inhibits the grain growth, improves densification and decreases the ferro-paraelectric phase transition temperature. Temperature dependent dielectric permittivity studies demonstrate significant decrease in peak-permittivity values in the substituted samples. Bulk longitudinal piezoelectric coefficient is significantly enhanced, up to ∼155 pC/N for (K0.48Na0.48Ca0.02)(Nb0.85Ta0.15O3) as compared to 95 pC/N for pristine KNN ceramic. Local piezoelectric properties have been observed by piezoresponse force microscopy (PFM) technique. Distinct piezocontrast was studied in both vertical and in-plane modes of PFM for all samples. The samples exhibit self-polarization effect in the unpoled state and effective local vertical piezoelectric coefficient was the largest in Ca and Ta co-substituted sample whereas the in-plane piezoelectric coefficient was maximum for Ca-substituted KNN sample. These studies are important for using substituted lead free KNN materials in various piezoelectric applications.

Structural and dielectric properties of Pb0.9(La1−ySby)0.1(Zr0.65Ti0.35)0.975O3 ferroelectric ceramics

A binary solid solution of Pb0.9(La1−ySby)0.1(Zr0.65Ti0.35)0.975O3 (PLSZT) was synthesized by a high-temperature solid-state reaction method, near the morphotropic phase boundary (MPB). Detailed studies of the dielectric permittivity (e) and loss tangent (tanδ) of PLSZT ceramics as a function of temperature (30–400 °C) at 10 kHz suggest that the compounds exhibit a phase transition of diffuse type. The transition temperature (Tc) is found to increase with an increase in Sb concentration. The activation energy (DC and AC) of PLSZT was found to be very small (<0.1 eV), which is comparable to other ferroelectric oxides of the family. The decrease of DC resistivity of PLSZT with an increase in temperature suggests a negative temperature coefficient resistance (NTCR) behavior of the compound.

Structural and Electrical Properties of Magnesium Tellurite Ceramics

Polycrystalline samples of MgTeO 3 were prepared by a conventional solid-state reaction technique at 750°C. An X-ray powder diffraction (XRD) technique was used to check the formation of a single phase MgTeO 3 compound with cell parameters a = 4.421(1) Å, b = 14.916(1) Å and c = 12.289(1) Å in an orthorhombic crystal system. Detailed studies of dielectric and electrical properties show that the compound has a sharp ferroelectric phase transition of first order.

Dielectric relaxation and ac conduction in multiferroic Bi0.8Gd0.1Pb0.1Fe0.9Ti0.1O3 ceramics: impedance spectroscopy analysis

ABSTRACT The solid solutions of Bi0.8Gd0.1Pb0.1Fe0.9Ti0.1O3 have been prepared by the solid-state reaction method. The preliminary structural studies were carried out by X-ray diffraction technique showing the formation of polycrystalline sample with ABO3 type of perovskite structure with hexagonal symmetry for the Bi0.8Gd0.1Pb0.1Fe0.9Ti0.1O3 ceramic system at room temperature. Dielectric properties and impedance study of this ceramic have been characterized in the temperature range room temperature to 375 °C and frequency range 100 Hz–1 MHz. The maximum ferroelectric transition temperature (Tc) of this system was in the range 200 °C–260 °C with the dielectric constant of peak to be ∼30,170 at 1 kHz. The complex impedance plot exhibited one impedance semicircle observed at low temperature, whereas two semicircles above 80 °C and the centres of the semicircles lie below the real axis, which indicates that the material is non-Debye type. Single semicircle is explained by the grain effect of the bulk and double semicircle is due to the bulk and grain boundary effect. The bulk resistance and grain boundary resistance of the materials decrease with the increasing temperature, showing negative temperature and a typical semiconducting property, i.e. negative temperature coefficient of resistance behaviour.

Study of the structural and electrical behavior of Bi(Mg,Ti)O3 modified (Ba,Ca)TiO3 ceramics

The ability of BaTiO3 to form solid solutions with different dopants (both iso- and aliovalent) makes it versatile for various applications. In the present study, (Ba,Ca)TiO3 (BCT) is modified with Bi(MgTi)O3 (BMT) in search for new lead-free ferroelectric material and improve their properties. For this purpose, BCT acts as a main base material and BMT acts as a modifier to fabricate a multifunctional material. In this study, we report the structural and electrical properties of lead free piezo-ceramics (1−x)(Ba0.8Ca0.2)TiO3–xBi(Mg0.5Ti0.5)O3 with x=0.2, 0.4, 0.5 prepared by solid-state sintering technique. Single perovskite phase with tetragonal structure is obtained for all the compositions, which is reconfirmed by the Raman Spectroscopic study. Dielectric study confirm the temperature stable behavior of the dielectric permittivity values above 300∘C. The dielectric constant value decreases with increase in BMT doping content. Impedance Spectroscopic study confirms non-Debye type dielectric relaxation in the specimen. The Nyquist plot and conductivity studies show the negative temperature coefficient of resistance behavior (NTCR) of the samples.

Study the Structural and Dielectric Properties of Rare-Earth La Doped (Ba1-xLax) (Ti0.815Mn0.0025Nb0.0025Zr0.18)0.995O3 Ceramics

The ferroelectric La doped (Ba1-xLax) (Ti0.815Mn0.0025Nb0.0025Zr0.18)0.995O3 (BLTMNZ) (where x = 0.04, 0.10 and 0.20) ceramics were prepared by using the solid state reaction method. The powders in the suitable stoichiometric ratio of the compositions were weighed and mixed thoroughly in acetone and calcined at 900°C for 12h in high temperature muffle furnace. Phase identification of ceramics was carried out in 2θ range of 20°-60° using X-ray diffraction technique. XRD pattern of the samples indicated that the compositions have an orthorhombic structure at room temperature. The average crystallite size of the BLTMNZ particle was found near 30nm. The ferroelectric phase-transition of BLTMNZ materials was studied by using dielectric measurements at different temperature. Dielectric constant and tanδ of the specimens was measured in the temperature range from 23°C to200°C at frequencies 1 kHz-1 MHz. The temperature dependence of dielectric measurement of lanthanum doped BLTMNZ samples indicate that the phase transition shifts towards low temperature with increasing La content. The value of diffusivity (γ) indicates that the compounds exhibit a diffuse type of phase transition. The ac conductivity was decreases with the increasing the frequency.