M. Venkata Ramana

SYNTHESIS OF LEAD FREE SODIUM BISMUTH TITANATE (NBT) CERAMIC BY CONVENTIONAL AND MICROWAVE SINTERING METHODS

Dielectric studies were carried out on a lead free Sodium Bismuth Titanate, NBT, (Na0.5Bi0.5TiO3) composition. The material was synthesized by conventional ceramic method (CS) and microwave sintering (MS). The presence of single phase has been confirmed by X-ray diffraction and scanning electron microscopy of NBT ceramic. The later technique (MS) resulted in material with high density, dielectric properties and improved microstructure. The transition temperature was observed slightly higher for microwave sintered (MS) material. Longitudinal modulus measurements are very sensitive property to identify the phase transitions in ceramics. Longitudinal modulus (L) measurements were also employed on these samples in the frequency 136 kHz and can be studied in the wide temperature range 30°C to 400°C. The elastic behavior (L) showed a break at two temperatures (~200°C and 350°C) in both the conventional and microwave sintered ceramics. In NBT ceramics, permittivity anomalies are connected to modulus anomalies. The results are correlated with the dielectric measurements. This behavior explained in the light of structural phase transitions in the ferroelectric ceramics.

Ferromagnetic-Dielectric Ni 0.5 Zn 0.5 Fe 1.9 O 4−δ /PbZr 0.52 Ti 0.48 O 3 Particulate Composites: Electric, Magnetic, Mechanical, and Electromagnetic Properties

Novel ferromagnetic-dielectric particulate composites of Ni0.5Zn0.5Fe1.95O4−δ (NZF) and PbZr0.52Ti0.48O3 (PZT) were prepared by conventional ceramic method. The presence of two phases in composites was confirmed by XRD technique. The variations of dielectric constant (𝜀) with frequency in the range of 100 kHz–1 MHz at room temperature and also with temperature at three different frequencies (50 kHz, 100 kHz, and 500 kHz) were studied. Detailed studies on the dielectric properties were done confirming that the magnetoelectric interaction between the constituent phases may result in various anomalies in the dielectric behaviour of the composites. It is proposed that interfaces play an important role in the dielectric properties, causing space charge effects and Maxwell-Wagner relaxation, particularly at low frequencies and high temperatures. The piezoelectric d33 constant was studied at room temperature, and the d33 constant value decreased with ferrite content. Magnetic properties like B-H loops traces were studied to understand the saturation magnetic (Ms) and magnetic moment (𝜇𝐵) of the present particulate composites. The magnetoelectric (ME) output was measured by varying dc bias magnetic field. A large ME output signal of 2780 mV/cm Oe was observed in the composite having 50% ferrite. The temperature variation of longitudinal modulus (L) and internal friction (Q−1) of these particulate composites at 104 kHz was studied in the temperature range 30°C–420°C by the composite oscillator technique. Longitudinal modulus showed a sharp minimum, and internal friction exhibits a sharp peak at ferroelectric-paraelectric phase transition. These ferroelectric-dielectric particulate composites were prepared with a view to using them as ME sensors and transducers.

Internal friction and longitudinal modulus behaviour of multiferroic PbZr0.52Ti0.48O3+Ni0.93Co0.02Mn0.05Fe1.95O4−δ particulate composites

Multiferroic particulate composites with composition xNi0.93Co0.02Mn0.5Fe1.95O4−δ + (1 − x)PbZr0.52Ti0.48O3 where the molar fraction x varies as 0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by the conventional ceramic method. The presence of two phases was confirmed by x-ray diffraction and scanning electron microscopy. The temperature variation of the longitudinal modulus (L) and the internal friction (Q−1) of these particulate composites at 104.387 kHz was studied in the wide temperature range 30–420 °C. The temperature variation of the longitudinal modulus (L) in each composition of these particulate composites showed two abrupt minima. One minimum coincided with the ferroelectric–paraelectric Curie transition temperature (θE) and the other with the ferrimagnetic–paramagnetic Curie transition (θM) temperature. The internal friction (Q−1) measurements also showed two sharp peaks in each composition corresponding to those temperatures where the minima were noticed in the temperature variation of the longitudinal modulus behaviour. The Curie transition temperature of pure ferrite was found to be 560 °C. Addition of 10% of ferrite to ferroelectric in a magnetoelectric (ME) composite resulted in a 360 °C fall in θM and with a further increase in ferrite content the θM variation was found to be very nominal. However, no significant ferroelectric Curie transition temperature shift could be noticed. This behaviour is explained in the light of structural phase transitions in these multiferroic particulate composites. These ME composites were prepared with a view to using them as ME sensors and transducers.

Possibility of NiCuZn Ferrites Composition for Stress Sensor Applications

NiCuZn ferrite with composition of (NCu0.10Zn0.60F) (where , 0.02, 0.04, 0.06, 0.08, and 0.10) was prepared by the conventional ceramic double sintering technique. The formation of single phase was confirmed by X-ray diffraction. The microstructural features were also studied by electronic microscopy and are reported. Initial permeability measurements on these samples were carried out in the temperature range of 30 to 300°C. The effect of external applied stress on the open magnetic circuit type coil with these ferrite cores was studied by applying uniaxial compressive stress parallel to the magnetizing direction and the change in the inductance was measured. The variation of inductance (ΔL/L)% increases up to certain applied compressive stress and there after it decreases, showing different stress sensitivities for different compositions of ferrites studied in the present work. The variation of ratio of inductance (ΔL/L)% with external applied compressive stress was examined. These results show that the Ni0.42Cu0.10Zn0.60Fe1.76O3.76 and Ni0.44Cu0.10Zn0.60Fe1.72O3.72 samples are found to be suitable for inductive stress sensor applications.

Effects of sintering temperature on structural and electromagnetic properties of MgCuZn ferrite prepared by microwave sintering

Abstract Nanocrystalline magnesium–copper–zinc (Mg0.30Cu0.20Zn0.50Fe2O4) ferrites were prepared by microwave sintering technique. The effects of the sintering temperature on particle size and magnetic properties were investigated. In this article, optimum sintering temperature required for MgCuZn ferrite system for obtaining good electromagnetic properties, suitable for applications in low temperature co-fired ceramics (LTCC) chip components was studied. The grain size, initial permeability, dielectric constant and saturation magnetisations were found to increase, and dielectric loss was found to decrease with the increasing sintering temperature. Mg–Cu–Zn ferrites with a permeability of μ = 1110 (at 1 MHz) were fully densified at the standard LTCC sintering temperature of 950°C.

Influence of Magnesium Substitution on Thermal and Electrical Properties of NiCuZn Ferrites for Microinductor Core Applications

Two series of NiMgCuZn ferrites, that is, (1) NixMg0.6−xCu0.1Zn0.3Fe2O4 and sample G: Ni0.3Mg0.3−yCu0.1Zn0.5−yFe2O4 with , 0.1, 0.2, 0.3 and (2) NixMg0.6−xCu0.1Zn0.3Fe2O4 with , 0.1, 0.2 were synthesized and prepared by conventional ceramic double-sintering process and to use them as core materials for microinductor applications. The formation of single phase was confirmed by X-ray diffraction. The temperature and compositional variation of DC, AC electrical conductivities (σ) and thermoelectric power were studied on these two series of polycrystalline ferrospinels. The studies were carried out in wide range of temperature from 30 to 350°C. On the basis of thermoelectric study, the ferrites under present work were found to be shown as n-type and p-type transition. The electrical conduction in these ferrospinels is explained in the light of polaron hopping mechanism. These ferrite compositions have been developed for their use as core materials for microinductor applications.

MAGNETO-ELECTRIC EFFECT IN MULTIFERROIC Ni0.93Co0.02Mn0.05Fe1.95O4-δ/PbZr0.52Ti0.48O3 PARTICULATE COMPOSITES: DIELECTRIC, PIEZOELECTRIC PROPERTIES

Magnetoelectric composites have been synthesized by sintering mixtures of highly piezoelectric component Pb(Zr0.52Ti0.48)O3, PZT and highly magnetostrictive piezomagnetic component Ni0.93Co0.02Mn0.05Fe1.95O4-δ, NCMF. These composites with generic formula (1 - x)PZT + xNi0.93Co0.02Mn0.05Fe1.95O4-δ, where x varies as 0.1, 0.3 and 0.5 mole fractions, were prepared from the powders of the pure components by the conventional ceramic route. The presence of two phases in multiferroic was confirmed by XRD technique. The variation of dielectric constant and dissipation factor, as a function of frequency from 100 Hz to 1 MHz and in the temperature range of 30–500°C were studied. The piezoelectric d33 coefficient of these composites was also studied in these composites. The magnetoelectric (ME) output voltage was measured in terms of the dE/dH as a function of magnetic bias field. A high value of ME output (1200 mV/Oe · cm) was obtained in the composite containing 70% ferroelectric phase (PbZr0.52Ti0.48O3) and 30% ferrite phase (Ni0.93Co0.02Mn0.05Fe1.95O4-δ). These multiferroic particulate composites are used as sensors and transducers.