N. Ramamanohar Reddy

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.

Effect of Temperature on the Elastic and Anelastic Behaviour of Magneto-Ferroelectric Composites Ba0.8Pb0.2TiO3 + Ni0.93Co0.02Mn0.05Fe1.95O4-δ in the Ferroelectric Rich Region

Composites with composition xBa0.8Pb0.2TiO3+ (1 −x) Ni0.93Co0.02Mn0.05Fe1.95O4-δ in which x varies as 1.0, 0.9, 0.7 and 0.5 in molar percent have been prepared by the conventional ceramic double sintering process. The presence of the two phases has been confirmed by X-ray diffraction. These composites were prepared for their use as magnetoferrolectric devices. Variation of longitudinal modulus (L) and internal friction loss (Q−1) of these samples with temperature at 142 kHz has been studied in the wide temperature range 300 to 630 K. The elastic behaviour (L) showed a break at the ferroelectric Curie temperature (498 K) in the case of pure ferroelectric material (Ba0.8Pb0.2TiO3). This break shifted to lower temperature side as the ferrite component increases in the composite. The temperature variation of internal friction loss (Q−1) showed a corresponding stress induced relaxation peak at the ferroelectric-non-ferroelectric phase transition. This behaviour is explained in the light of structural phase transition.

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.

Nanocrystalline Pb(Zr 0.52 Ti 0.48 )O 3 ferroelectric ceramics: mechanical and electrical properties

Nanocrystalline powders of the composition Pb(Zr0.52Ti0.48)O3 were obtained by Mechanical alloying (high-energy ball milling). X-ray diffraction studies show that these compounds are completely into the perovskite phase. Detailed studies of electrical and mechanical properties of PZT as a function of temperature (and frequency) showed the high permittivity of 20653 at Curie transition temperature. Temperature variation of longitudinal modulus and internal friction of these ceramics at 104 kHz frequency were studied in the wide temperature range of 30°C-420°C. The internal friction measurements showed sharp stress induced relaxation peaks in the present composition corresponding to those temperatures where the minima were noticed in temperature variation of longitudinal modulus behavior. This dielectric and internal friction behaviour was explained in the light of polaron hopping mechanism and structural phase transitions in the present piezoelectric compositions.

Microwave sintering of high-permeability MgCuZn ferrite at low sintering temperatures suitable for microinductor applications

Mg0.40Cu0.10Zn0.50Fe1.95O4-? ferrite samples were prepared by the microwave sintering (MS) and conventional sintering (CS) techniques. The samples were then characterized by the x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS) techniques. All the compositions showed single-phase cubic spinel structure. The lattice constants of MS samples were found to have lower magnitude than those of CS samples. The densities of microwave-sintered samples were higher than those of conventionally sintered samples. The temperature dependence of initial permeability was studied in the temperature range 30?150??C at 10? temperature intervals. It was noted that the initial permeability of MgCuZn ferrites prepared by the MS method was higher than that of MgCuZn ferrites prepared by the CS method. The initial permeability (?i) magnitude of about 2300 at 10?kHz is achieved for microwave-sintered (Mg0.40Cu0.10Zn0.50Fe1.95O4??) ferrite, at only 950??C sintering temperature. In addition, the sintering time of ferrites was reduced from 5?h to 20?min by using the MS technique. The low-temperature-sintered MgCuZn ferrites prepared possess good electromagnetic properties, as well as good microstructure, thus making them suitable materials for multilayer chip inductors (MLCIs) having high performance and low cost.

Internal friction and dielectric permittivity studies: barium lead titanate ferroelectric ceramics

Barium titanate (BT) has become one of the most important electroceramics since the discovery of its varied applications. Because of these important applications, there has been a great deal of interest in both the fabrication and the electrical properties of modified BT-based ceramics. Ba0.8Pb0.2TiO3 (BPT) ferroelectric ceramic was prepared by the conventional ceramic method. X-ray diffraction and SEM confirmed single-phase BPT. Temperature variations of dielectric constant, dielectric loss, longitudinal modulus and internal friction were measured. The electrical properties of BT-based ceramics depend strongly on both microstructure and composition. Dielectric properties and mechanical properties have been discussed in relation to phase transitions.

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.

Mechanical properties of Ni0.83Co0.15Cu0.02Fe1.9O4-δ+PbZr0.52Ti0.48O3 particulate composites by composite oscillator technique and the correlation with the results of magnetoelectric properties

The xNi0.83Co0.15Cu0.02Fe1.9O4−δ (NCCF) + (1−x)PbZr0.52Ti0.48O3 (PZT) particulate magneto ferroelectric composites with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mole fraction were prepared by conventional ceramic double sintering method. The presence of two phases (perovskite structure of ferroelectric phase and spinal structure of ferromagnetic phase) was confirmed by X-ray diffraction. The magnetoelectric (ME) property of the particulate composites was determined at room temperature as a function of intensity of magnetic field. The temperature variation of the longitudinal modulus (L) and the internal friction (Q−1) of these particulate composites at 104.3 kHz was studied in the wide temperature range 30–420 °C. The temperature variation of the longitudinal modulus 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 ferromagnetic-paramagnetic Curie transition temperature (θM). The internal friction measurement 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.

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.