Shibendra Shekher Sikder, Department of Physics, Khulna University of Engineering & Technology (KUET), Khulna, for considering me as a thesis student. Joly Sultana, Department of Physics, KUET, for his cooperation and inspiration during this work.
CHAPTER-IV
RESULTS AND DISCUSSION
CHAPTER-V CONCLUSIONS
List of Symbols
INTRODUCTION
- Introduction
- Motivation
- The Aims and Objectives of the Present Work
- Experimental Reason for this Research Work
- Background of Material Selection: Literature Review
- Europium Doped Bismuth Ferrite (BEFO)
- Nickel Zinc Ferrite (NZF)
- BEFO-NZF Multiferroic Composites
- Outline of the Thesis
Multiferroic composites will be prepared with very pure materials using the conventional solid state reaction method with various dispersion techniques. It is expected that the explored compounds will have large electrical polarization and magnetization with small losses at room temperature and will be useful applications.
Introduction
Recently, many researchers have reported the structural, magnetic, and electrical properties of NZF and/or substituted NZF in bulk and nanoforms. 1.55] in her work, successfully prepared perovskite-spinel di-phase BFO-NZF and Mn doped BMFO-NZF composites and reported that BMFO-NZF composite was effective in reducing the conductivity, dielectric losses and also improving impedance properties.
Theoretical Background
Experimental Procedure
Results and Discussion
Conclusions
THEROETICAL BACKGROUND
Overview of Multiferroic
A ferroic material is essentially a material that exhibits one of the three ferroic orders (currently expanded to four): ferroelectricity, ferromagnetism, ferroelasticity, or ferrotoroidicity. Multiferroics are a class of unique functional materials that exhibit two or more of the above ordering mechanisms and have attracted considerable interest due to the coexistence of at least two switchable states (e.g., polarization, magnetization, and strain), i which promises a wide range of applications in multifunctional devices.
THEORETICAL BACKGROUND
Overview of Multiferroic
Types of Multiferroic
- Single-phase Multiferroic Material
- Multiferroic Composites Material
In composite materials the ME effect. product property' of the two phases in the composite and was first proposed by This effect in composites is due to the strain induced in the ferrite. The product property is more interesting, which is absent in individual phases effect comes as it was first proposed by This effect in composites is due to the strain induced in the ferrite.
Spinel Ferrite and Its Structure
Many bulk ME composites have been found to exhibit such strain-mediated ME effect above room temperature.
Perovskite Structure
Perovskite Structure
Perovskite BiFeO
Perovskite BiFeO 3
Piezoelectrics
- Ferroelectric
Ferroelectricity is a phenomenon that refers to the state of spontaneous polarization, i.e. the polarization of the material v.
Piezoelectrics
Ferroelectricity and Ferroelectric Materials
Dielectrics
- Dielectric Polarization
Dielectrics are basically electrical insulators that usually do not contain any free charge carriers for conduction, but. The material is said to be polarized with a polarization defined as the dipole moment per volume unit of the material. When a dielectric is placed in an external electric field, it becomes polarized and creates an internal electric field in the opposite direction, reducing the total field.
Dielectric Polarization
Dielectric Constant
The dielectric constant is defined as the ratio of the capacitance of a capacitor filled with a given dielectric to the capacitance of the same capacitor with a vacuum. The electrical susceptibility χ of a dielectric material is a measure of the polarization produced in the material per unit of resultant electric field. This, in turn, determines the electrical permeability of the material and thus affects many other phenomena in this medium.
- Dependence of Dielectric Constant on Frequency
- Dielectric loss
- Temperature Dependence of Resistivity
- Methodology of Nanostructured Multiferroic Composites Preparation
- Aspects of Present Work
- Problems with Conventional Methods
- Reason of Using Oxide Materials
- Selection of Raw Materials
- Weighing the Raw Materials at Precise Ratio
- Mixed and Milled the Samples (Hand Milling)
- Stirred the Samples in Magnetic S
Therefore, the dielectric constant can also be defined as the ratio between the permittivity of a substance and the permittivity of free space. Therefore, the polarization mechanism of a system depends on the frequency of the applied electric field. The dielectric constant (ε') is a measure of the polarization of a system and also depends on the frequency of the applied field.
Further Dispersion by Ultrasonicator
As it contracts, the negative pressure causes the fluid to rise, and as it expands, it pushes the fluid. The voids form and collapse in microseconds, releasing enormous energy into the liquid, causing their molecules to break apart [3.3]. The water level should be as high as the solution or to cover the maximum part of the solution.
- Centrifugation
- Drying the Samples in a Microwave Oven
- Pressing to Desire Shapes
- Annealing
- Sintering
- X-ray Diffraction (XRD)
At a fixed centrifugal force, the sedimentation rate is proportional to the particle size and to the difference between the particle density and the density of the solution [3.4]. The effect of high rpm caused the solid particles to settle at the bottom of the tube and the. Removal of the pressing lubricant by evaporation and combustion of the vapors Reduction of the surface oxides of the powder particles in the compact.
Different Parts of the PHILIPS X’Pert PRO XRD System
The wavelength of the X-rays used is (λ = 1.5418 Å) and is of the same order of magnitude as that of the lattice constant of crystals, and this is what makes it so useful in structural analysis of crystal structure.
Interpretation of the XRD Data
Where λ is the wavelength of X-ray radiation, θ is the diffraction angle, and n is an integer representing the order of diffraction, and h, k, l are the Miller indices. It shows that the angle increases with (h2 + k2 + l2) and higher order Miller indices result in wider diffraction angles. Bragg's law for cubic crystals in equation (iv) is a necessary but not sufficient diffraction condition because diffraction involves the interaction of EM waves with electrons in the crystals.
X-ray Density and Bulk Density
If reflections are present only when h and k are unmixed, or when k and are unmixed, then the cell is centered on the B or A face, respectively. Table-3.2 shows the conditions for presence and absence of peaks from different planes in cubic crystal structures [3.8].
Porosity
Crystalline Size
Where, D is the average crystal domain size, which may be less than or equal to the grain size.
Field Emission Scanning Electron Microscope (FESEM)
Vibrating Sample Magnetometer (VSM)
The working principle of VSM is the measurement of the electromotive force induced by a magnetic sample when it is vibrated at a constant frequency in the presence of a static and uniform magnetic field. It is then vibrated sinusoidally, creating a corresponding vibration of the magnetic flux in the pickup coils nearby and inducing a sinusoidal voltage. A small part of the samples (9 -11 mg) was used and was made to avoid movements inside the sample container.
Frequency Characterization of the Present Samples
- Electric and Dielectric Measurements
- Complex Permeability Measurements
- Impedance Analysis
The magnitude of the complex impedance is the ratio of the voltage amplitude to the current amplitude. L0 is the inductance of the circuit is the real and imaginary part of the complex permeability. The real and imaginary part of impedance with resistance variance polar form of the complex.
X-ray Diffraction Analysis
- The Perovskite BEFO Phase
- The Cubic NZF Phase
- The Composite Phase
The most prominent (311) peak is found in superstructural form as shown in figure 4.1 which refers to the undeformed lattice structure of the NZF phase. The intensity and number of the XRD peaks of the parent phases in the composites depend on the amount of corresponding phases in the composites. It can be noted from the figure 4.2 that the intensity of the peaks corresponding to ferrite phase increases with increasing ferrite composition while that of the perovskite peaks decreases.
Confirmation of Nanostructure
- Study of Microstructure and Morphology with the Variation of Annealing Temperature
The average grain size of the composites was calculated using imageJ software and is shown in Table-4.4. Again, it is expected that the grain size of the composites will decrease with increasing NZF content. This can be attributed to the secondary phase formed in the BEFO phase as shown in the XRD spectra.
Measurement of Ferromagnetic Effect on Multiferroic
The resulting magnetization is therefore the difference between the magnetization of the octahedral lattice (B) and that of the tetrahedral lattice (A). It is seen that the saturation magnetization M of the composite increases with the increase of NZF component and closely follows the rule of mixtures expressed as The spontaneous magnetization of the composites originates from the unbalanced anti-parallel spins leading to the net spins [4.17].
Study of the Frequency Dependent Complex Permeability
In the inset of figure 4.7, it can be seen that the hysteresis curves of the samples have been shifted to the right from the origin and are attributed to the exchange bias effect. So it was expected that the magnetic permeability of the composites should increase with the increase of NZF content. These increased eddy currents shield the inside of the sample from the applied field and therefore increased the loss tangent [4.22].
Study of the Frequency Dependent Dielectric Properties
It has been found that the resistivity decreases with the increase in frequency (f) of the applied alternating current. A relatively lower resistivity is observed for x = 0.0 and can be attributed to the ferroelectric nature of the BEFO content, but the lowest resistivity is. In x = 0.1, the intergranular gap is minimum, so the grains can be easily shorted and the electrical conductivity can increase, which in turn decreases the resistance.
Finding the Optimum Value
From figure 4.17 it can be seen that both the dielectric and magnetic loss tangents have become minimal for the mass fraction x = 0.1. Therefore, based on the above discussion, for the mass fraction x = 0.1, the composite shows the most magneto-electrical and multiferroic coupling properties.
CONCLUSIONS
Conclusions
The following conclusions follow from the systematic investigation of crystallization, structural and magnetic properties: i) XRD patterns of the prepared samples confirm the successful formation of the rhombohedrally distorted perovskite BEFO phase and the cubic spinel NZF phase. The purity of the composition of the prepared samples was verified by EDS spectra and confirms the presence of distinct elements on the composites. iv). ε' exhibits excellent frequency stability in the high-frequency range due to the inability of electric dipoles to follow rapid changes in the alternating applied electric field.
Scope for Future Work
An enhanced magnetization is observed in BEFO than the pure BFO and can be attributed to the magnetically active Eu doping. So from this result, it can be easily concluded that the optimal multiferroic parameters can be obtained from the composition of x = 0.1. ii) Polarization versus electric field P-E loop measurement can be performed to know the ferroelectric behavior of the studied composites. iii). Magnetoelectric coefficient can be measured to understand its degree of multiferroic behavior. iv) Neutron diffraction analysis can be performed for the present compositions to obtain the distribution of the substituted ions between the A and B sites. v) Mӧssbaurer spectroscopy can be performed to know the cation distribution in the A and B sites and to have information about the valence state of the ions. we).
1.31] Dai H., Li T.; Xue R.; Chen Z.; "Effects of Europium Substitution on the Microstructure and Electrical Properties of Bismuth Ferrite Ceramics." J. S.; "Impedance spectroscopy and dielectric properties of multiferroic BiFeO3/Bi0.95Mn0.05FeO3 - Ni0.5Zn0.5Fe2O4 composites", Ceram. Kumar et al.; "Influence of Eu substitution on structural, magnetic, optical and dielectric properties of BiFeO3 multiferroic ceramics" J.
