METAMATERIALS ׃ NOVEL RELAXOR AND MAGNETOELECTRIC NANOCOMPOSITE
Open Access
- Author:
- Maiti, Tanmoy
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 24, 2007
- Committee Members:
- Amar S Bhalla, Committee Chair/Co-Chair
Ruyan Guo, Committee Chair/Co-Chair
Leslie Eric Cross, Committee Member
Dinesh Kumar Agrawal, Committee Member
Jiping Cheng, Committee Member - Keywords:
- Relaxor Ferroelectrics
Magnetoelectrics
Nanocomposite
Electroceramics
Metamaterial - Abstract:
- The aim of this thesis work is to design both scientifically and technologically important two different classes of novel materials: (i) an environmental friendly lead free relaxor system constituting two different kinds of materials neither of which exhibits the relaxor behavior in pure form (ii) a unique diphasic nanocomposite in combination of ferroelectric and magnetostrictive materials resulting magnetoelectric response which is not observed in either of the phases. Although Extensive research has been carried out on the ferroelectric relaxor behavior ever since the discovery of exceptional dielectric properties of the lead based disordered perovskites like PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3 (PZN), the origin of the physical phenomena of relaxor ferroelectrics is still not understood completely. Recently, research emphasis is leaning towards barium-based relaxors, as these are environmental friendly lead free oxide. Among the doped BaTiO3 systems, BaZrxTi1-xO3 (BZT) solid solution has attracted considerable attention in both bulk and thin film due to its potentiality for various device applications. Although BaTiO3-BaZrO3 system was identified as a solid solution as in early 1950s most studies were focused on the temperature dependence of the dielectric constant, the nature of the phase transitions and the ferroelectric relaxor behavior of this materials in lower concentration (x< 0.40) of Zr in Ba(ZrxTi1-x)O3 system over the years. In this thesis, we have studied structure-property correlation of the various Ba(ZrxTi1-x)O3 compositions and a new complete phase diagram of Barium Zirconate Titanate, Ba(ZrxTi1-x)O3 has been developed in the composition range 0≤x≤1.00. Barium Zirconate Titanate, Ba(ZrxTi1-x)O3 system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO3) to polar cluster dielectric, relaxor ferroelectric, 2nd order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO3). So far there has been no other single solid solution system that demonstrates all complex aspects of ferroelectricity. Ba(ZrxTi1-x)O3 (BZT) ceramics of the several compositions have been prepared by convention solid state synthesis route. All the BZT compositions were verified to be single phase perovskite by studying the room temperature XRD behavior of these compositions. Dielectric behavior of the BZT ceramics has been studied with and without bias in the temperature range from 300 K to 15 K. The dielectric properties of the material show typical relaxor-like behavior for the BaZrxTi1-xO3 compositions with 0.25<x<0.75. However, in the Zr4+ rich BaZrxTi1-xO3 solid solution compositions (0.80≤x≤1.00) polar cluster like behavior has been observed In contrary to the classic relaxor ferroelectrics like PMN, PZN etc where intrinsic disorder prevails, in our present investigation we have introduced the disorder gradually through breaking the long range translational symmetry of BaZrO3 by the incorporation of Ti4+ ion in BaZrO3 lattice to observe the relaxor behavior in a non-ferroelectric material like BaZrO3 with low dielectric constant (<40). From the thermal hysteresis in dielectric behavior and d.c. field dependent dielectric studies it has been concluded that with the incorporation of Ti4+ ion in the BaZrO3 matrix BaZrxTi1-xO3 compositions (x≥0.80) start showing polar-cluster like behavior. Beyond an optimum content of polar BaTiO3 in the non polar matrix of BaZrO3 probably a critical size and distribution density of the polar regions are reached when polar cluster like BaZrxTi1-xO3 ceramics start showing the relaxor-like behavior (x≤0.75). This has been further confirmed from the calculation of degree of relaxation (γ) and Vogel-Fulcher freezing temperature (TVF). To enhance our understanding the relaxor behavior in BaZrxTi1-xO3 ceramics pyroelectric, thermal strain measurements have been carried out from the cryogenic temperature to very high temperature (~650 K). Powder neutron diffraction measurements have been carried out to determine the structure of the BZT relaxor compositions. Structural analysis of the powder neutron diffraction by Rietveld refinement reveals the global structure of the BZT relaxors as cubic. High q-resolution neutron scattering data has been collected on the BZT relaxor compositions by triple axis spectrometer. However, no such splitting in the Bragg peaks of BZT ceramics has been observed even at 4 K and mirror the results obtained from the powder neutron diffraction data predicting the global structure of BZT relaxors as cubic. The local structure of the BZT ceramics has been investigated by Raman spectra. It is seen from the Raman investigation that local polar regions exist in the BZT ceramics even at 550 K at which temperature both end members of the phase diagram BaZrO3 and BaTiO3 are cubic in pure form. From the detailed investigation on the structure and properties of BaZrxTi1-xO3 compositions it can be said that BZT is an engineered material designed by self-assembled polar nano-regions resulting some unusual properties, which can not be predicted from its constituents BaTiO3 and BaZrO3. Hence BaZrxTi1-xO3 is qualified as meta-materials. Further we have shown that one can engineer a meta-material, which can show dielectric relaxation behavior even none of the constituents of the materials does not show such properties. We have shown a potential approach to fabricate the relaxor materials by making the ceramic composite of environmental friendly Ba-based diffuse ferroelectric BaZrxTi1-xO3 (x= 0.20 and 0.25) with non-ferroelectric MgO. Magnetoelectric composites were prepared using both conventional sintering and single mode microwave sintering techniques in the environment of the E-field. In thesis work PbMg1/3Nb2/3O3-31% PbTiO3 (PMN-PT) has been used as the ferroic material and ferrites like CoFe2O4 and Mn0.1Zn0.9Fe2O4 are used as the magnetostrictive materials to make the magnetoelectric metamaterial composites. The magneto-electric coefficients on these samples were calculated by applying the magnetic field and observing the changes in the electric polarization in the composites.