Kuzhichalil Peethambaran Surendran

Microwave Dielectric Properties of RETiTaO6 (RE = La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) Ceramics

Microwave dielectric ceramics based on RETiTaO 6 (RE = La, Cc, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) were prepared using a conventional solid-state ceramic route. The structure and microstructure of the samples were analyzed using x-ray diffraction and scanning electron microscopy techniques. The sintered samples were characterized in the microwave frequency region. The ceramics based on Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, which crystallize in orthorhombic aeschynite structure, had a relatively high dielectric constant and positive τ f while those based on Ho, Er, and Yb, with orthorhombic euxenite structure, had a low dielectric constant and negative τf. The RETiT a O 6 ceramics had a high-quality factor. The dielectric constant and unit cell volume of the ceramics increased with an increase in ionic radius of the rare-earth ions, but density decreased with it. The value of τf increased with an increase in RE ionic radii, and a change in the sign of τf occurred when the ionic radius was between 0.90 and 0.92 A. The results indicated that the boundary of the aeschynite to euxenite morphotropic phase change lay between DyTiTaO 6 and HoTiTaO 6 . Low-loss ceramics like ErTiTaO 6 (e r = 20.6, Q u xf = 85,500), EuTiTaO 6 ( r = 41.3, Q u xf = 59,500), and YtiTaO 6 (e r = 22.1, Q u xf = 51,400) are potential candidates for dielectric resonator applications.

Synthesis, characterization and properties of [RE1−xREx′]TiNbO6 dielectric ceramics

Abstract Dielectric ceramics based on solid solution phases of [RE 1− x RE x ′]TiNbO 6 , where RE 1− x =Nd, Pr, Sm and RE x ′=Dy, Gd and Y, were prepared by the conventional solid-state ceramic route for values of x . The ceramic samples are characterized by X-ray diffraction and microwave methods. Ceramics based on RE (Pr, Nd and Sm) belonging to aeschynite group shows positive value of τ f and those based on RE (Gd, Dy and Y) belonging to euxenite group show negative value of τ f . The solid solution phases between the aeschynite and the euxenite group shows intermediate dielectric constant and τ f values. The results indicate the possibility of tailoring the dielectric properties by varying the composition of the solid solution phases. The range of solid solubility of euxenite in aeschenite and aeschenite in euxenite are different for different rare earth ions.

Low Loss Dielectrics in Ba[(Mg1/3Ta2/3)1−xTix]O3 and Ba[(Mg1−xZnx)1/3Ta2/3]O3 Systems

The microwave dielectric properties of ceramics based on Ba[(Mg 1/3 Ta 2/3 ) 1− x Ti x ]O 3 (BMT-BT) and Ba[(Mg 1−x Zn x ) 1/3 Ta 2/3 ]O 3 (BMT-BZT) were investigated as a function of composition x. In BMT-BT solid solution, the dielectric properties deteriorated with increasing concentration of Ti substitution at the B-site of BMT. A correlation was established between the quality factors of the solid solution phases and their tolerance factor. In BMT-BZT solid solution, where both the end compounds are ordered perovskites, the unit cell expands with increasing mole fraction of the Zn in Mg site of BMT while the dielectric constant increases monotonously from 24.8 (for BMT) to 29.7 (BZT). In BMT-BZT solid solution, the quality factor reaches a maximum (Q u ·f = 109,900 GHz) for 60 mol/ of BZT.

Raman scattering study of RETiTaO6 dielectric ceramics

In this work we have investigated microwave-dielectric ceramics RETiTaO6 (RE=Al, Y, In, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er or Yb) by Raman scattering measurements at room temperature. The observed Raman-active phonons were analysed in conformity with two orthorhombic structures proposed for these ceramics, namely aeschynite (for lanthanide ions with atomic number between 58 and 66) or euxenite (for Y, Ho, Er and Yb). The results indicate that the phonon spectra remained relatively unchanged with respect to the RE ion substitution within each structure. For the three remaining materials with RE=La, Al and In, which are known to present multiphases, the Raman phonon spectra showed significant differences in comparison with those of ceramics with aeschynite and euxenite structure. # 2003 Elsevier Ltd. All rights reserved.

The effect of dopants on the microwave dielectric properties of Ba(Mg0.33Ta0.67)O3 ceramics

The effect of dopants with different valencies and ionic radii on the densification, structural ordering, and microwave dielectric properties of Ba(Mg1∕3Ta2∕3)O3 (BMT) is investigated. It is found that dopants such as Sb2O5, MnO, ZrO2, WO3, and ZnO improve the microwave dielectric properties of BMT. Addition of trivalent dopants is detrimental to the cation ordering and dielectric properties of BMT. A correlation between the microwave dielectric properties of BMT and ionic radii of the dopant has been established. The variation of the dielectric properties of pure and doped BMT at cryogenic temperatures is also discussed.

Ni and Zn doped MgTiO3 thin films: Structure, microstructure, and dielectric characteristics

The addition of low loss ilmenite impurities, can effectively tailor the dielectric properties of MgTiO3 without modifying the crystal structure. In the present study, the modification of the structural and dielectric properties of sol gel derived MgTiO3 films by doping with Ni and Zn is exploited. The change of the dielectric response and unit cell parameters of doped MgTiO3 is correlated with Ni and Zn occupancy. The temperature stability of MgTiO3 thin films is improved with doping, while the dielectric losses are aggravated with both Zn and Ni doping, which is correlated with the localized d electrons of the dopant cations. The dielectric permittivity decreased with Ni doping while it increased with Zn, which is attributed to the lower ionic polarizability of Ni2+ (1.23 A3) as in comparison with Mg2+ (1.32 A3) while Zn2+ has a higher ionic polarizability (2.04 A3).

Infrared reflectivity and intrinsic dielectric behavior of RETiTaO 6 (RE = Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb) microwave ceramics

In this work, we performed infrared reflectivity measurements of RETiTaO 6 dielectric ceramics for rare-earth (RE) = Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb. The infrared spectra were analyzed through the four-parameter semi-quantum model based on two orthorhombic (aeschynite and euxenite) structures presented by the ceramics. We discerned the strongest phonon modes that contribute to the intrinsic dielectric behavior of the two families. Then the unloaded quality factors and the dielectric permittivities were estimated at the microwave region. The variations of the intrinsic dielectric response of both systems with RE ion substitution are discussed in terms of changes in their dielectric polarizabilities. It is proposed that the covalency of the RE–O bonds play an important role in the evolution of dielectric permittivity as well as in the sign of the temperature coefficient of the resonant frequency.