Abstract
Single-phase Ba(Cd 1/3Ta 2/3)O 3 ceramics have been produced using conventional powder processing methods. In our initial investigations, 2wt% ZnO powder was added to act as a sintering aid since a high-density ceramic was not formed from solid-state diffusion alone. The resulting Ba(Cd 0.327Zn 0.006Ta 2/3)O 3 material sintered at 1550°C exhibits a dielectric constant of ∼33 and loss tangent of <5×10 -5 at 2 GHz. In our more recent work, we have used boron as a sintering aid to facilitate sintering at temperatures as low as 1300°C, enhance the structural quality and improve the microwave properties of Ba(Cd 1/3Ta 2/3)O 3 dielectrics. TEM results indicate that the liquid sintering mechanism is an important factor for boron concentrations exceeding 0.5wt%, while a point defect mechanism plays the dominant role at lower boron concentrations. The presence of superstructure peaks and splitting of the (220) and (214) peaks in X-ray diffraction spectra are direct evidence for the distortion from cubic symmetry as a result of Cd and Ta ordering on the B-site. Ab-initio electronic structure calculations within the local density functional approximation have been used to give insight into the unusual properties of this class of materials. In both Ba(Zn 1/3Ta 2/3)O 3 and Ba(Cd /3Ta 2/3)O 3, the conduction band maximum and valence band minimum are composed of mostly weakly itinerant Ta 5d-and Zn-3d/Cd-4d levels, respectively. The covalent nature of the directional d-electron bonding in these high-Z oxides plays an important role in producing a more rigid lattice with higher melting points and enhanced phonon energies, and possibly inherently lower intrinsic microwave loss than comparable ionic materials.
Original language | English (US) |
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Title of host publication | Materials Research Society Symposium - Proceedings |
Editors | P. Muralt, Y.S. Cho, M. Klee, J.-P. Maria, C.A. Randall, CH. Hoffmann |
Pages | 35-40 |
Number of pages | 6 |
Volume | 783 |
State | Published - 2003 |
Event | Materials, Integration and Packaging Issues for High - Frequency Devices - Boston, MA, United States Duration: Dec 1 2003 → Dec 3 2003 |
Other
Other | Materials, Integration and Packaging Issues for High - Frequency Devices |
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Country/Territory | United States |
City | Boston, MA |
Period | 12/1/03 → 12/3/03 |
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials