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Theoretical and Experimental Study of Barium Zinc-Cadmium Tantalate-based Microwave Dielectrics

Published online by Cambridge University Press:  01 February 2011

Shaojun Liu
Affiliation:
Chemical and Materials Engineering Department Science and Engineering of Materials Program
Mark Van Schilfgaarde
Affiliation:
Chemical and Materials Engineering Department Science and Engineering of Materials Program
Jian Sun
Affiliation:
Center for Solid State Science, Arizona State University, Tempe, AZ 85287–6006
Louisa Badd
Affiliation:
Chemical and Materials Engineering Department
David Smith
Affiliation:
Chemical and Materials Engineering Department Science and Engineering of Materials Program Center for Solid State Science, Arizona State University, Tempe, AZ 85287–6006
Novak S. Petrovixc
Affiliation:
Electrical and Computer Engineering Department, Queens land University, Paddington, Australia 4064
R. Taylor
Affiliation:
Electrical and Computer Engineering Department, Queens land University, Paddington, Australia 4064
N. Newman
Affiliation:
Chemical and Materials Engineering Department Science and Engineering of Materials Program
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Abstract

Single-phase Ba(Cd1/3Ta2/3)O3 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(Cd0.327Zn0.006Ta2/3)O3 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(Cd1/3Ta2/3)O3 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(Zn1/3Ta2/3)O3 and Ba(Cd/3Ta2/3)O3, 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.

Type
Research Article
Copyright
Copyright © Materials Research Society 2004

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References

1. Vanderah, Terrell A., Science 298, 11821184 (2002)CrossRefGoogle ScholarPubMed
2. Davies, P., Ceramic transaction: Materials and processes for wireless communication, Vol.53, 137149, (1995)Google Scholar
3. Rong, G., Newman, N., Shaw, B., and Cronin, D., J. Mater. Res. 10, 4011 (1999)CrossRefGoogle Scholar
4. Liu, Shaojun, Taylor, Richard, Budd, Louisa, Petrovixc, Novak S., Schilfgaarde, Mark Van, Newman, N., submitted to J. Am. Ceramc. Soc. (2003)Google Scholar
5. Liu, Shaojun, Sun, Jian, Taylor, Richard, Smith, David. J. and Newman, N., in preparation.Google Scholar
6. Gui, Hong, Gu, Bing-lin, and Zhang, Xiao-wen, J. Am. Ceram. Soc., 79 (2) 381384 (1996)CrossRefGoogle Scholar
7. Sun, J., Liu, Shaojun, Newman, N., McCartney, M. R. and Smith, David. J., submitted to J. Mater. Res. (2003)Google Scholar

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Theoretical and Experimental Study of Barium Zinc-Cadmium Tantalate-based Microwave Dielectrics
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