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

  • Shaojun Liu (a1) (a2), Mark Van Schilfgaarde (a1) (a2), Jian Sun (a3), Louisa Badd (a1), David Smith (a1) (a2) (a3), Novak S. Petrovixc (a4), R. Taylor (a4) and N. Newman (a1) (a2)...

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.

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4. Liu, Shaojun, Taylor, Richard, Budd, Louisa, Petrovixc, Novak S., Schilfgaarde, Mark Van, Newman, N., submitted to J. Am. Ceramc. Soc. (2003)
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Theoretical and Experimental Study of Barium Zinc-Cadmium Tantalate-based Microwave Dielectrics

  • Shaojun Liu (a1) (a2), Mark Van Schilfgaarde (a1) (a2), Jian Sun (a3), Louisa Badd (a1), David Smith (a1) (a2) (a3), Novak S. Petrovixc (a4), R. Taylor (a4) and N. Newman (a1) (a2)...

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