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 w...
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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 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(Zn 1/3Ta2/3)O3 and Ba(Cd/3Ta 2/3)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.
Ordered structures of Ba(Cd1/3Ta1/2)O3 ceramics with and without boron additive were investigated systemically by electron diffraction and high resolution transmission electron microscopy. The results showed a well-or...
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Ordered structures of Ba(Cd1/3Ta1/2)O3 ceramics with and without boron additive were investigated systemically by electron diffraction and high resolution transmission electron microscopy. The results showed a well-ordered structure of 1:2 with hexagonal symmetry for Ba(Cd1/3Ta1/2)O3 with boron additive. No significant changes in ordered structures were observed after long-period annealing. The 1:2 ordered domain structures (average domain size ∼ 18 nm) and high-density domain boundaries induced by ordering were observed for Ba(Cd1/3Ta1/2)O3 without boron additive sintered at relatively high temperature. The sintering process has a profound influence on the microstructure of Ba(Cd1/3Ta2/3)O 3 ceramics.
Measurements of the hardness and Young’s modulus of superhard coatings (HV≥40 GPa) by means of automated load-depth-sensing indentation technique can be subject to a number of errors that are discussed and exemplifi...
Measurements of the hardness and Young’s modulus of superhard coatings (HV≥40 GPa) by means of automated load-depth-sensing indentation technique can be subject to a number of errors that are discussed and exemplified here. Only load-independent values of hardness for loads larger than 30–50 mN can be considered reliable when the technique of Doerner and Nix (linear extrapolation of the unloading curve) is used to determine the corrected indentation depth. The results are compared with values of Vickers hardness calculated from the contact area of the remaining plastic deformation which was measured by means of calibrated scanning electron microscope. The values of Young’s modulus obtained from the indentation are close to the zero-pressure shear modulus of the coatings as measured by means of Vibrating Reed and surface Brillouin scattering techniques.
High quality AlN thin films were grown by Low Pressure Organometallic Vapor Phase Epitaxy(LP-OMVPE) on sapphire and Si substrates. oxygen contamination in the Al layers can be reduced drastically by fine tuning of the...
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Thin films composite materials consisting of metallic nanocrystals embedded in an insulator host have been synthesized using alternating-target pulsed laser deposition of Fe/Ni and Al2O3. The evaluation of structural ...
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We report here a novel thin film processing method based upon pulsed laser deposition to process nanocrystalline materials with accurate size and interface control with improved mechanical and magnetic properties. Usi...
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