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Yttria‐stabilized‐zirconia samples with fairly narrow pore size distributions give well‐defined microstructure impedance semicircles which can be characterized by a blocking factor αR, a capacitance ratio αC and a frequency ratio αF. On an αR vs. αC diagram, the regimes where either the pores or the grain boundaries are dominant are clearly separated. As expected from the reference model, the αRαF product was found proportional to porosity. The fairly continuous variations of αF from the densification to the grain growth regime revealed that voids remained present along the grain boundaries. Comparison of different results shows a remarkable constancy of the average thickness of the grain‐boundary blockers in the samples sintered at high temperature. The electrical bulk properties obey simple laws as functions of porosity, which allows us to correct the conductivity and dielectric‐constant data obtained with imperfectly densified materials.

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Abstract--Hydrotalcite-like compounds, described by the formula [Zn, xAlx(OH)2] [(CO3)x/2 9 nHzO], were prepared by coprecipitation methods at 80~ and characterized by bulk chemical analysis, X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning-transmission electron microscopy (STEM). An x value of 0.33 was previously assumed to be an upper limit, but recently, Al-rich hydrotalcitelike compounds have been prepared with x as large as 0.44 by hydrothermal synthesis. In the Zn-Al system, #p-rich hydrotalcite was synthesized at normal pressure by coprecipitation. Zn-#P hydrotalcitelike compounds were obtained in the range of x = 0.3 to 0.4. An #P-rich hydrotalcite-like compound with x = 0.44 was formed in mixtures containing large amounts of a poorly crystalline Zn-A1 phase. A continuous contraction of the hydrotalcite-like structure occurred as x increased, both the a and c lattice parameters decreasing for x values as large as 0.44. This study illustrates the advantages of using quantitative analytical electron microscopy with high spatial resolution to complement conventional (and bulk) characterization techniques for correlating structural and compositional characteristics of finely divided materials.

International audienceThe structures of the B6O samples prepared by oxidizing boron with ZnO at temperatures of 1350-1500°C in an argon atmosphere have been refined by the Rietveld method. The B6O samples were found to contain an amorphous phase from their X-ray diffraction profiles in addition to B6O diffraction peaks. The results indicate that the B6O samples, space group R¯3m, no.166, a hex = 0.5367(1) nm and c hex = 1.2328(2) nm in the hexagonal unit cell, have oxygen deficiencies with 0.76(6) oxygen occupancy. A radial distribution function method applied to an extracted portion of the amorphous phase, suggests that each amorphous phase has nearly similar short-range order structure to that of the α-tetragonal boron type rather than to those of any other related boron phases

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