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The correlation between grain size, optical birefringence, and transparency is discussed for tetragonal zirconia (ZrO2) ceramics using the Mie, Rayleigh, and Rayleigh–Gans–Debye scattering models. Our results demonstrate that at the degree of mean birefringence in the range (0.03–0.04) expected for tetragonal ZrO2, only the Mie theory provides reasonable results. At small particle size (<50 nm) the more straightforward Rayleigh approximation correlates with the Mie model. A real in‐line transmission of ∼50% at visible light and 1 mm thickness is expected at a mean grain size <40 nm and ∼70% at a mean grain size <20 nm. At an infrared (IR) wavelength of 5 μm there should not be any scattering caused by birefringence for grain sizes <200 nm. Our simulations were validated with experimental data for tetragonal ZrO2 (3 mol% Y2O3) ceramics made from a powder with an initial particle size of ∼10 nm by sintering in air and using hot‐isostatic pressing. The maximum in‐line transmission of about 77% was observed at IR wavelengths of 3–5 μm.

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A quantitative assessment of the homogeneity of particle coordination in green bodies is achieved by addressing pore structures. Avoiding a coarser tail of the pore size distribution is important but insufficient for optimum sintering. Instead, the steepest slope of the main body of the distribution is responsible for a maximum density at lowest temperature, and further progress is enabled by minimizing interparticle spacing (the average pore size). Ranking different technologies with different associated pore size distributions, the same correlation holds for the impact of homogeneity on (i) sintering densification as (ii) for the onset of intense grain growth during the final sintering stage. For all of the investigated processing approaches the pore size distributions are observed to remain constant through the initial and intermediate states of sintering. 1985J ournal