The thermal conductivity of monolithic Y‐Sm/α‐SiAlON was evaluated using experimental data and finite element analysis. The thermal diffusivities of Y, Y‐Dy, and Y‐Ce/α‐SiAlON ceramics were also investigated experimentally for comparison. The maximum achievable thermal conductivity of Y‐Sm/α‐SiAlON has been calculated by the linear extrapolation of the temperature‐based experimental inverse diffusivity data and was used for the numerical calculations. Two‐dimensional model microstructures were built on the base of real microstructure images and applied for calculations. Experimental data and numerical calculations were compared for Y‐Sm/α‐SiAlON, and it was revealed that both results are in good agreement.

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α-SiAlON ceramics with elongated grains were previously observed in different studies. Sintering conditions are known to have a significant role on the microstructural development. By the nucleation treatment application during sintering, α-SiAlON with needle-like microstructure can be achieved also in a nitrogen rich composition and utilizing commercial α-Si 3 N 4 , whereas typical equiaxed grains are formed if the nucleation was not applied prior to growth in the same system. In this study, Ca-Ce containing multication systems for two different compositions are chosen to combine the facility of Ce for elongated grain formation with the convenient separation of maximum rates for nucleation and grain growth of Ca. The effects of different nucleation temperatures are examined to understand the microstructural development behaviour of α-SiAlON grains in this system.