Synthesis, and thermal and mechanical properties of Baℓℓ[subscript x]ZrℓPℓℓℓ[subscript x]Siℓ[subscript x]Oℓℓ

Ba_1+xZr₄P_6-2xSi_2xO_{24,/sub> or BaZPS belongs to the family of ultra-low expansion materials popularly known as NZP, after the prototype composition, NaZr2P3,/sub>O12. BaZPS compositions with x=0.000, 0.175, 0.250, 0.375, and 0.500 were synthesized by a solid-state reaction method, and the mechanical and thermal properties were investigated as a function of silicon content. In addition, the grain size effect on the mechanical and thermal properties was studied for BaZPS with x=0.000, 0175, and 0.500, and the critical grain sizes were determined. The bulk linear thermal expansion values were found to decrease with increasing silicon content, and was negative for BaZPS with x=0.500. BaZPS with x=0.175 had very low thermal expansion anisotropy and exhibited good mechanical behavior as well. BaZPS with x=0.375 had the highest strength, and hardness values, and is likely suitable for high temperature applications. All the BaZPS compositions showed an increase in flexural strength with increasing temperature, and this behavior was ascribed to the healing of microcracks at higher temperatures. The critical grain size transitions were found to be proportional to the inverse square of the maximum thermal expansion difference. For example, BaZPS with x=0.500 had the highest thermal expansion anisotropy, and showed the smallest critical grain size transition.}