  Zirconia (ZrO2) has emerged as a promising technical ceramic, both as high
temperature structural material and thermal barrier coating material, etc. The
traditional synthesis of ZrO2 with spark plasma sintering (SPS) usually
requires a sintering temperature as high as 1200C. General interest in lowering
the sintering temperature to reduce energy consumption and thermal stresses has
led to research on two promising routes, cold sintering via
temperature-dependent chemical reactivity and sintering aids, which facilitates
mass transport and improves densification. Here we combine both by developing a
single-step sintering process benefitting from both water vapor through the
in-situ conversion of Zr(OH)4 to ZrO2 and liquid phase Bi2O3 as a sintering
aid. The resultant ZrO2 has a relative density above 80 percent with a
sintering temperature as low as 900C.
