Effect of Doping on the Thermal Expansion of β‐Eucryptite Prepared by Sol–Gel Methods

Abstract

The thermal expansion behavior of pure β‐eucryptite and Zn‐doped β‐eucryptite (substituting Zn for Li), prepared using sol–gel methods and hot pressing, were investigated. β‐eucryptite exhibits an anisotropic negative coefficient of thermal expansion (CTE), which leads to microcrack formation in sintered polycrystalline samples. This is manifested by the presence of a hysteresis in the thermal expansion curves. The hysteresis disappears when a small amount of Zn (0.5–3 mol% Zn) is present. Furthermore, the bulk CTE increases significantly in magnitude (from −4 × 10−6/°C for pure β‐eucryptite to 1 × 10−6/°C to 2 × 10−6/°C), and is slightly positive in the range from 25°C to 1000°C. No difference in grain size was observed between the pure and doped samples, and all the ceramics exhibited high relative densities. It is likely that Zn substitutes for Li in the β‐eucryptite structure and reduces the c‐axis thermal expansion, thereby lowering the CTE anisotropy and lowering the tendency for microcracking.