Negative thermal expansion performance of (NaMg)xCr2-x(MoO4)3 (0≤x≤1) ceramics

Abstract

Cr2Mo3O12 ceramics show negative thermal expansion (NTE) in a narrow high-temperature range due to the phase transition around 385 °C. To widen its NTE temperature range, a series of (NaMg)3+ co-doped Cr2Mo3O12 ceramics has been synthesized via a solid reaction process in this work. The effects of double cation (NaMg)3+ co-doping on the phase composition, morphology, phase transformation, and thermal expansion performance of Cr2Mo3O12 ceramics were studied using XRD, Raman, XPS, SEM, and TMA. Results indicate that double cation (NaMg)3+ can partially substitute Cr3+ in Cr2Mo3O12, which causes a phase transition from monoclinic Cr2Mo3O12 to hexagonal (NaMg)xCr2-xMo3O12. The single-phase (NaMg)xCr2-xMo3O12 ceramics with hexagonal structure is obtained when x = 0.5. (NaMg)3+ co-doping promotes the growth of grains and the density of hexagonal (NaMg)0·5Cr1·5Mo3O12 ceramics. (NaMg)3+ co-doping also successfully eliminates the temperature-induced phase transition of Cr2Mo3O12 at 385 °C. Hexagonal (NaMg)0·5Cr1·5Mo3O12 ceramics presents a better NTE with a coefficient of thermal expansion (CTE) of −3.97 × 10−6 °C−1 over a larger temperature range from 30 °C to 700 °C.