Negative thermal expansion performance of (NaMg)xCr2-x(MoO4)3 x Cr 2-x (MoO 4 ) 3 (0≤x≤1) ≤ x ≤ 1) ceramics

Cr2Mo3O12 2 Mo 3 O 12 ceramics show negative thermal expansion (NTE) in a narrow high-temperature range due to the phase transition around 385 degrees C. To widen its NTE temperature range, a series of (NaMg)3+ 3+ co-doped Cr2Mo3O12 2 Mo 3 O 12 ceramics has been synthesized via a solid reaction process in this work. The effects of double cation (NaMg)3+ 3+ co- doping on the phase composition, morphology, phase transformation, and thermal expansion performance of Cr2Mo3O12 2 Mo 3 O 12 ceramics were studied using XRD, Raman, XPS, SEM, and TMA. Results indicate that double cation (NaMg)3+ 3+ can partially substitute Cr3+ 3+ in Cr2Mo3O12, 2 Mo 3 O 12 , which causes a phase transition from monoclinic Cr2Mo3O12 2 Mo 3 O 12 to hexagonal (NaMg)xCr2-xMo3O12. x Cr 2-x Mo 3 O 12 . The single-phase (NaMg)xCr2-xMo3O12 x Cr 2-x Mo 3 O 12 ceramics with hexagonal structure is obtained when x = 0.5. (NaMg)3+ 3+ co-doping promotes the growth of grains and the density of hexagonal (NaMg)0 & sdot;5Cr1 & sdot;5Mo3O12 0 & sdot;5 Cr 1 & sdot;5 Mo 3 O 12 ceramics. (NaMg)3+ 3+ co-doping also successfully eliminates the temperature- induced phase transition of Cr2Mo3O12 2 Mo 3 O 12 at 385 degrees C. Hexagonal (NaMg)0 & sdot;5Cr1 & sdot;5Mo3O12 0 & sdot;5 Cr 1 & sdot;5 Mo 3 O 12 ceramics presents a better NTE with a coefficient of thermal expansion (CTE) of-3.97 x 10-6-6 degrees C- 1 C- 1 over a larger temperature range from 30 degrees C to 700 degrees C.