Anomalous thermal expansion in K0.55WO3.275

Abstract

Monoclinic K0.55WO3.275 has been synthesized by solid state reaction method. The space group is P2/m with cell parameters a = 15.9753(2) Å, b = 7.73149(8) Å, c = 10.9393(1) Å and β = 108.477(1) ° at 313 K. The intrinsic linear coefficients of thermal expansion calculated by temperature-dependent X-ray diffraction data are 14.70 × 10−6 K−1 (253–323 K), 3.38 × 10−6 K−1 (323–363 K) and 11.52 × 10−6 K−1 (363–433 K), respectively, which are consistent with the apparent ones obtained by thermal dilatometer. The a axis shows positive thermal expansion from 253–433 K. The b and c axes display negative thermal expansion in the range of 323–363 K, and positive thermal expansion in two ranges of 253–323 K and 363–433 K. Three W–O–W bending modes with negative Grüneisen parameter may be responsible for the low thermal expansion in the range of 323–363 K.