Large negative thermal expansion promoted by microstructure in hexagonal Fe1−xCoxS

Abstract

Materials showing negative thermal expansion (NTE) can be used as thermal expansion compensators. Here, we report the NTE behavior in hexagonal Fe1−xCoxS (0 ≤ x ≤ 0.15) alloys. NTE appears near room temperature when x is increased to 0.09, shifts to lower temperature as x increases, and finally disappears for x ≥ 0.15. For x = 0.10, the inherent volumetric coefficient of thermal expansion (αV) measured by diffraction method is about − 29.8 ppm/K. However, the value obtained by dilatometric method is increased to − 97.2 ppm/K. The pores among the grains in polycrystalline sample are suggested to account for the extra NTE performance. The present study suggests that the NTE of the alloys with anisotropic lattice thermal expansion can be adjusted effectively by controlling the microstructure.