Phase transition and negative thermal expansion of HfMnMo 3 O 12

Abstract A novel compound HfMnMo 3 O 12 with negative thermal expansion (NTE) was synthesized using solid state method. The crystal structure, fracture morphology and NTE properties of the material were investigated by temperature-dependent X-ray diffraction (XRD), scanning electron microscope (SEM) and temperature-dependent Raman spectra. Our experimental results show that the compound adopts a monoclinic symmetry below room temperature and transforms to an orthorhombic phase above 348 K. In the orthorhombic phase the compound exhibits NTE property with a linear coefficient of thermal expansion (CTE) −3.8 × 10 −6  K −1 from 400 K to 700 K. The physical mechanism of the NTE is discussed and elucidated according to our experiments.