Low positive thermal expansion in HfMgMo3O12

In the search for materials with negative thermal expansion, the HfMgMo3O12 phase has been synthesized and characterized for the first time. It is established that this phase belongs to a new class of ceramics with the general formula A4+B2+M6+3O12 that crystallizes in orthorhombic symmetry of space group Pnma (62) or Pna21 (33). No evidence is observed for any phase transition of orthorhombic HfMgMo3O12 through differential scanning calorimetry and high-temperature X-ray diffraction measurements in the investigated temperature range (298-1013 K). This new phase exhibits unusually low thermal expansion (αl=1.02 x 10-6 K-1) as determined by high-temperature X-ray diffraction using a synchrotron source. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)