Syntheses of negative thermal expansion materials Sc2(MO4)3 (M=W, Mo) with a CO2 laser and their Raman spectra

Abstract

Negative thermal expansion materials Sc2(MO4)3 (M={W}, Mo) are synthesized with a CO2 laser. It is shown that the synthesis of Sc2(WO4)3 or Sc2(MoO4)3 by laser sintering is a rapid process so that a sample can be synthesized within a few or tens of seconds and has the characteristic of rapid solidification. X-ray diffraction and Raman spectrum analyses demonstrate that the synthesized Sc2(MO4)3 (M={W}, Mo) are crystallized into orthorhombic structures and each have a high purity. Temperature dependent Raman spectrum analysis suggests that the synthesized samples do not have phase transitions above room temperature but possibly have weak hygroscopicities. According to the Raman analyses of MoO3, WO3, Sc2(MoO4)3, and Sc2(WO4)3, we draw a diagram describing their phonon energy levels and the photon energy of the laser, and then assess the mechanism of the synthesis by laser sintering. Transferring the laser photon energy to phonon energy is the channel of light-heat converting. The materials react in the molten pool and are solidified rapidly, forming the final products.