Thermal expansion investigation of new langbeinite type phosphomolybdates: K2-xZr2P2-xMoxSiO12 (x = 0, 0.1, 0.2)

Abstract

Members of A2(MO4)3 structure type have been identified as negative thermal expansion (NTE) materials. Specifically, tungstates (Sc2(WO4)3) and molybdates (Al2(MoO4)3) with orthorhombic structure exhibits NTE due to the transverse thermal vibration of A-O-M linkage. Langbeinite is a similar type structure consist of three-dimensional open framework with MO6 octahedral and PO4 tetrahedral interconnection. In the present work, we synthesized orthorhombic phosphomolydates of the chemical formula K2-xZr2P2-xMoxSiO12 (x = 0, 0.1, 0.2) to develop new low/zero/NTE materials with langbeinite structure. The compounds were synthesized by solution method and characterized by powder XRD, FT-IR, SEM and TG-DTA. Least square refinement method revealed that the synthesized compounds are crystallize in orthorhombic structure with P212121 space group. The characteristic stretching and bending vibrational bands of P-O, Si-O and Mo-O are observed from the FT-IR spectra. The compounds are thermally stable up to 600 °C and the effect of Mo substitution is observed from the micrographs with particle size variation. In contrary to A2(MO4)3 structure type, the average thermal expansion coefficient of K1.9Zr2Mo0.1P1.9SiO12 and K1.8Zr2Mo0.2P1.8SiO12 are found to be 8.19 and 6.89 × 10-6/ °C.