Phase transition and negative thermal expansion in A2(MoO4)3 system (A=Fe3+, Cr3+ and Al3+)

Thermal expansion behavior of A(2)(MoO4)(3) compounds, where A = Fe3+, Cr3+ and Al3+, was studied in static air in the temperature range of 298-1073 K by a thermo-dilatometer. All the compounds showed a positive thermal expansion in the beginning, followed by a phase transition and then a negative thermal expansion (NTE). They have a monoclinic unit cell at room temperature. The negative thermal expansion coefficients (NTEC) of Fe-2(MoO4)(3), Cr-2(MoO4)(3) and Al-2(MoO4)(3) are: -14.82 X 10(-6) K-1, -9.39 X 10(-6) K-1 and -2.83 X 10(-6) K-1, respectively. It is for the first time that some of the transition metal molybdates are shown to exhibit NTE. (C) 2002 Elsevier Science B.V. All rights reserved.