Synthesis, structures and thermal properties of solid solutions ErxDy2−xMo4O15 (x = 0.0–2.0)

A new series of rare earth solid solutions of ErxDy2−xMo4O15 (x = 0.0–2.0) were successfully prepared. Their structures and thermal properties were studied by X-ray diffraction for temperature ranging from 25 to 500 °C. These solid solutions are found to crystallize in a monoclinic space group P21/c. The lattice parameters a, b and c of ErxDy2−xMo4O15 decrease linearly with increasing erbium content. High-temperature XRD results show that these solid solutions show positive thermal expansion with rising temperature, very likely related to the weak bond Mo⋯O14 in ErxDy2−xMo4O15. To make compounds of Ln2Mo4O15 family show negative thermal expansion, a possible way is to strengthen the weak Mo⋯O14 bond by shortening the Mo⋯O14 bond length.