Suppression of phase-transition temperature in aluminium indium tungstate and aluminium indium molybdate

Abstract

Aluminium indium tungstate (AlInW3O12) and aluminium indium molybdate (Al0.84In1.16Mo3O12) were synthesized by non-hydrolytic sol–gel chemistry, and their crystal structures, phase transition and thermal expansion behavior were studied using variable-temperature synchrotron powder diffraction. AlInW3O12 adopts an orthorhombic phase above 260 K and gradually transitions to a monoclinic polymorph below this temperature. Al0.84In1.16Mo3O12 also shows a gradual transition between the monoclinic and orthorhombic structures between 330 and 445 K. Both materials display much lower phase-transition temperatures than predicted on the basis of the parent compounds and Vegard's law. This suppression is attributed to the large size difference between Al3+ and In3+. Interestingly, both samples display positive thermal expansion along all unit-cell axes instead of the typically observed negative expansion of orthorhombic A 2 M 3O12 compositions.