Suppression of phase‐transition temperature in aluminium indium tungstate and aluminium indium molybdate. Issue 4 (5th July 2022)

• Record Type: Journal Article
• Authors: Lovings, La'Nese; Dietzel, Dominik; Lind, Cora
• Is Part Of: Journal of applied crystallography. Volume 55:Issue 4(2022)
• Page Start: 851
• Page End: 859
• Publication Date: 2022-07-05
• Subjects: negative thermal expansion materials -- scandium tungstate family -- expansion behavior -- phase‐transition temperature -- powder diffraction; Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S1600576722005751
• Languages: English
• ISSNs: 0021-8898

Abstract

Abstract : A variable‐temperature synchrotron diffraction study shows that aluminium indium molybdate and aluminium indium tungstate undergo phase transitions from monoclinic to orthorhombic structures from the parent compounds at much lower temperatures than predicted by Vegard's law. In contrast to many orthorhombic A 2 M 3 O12 compositions, both compounds display positive thermal expansion. Abstract : Aluminium indium tungstate (AlInW3 O12 ) and aluminium indium molybdate (Al0.84 In1.16 Mo3 O12 ) 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. AlInW3 O12 adopts an orthorhombic phase above 260 K and gradually transitions to a monoclinic polymorph below this temperature. Al0.84 In1.16 Mo3 O12 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 Al 3+ and In 3+ . Interestingly, both samples display positive thermal expansion along all unit‐cell axes instead of the typically observed negative expansion of orthorhombic A 2 M 3 O12 compositions.