Near-zero thermal expansion and phase transition in In 0.5 (ZrMg) 0.75 Mo 3 O 12
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ldeci Paraguassu Faculdade de Física, Universidade Federal do Pará, Belém, PA 66075-110, Brasil
Carl P. Romao Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
Mary Anne White Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada; Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada; and Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
Bojan A. Marinkovica) Departamento de Engenharia Química e de Materiais, Pontifícia Universidade Católica, 22451-900 Rio de Janeiro, RJ, Brasil (Received 9 March 2016; accepted 24 August 2016)
Physical properties of In0.5(ZrMg)0.75Mo3O12, including the coefficient of thermal expansion, phase stability, hygroscopicity, and decomposition temperature have been thoroughly studied by in situ x-ray powder diffraction, Raman spectroscopy and thermal methods. These investigations show that In0.5(ZrMg)0.75Mo3O12 exists in a monoclinic phase (P21/a) at room temperature and transforms to an orthorhombic (Pbcn) phase at ;82 °C. In the orthorhombic form this material presents intrinsic near-zero thermal expansion ( 0.16 10 6 K 1) in the range between 100 and 500 °C. The phase is not hygroscopic, but starts to decompose into its constituent oxides at temperatures higher than 700 °C. In comparison to the end member phase ZrMgMo3O12 in the In2Mo3O12–ZrMgMo3O12 solid solution, In0.5(ZrMg)0.75Mo3O12 is less promising for near room-temperature applications due to the phase transition from monoclinic to orthorhombic slightly above room temperature. However, the orthorhombic phase of In0.5(ZrMg)0.75Mo3O12 has potential for applications that require zero thermal expansion at temperatures higher than 100 °C.
I. INTRODUCTION
The orthorhombic space group Pbcn (60) accommodates a large number of open-framework phases with the general chemical formula A2M3O12.1–3 In this formula M is a hexavalent cation, such as Mo61 or W61 (although, P51 has been reported4 as an element capable of partial substitution for W61 or Mo61) forming 4-coordinated polyhedra, while A can be any small rare earth or some other trivalent cation from Al31 to Y31, within an octahedral environment.5–8 Tetrahedra and octahedra build an open-framework crystal structure through connected vertices. Strain screening is made possible by the open-framework structure9 and solid solutions can be synthesized with almost any combination of these cations and, therefore, there is considerable chemical and physical Contributing Editor: Ian M. Reaney a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.329
flexibility within the A2M3O12 family. Trivalent cations occupy one independent general 8d site, while hexavalent cations occupy two independent crystallographic positions, one general 8d and one special 4c, and oxygens adopt six independent general 8d positions. This peculiar open framework, which is related to the garnet structure by removal of t
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