The study of thermal expansion properties in solid solutions Ln2−xCrxMo3O12 (Ln=Ho and Lu) by high temperature X-ray diffraction

A systematic study of the formation, crystal structures and thermal expansion properties of solid solutions Ln2−xCrxMo3O12 (Ln=Ho and Lu) has been performed. Rietveld refinement results indicate that compounds Ho2−xCrxMo3O12 with 0≤x≤0.2 and Lu2−xCrxMo3O12 with 0≤x≤0.5 have orthorhombic structures and show negative thermal expansion in the temperature range of 200–800 °C. Compounds Ln2−xCrxMo3O12 with 1.7≤x≤2.0 have monoclinic structures and show strong positive thermal expansion in the temperature range of 25–300 °C. While compounds Ln2−xCrxMo3O12 with 1.7≤x≤2.0 adopt orthorhombic structures and show very low positive thermal expansion from 500 to 800 °C. Though the crystal structure plays the key rule in determining the thermal expansion properties, chemical composition and temperature also show important effect on the thermal expansion properties of these compounds.

Evolution of Cr2Mo3O12 diffraction patterns from 25 to 800 °C.Figure optionsDownload as PowerPoint slideHighlights
► TE coefficients of orthorhombic Ln2−xCrxMo3O12 become less negative with increasing Cr.
► Monoclinic Ln2−xCrxMo3O12 show very strong positive thermal expansion.
► Ln2−xCrxMo3O12 with 1.7≤x≤2.0 show very low positive thermal expansion from 500 to 800 °C.