A cautionary tale on the use of GE‐7031 varnish: low‐temperature thermal expansion studies of ScF3. (15th May 2013)

• Record Type: Journal Article
• Authors: Morelock, Cody R.; Suchomel, Matthew R.; Wilkinson, Angus P.
• Is Part Of: Journal of applied crystallography. Volume 46:Part 3(2013:Jun.)
• Page Start: 823
• Page End: 825
• Publication Date: 2013-05-15
• Subjects: GE‐7031 varnish -- scandium trifluoride -- low‐temperature X‐ray diffraction -- powder X‐ray diffraction -- negative thermal expansion -- composites; Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S0021889813005955
• Languages: English
• ISSNs: 0021-8898

Abstract

Abstract : GE‐7031 varnish, a commonly used low‐temperature adhesive and electrical insulator owing to its high thermal conductivity and mechanical strength at low temperatures, was used as a sample matrix for low‐temperature powder X‐ray diffraction measurements of the negative thermal expansion (NTE) material ScF3 . When ScF3 powder was mixed with GE‐7031 varnish, an unexpected cubic to rhombohedral phase transition in the ScF3 sample was observed at ∼50 K, and it exhibited smaller low‐temperature unit‐cell volumes than samples without the varnish matrix. Experimental observations and quantitative estimates suggest that these anomalies are the result of stress induced by a thermal expansion mismatch between the varnish matrix (large positive coefficient of thermal expansion, CTE) and ScF3 (quite large negative CTE). The use of GE‐7031 varnish as a sample matrix for low‐temperature measurements should be approached with caution if a large thermal expansion mismatch is expected.