Thermal expansion in Cr:LiSrGaF₆

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• 作者：Andrzej Grzechnik ; Zunbeltz Izaola Azcona ; Pablo Bereciartua ; Karen Friese and Stephen Doyle
• 关键词：A. Fluorides ; A. Optical materials ; C. X-ray diffraction ; D. Crystal structure ; D. Thermal expansion
• 刊名：Materials Research Bulletin
• 出版年：2005
• 出版时间：2005
• 年：2005
• 卷：40
• 期：11
• 页码：1976-1984
• 全文大小：218 K

文摘

High-temperature behaviour of LiSrGaF₆ doped with 1.5 at. % of Cr³⁺ was studied with high-resolution synchrotron angle-dispersive X-ray powder diffraction in the temperature range 298–539 K. No phase transitions were detected. The origin of negative thermal expansion along the c axis is discussed based on the temperature dependencies of structural parameters and octahedral distortions obtained with the Rietveld method. The SrF₆ slab contracts with increasing temperatures because of the diminishing F–Sr–F octahedral angles without any changes in the F–F octahedral edges not only around strontium but also around lithium and gallium. At the same time, the angular distortions of the SrF₆ octahedra are largely diminished. Such a behaviour is discussed in comparison with the thermal expansion of LiCaAlF₆ and LiSrAlF₆.