Unusual thermal expansion of Sr2IrO4: A variable temperature synchrotron X-ray diffraction study

•Thermal expansion of Sr2IrO4 was studied using Synchrotron-XRD.•Unusual negative thermal expansion along c-axis observed.•I41/acd→I4/mmm phase transition detected near 1120 K.•Tilting of the corner sharing IrO6 octahedra related to the observed NTE.

The structure of Sr2IrO4 has been studied between 20 and 1273 K using synchrotron X-ray diffraction. Sr2IrO4 undergoes an apparently continuous transition from I41/acd to I4/mmm near 1123 K. The cooperative tilting of the corner sharing IrO6 octahedra in I41/acd results in highly anisotropic and unusual thermal expansion behavior with negative thermal expansion along the c-axis.

Graphical abstractThe progressive reduction in the magnitude of the tilting of the corner sharing IrO6 octahedra in Sr2IrO4 results in negative thermal expansion along the c-axis before undergoing an apparently continuous transition from I41/acd to I4/mmm near 1123 K.Figure optionsDownload full-size imageDownload as PowerPoint slide