Temperature dependent structural modulation in Ca0.82La0.18FeAs2 pnictide superconductors

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Temperature dependent synchrotron x-ray powder diffraction data on FeAs2 pnictide superconductor demonstrate anisotropic thermal expansion along the out-of-plane and in-plane lattice parameters. Thermal expansion along the c-axis shows a distinct change from 2.9 × 10−4 Å K−1 at ∼300 K to 1.0 × 10−4 Å K−1 at ∼110 K, whereas the in-plane axes, a and b, in the temperature range 300 to 100 K, show a constant thermal expansion that is an order of magnitude smaller (∼0.3×10−4 Å K−1). The temperature dependence of the out-of-plane lattice parameter is found to have a good correlation with the behavior of the resistivity indicating the importance of the interlayer interaction in governing the transport properties of 112 pnictide superconductors.