Abstract: The structural behavior of Sr2ZnIrO6 double perovskite has been systematically studied under extreme conditions, both at high temperature and high pressure with synchrotron powder X-ray diffraction. At high temperatures, three structural phase transitions are detected at 473, 673, and 873 K, giving the sequence P21/n -> I2/m -> I4/m -> Fm3?m. At high pressure, a phase transition from monoclinic P21/n to tetragonal I4/m symmetry is observed at 7.5(1) GPa, as confirmed by ab initio calculations. The tetragonal high-pressure I4/m polymorph appears at both high and intermediate temperatures, highlighting a displacive transition with an estimated negative pressure dependence of the critical temperature (dTc/dp = ?51 K/GPa). The bulk modulus (?150 GPa) and the volumetric thermal expansion (?3.4 × 10-5 K-1) are determined for the low- and high-pressure phases (P21/n and I4/m).

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