Structural and physical properties of 1:2 B-site-ordered perovskite Ba3CaIr2O9

The high-pressure phase of iridium-based compound Ba3CaIr2O9 was synthesized using high-pressure sintering. Being different from the distorted hexagonal BaTiO3 structure of the ambient Ba3CaIr2O9, the high-pressure phase crystals into the 1:2 B-site-ordered perovskite structure with the space group P-3m1 (Z=1). Through fitting the X-ray powder diffraction (XRD) data with Rietveld analysis, in which the obtained Rp, Rwp, and Rexp factors are 7.49%, 11.4%, and 4.82%, respectively, the lattice parameters are a=5.8296(1) Å and c=7.1659(2) Å. The atomic coordinates and the main interatomic distances and bond angles were also obtained. The relationship of electrical resistivity versus temperature shows that the high-pressure phase of Ba3CaIr2O9 is a semiconductor in the temperature range of 5–300 K. The measurement of temperature dependence of magnetic susceptibility indicates that it is paramagnetic.