High-pressure synthesis, structural, magnetic and electronic properties of Ca-substituted post-perovskite Na1-xCaxIrO3 (x=0-1)

摘要

We report the synthesis of Na1-xCaxIrO3 (x = 0-1) at 3GPa and 900 degrees C by using the high-pressure technique. Structure analysis indicates that all samples characterize in the post-perovskite (Ppv) structure. Physical properties characterizations reveal that Na1-xCaxIrO3 shows an insulator-metal transition (IMT) at x = 0.1, and then exhibits a metal-insulator transition (MIT) with further increasing the Ca concentration to a level between x = 0.6 and 0.7. The transitions are associated with a gradual alternation of the paramagnetic ground state to an antiferromagnetic one due to the increase of Ir4+ ions (S = 1/2, t(2g)(5)) in the nonmagnetic Ir5+ (S = 0, t(2g)(4)) host. The IMIT are discussed by involving the delicate interactions in 5d oxides such as the spin-orbit coupling (SOC), electronic correlation, width of the 5d t(2g) band, and the crystal-field splitting energy within the t(2g) shell. The observation not only would be instructive for inducing novel electronic states via tuning the delicate interactions in 5d oxides but also might pave a way for studying the continuous crossover of a band insulator to a Mott insulator. (C) 2018 Elsevier B.V. All rights reserved.