Discovery of Rhombohedral NaIrO₃ Polymorph by In Situ High-Pressure Synthesis of High-Oxidation-State Materials Using Laser Heating in Diamond Anvil Cells

Abstract

We report a new in situ synthesis method effective for discovery of high-oxidation-state materials using laser-heated diamond anvil cells. The issue of chemical reduction during thermally induced phase transitions that occur spontaneously in a noble gas pressure transmitting media (PTM) can be overcome by thermal decomposition of an oxygen-rich solid PTM (NaCl + NaClO 3 ). To illustrate the technical challenges the method overcomes, we applied this new method for two known pentavalent A (I) B (V) O 3 postperovskite compounds. We successfully synthesized the two postperovskites, NaOsO 3 and NaIrO 3 , and quenched to ambient conditions. Furthermore, we report the discovery of a new low-pressure polymorph of NaIrO 3 , illustrating the high potential for new materials discovery. This new method will enable realization of new high-oxidation-state postperovskites and can be applied for many other structure families in a P, T parameter space that is not easily accessible using conventional high-pressure synthesis methods.

High-Pressure, High-Temperature Studies of Phase Transitions in SrOsO3─Discovery of a Post-Perovskite

“…The bream size was focused down to 3 × 5 μm 2 , and the photon energy was 30.5 keV (λ = 0.40663 Å). A newly developed high-pressure, laser heating method was used for the experiment and is described in detail in a previous publication . A Mao-Bell-type DAC with a culet of 200 μm was used for the experiment.…”

“…A newly developed high-pressure, laser heating method was used for the experiment and is described in detail in a previous publication. 21 A Mao-Bell-type DAC with a culet of 200 μm was used for the experiment. SrOsO 3 was ground, filtered to sub-micron grain size, and finally pressed to a circular slap with ∼10 μm thickness.…”

“…Here, we report the discovery of the post-perovskite structure in SrOsO 3 . Using a newly developed method for in situ laser heating in diamond anvil cells (DACs), 21 we transformed the orthorhombic perovskite of SrOsO 3 to the post-perovskite structure at 44 GPa and 1350 K. In addition, we report the first compression study of perovskite SrOsO 3 up to 66 GPa at ambient temperature. This study revealed a continuous phase transition to the monoclinic P2 1 /n symmetry at 36 GPa and going back to orthorhombic Pbnm symmetry above 58 GPa.…”