A STUDY ON THE BAIRO3 SYSTEM

The compound BaIrO3 has been studied over the years but a complete characterization, both in terms of structure and properties, has not yet been reported. A recent publication on the structure of Ba7Ir6O19 prompted us to complete our studies on the parent compound BaIrO3, and to report the physical properties obtained on several polytypes having this particular chemical composition. Thermal decomposition of the precursor BaIr(OH)6 led to a series of BaIrO3 polytypes, "6H", "3H", and "18R", with final decomposition to the monoclinic Ba7Ir6O19 compound. Solid state preparations, performed at high temperatures, yielded only the "18R" polytype. Crystal growth attempts at approximately 1000-degrees-C in a BaCl2 flux yielded large crystals. These were found to possess a pseudorhombohedral structure which approximated an "18R" structure. On closer examination, however, a monoclinic cell was observed for untwinned crystals. Several polytypes or polymorphs of BaIrO3 were formed as a function of temperature, but only one polytype was obtained in single-crystal form for structural studies. The unit cell parameters of the hydroxide precursor and of all the single-phase polytypes are presented. The magnetic properties of two pure BaIrO3 polytypes, studied as a function of temperature, exhibited an interesting magnetic transition at 160 K. The electrical properties, on powder compacts, indicated low resistivity at room temperature which increased rapidly on cooling to lower temperatures.