Phase Formation in the Calcium Hexaboride–Iridium System

Abstract

The processes occurring in the Ca–Ir–B system were studied. The elemental and phase compositions and morphology of the products formed in the reaction of iridium metal with calcium hexaboride in the 700–1600°C temperature range were investigated. The signs of the onset of the reaction are already visible at 700°C. The first reaction products are iridium borides IrB0.9 and IrB1.1, where IrB0.9 is formed as a low-temperature and metastable high-temperature polymorphs. An increase in the treatment temperature in the 1000–1600°C range leads to the formation of three ternary compounds, presumably, Ca3Ir8B6, CaIr4B4, and CaIr2B2; the first two of these phases were previously unknown. The unit cell parameters of the new compounds, Ca3Ir8B6 (based on Sr3Rh8B6) and CaIr4B4 (based on LaIr4B4), were determined. The results attest to the complexity of the processes occurring in the Ca–Ir–B system and the diversity of ternary boride phases. The ternary boride phases can be of interest by themselves for high-temperature materials science.