Valence transition in ordered perovskites Ba2PrRu1-xIrxO6

The crystal structures and magnetic properties of ordered perovskites Ba2Pr Ru1-xIrxO6 are investigated. Powder X-ray diffraction measurements at room temperature show the Pr and (Ru,Ir) ions to be in the trivalent and the pen tavalent states, respectively, for the Ru-rich compounds, while both of the Pr and (Ru,Ir) ions to be in the tetravalent state for the Ir-rich compoun ds. Two phases exist in the 0.1 less than or equal to x less than or equal to 0.5 region, which are composed of the two ordered perovskites, Ba2Pr3+ ( Ru,Ir)O-5+(6) and Ba2Pr4+(Ru,Ir)O-4+(6). The magnetic susceptibilities of B a2PrRu0.90Ir0.10O6 show a magnetic anomaly in the temperature range 60 less than or equal to T less than or equal to 200 K, i.e. the hysteresis of the magnetic susceptibilities has been observed in this temperature range. Sim ilar magnetic behavior has been observed for the susceptibility vs. tempera ture curves of the compounds with 0.15 less than or equal to x less than or equal to 0.40. The results of the X-ray diffraction and magnetic susceptib ility measurements suggest the occurrence of valence transition. (C) 2001 E lsevier Science Ltd. All rights reserved.