Characterization of RMnO3 (R=Sc, Y, Dy-Lu): High-pressure synthesized metastable perovskites and their hexagonal precursor phases

Abstract

Abstract A series of R MnO 3 samples with R = Sc, Y, Dy-Lu was synthesized through a two-step route in which first the hexagonal oxides, h - R MnO 3 , were prepared under normal pressure using an EDTA method and then converted to orthorhombic perovskites, o - R MnO 3 , through a high-pressure treatment at 5 GPa and 800 °C. Since all the aforementioned members but the R = Sc member were converted to an orthorhombic perovskite phase under the 5-GPa high-pressure condition, an additional sample of InMnO 3 of the hexagonal structure was prepared and tested for the high-pressure conversion. The stability limit of the orthorhombic perovskite structure under the 5-GPa high-pressure condition was concluded to be located between InMnO 3 and LuMnO 3 in terms of the size of the A-site cation constituent, R III or In III . The decrease in the size of R III was found to increase the distortion of o - R MnO 3 with a decrease in the Mn O Mn bond angle from 144.3° for Dy to 140.3° for Lu. All the hexagonal and orthorhombic R MnO 3 phases exhibited antiferromagnetic characteristics at low temperatures.