A series of RMnO3 samples with R = Sc, Y, Dy-LU Was synthesized through a two-step route in which first the hexagonal oxides, h-RMnO3, were prepared under normal pressure using an EDTA method and then converted to orthorhombic perovskites, o-RMnO3, through a high-pressure treatment at 5 GPa and 800 degrees 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 InMnO3 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 InMnO3 and LuMnO3 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-RMnO3 with a decrease in the Mn-O-Mn bond angle from 144.3 degrees for Dy to 140.3 degrees for Lu. All the hexagonal and orthorhombic RMnO3 phases exhibited antiferromagnetic characteristics at low temperatures. (C) 2008 Elsevier B.V. All rights reserved.