Mechanosynthesis of the Orthorhombic Perovskites ErMn_1−xNi_xO₃ (x = 0, 0.1). Processing and Characterization of Nanostructured Ceramics

Because of the Jahn−Teller effect and low tolerance factor, the only reported method to obtain ErMnO 3 materials with orthorhombic perovskite structure is to apply a high external pressure (on the order of GPa) at high temperature that transforms the stable room-temperature hexagonal structure to the more dense perovskite one. In this work, single-phase ErMnO 3 and ErMn 0.9 Ni 0.1 O 3 compositions with orthorhombic perovskite structure have been obtained for the first time by mechanosynthesis, after 24 h of milling in a tungsten carbide planetary mill. The high energy state achieved after the prolonged milling allows the perovskite structure to be isolated, instead of the habitual hexagonal one, without any external pressure. Subsequent thermal treatments transform the mechanosynthesized powder to the hexagonal structure at temperatures on the order of 1000 °C or higher. With the aim of obtaining ceramics with perovskite structure, spark plasma sintering (SPS) at 900 and 950 °C and 120 MPa was successfully tested. Ceramics processed by this way have densities greater than 90%.