A comprehensive variable temperature study of the layered oxide, Ca2Mn3O8

• Published in: Journal of alloys and compounds Vol. 843; p. 155633
• Main Authors: Vera Stimpson, Laura J., McNulty, Jason A., Morrison, Finlay D., Mahajan, Amit, McCabe, Emma E., Gibbs, Alexandra S., Stenning, Gavin B.G., Jura, Marek, Arnold, Donna C.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 30.11.2020; Elsevier BV
• Subjects: Calcium ions; Conductors; Electronic measurements; Layered oxides; Manganese ions; Moisture content; Neutron diffraction; Perovskites; Thermal analysis; Layered oxides; Neutron diffraction; Electronic measurements
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.155633

Ca2Mn3O8 forms a delafossite-related layered structure, which crystallises with monoclinic C2/m symmetry. Compared with the delafossite-structure, the MnO6 layers in Ca2Mn3O8 exhibit an ordered cation void which forms a magnetic ‘bow-tie’ like connectivity of Mn4+ ion layers separated by Ca2+ ions. In-situ variable temperature diffraction data demonstrates that the structure is robust up to a temperature of approximately 1173 K before the material decomposes into the perovskite, CaMnO3 and marokite, CaMn2O4 phases. Simultaneous thermal analysis suggests that a very small amount of water remains within the layers post synthesis. Impedance spectroscopy indicates that Ca2Mn3O8 is an electronic conductor in the range ∼400–700 K with an activation energy of 0.50 ± 0.01 eV. Recently we have pioneered the synthesis of high-quality single phase Ca2Mn3O8. This has allowed us to;•Perform the first variable temperature in-situ powder neutron and x-ray diffraction studies of Ca2Mn3O8 in different atmospheres, allowing us to show that thermal expansion, unusually for a layered material, is largely isotropic.•Report complementary variable temperature Raman spectroscopy studies.•Using Spark Plasma Sintering (SPS) we have been able to prepare high density pellets allowing us to show that Ca2Mn3O8 is an electronic conductor in the range ∼400 – 700 K with an activation energy of 0.50±0.01 eV.