A comprehensive variable temperature study of the layered oxide, Ca2Mn3O8

Phase stability of the layered oxide, Ca2Mn3O8; probing interlayer shearing at high pressure

“…18 The Rietveld fit to the data clearly indicates an excellent fit to the monoclinic, C2/m, model expected for Ca 2 Mn 3 O 8 . 18,30,31 Additional phases of Pb (Fm% 3m) from the pressure calibrant and, ZrO 2 (P4 2 /nmc) and Al 2 O 3 (R% 3c) from the anvil were also refined.…”

“…This is in contrast with the behaviour of the MnO 6 polyhedra where the Mn 2 with respect to each other in adjacent layers. [17][18][19][20][29][30][31] This means the Ca-O-Mn bond environments are different above and below the Ca 2+ cation as shown in Fig. 7.…”

“…30 The high crystallinity of these materials allowed us to perform more comprehensive studies of the thermal stability and magnetic behaviour of Ca 2 Mn 3 O 8 . 30,31 Low temperature studies (1.8-300 K) showed that Ca 2 Mn 3 O 8 orders antiferromagnetically with an mmkk arrangement of the magnetic spins at a Néel temperature (T N ) of approximately 58 K. 30 Additionally, an invariant behaviour below 130 K is seen in the lattice parameter, b and the monoclinic b angle. This occurs at the same temperature as a deviation from Curie-Weiss behaviour observed in magnetic susceptibility measurements and is consistent with short-range spin correlations.…”

“…30 Data collected between 300 and 1273 K show that the monoclinic structure is remarkably stable up to a temperature of approximately 1200 K before it decomposes into the perovskite, CaMnO 3 and marokite, CaMn 2 O 4 phases. 31 Moreover, electrical measurements confirm that Ca 2 Mn 3 O 8 is an electronic conductor in the temperature range, 400-700 K with an activation energy of approximately 0.50(1) eV. 31 Given the interesting nature of Ca 2 Mn 3 O 8 and the phase stability of the C2/m structure as a function of temperature it is of importance to determine the distortion of this structure on the application of hydrostatic pressure.…”

“…31 Moreover, electrical measurements confirm that Ca 2 Mn 3 O 8 is an electronic conductor in the temperature range, 400-700 K with an activation energy of approximately 0.50(1) eV. 31 Given the interesting nature of Ca 2 Mn 3 O 8 and the phase stability of the C2/m structure as a function of temperature it is of importance to determine the distortion of this structure on the application of hydrostatic pressure. Applied pressure is an effective way to change co-ordination environments and tune property behaviour driving very different distortion behaviour upon increasing pressure.…”