Bond lengths in ‘CaMn3’ (Mn4)O12: A new Jahn-Teller distortion of Mn3+ octahedra

Soft vibrational mode associated with incommensurate orbital order in multiferroicCaMn7O12

“…Our result constitutes the first direct observation of amplitude excitations associated with an orbital order, and it suggests the importance of lattice degrees of freedom in the formation of the orbital order in CaMn 7 O 12 . 24 whereas the C-site Mn 3+ (denoted as Mn1) ions are in MnO 4 rhombus configuration. Upon cooling through a first-order phase transition at T s ≈ 440 K, one of the body diagonals of the cubic cell shrinks, making the crystal structure rhombohedral (space group R3) at room temperature.…”

“…Upon cooling through a first-order phase transition at T s ≈ 440 K, one of the body diagonals of the cubic cell shrinks, making the crystal structure rhombohedral (space group R3) at room temperature. 24,25 The rhombohedral c-axis in the hexagonal basis is parallel to the shortened cubic body diagonal (Fig. 1a).…”

High Pressure Induced Insulator-to-Semimetal Transition through Intersite Charge Transfer in NaMn7O12

“…These materials are characterized by A site cation ordering, where 3 4 of the original perovskite A sites are occupied by Mn 3+ ions in an uncommon square planar coordination (Figure 1), only stabilized by high-pressure/high-temperature (HP/HT) synthesis. The valence of the A ion tunes the Mn 3+ /Mn 4+ ratio on the B site, determining the crystal symmetry based on the specific charge and orbital ordering, as reported for compounds with A = Na [23], Ca [24], (Sr, Cd) [25], Pb [26], La [27,28], Bi [29,30], Y [31], and Pr [32]. The high electronic correlations, the significant lattice distortions, the full oxygen occupation (contrary to what usually happens in the conventional "simple" perovskites) and the chemical order (hetero-valent manganese atoms occupy different crystallographic sites), make this class of materials an intriguing playground for the study of possible instabilities induced by external stimuli on both the structural and physical properties.…”

Thermal Lattice Parameters Variation of CaCuxMn7-xO12Compounds with Trigonal Crystal Structure

“…Below 400 K CaMn 7 O 12 crystallises in the trigonal space group R3 [5,8]. Below 90 K magnetic long-range ordering with a series of complex magnetic phases and simultaneous magnetic phase separation is observed [6].…”

“…The undoped CaMn 7 O 12 system has been extensively studied using high resolution neutron diffraction [5][6][7] and high resolution synchrotron X-ray diffraction [7,8]. Below 400 K CaMn 7 O 12 crystallises in the trigonal space group R3 [5,8].…”