Phase transitions of modulated Co-åkermanite, Ca2CoSi2O7
Abstract
This paper deals with X-ray single crystal experiments of modulated cobalt åkermanite at temperatures between 30 K and 600 K. The primary objective of these investigations was to study the predicted lock-in phase transition into a commensurate low temperature phase. Upon cooling the phase transition occurs at 160 K, provided that the time for thermodynamic equilibration at each temperature step is guaranteed. The low temperature phase turns out to be incommensurate with a modulation wavelength of 3.086(6) · a0. This is very close to the predicted commensurate value of 3 · a0 The standard deviations of the q-values are small enough to determine this low temperature phase as significantly incommensurate. A fourier synthesis of the complementary structure (as a 3-fold superstructure) reveals a tetragonal displacement pattern of the cobalt-atoms at low temperatures. The second order phase transition to the parent structure occurs at 498(1) K. It is characterized by a critical exponent β = 0.31(1)°.
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Artikel in diesem Heft
- Icosahedral coincidence rotations
- Localization and integration of diffraction spots from two-dimensional X-ray detector images by digital filtering
- Finite periodicity and crystal structures
- Structure determination from powder data using anomalous scattering: difference and partial, Patterson densities, and phases of structure factors
- Phase transitions of modulated Co-åkermanite, Ca2CoSi2O7
- Preparation and single crystal structure refinement of mixed orthophosphates M3Cr4(PO4)6 (M = Mg, Zn, Cu) – copper(II) in compressed octahedral coordination1
- Crystal structures of Ca5Ge3O11 and wollastonite-type GaGeO3
- One-dimensional staircase aggregates in crystals of 1,7-bis(dimethylamino)heptamethinium hexafluorophosphate, a polymethine dye
- Crystal structures of N-4-methyl phenyl)-2,2,2-trichloroacetamide, N-2,3-dimethyl phenyl)-2,2,2-trichloroacetamide and N-(2-nitro phenyl)-2,2,2-trichloroacetamide
- The structure of 6-(2-hydroxybenzylamino)purine acetic acid solvate
- Structural variations in the mercury(II) bis(1,1-dithiolate)s: the crystal and molecular structure of [Hg(S2CNMe2)2]
Artikel in diesem Heft
- Icosahedral coincidence rotations
- Localization and integration of diffraction spots from two-dimensional X-ray detector images by digital filtering
- Finite periodicity and crystal structures
- Structure determination from powder data using anomalous scattering: difference and partial, Patterson densities, and phases of structure factors
- Phase transitions of modulated Co-åkermanite, Ca2CoSi2O7
- Preparation and single crystal structure refinement of mixed orthophosphates M3Cr4(PO4)6 (M = Mg, Zn, Cu) – copper(II) in compressed octahedral coordination1
- Crystal structures of Ca5Ge3O11 and wollastonite-type GaGeO3
- One-dimensional staircase aggregates in crystals of 1,7-bis(dimethylamino)heptamethinium hexafluorophosphate, a polymethine dye
- Crystal structures of N-4-methyl phenyl)-2,2,2-trichloroacetamide, N-2,3-dimethyl phenyl)-2,2,2-trichloroacetamide and N-(2-nitro phenyl)-2,2,2-trichloroacetamide
- The structure of 6-(2-hydroxybenzylamino)purine acetic acid solvate
- Structural variations in the mercury(II) bis(1,1-dithiolate)s: the crystal and molecular structure of [Hg(S2CNMe2)2]
