Structure types and phase transformations in \KMnCl3\ and TlMnCl3

Title Structure types and phase transformations in \KMnCl3\ and TlMnCl3
Author: Horowitz, A; Amit, M; Makovsky, J; Dor, L.Ben & Kalman, Z H
Journal of Solid State Chemistry, 1982
More details: \{KMnCl3\} and TlMnCl3 are known to crystallize in tetragonal and cubic perovskite structures, respectively. Room temperature X-ray diffraction data obtained in our laboratory proved that the perovskite structure of KmnCl3 is orthorhombic. The space group is Pnma and Z . Unit cell parameters are a .08(1), b .97(1), and c .98(1) \AA. Experimental data showed that the perovskite structures of \{KMnCl3\} and TlMnCl3 are not stable, and that both materials transform slowly into another orthorhombic, nonperovskite \{KCdCl3\} structure with space group Pnma and Z . Cell parameters of these structures are a .769(7), b .883(9), and c 4.42(1) \AA for \{KMnCl3\} and a .926(8), b .839(9), and c 4.77(1) \AA for TlMnCl3. The nonperovskite structures of \{KMnCl3\} and TlMnCl3 transform on heating to the perovskite structures and these phase transitions are not immediately reversed. No correlation could be found between the \{KCdCl3\} structure and water incorporation in the crystal lattice as has been previously suggested. An analysis of the factors that cause the K structure to be exhibited in chloride and to be absent in the fluoride compounds is also presented.

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