Structure types and phase transformations in KMnCl3 and TlMnCl3 |
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Authors: | A. Horowitz M. Amit J. Makovsky L.Ben Dor Z.H. Kalman |
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Affiliation: | Nuclear Research Center-Negev, P.O.B. 9001, Beer Sheva, Israel;Hebrew University of Jerusalem, Jerusalem, Israel |
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Abstract: | 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 = 4. Unit cell parameters are a = 7.08(1), b = 9.97(1), and c = 6.98(1) Å. 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 = 4. Cell parameters of these structures are a = 8.769(7), b = 3.883(9), and c = 14.42(1) Å for KMnCl3 and a = 8.926(8), b = 3.839(9), and c = 14.77(1) Å 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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Keywords: | Author to whom correspondence should be addressed. |
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