1961 Volume 16 Issue 4 Pages 671-675
The crystal structures of the antiferromagnets KMnF3, KFeF3 KCoF3, KNiF3 and KCuF3 have been determined above and below their Néel temperatures (TN) by X-ray diffraction using single crystals. At room temperature (above TN) the structures of these compounds are of the ideal perovskite type (cubic) except for that of KCuF3 which crystallizes as a tetragonal modification (a>c) of the perovskite type. At 78°K (below TN) the lattice symmetries of KMnF3, KFeF3 and KCoF3 are monoclinic, rhombohedral (α<90°) and tetragonal (a>c), respectively, while KNiF3 and KCuF3 retain their own symmetries at room temperature. The lattice constants have been determined between these temperatures and their changes near the transition temperature were closely followed. This temperature region was extended up to 670°K for KCuF3.
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