Borides of calcium and lanthanum

It can therefore be concluded that the unexpected ferromagnetism obtained independently for CaB2C2 and for lanthanum-doped CaBg does not reflect an intrinsic property of these compounds [7]. 

For example, the difference between the monoclinic CaC2 phases is the presence of only one type of acetylide ion in phase II and two distinct C2 species in phase III, as concluded from their crystal structures and from C-NMR studies (Fig. 8.3) [8]. The transformation between phases II and III is induced by heating phase II above 150°C until the metastable phase. III, is formed. Phase III remains stable even when being cooled down to room temperature. However, when the metastable phase III is ground in a mortar at room temperature, it transforms back into phase II. 

The phase relationship between the most commonly known tetragonal phase CaC2-I and phase(s) II (or III) is still in question. CaC2-I transforms reversibly into the cubic phase IV, as does the phase (II -r) III. It is interesting to note that the cubic phase IV seems to have a memory for its respective precursor phase (III or I) that is regained after cooling down phase IV. The synthesis of 

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