Springer Online Journal Archives 1860-2000
Abstract The crystal structure of the cubic modification of the natural mineral loparite has been studied for the first time by the methods of the X-ray diffraction analysis (γMoK α radiation, 105 independent reflections with I 〉 3σ(I), R = 0.041 in the anisotropic approximation). The structure belongs to the perovskite type (ABO 3) with the double period of the cubic unit cell, a = 7.767(1) Å (sp. gr. Pn3m; Z = 2 for the composition (Ca,Na,Ce)(Na,Ce)3(Ti,Nb)2Ti2O12. Period doubling is explained by ordering of cations both in the A and the B positions.
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