4-DIMENSIONAL STRUCTURE DETERMINATION OF THE INCOMMENSURATE MODULATED COMPOUND (ND4CA2)TI6O20

The structure of the incommensurate modulated compound (Nd//4Ca//2)Ti//6O//2//0 has been analyzed on the basis of a four-dimensional description in the space group S(1-2) 2/m//c// plus //e//4 (a equals 3. 832Angstrom, b equals 36. 64Angstrom, c equals 5. 436Angstrom, q* equals 0. 49a*, Z equals 2). The modulation involves rotations of the TiO//6 octahedra of the perovskite-like structure around the left bracket 010 right bracket direction, coupled with a substitutional modulation of the Nd-Ca species. R-factors are respectively 0. 087, 0. 070 and 0. 113 for all, main and satellite reflections (1699 observed intensities).