Crystal structure and microtwinning of Na5(Na0.5+xCa0.5-x)2(NdxCa1-x)2 [Si6O18]

The X-ray structural study of atomic structure and microtwinning of crystals of the compound given in the title is performed. Twinning lattice parameters are a=14.926(5), b=15.003(4), c=7.446(5)A, γ=91.79(3) deg. X-ray structural studied have shown that the above crystals twin in the reticular pseudomerohedrism (twin index n=2) and the elemntary cell of monocrystal is described by the monoclinic symmetry (ph.gr. P21/b) with the following parameters a=7.501, b=14.926, c=7.446 A, γ=91.79 deg. The structure is specified with respect to microtwinning in the anisotropic approximation up to R=0.041