A. V. Arakcheeva

Crystal Structure and Optical and Magnetic Properties of Pr2(MoO4)3

Praseodymium molybdate Pr(2)(MoO(4))(3) was synthesized using the standard ceramic route. The crystal structure of the material has been successfully solved in superspace group I2/b(alphabeta0)00 with lattice constants a = 5.30284(4), b = 5.32699(3), c = 11.7935(1) A, gamma = 90.163(1) degrees , and the modulation vector q = 2/3a* + 0.88810(2)b*. The deviation of the q vector from a rational value allows a description of the structure in terms of nanosize domains with the La(2)(MoO(4))(3)-like structure separated by stacking faults. Under 450 nm excitation, ((3)P(0) level) Pr(2)(MoO(4))(3) exhibits the characteristic red emission, with the most intense band at 649 nm corresponding to a (3)P(0) --> (3)F(2) transition. Magnetic susceptibility measurements reveal Curie-Weiss paramagnetism with predominating antiferromagnetic interactions between Pr(3+)-magnetic moments and no evidence of magnetic transitions down to T = 5 K.

The LT phase of Cs3Bi2I9

Abstract The low temperature (LT) modification of Cs3Bi2I9 has been refined to R(F) = 0.055 on the basis of X-ray diffraction measurements at T = 130 K from a twin crystal with six fractions connected by 3-fold axis and m-planes symmetry operations. Data were collected on a KM4CCD diffractometer; MoKα-radiation; 1769 independent reflections with F > 4σ(F) were obtained. Below the LT phase transition each reflection were split. The absorption correction was accounted for by the Gaussian integration method. The parameters of the monoclinic unit cell are: a = 8.346(8), b = 14.47(1) and c = 21.10(1) Å, β = 91.00(7)°; space group C2/c. The structure of the monoclinic LT phase is slightly distorted in comparison to the hexagonal RT phase (am = ah; bm = 2ah + bh, cm = -ch). The phase transition at T = 218 K between the RT and LT modifications is reversible. The additional maxima observed in the Fourier-syntheses are associated with coherent parts in domains belonging to various twin fractions. The nature, the probable structure and the temperature variations of the domain boundaries are considered and discussed. It is suggested that the specific effect observed on 127I NQR spectra for the LT modification between 205 < T K < 218 may be due to the incommensurate nature of the domain boundaries.

Crystal structure of loparite

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 (γMoKα radiation, 105 independent reflections with I > 3σ(I), R = 0.041 in the anisotropic approximation). The structure belongs to the perovskite type (ABO3) 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.

The crystal structure of lewisite, (Ca,Sb3+,Fe3+,Al,Na,Mn,□)2(Sb5+,Ti)2O6(OH)

Abstract The crystal structure of lewisite, ideally (Ca,Sb 3+ ,Fe 3+ ,Al,Na,Mn,□) 2 (Sb 5+ ,Ti) 2 O 6 (OH), cubic, space group Fd3m , a =10.311(7) A, V =1096.23 A 3 , Z =8, d calc. =4.73, d obs. =4.95 g/cm 3 , F (000)=1531, has been solved by single-crystal X-ray diffraction analysis and refined to R =0.015 for 218 unique reflections with ∣ F ∣>4 σ ( F ). The pyrochlore-like structure contains distorted A cubes and B octahedra. A comparison among lewisite and several other pyrochlore-like structures with B=Sb 5+ shows that increase of the unit cell parameter depends on the size of the A-cations. XRD study of lewisite did not reveal the intergrowth of two sublattices, previously anticipated in this structure. A comparison of two models with a static distribution of Sb 3+ (splitting of the A site) and a dynamic distribution (anharmonic thermal displacements of cations in the A site) led us to prefer the latter. A structural study of romeite is now necessary to establish the identity of lewisite and romeite.

New boron-oxygen layer in the structure of barium hydrodecaborate Ba-5[B20O33(OH)(4)]center dot H2O

The crystal structure of the new synthetic compound Ba5[B20O33(OH)4] ⋅ H2O was established by the methods of X-ray diffraction (a Stoe IPDS diffractometer, λMoKα?, 1860 independent reflections, anisotropic refinement, R = 1.95%, localization of hydrogen atoms): a = 9.495(2) Å, b = 6.713(1) Å, c = 11.709(2) Å, β = 95.09(1)°, sp. gr. P2, Z = 1. The structure is based on double pseudohexagonal layers consisting of BO4-tetrahedra and BO3 triangles linked into three-membered rings in two mutually perpendicular directions. The double layers adjacent along the [100] direction are linked together through the Ba-polyhedra and hydrogen bonds with the participation of the OH-groups occupying the “end” vertices of two B-triangles. The interlayer space is also filled with a sheet of Ba-polyhedra. The structure of the compound is compared to the structures of topologically similar Ba and Ca borates and hydroborates.

Crystal structure of new decaborate Na2Ba2[B10O17(OH)2]

AbstractThe crystal structure of a newly synthesized compound Na2Ba2[B10O17(OH)2] has been determined (Syntex n

Magnetic properties and crystal structure of β-Ta

Pbar 1

Analysis of the structure of an amorphous sediment obtained upon decomposition of potassium oxofluroniobate in water

n diffractometer, MoKα radiation, 1784 crystallographically nonequivalent reflections, anisotropic approximation, R = 1.7%). The parameters of the monoclinic unit cell are a = 11.455(7), b = 6.675(4), c = 9.360(7) Å, β = 93.68(5)°, Z = 2, sp. gr. C2. The structure consists of double pseudohexagonal layers built by BO4-tetrahedra and BO3-triangles forming three-membered rings of two mutually orthogonal orientations. The neighboring layers along the [001] direction are bound by Na-polyhedra and hydrogen bonds with participation of OH groups. The interlayer tunnels along the [100] direction are filled with columns of Ba-polyhedra. The crystallochemical characteristics of a number of synthetic Ba-borates (to which the structure of new decaborate is related) are considered in terms of borate building blocks singled out in the structure.