Synthesis and Ab Initio Structure Determination from Powder Diffraction Data of K4Sn2Si6O18 (original) (raw)

The new Pb5Sb2MnO11 compound was synthesized using a solid-state reaction in an evacuated sealed silica tube at 650C. The crystal structure was determined ab initio using a combination of X-ray powder diffraction, electron diffraction and high-resolution electron microscopy (a ¼ 9:0660ð8ÞA ˚ , b ¼ 11:489ð1ÞA ˚ , c ¼ 10:9426ð9ÞA ˚ , S.G. Cmcm, RI ¼ 0:045; RP ¼ 0:059). The Pb5Sb2MnO11 crystal structure represents a new structure type and it can be considered as quasi-one-dimensional, built up of chains running along the c-axis and consisting of alternating Mn+2O7 capped trigonal prisms and Sb2O10 pairs of edge sharing Sb+5O6 octahedra. The chains are joined together by Pb atoms located between the chains. The Pb+2 cations have virtually identical coordination environments with a clear influence of the lone electron pair occupying one vertex of the PbO5E octahedra. Electronic structure calculations and electron localization function distribution analysis were performed to define the nature of the structural peculiarities. Pb5Sb2MnO11 exhibits paramagnetic behavior down to T ¼ 5K with Weiss constant being nearly equal to zero that implies lack of cooperative magnetic interactions.

The present work deals with the ab initio structure determination and study the crystal chemistry of the heavy metal framework in Bi 0.245 Pb 2.351 U 1.25 Zr 0.8 O 4.5 from precession X-ray diffraction intensities. The metal framework of the compound was solved in this investigation via direct methods by ab initio method from precession XRD diffraction intensities recorded with a Philips EM400 at 100 kV. A subsequent (kinematical) least-squares refinement with X-ray intensities yielded slightly improved coordinates for the 11 heavy atoms in the structure. Chemical analysis of several crystallites by EDX is in agreement with the formula Bi 0.245 Pb 2.351 U 1.25 Zr 0.8 O 4.5. Moreover, the structure was independently determined by Rietveld refinement from X-ray powder data obtained from a multi-phasic sample using JANA computer software programme. The compound crystallizes in the triclinic crystal system and space group P-1 with refined lattice parameters a=6.3458(Å), b=7.9400(Å),c=9.1040(Å), α=77.3239° β=81.0395° γ=70.6732° The refinement values are Rwp = 0.0680, Rp = 0.030 and GOF=0.031 the structure factors F0 =3024 and Fc = 3024 and the volume =420.132 and particle size 80.124nm.

Since the discovery of superconductivity in Sr2CuO2F2+δ there has been an increased interest in ternary oxide-fluorides. Sr2CuO2F2+δ is prepared via low temperature (T = 220 °C) reaction routes. Low temperature fluorination induces an interesting structural rearrangement in the parent compound Sr2CuO3, which is a one-dimensional material containing linear chains of vertex sharing CuO4 squares along the crystallographic b axis. Upon fluorination, one oxide is substituted by two fluorides and Cu2+ becomes octahedrally coordinated by four oxides and two fluorides. The fluorinated compound Sr2CuO2F2+δ displays the T-type structure (La2CuO4). Insertion of excess fluorine, δ, also takes place and this fluorine occupies interstitial sites in the T structure. Although the starting material Ca2CuO3 is isostructural to Sr2CuO3, Ca2CuO2F2+δ displays the T′ (Nd2CuO4) structure due to the smaller radius of Ca2+ compared to that of Sr2+.The alkaline-earth palladates with the general formula A2PdO3 (A = Ba, Sr) are isostructural with the A2CuO3 (A = Ca, Sr) materials. We prepared the Ba2−xSrxPdO3 (x = 0–2) series and performed low temperature fluorination, which led to the synthesis of the series Ba2−xSrxPdO2F2+δ (0 ≤ x ≤ 1.5). All the compounds in the Ba2−xSrxPdO2F2+δ series show T′ structure (Ca2CuO2F2+δ). Similarities and differences with Sr2CuO2F2+δ and Ca2CuO2F2+δ will be discussed.

The title compound was synthesized in the form of a powder, and was studied by elemental analysis, IR spectroscopy, thermogravimetry and mass spectroscopy. Its crystal structure was then determined by X-ray powder diffractometry, using X-ray diffraction data collected in the reflection Bragg–Brentano geometry. The methodology followed in the present study to resolve the crystal structure consisted of peak indexing, then the use of the Monte-Carlo/parallel tempering search algorithm, and finally Rietveld refinement coupled with difference-Fourier synthesis. We found that the crystals are composed of monoclinic unit cells, with 1.5 molecules in the asymmetric unit and therefore six molecules per unit cell. In addition, we concluded that the complexes adopt a planar conformation, forming trimers created by groups of parallel molecules.