Molecular motion and phase transition in perovskite-type (CH3)nNH4−nSnCl3 (n=1–4) studied by proton NMR spin–lattice relaxation

Powder X-ray diffraction, ¹¹⁹Sn NMR spectra, and ¹H NMR spin–lattice relaxation times, T₁, were measured for (CH₃)_nNH_4−nSnCl₃ (n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of ¹H T₁ was analyzed in terms of the CH₃ reorientation and other motions of the whole cation. Except for the phase transition in CH₃NH₃SnCl₃, which is from monoclinic to rhombohedral at 331 K, ¹H T₁ was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl₃]_nⁿ⁻ perovskite lattice.     

X‐ray powder diffraction study of the semiconducting alloy Cu2Cd0.5Mn0.5GeSe4

The structure of the semiconducting alloy Cu₂Cd_0.5Mn_0.5GeSe₄ was refined from an X‐ray powder diffraction pattern using the Rietveld method. The present alloy crystallizes in the wurtz‐stannite structure, space group Pmn2₁ (N^o 31), and unit cell parameters values of a = 8.0253(2) Å, b = 6.8591(2) Å, c = 6.5734(2) Å and V = 361.84(2) ų. The structure exhibits a three‐dimensional arrangement of slightly distorted CuSe₄, Cd(Mn)Se₄ and GeSe₄ tetrahedras connected by corners. © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Crystal structure of zirconia by Rietveld refinement

The crystal structures and phase transformation of zirconia ceramics have been investigated by means of X-ray powder diffraction and Rietveld powder diffraction profile fitting technique. A structural transition from monoclinic to tetragonal occurs when Y₂O₃ and₂ are doped into zirconia. The space group of the tetragonal structure is P4₂/nmc,Z=2. The lattice parameters are α=0.362 6(5)nm,c=0.522 6(3)nm for CeO₂ doped zirconia and α=0.360 2(8)nm,=0.517 9(1)nm for Y₂O₃ doped zirconia, respectively. In each unit cell, there are two kinds of equivalent positions, i.e. 2b and 4d, which are occupied by Zr⁴⁺, M(M=Y³⁺, Ce⁴⁺) cations and O^2- anions, respectively. The crystallographic correlation among the cubic, tetragonal and monoclinic structures of ZrO₂ is discussed.     

Polyesters with semifluorinated side chains: A proposal for the solid‐state structure

A proposal for the solid‐state structure of poly(p‐phenylene isophthalate) with oxydecylperfluorodecyl side chains is presented, which was calculated by the new Rietveld refinement program BGMN®. A triclinic unit cell with a = 0.575 nm, b = 4.06 nm, c = 2.1 nm, α = 91.2°, β = 85.7°, and γ = 66.1° was obtained using space group symmetry P1¯ (No. 2) with Z = 2. All fractional atom coordinates, reflections and structure factors F were determined. The results show that highly occupied netplanes lie in plane and perpendicularly to the side chains. It may be supposed that these net planes will form the low‐energy surface of the polymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1617–1625, 2000     

铬在纳米晶氧化铁中的掺杂研究

Fe^3^+(Cr^3^+)/Fe^2^+混合离子(M^3^+/M^2^+原子比为2:1)共沉淀法制备的Cr~2O~3掺杂量O～14%(质量分数)系列纳米氧化铁,XRDRietveld分析表明全是晶态γ-Fe~2O~3和非晶Fe~2O~3的混合物。非晶丰度范围为21.72%～48.6%。Mossbauer谱分析发现,掺杂量少于2%(质量分数)的氧化铁,晶态和非晶态均是磁性六线谱,大于2%(质量分数)后,另出现强度随掺杂量增加线性递增的超顺磁二线谱。共沉淀过程中,Fe^3^+为主夹杂定量Cr^3^+的Fe^3^+水合配合物网络与Cr^3^+为主夹杂定量Fe^3^+的Cr^3^+水合配合物网络,是形成磁性氧化铁和非晶非磁氧化铁的基础,后者镶嵌在前者中间,阻碍其晶化和晶粒长大,自身形成非晶非磁含铬氧化铁。