Abstract: Spinel samples of Li1.33xCo2-2xTi1+0.67xO4 crystallize in two space groups: Fd- 3 m for 0≤x≤0.40 and x=1, and P4332 for 0.50≤x≤0.875. In S.G. P4332 magnetic Co2+ ions occupy 8c sites (for x=0.75 and 0.875), or 8c, 4b and 12d sites (for x=0.50). In x=0.25 and 0.40 samples Co2+ occupy both 8a and 16d cation sites of the S.G. Fd- 3 m . Observed differences in magnetic behaviour of the samples are induced by crystallographic distribution of Co2+. Possible paths for exchange interactions in S.G. P4332 were analysed. It was found that the superexchange is the dominant exchange mechanism where Co2+
(8c)-O(24e)-Co2+(12d) path was the most important
one. On the basis of the results on crystallographic distribution we suggest x=0.50 sample as potential electrode material in Li ion rechargeable batteries.
Abstract: The double perovskites Ca2-xSrxMnWO6 (x = 0.0, 0.5, 1.0, 1.5, 2.0) have been prepared as pure phases by a conventional solid-state reaction process. Stoichiometric amounts of CaCO3,SrCO3, MnO and WO3 were mixed, ground and calcined in a nitrogen atmosphere. X-ray and neutron powder diffraction (NPD), together with magnetisation measurements were carried out in order to characterise the materials. The NPD and magnetisation measurements, performed at
different temperatures, were made in order to correlate the materials structural and magnetic properties. Susceptibility- Temperature (ϰ-T) curves were measured between 2K and 200K in field cooled (FC) and zero-field-cooled (ZFC) modes with an applied field (H) up to 3T. Rietveld analysis of NPD data shows that the samples were B-site ordered perovskites with different types of lattice symmetry. Magnetisation measurements at low temperatures indicate an antiferromagnetic
ordering of the magnetic moments.
Abstract: The magnetic structure of CrNiAs was determined from magnetisation and powder
neutron diffraction experiments. In the 110-182 K temperature range, the compound is ferromagnetic, resulting mainly from the Cr moment of 1.25(5) μB. Below 110 K, neutron diffraction data reveals typical satellite reflections which propagation vector is 0.228 c*. A model of oscillating magnetic moments was refined from the integrated intensity of the few additional lines.
Abstract: Structural, magnetic, dielectric properties and Mossbauer effect were
investigated on complex perovskite with composition AFe2/3B1/3O3 (A=Ca,Sr,Pb,Ba;
B=W,Te). The most striking feature of this type of complex perovskites is the coexistence of magnetic and antiferroelectric types of ordering in a certain temperature interval. It was found that ferrimagnetic Ca and Sr compounds belong to a partially ordered perovskite structure, and antiferromagnetic Pb phase to a disordered one. The possible models for nuclear and magnetic structures were proposed in accordance with the observed dielectric and magnetic properties.
Abstract: The Tb2Ti2S2O5 compound belongs to the lanthanide titanium oxysulfides family Ln2Ti2S2O5. The 3D-structure can be schematically described as a 2D-stacking of [Tb2S2] layers alternating with [Ti2O5] ones. The magnetic structure of this compound was determined from neutron diffraction experiments on a powder sample in the 1.4 K - 15 K temperature range. An incommensurate antiferromagnetic long-range order (LRO) occurs at temperatures ranging from 4.1 K to 2.9 K, which turns to a commensurate state below 2.4 K. The evolution of the propagation vector from ki, ⃗ (kx,0,0), kx ≈ 0.46 to kc, ⃗(1/2,0,1/2) is quite unusual. The origin of this unusual
change in direction of the propagation vector is not yet explained. On the other hand, a quite large part of the total magnetic moment is involved in a short range ordering (SRO). The refinement procedure taking into account the different coexisting magnetic phases leads to a smooth variation of the total magnetic moment versus temperature.
Abstract: Evidence of the coexistence of an ordered antiferromagnetic and a spin glass state is given by studying a polycrystalline Tb2CuIn3 sample with neutron diffraction in a non-magnetic and a magnetic environment. Tb2CuIn3 is an antiferromagnet with competing exchange interactions (J1> 0 for nearest neighbours and J2 < 0 for next nearest neighbours) and an ordering temperature TN =33 ± 1 K. Powder diffraction measurements reveal a broad diffuse peak - due to short-range
magnetic order - underneath the (100) long-range order magnetic Bragg reflection. The exposure of the sample in magnetic fields up to 7.5 T, under both zero field and field-cooled conditions, show that neither the long-range magnetic order nor the short-range order are destroyed by the outer magnetic fields. The almost field independent behaviour of the magnetic intensities is explained by
the existence of a spin glass state. Support on the simultaneous presence of antiferromagnetic and spin glass states is given by recent ac-dc magnetic measurements. The infinite range model for spin glasses with strong uniaxial anisotropy has predicted this kind of magnetic behaviour.
Abstract: The crystal structure of Ni1.99Mn1.14Ga0.87 single-crystal that exhibits large magnetic field induced strain in the martensitic phase is studied by neutron diffraction within temperature range 300K-4K. The 5-layered modulated structure is observed within the whole temperature interval and no another martensitic transformations occur. The anisotropic change of the martensite lattice
parameters during cooling from 300K down to 4K is found. The combined change in the a- and c-lattice parameters affects change of the (c/a) ratio in martensite with cooling down by 2.32%. Redistribution of twin martensitic variants in the external magnetic field is studied in-situ at temperatures 98K-296K.
Abstract: Thermal expansion of some members of the synthetic solid solution åkermanite-gehlenite was measured (in the range 25-1200°C) for the very first time, with the aim of clarifying the behaviour of this solid solution both with respect to composition and temperature. The results confirmed the non-ideal behaviour at room temperature (negative excess molar volume), and showed a different non-ideal response at high temperature. In fact, excess molar volume is different during the heating and cooling stages: for Xak<0.5 it becomes, from almost ideal, strongly positive at high temperature, while for Xak>0.5 it is always negative. It can then be inferred that (i) lattice dimensions are very sensitive to cation diffusion activated by temperature, (ii) intra-crystalline partition mechanisms, and their effects on the structural features, vary as a function of composition in the solid solution studied.
Abstract: Docetaxel (form A), a stoichiometric hydrate containing three water molecules
per molecule of drug substance (Taxotere®), is thermodynamically stable under ambient conditions of pressure, temperature and relative humidity. In order to gain a better understanding of docetaxel system at the atomic scale a structural study was performed. Due to strong anisotropy of crystals (thin plates), the crystal structure of docetaxel (29 degrees of freedom) was solved and refined using high resolution XRPD data applying an ab initio direct space method. In parallel, an in-depth crystal growth study was carried out until single crystals suitable for XRSCD structural resolution were obtained: surprisingly, a new polymorph of docetaxel, called form B, was isolated.