水热合成NiS2粉晶及Rietveld结构精修

采用水热法一步合成了二硫化镍粉晶,利用XRD、SEM对样品进行了表征并使用Rieteveld粉末衍射峰形全谱拟合方法对不同水热反应条件下合成二硫化镍粉晶的晶体结构进行了研究.并用多相全谱拟合相定量分析法对水热合成二硫化镍粉晶中的杂相质量百分比进行了计算,分析了NiS2粉晶的合成机理.     

Structure Changes in an Al-4.5 at.% Zn-2.0 at.% Mg Alloy during Continuous Heating in Dependence on the Starting Conditions

Die in einer AlZn(4.5 at.-%) Mg(2.0 at.-%)-Legierung beim kontinuierlichen Aufheizen vonstatten gehenden Strukturumwandlungen wurden mit Hilfe von DSC und RKWS in Abhängigkeit vom Startradius, r_S = (0.7 … 2.7) nm, der metastabilen Phasen (GP-Zonen und/oder η'-Phase), die bei T_pre = R.T. oder 100°C gewachsen waren, untersucht. Die Stabilität der bei T_pre gebildeten metastabilen Phasen nimmt mit deren Größe zu, während eine Veränderung von T_pre keinen merklichen Einfluß zeigt. Startet man mit Partikeln von r_S > 1.6 nm, so erscheinen die Minima, die durch die Bildung von η'-Phase aus den aufgelösten GP-Zonen (1. Minimum) bzw. aus überkritischen Zonen entstanden sind (2. Minimum), mit Zunahme von r_S immer undeutlicher.     

Accurate Crystal Structure Refinement of Natrolite and Localization of Free Water

Crystallography Reports - Crystals that contain water molecules spaced by distances excluding their chemical interaction are model systems for studying the so-called “water...     

Structure of the grain boundary region in an Al–15 at.% Zn and Al–2.0 at.% Zn–1.3 at.% Mg alloy aged at elevated temperatures

The results of TEM investigations are presented of the effects of various solutions and ageing treatments, cooling and quenching rates as well as of tensile stress at elevated temperatures on the microstructure of the grain boundary (GB) region of the examined Al Zn and Al Zn Mg alloys. A pronounced influence was found of partial coherency of GB stable β(Zn) precipitates with the α matrix in the Al Zn alloy on the asymmetry of Zn depleted GB region and on the shape of GB precipitates. The role of GB's as sources and sinks of vacancies and the effect of stress gradients in GB regions were emphasized in the establishment of differences in the nucleation and decomposition characteristics within the GB region as compared to those within the grain interior. The existence of a negative stress gradient towards the GB has been suggested to lead to the observed gradual retardation of transformation kinetics within the GB region in Al Zn alloys. A rapid quench from annealing to ageing temperature introduced large local stresses close to GB giving rise to “band of precipitates” on subsequent ageing within the former precipitate free region (PFZ) in Al Zn Mg alloy. Similar enhancement of local stresses accompanied by acceleration of decomposition kinetics was also observed in the aged Al Zn sample subjected to a prior tensile creep exposure within the one-phase region.     

Rietveld Refinement of the Crystal Structure of Nickel Hexaamina Perchlorate and -Tetrafluorborate

Room-temperature phases of nickel hexamina perchlorate (NHP) and nickel hexaamina tetrafluorborate (NHT) were analysed by means of X-ray powder diffractometry. Both compounds crystallize in the cubic system (Fm3 m space group) with cell parameters: a = 11.4689 Å for NHP and a = 11.2692 Å for NHT structure, respectively. The crystal structures of these compounds were refined using Rietveld method.     

Structural analysis according to reduced data: VIII. Refinement of the extended model of aspherical atoms

A program for the refinement of the model of aspherical atoms within the Stewart-Hansen-Coppens formalism has been developed. Deformation scattering up to the 8th expansion order in multipoles has been taken into account for the first time. The program was tested for 11 crystals. The effect of the result of interpolation of radial scattering curves on the model parameters is considered. The importance of introduction of multipoles of high (5th–8th) orders into the model for a number of crystals is shown. The use of the extended multipole model for a silicon crystal revealed some new specific features of the electronic structure: consideration of multipoles up to the 7th order makes it possible to explain the intensity of the forbidden 222 reflection.     

Crystal structure and conformational analysis of N-formyl and N-nitroso derivatives of piperidinone

Single crystal X-ray studies for N-formyl-2,6-diortho chlorophenyl-3,5-dimethyl piperidin-4-one (FOCDMPO) and N-nitroso-2,6-di(3,4,5-trimethoxyphenyl)-3,5-dimethyl piperidin-4-one (NTMPO) are reported. Crystals of FOCDMPO and NTMPO belong to the monoclinic space groups P2₁/n and C2/c, respectively. FOCDMPO: a = 9.147(2), b = 14.586(3), c = 13.665(5) Å and = 101.68(2)° NTMPO: a = 38.52(2), b = 13.727(5), c = 9.564(3) Å and = 98.60(1)°. In both the structures, the piperidine ring adopts a boat conformation with slight distortion. In FOCDMPO, one of the phenyl and methyl groups are in axial positions while the other phenyl and methyl groups are in equatorial orientations. In NTMPO, the situation is reversed. The molecules are stabilized by weak intermolecular C—H ··· O interactions in addition to van der Waals forces.     

On the influence of the pre-ageing temperature on the reversion behaviour of an Al-4.5 at.% Zn-2.0 at.% Mg alloy

The reversion behaviour of an Al-Zn(4.5)-Mg(2.0) alloy was investigated by SAXS in dependence of the pre-ageing temperature, T_pre, (ranging between 60°C and 100°C) and the reversion temperature, T_rev, (120°C till 200°C) starting with precipitates having a radius of (1.2 ± 0.1) nm and (1.5 ± 0.1) nm, respectively. During the reversion treatment applied up to T_rev = 160°C three stages could be distinctly distinguished, namely the dissolution of unstable zones, the growth of the stable zones on the expense of the dissolved one, and at last the coarsening of the precipitates by the OSTWALD-ripening process, where the structure changes become independent of the pre-history (start radius). The change of T_pre from 60°C to 100°C does not influence the structure changes going on at T_rev, that means between 60°C and 100°C the same type of G.P. zones grows.     

Structure analysis by reduced data. III. Method of interexperimental minimization

Being logically justified, a new algorithm of the interexperimental minimization (IEM) has been formally described. The IEM method is the generalization of the optimization method to the case of several independent measurements and is characterized by the following basic features: (1) the structural model refined is divided into the basic model and the model-perturbation; (2) the goal function of the method has four terms, of which the first two correspond to independent measurements, the third one, to averaged measurements, and the fourth one, to the normalized interexperimental difference; (3) in the IEM refinement, the weighting scheme adequately reflecting the accuracy of the experimental data is automatically formed; (4) the interexperimental minimization method includes the algorithm for reducing interparametric correlations; (5) the basic criterion of the IEM method is the statistical test of reproducibility of the results; (6) the IEM method uses the quantum-mechanical and molecular-dynamics calculations to normalize the experimental data; and (7) the physical reliability of the results obtained upon the refinement by the IEM method also depends on the coupling relations imposed onto the structural and functional parameters.     

Structure analysis by reduced data. IV. IEM—A new program for refinement of structure models of crystals

A new program for the refinement of models of atomic structures by the X-ray, neutron, and electron diffraction data has been described. The program is based on a special form of the goal function including the term responsible for minimizing the difference between the normalized measurements [the interexperimental minimization (IEM) method] and the adaptive nonlinear algorithm of minimization based on the Lavrent’ev-Levenberg-Marquardt regularization. As a result, it became possible to determine a new solution to the problem different from that obtained by the classical least squares method. To a large extent, the program allows one to overcome the effect of parameter correlations on the procedure of refinement and the results obtained. The test of the program on 17 experimental data sets showed the fast and stable convergence in all the cases. Under the identical initial conditions, the new program provided lower reliability factors for most of the crystals studied.     

Crystal and molecular structures of quinazolines: A ring conformational study

The solid state structures of two dihydropyrimidines (DHPM) viz, 2-[(4-dimethylamino)phenyl]-1-phenethyl-2,3-dihydro-1H-quinazolin-4-one (compound 1) and 1-phenethyl-2p-tolyl-2,3-dihydro-1H-quinazolin-4-one (compound 2) are reported here. The compound 1 belongs to triclinic (P-1) space group with cell parameters a = 7.4314(12) Å, b = 9.9747(16) Å, c = 14.658(2) Å, = 104.142(3), = 102.584(3), = 98.188(3). The compound 2 also belongs to triclinic (P-1) space group with cell parameters a = 9.8707(11) Å, b = 9.9225(11) Å, c = 10.7425(13) Å, = 79.227(2), = 80.568(2), = 63.649(2). The structures show that the substituent at 2-position will play a key role in defining the pyrimidine ring conformation. The central dihydropyrimidine ring in both the structures are affected by conjugation. The sum of the valence angles around all the nitrogens is very close to 360, indicating that the state of hybridization of these atoms is sp². The DHP ring is puckered in such a manner that the atoms N1, C3, C4, C5, and N2 are coplanar and the sixth atom C2 is displaced 0.605 Å (0.18 Å for compound 2) above the least squares plane. The conformation of dihydropyrimidine ring can be described as a sofa with asymmetric parameters C_s[C2] = 6.09 (compound 1) and 4.73 (compound 2), respectively. The phenethyl group has a fully extended conformation with respect to the central pyrimidine ring (N2–C16–C17–C18 174.8(2) and 179.1(6) for compounds 1 and 2, respectively). The substituents on the DHPM ring, dimethylamino-phenyl/p-tolyl groups of compound 1/2 occupy equatorial/axial positions at C2. In the crystal packing, six membered rings form through dimerization using N–HO hydrogen bonding.     

Crystallographic and conformational analysis of 1,3-bis(2,4-dimethoxyphenyl)imidazolidine-2-thione

The molecular and crystal structures of the title compound, C₁₉H₂₂N₂O₄S, were determined by single crystal X-ray diffraction technique. The title compound crystallizes in space group F d d 2, with a = 30.785(3) ?, b = 10.6455(9) ?, c = 11.0036(8) ?, Z = 8, D _calc = 1.379(2) g cm⁻³, μ(Mo-K_α) = 0.207 mm⁻¹, and its crystal system is orthorhombic. The structure was solved by direct methods and refined to a final R = 0.042 for 1530 reflections with I > 2σ (I). There is a half-independent molecule in the asymmetric unit. The title molecule has twofold rotational symmetry along with the C–S bond. Classically no hydrogen bond is found in the crystal structure. The crystal structure is stabilized by π–π stacking and edge to face (C–H…π-ring) interactions. To elucidate conformational features and steric hindrances of the title molecule, selected torsion angle is varied from −180° to +180° in every 10° and thus molecular energy profile is calculated by PM3 semi-empirical method.Supplementary materials CCDC 261789 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: $+$44 1223 336033.     

Development of the microhardness of an al-2.0 at.% zn-1.3 at.% mg alloy with additions of technical impurities during a two-step ageing treatment (ii)

The alloy was preaged in the temperature range between T_pre = 50 °C and 160 °C for various times and afterwards postaged at R.T. The course of the microhardness and the related structure changes (TEM and SAXS investigations) were investigated. The main results are the following: – Preageing the samples times less than the incubation time no essential structure changes take place at least not in the sense that the further decomposition happening during the postageing at R.T. is remarkably influenced. – The samples preaged at T_a 110 °C for times somewhat longer than the incubation time show a distinct minimum after the end of the postageing period of 42 d at R.T. Most probably at T_a 110 °C in the starting period of the decomposition nuclei of the α-phase or of spherical hexagonal zones were formed. These nuclei lessen considerably the amount of G.P. zones able to be nucleated during the R.T. postageing.     

On the influence of impurity additions and quenching temperature on the course of the microhardness (HV) during a two-step ageing treatment of an Al-2.0 at.%Zn-1.3 at.%Mg Alloy

A pure as well as the analogous technical alloy were directly quenched from T_q = 400 °C or 490 °C to T_a, preaged at T_a (ranging between 50 °C and 160 °C) various times (t_a), and subsequently postaged at R.T. up to t_post = 42 d. — Ageing the samples below the upper limit temperature of the homogeneous formation of G.P. zones (T_hn) no essential difference in the course of the HV-number attained after one- as well as two-step ageing in dependence on the addition of impurity atoms and T_q could be found. — Contrary to this behaviour after pre-ageing at T_a > T_hn and postageing at R.T. a variation of both T_q and the content of impurity atoms shows a considerable effect. The reason is the difference in the density of nucleation sites for heterogeneous formation of precipitates of the η′- and/or η-phase in dependence of T_q and impurity content.     

The Effect of Additions of Mn and Fe on the Structure of an Al-2 at.% Zn-1 at.% Mg Alloy

The structure of an Al-1.9 at.% Zn-1.3-at.% Mg mother alloy with additions of Mn and Fe, respectively, were investigated by TEM and microprobe analysis for two different heat treatments, namely direct quench from 490 °C to 160 °C and a two-step ageing treatment (preageing at RT for 7d before storing at 160 °C), to explain the differences in the course of the hardness obtained during the ageing at 160 °C. The differences of the structure observed are explained in terms of the tendency of the additives to form intermetallic phases, particularly in the grain boundaries.     

Comparison of P- and B-Contents in Si Determined by Photoluminescence (PL) at 4.2 K and 2.0 K

Calibration curves to determine the concentrations of shallow impurities in Si were usually established with the help of homogeneous doped samples at 4.2 K. The improvement of the lateral resolution power necessary to characterize inhomogeneous samples can be conveniently achieved by the use of superfluid helium. The calibration curves required for it were established at 2.0 K for P- and B-doped Si and compared with the dependences measured at 4.2 K. Existing differences between these curves are discussed.     

Structure analysis by normalized data. I. Increase of relative accuracy of diffraction data

A new method for obtaining physically reliable values of atomic parameters in the refinement of the structure model by the least squares method has been suggested. The method requires the use of experimental data reduced to a scale corresponding to the Bragg scattering from an ideal defect-free crystal. The reduced experimental data can be obtained by interexperimental-minimization (IEM) method—a new algorithm minimizing the difference “experiment 1-experiment 2” (between the data obtained in two experiments, 1 and 2) used in addition to the model-experiment minimization performed in the conventional least square procedure. The use of four different experimental data sets for alexandrite crystals, Al₂BeO₄: Cr³⁺, allowed us to show that the application of the IEM algorithm considerably increases the reproducibility level of the experimental data, which, in turn, increases by 30–60% the agreement between the model and the experiment.