New methods in investigations of polycrystalline materials

In this chapter, information on good laboratory practice in the field of structural powder diffractometry has been collected. The authors attempt to describe how to plan a measurement, how to find the cell parameters, how to build a model of the structure, and how to refine and verify it. There are many methods and procedures which lead to solving a crystal structure. However, the experience of recent years shows that, in the case of many materials, an investigator has to attempt the problem of structure solution using many different methods. The software is easily available (from ‘trial and error’ or classic to sophisticated modern approaches), as is a lot of good equipment. On the other hand, the complexity of the structures studied using powder diffraction methods is continually increasing. No description of any methods of research other than diffraction techniques is presented. We have also focused on polycrystalline materials. Amorphous substances and methods using the formalism of ‘pair distribution functions’ are beyond the scope of this paper. New methods of structural studies (including algorithms from research described in the literature, even if their applicability has been relatively slight) were treated with particular attention. In addition to the description of methods, we also collected some useful (in our opinion) information about available software and crystallographic databases

Lattice Parameter of Polycrystalline Diamond in the Low-Temperature Range

The lattice parameter for polycrystalline diamond is determined as a function of temperature in the 4-300 K temperature range. In the range studied, the lattice parameter, expressed in angstrom units, of the studied sample increases according to the equation a = 3.566810(12) + 6.37(41) × $10^{-14} T^{4}$ (approximately, from 3.5668 to 3.5673 Å). This increase is larger than that earlier reported for pure single crystals. The observed dependence and the resulting thermal expansion coefficient are discussed on the basis of literature data reported for diamond single crystals and polycrystals

Lattice Parameter of Polycrystalline Diamond in the Low-Temperature Range

The lattice parameter for polycrystalline diamond is determined as a function of temperature in the 4-300 K temperature range. In the range studied, the lattice parameter, expressed in angstrom units, of the studied sample increases according to the equation a = 3.566810(12) + 6.37(41) × $10^{-14} T^{4}$ (approximately, from 3.5668 to 3.5673 Å). This increase is larger than that earlier reported for pure single crystals. The observed dependence and the resulting thermal expansion coefficient are discussed on the basis of literature data reported for diamond single crystals and polycrystals

Effect of Cation Substitution in "123"-type Superconducting Oxides on Powder Diffraction Intensities

This research was undertaken to determine whether by powder diffraction substitution in the "123"-type high T$\text{}_{c}$ oxides, Ln$\text{}_{1-x}$M$\text{}_{x}$Ba$\text{}_{2-y}$M$\text{}_{y}$Cu$\text{}_{3-z}$M$\text{}_{z}$O$\text{}_{6.5+δ}$ (where Ln = lanthanoid, M$\text{}_{x}$ = Me$\text{}^{3+}$, M$\text{}_{y}$ = Me$\text{}^{3+}$ and M$\text{}_{z}$ = Me$\text{}^{3+}$ and Me$\text{}^{2+}$) could be detected unequivocally. Numerous X-ray and a few neutron powder diffractograms were calculated for substituted compounds. Reflections most sensitive to substitution and the influence of site occupancy for Cu and O atoms are also characterized. The results are compared with some experimental data reported in the literature

The Y–Mg–Co ternary system: alloys synthesis, phase diagram at 500 °C and crystal structure of the new compounds

International audienceThe ternary phase diagram of the Y-Mg-Co system have been studied at 500 °C by combining X-ray diffraction (XRD), energy dispersive X-ray (EDX) and wavelength dispersive X-ray (WDX). The existence of four ternary compounds Y4MgCo (Gd4RhIn-type), Y9Mg30Co2 (own structure type), Y6Mg9Co2 (own structure type) and Y9Mg4Co (Hf9Mo4B-type) was confirmed. For all of them homogeneity range has been defined. Two new ternary compounds were identified in this work: Y12MgCo5 (Ho12BiCo5-type, orthorhombic, Space Group Immm, a= 9.5078(5)-9.538(4) Å, b =9.4741(4)-9.531(4) Å, c = 10.0217(5)-10.061(5) Å) and ~Y52Mg3Co45 (unknown crystal structure). YCo3 and YCo2 compounds form extended solid solutions where maximum solubility of Mg is 8 and 16 at. %, respectively. The solubility of Mg in YCo2 leads to a structure change from MgCu2-type to SnMgCu4-type. It was also found that binary MgCo2 compound dissolve 4.9 at. % Y and YMg can dissolve up to 2.5 at. % of Co. New binary Y5Co6 compound was determined with two structures: a e low- and b e high-temperature. The a-Y5Co6 was indexed asmonoclinic (a = 22.214 Å, b = 7.509 Å, c = 5.885 Å and b = 108.22°), while b-Y5Co6 crystalizes in the orthorhombic structure (space group Cmcm) with lattice parameters a = 4.104(1) Å, b = 10.246(1) Å and c = 20.336(3) Å. Detailed crystallographic data were collected for the Y5Mg0.07(1)Co5.93(1) and Y12MgCo5 single crystals. The metallic type bonding for Y12MgCo5 was confirmed by electronic structurecalculations