Volume 26(2) - Summer 2010

Rigaku SmartLab is a multipurpose, fully-automated horizontal X-ray diffractometer that allows many types of measurements and evaluations of materials ranging from powders to thin films. Rigaku’s expansion system and Cross Beam Optics (CBO) system enable configuration of a wide range of optics, while the SmartLab Guidance control software permits easy switching between optics for added versatility. The many optics systems offered by Rigaku for SmartLab include CBO system incorporating a parabolic multilayer mirror, CBO-E system incorporating an elliptical multilayer mirror, and optics configured with the Kα1 unit with a Johansson Ge crystal for monochromatization of incident X-rays to the Kα1, designed to measure powder samples. These systems allow the user to configure the ideal optics for specific measurement or evaluation purposes. The new and unique Kα1 system enables various types of measurement while maintaining samples in a horizontal position.
 

The fusion bead method is an effective sample preparation technique for accurate XRF analysis results of ores, rocks and refractory materials since the technique eliminates heterogeneity due to grain size and mineralogical effect.

This report describes various data processing methods to obtain more accurate analysis results showing practical examples of analysis obtained by using a wavelength dispersive X-ray fluorescence spectrometer (WDXRF), ZSX Primus II, and its data processing system.
 

X-ray fluorescence (XRF) analysis is widely used in a number of fields, including quality control and research & development, due to its high degree of accuracy and extremely simple sample preparation. Quantitative analysis with XRF spectrometry requires reference materials in order to generate calibration curves.

The rapidly improving performance of personal computers has opened the door to sophisticated data processing techniques like SQX Scatter FP (Fundamental Parameter) method, improving the accuracy of semi-quantitative analysis, where reference material is not used for quantitative calculation by the FP method. The even more accurate quantitative analysis method, however, requires the user to generate calibration curves using calibration standards made of the same material as the samples to be analyzed.

While quantitative analysis provides an unparalleled level of accuracy, correctly setting up the sample measurement conditions and creating the calibration curves requires expertise in XRF spectrometry and can be a time-consuming process. Rigaku has seen a growing need among XRF spectrometry users to be able to start up quantitative analyses quickly and easily.  The Application Package for XRF analysis introduced here is a product which is designed to enable even novices in XRF to start up quantitative analyses easily.  The package provides the user with reference materials for calibration, drift correction samples for daily analysis and analysis parameters such as measurement conditions and correction coefficients for calibration.
 

In thermal analysis, the measurement condition influences the measurement results. Therefore, it is important to select the most desirable measurement condition in response to the objective of the measurement.

Conditions such as sample amount, heating rate as well as the measurement atmosphere are selected freely in thermal analysis measurement. Especially the measurement atmosphere, where it directly affects the sample’s reaction, for example, measuring under atmospheric air may cause combustion or oxidation reaction and the suppression of these reactions can be confirmed by measuring under inert atmosphere.  Therefore, it is essential to select the appropriate atmospheric gas suitable to the objective of the measurement.

But the difference among atmospheric gases is not only the presence or absence of oxygen (O₂), such as when using an air pump for an air atmospheric measurement also includes the room humidity (water vapor partial pressure) while using a gas cylinder for an inert gas atmospheric measurement creates a dry atmosphere.

The dehydration behavior of the sample is most affected by the effects of humidity and in some cases degradation reaction may also be affected. Hence, it is important to measure under a predetermined humidity to perform simulation on the sample’s thermal behavior.  Also, evaluating the material’s hygroscopic behavior (percentage of water absorption) as a property is the most important factor. On the other hand, since dehydration behavior is determined from the heating process, accurately estimating the coefficient of water absorption is extremely difficult in the conventional thermal analysis.

In recent years, various fields of specialization have applied thermal measurements where humidity in the atmosphere is controlled because of its ease and simplicity. Although the effects of humidity on the measurement results were thoroughly discussed in 2009, this paper discusses the basic terminologies related to humidity, thermal analysis under water vapor atmosphere and its measurement methods. It also includes applications such as effects of water vapor on the thermal degradation of polymers and organic metal compounds; and measurement of adsorption and desorption of moisture levels in relation to change in humidity. Finally, this paper ends with a general conclusion.
 

This is the fifth article in the series of X-ray thin-film measurement techniques. The second, third and forth articles of this series, previously published in the Rigaku Journal, describe out-of-plane, high-resolution and in-plane XRD measurements to obtain crystallographic information on crystal size, lattice strain and orientation relationship of a thin-film material. These measurements have been based on the premise of a crystalline thin film.  On the other hand, the X-ray reflectivity (XRR) measurement is not a technique to evaluate diffraction phenomenon. The XRR measurement technique described in this article is used to analyze X-ray reflection intensity curves from grazing incident X-ray beam to determine thin-film parameters including thickness, density, and surface or interface roughness.  This article will provide an overview of the principles of X-ray reflectivity, measurement procedures, and analysis methods. It also discusses the procedural flow from measurement to analysis, as well as precautions.

Physical and chemical properties of a crystalline solid depend strongly on the molecular arrangement, that is, on both the crystal structure and the composition of the molecule comprising the solid. In order to understand the mechanisms and developing properties of a crystalline solid, it is essential to know the crystal structure. Typically, crystal structure analysis has been performed using hundreds or thousands of X-ray intensity data collected from a single crystal. The data is collected with a four-circle diffractometer or a diffractometer equipped with an image plate or other 2D detector. Just 10 years ago, single crystals several hundred microns in diameter were needed. Recent improvements in X-ray sources and detectors enable the collection of intensity data which can be used in the analysis of crystal structures from crystal specimens measuring only a few microns across.

There are many substances which cannot be grown to a single crystal of quality and size sufficient for single crystal diffraction measurements. Inorganic compounds have often had their crystal structures analyzed using the Rietveld method devised in 1969. Fundamentally, the Rietveld method is used to refine crystal structure parameters such as lattice constants, atomic coordinates, occupancies, temperature factors, etc. based on powder diffraction data. There are many groups of inorganic compounds which have almost identical composition and crystal structure. In these cases, the crystal structure can usually be solved using the Rietveld method using the structure parameters of an analogous compound as the initial structural model.

On the contrary, since organic compounds are formed molecular crystals, their crystal structures are affected by even very small changes in composition. This makes it exceptionally difficult to perform ab initio crystal structure analysis of organic compounds using only the Rietveld method.

Then, how can we determine the ab initio crystal structure of organic compounds from powder diffraction data? There are several steps in the analysis procedure. While intensity data of independent diffraction spots are collected from single crystal diffraction measurements, with powder diffraction measurements, the diffraction spots, 3-dimensionally arranged in the reciprocal space, are compressed to 1- dimensional diffraction patterns. As a result, the number of intensity readings from independent diffraction spots decreases. For this reason, crystal structure analysis based on powder diffraction data collected with the methods used for single crystal diffraction data is often unsuccessful.

This paper describes the analytical process used for the ab initio crystal structure determination of, in particular, organic compounds based on powder diffraction data. It also introduces PDXL, the integrated X-ray powder diffraction software package in which all these features are implemented.