The Rigaku Ultima IV represents state-of-the-art multipurpose X-ray diffraction (XRD) system. Different types of samples for instance powder/granular samples, thin films and solid membranes can be probed from 2-theta as small as 2° to 90° without having any hazel. Traditional powder diffraction measurements of Bruker Ultima IV use the Bragg-Brentano focusing geometry to provide high-intensity, high-resolution measurements of well-powdered samples. The more common applications of X-ray diffraction includes but not limited to
- Phase identification
- Quantitative analysis
- Determination of percent crystallinity
- Crystallite size/strain analysis
- Precise lattice parameter determination and so on.
Currently, the IC-FAS has set of glass sample holders with 0.2 mm depth as shown in following figure for loading the samples. Powder/granular samples, membranes or thin films coated on other substrates can be placed on the well.
However, one sample can be mounted in for the measurements at a time since we do not currently have the auto sample changer. The time taken for one measurement depends of the basic settings such as scan range, scan speed and step size used for the measurements. The S/N ratio of the measurement depends on many factors including but not limited to the quality of the sample, the composition of the sample, scan speed, step size and so on. Proper instrumental parameters to get good S/N ratio of your sample can be set by a quick-run.
The instrument’s goniometer uses the following geometry for the collection of data.
Specifications and Settings Use for the Usual Measurements
|X-ray generator||Maximum rated output||1.2 kW|
|Tube voltage||40 kV|
|Tube current||30 mA|
|Wave length (Kα1)||1.54059292 Å|
|Focus size||0.4 x 12 mm|
|Focus selection||Line beam|
|Goniometer||Scan type||2 theta/theta|
|Goniometer radius||285 mm|
|Scan speed||2°min-1 (depends on your requirement)|
|2θ measuring range||2 to 90° (depends on your requirement)|
|Step size||0.02° (depends on your requirement)|
|Divergence height slit||10 mm|
|Receiving slit||0.3 mm|
Sample Preparation Guide
It is important to emphasize that the quality of the collected data cannot be superior to the quality of the sample and to the quality of its preparation and deposition. One of the basic assumptions of meaningful XRD is the homogeneous spatial and angular, distribution of the crystallite orientations in the different directions. Any deviations from homogeneity make the reproducibility of the measurement rather difficult. Elimination of preferred orientation effects (one of the most common experimental problems) would not exist if the crystals were morphologically spherical. But the crystal world is intrinsically vectorial, not scalar, and anisotropy (structural and morphological) in the rule, not the exception. Thus, preferred orientation cannot completely avoidable, must be reduced as much as possible.
It has absolutely no meaning to lose instrument-time by errors arbitrarily introduced by the poor care taken in sample preparation. Thus, the users must pay careful attention on preparing the samples. It is better to follow the following guide for your general sample preparation. It is always welcome to tailor your sample preparation method according to your research needs.
The majority of the materials such as rocks, minerals, lacquers, tablets, etc. initially appears in a “non-optimal” aggregation state and thus it is needed to be ground to obtain a fine powder. For this purpose a motor and pestle can be generally used. If you have a hard sample a mechanical miller (ball-miller) with suitable beads can be used to powder the sample. However special caution must be taken because a prolonged grinding may create a large specific surface (with surface reconstruction or transformation), merging of particles, loss of crystallinity or even chemical reactions (phase transitions, desolvation, polymerizations) which may change the X-ray diffraction pattern. However, contamination may be possible by the mortar or by the miller. As a trick one can perform the grinding or milling within a liquid nitrogen environment. Repeated heating (10-30 min) of the sample at about 1/3 of its melting point (in K) may eliminate defects. Further, usage of a chemically inert liquid to avoid clustering of soft particles is also possible.
Sample Deposition on Glass Sample Holder
We have 0.2 mm depth glass samples holders to load the samples. You have to load the dry samples only in the hollow space. It is important to avoid vertical loading. For that a razor blade or glass slide can be used as shown in the following schematic.
Other Methods for Sample Deposition
- Dry Dusting
- Dusting in oil, grease, silicones, etc.
- Back filling or Side Loading
- Mixing with inert powder
- Volatile inert liquids (acetone, ethanol, etc.)
- Non volatile suspending inert liquids (amyl acetate, + 5% collodion)
- Spray drying (with “spherical” particles)
- Thin film (for transparent materials and indexing procedures…)
Note: often it is better to use a zero background plate as sample holder (Si or SiO2 single crystals). If any user wants to purchase the right sample holder the CIF is willing to help you.
Dr. Thusitha Etampawala
Click following link for the reservation of the XRD instrument