Laboratório Nacional
de Luz Síncrotron

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TÉCNICAS

VOLTAR

TÉCNICAS DISPONÍVEIS


As técnicas e configurações experimentais a seguir estão disponíveis nesta linha de luz. Para saber mais sobre as limitações e requerimentos das técnicas, contate o coordenador da linha de luz antes de submeter sua proposta.

AMBIENT MEASUREMENTS


Ambient measurements are conducted on samples which require the high resolution capability of the beamline. Here samples are measured under ambient temperatures and are exposed to the atmosphere during measurements. The setup gives accurate peak position and shape and reduces peak overlap of highly crystalline materials while reducing background signal. This set-up is normally required for quantitative analysis of samples, i. e. Structure determination of performing Rietveld Refinement to determine crystalline parameters, such as cell parameter and volume, crystal size, investigation of strain, lattice defects and micro-structure of materials. It is carried out at ambient conditions (room temperature) in Bragg-Bretano geometry or at cryogenic temperature with a cryostat. It is important to note that the cryostats work without sample spinning and the theta angle is fixed during the measurement. High resolution requires an analyzer crystal, a Ge (111) crystal, installed before the point detector (Cyberstar scintillation detector), which provides a step-size resolution of 0.02o in 2theta. This analysis mode results in low photons flux and thus a lower intensity of the diffracted beam and consequently, longer data acquisition times (4-10 hours for each sample).

 

IN-SITU MEASUREMENTS


These measurements involve the use of a furnace with the additional capability of gas flow. With this setup various types of reactions can be simulated. The temperature range is dependent on the furnace used (please see types of furnaces available at the beamline). Various gas environments are allowed to simulate chemical reactions. Some restrictions are in place for safety as well as preventing damage to the furnaces. Thus, no corrosive gases are allowed. Further, restrictions apply to the use of hydrogen (5% max) and oxygen (20% max). We strongly urge you to contact the beamline staff prior to sending a beamtime proposal to certify that your experiment fits into our safety regulations. A mild vacuum may be applied to the furnace as well as humidity if required. A mass spectrometer is also available to analyze the chemical composition at the outlet of the furnace. The appropriate furnace will be selected by the beamline staff depending on the needs of the user.

The in-situ setup works for both fast measurements (lower resolution) using the Mythen 1K detector as well as the High resolution setup using the Cyberstar point detector. Please note the large time differences in collecting data between these two detectors. For further information about more complex setups, please contact the beamline staff.

fig1 fig2

Legenda – Left: Anton Paar XRK 900 (only available with Cyberstar detector). Right: Canario Furnace

 

SAMPLE PREPARATION


Depending on the type of experimental setup required samples may be prepared as either a powder or pellet. Powder samples are preferred however. Samples need to be ground down to the finest possible size to avoid sample related effects affecting the data. This applies to all data collections.

Legenda - Sample holders from left to right: Furnace, cryostat, High-resolution

Legenda – Sample holders from left to right: Furnace, cryostat, High-resolution

 

CRYOSTAT


For low temperature measurements, a cryostat from Advanced research systems is available. The lowest temperature achievable is around 2 K using He or 10 K using N. Samples measured using the cryostat are also considered as high resolution and thus long measurement times are required (3-6 hours per sample).

fig3

Legenda – Cryostat from Advanced research systems

 

BEAMLINE ENERGY


XPD is normally fixed at 8 keV (=1.5498Å) which corresponds to the highest photon flux and is equivalent to Cu Kα wavelength used in conventional X-ray sources. However, the energy may be changed if anomalous diffraction experiment are required or if the sample is composed of Fe and/or Co. The energy is then set to 7 keV to avoid fluorescence. It is also possible to work at higher energies if it is important to increase the penetration depth of the X-rays into the sample, in the case of samples composed of high Z materials.