GONIOMETER AND SAMPLE STAGES - Two-Dimensional X-Ray Diffraction - page 145

opticalmagnificationwitha zoomof 1-7, overallmagnificationof 40-280with
13 00 display, field of view of 6-0.9mm, and pixel resolution of 768 H494 V.
Integrated with motorized XYZ stage and controlled by the software, the system can
also automatically align the sampling area into the instrument center [16]. This is
essential for multitarget microdiffraction or diffraction mapping.

5.4 ENVIRONMENT STAGES

X-ray diffraction under controlled environmental and temperature conditions can
reveal many materials characteristics that cannot be measured at ambient condition.
Therefore, the technique is also referred to as nonambient X-ray diffraction. Non-
ambient X-ray diffraction can be used for measuring phase transition, lattice thermal
expansion, chemical reaction, lattice defects, orientation distribution, and stresses
variation with temperature [17,18]. Nonambient conditions can include humidity,
vacuum, gas environment, low temperature, or high temperature. Themost commonly
used nonambient sample stage is a high temperature stage.

5.4.1 Domed High Temperature Stage

Two-dimensional X-ray diffraction has special advantages in nonambient study, such
as high speed and large angular coverage [19]. Since the complete diffraction pattern
can bemeasured simultaneously with a single exposure, it is very suitable for in situ or
time resolved applications. Accordingly, the environment stages used for XRD 2
should also have large angular window for the incident beam and diffracted X-rays.
An environment stage used for the conventional diffractometers typically has a
limited window opening, which may be used with a linear detector [20], but may not
be able to take the advantage of the large solid angle with the area detector. Ideal
environment stages for XRD 2 should have a window opening covering all possible
orientations of the sample surface. For reflectionmode diffraction, the opening should
have a solid angle of 2p (one hemisphere).
Figure 5.8 shows a hot stage (Anton Paar DHS 900) with domed window
mounted on the XYZ stage of a two-dimensional diffractometer (Bruker AXS D8
DISCOVER GADDS with Hi-Star detector) [21,22]. The domed hot stage has a
light and compact design, suitable to be mounted on the quarter-circle Eulerian cradle
or XYZ stage. The heating plate is made of a nickel-chromium alloy with good
oxidation resistance at high temperature. The heating plate contains Ni (72 percent),
Cr (14-17 percent), Fe (6-10 percent) and Mn ( 1 percent), hence caution must be

taken that the heating plate is not exposed to the direct beam, which may produce
fluorescence radiation when Cu or Co tubes are used. The stage can be operated at
temperatures up to 1173 K. The temperature is measured by a Ni-Cr sheath
thermocouple. The thermocouple is mounted below the sample mounting surface
at the center of the heating plate. The dome is made of PEEK, a high-performance
polymer with a unique combination of mechanical properties, temperature resistance,
chemical resistance, and high X-ray transmission. The sample chamber inside the
dome can be kept in vacuum, with air, or other gas environment. The sample chamber

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