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J.A. Aitken et al. / Journal of Solid State Chemistry 182 (2009) 141–146
2.2. Synthesis
least-squares refinement on F2 were performed using SHELXTL-97
[24]. Probable space groups based on systematic absences
were Cmc21 (No. 36) and Ama2 (No. 40), both of which are
noncentrosymmetric. The structure could only be solved and
refined in the Ama2 space group. Pertinent crystallographic data
and structure refinement details for EuCu2SnS4 are provided in
Table 1. The atomic coordinates, equivalent displacement
parameters and selected bond lengths and angles for EuCu2SnS4
are provided in Tables 2 and 3.
2.2.1. Synthesis of EuCu2SnS4 microcrystalline powder
A 1 mmol sample of EuCu2SnS4 was synthesized from a
stoichiometric mixture of the elements. The starting materials
were ground for 15 min in an argon-filled glovebox and placed
into a graphite crucible. The crucible was then sealed under a
vacuum of 10ꢀ3 mbar in a 12 mm o.d. fused-silica tube. The tube
was placed into a programmable furnace and heated to 700 1C in
12 h. The sample was held at this temperature for 125 h and then
quenched in an ice-water bath. The tube was opened and the
sample removed from the crucible. The product consisted of a
dark red microcrystalline powder that was ground in preparation
for characterization. The material is air-stable.
2.3.4. Differential thermal analysis (DTA)
DTA was performed using
a Shimadzu DTA-50 thermal
analyzer. DTA data were recorded using the TA60-WS collection
program. The instrument was calibrated with a three-point
calibration curve using the melting points of indium, zinc and
gold metals. The temperature was programmed to increase at a
rate of 10 1C/min from 25 to 1000 1C. The temperature then
decreased to 100 1C at 10 1C/min. To determine reproducibility, a
second cycle was performed in the same manner. The reference,
Al2O3, and sample were contained in fused-silica ampoules
(carbon coated for the sample) and sealed under a vacuum of
ꢂ10ꢀ3 torr. Approximately 20 mg of sample and 20 mg of
reference material were used for the measurement. The melting
point was determined from the peak (minimum) of the en-
dothermic event. The X-ray powder diffraction pattern of the DTA
residue was collected and analyzed to determine if the material
had decomposed or changed phase during thermal analysis.
2.2.2. Synthesis of EuCu2SnS4 single crystals
The same procedure as that described above was used, with
the exception of the heating profile. This reaction was heated to
800 1C in 12 h, held at 800 1C for 125 h, slow cooled to 500 1C in
50 h and then rapidly cooled to room temperature. The product
consisted of dark red block-like crystals.
A suitable single
crystal was selected for single crystal X-ray diffraction studies.
Although this reaction produced the best crystals, it had a larger
amount of impurity/unwanted phases and was not used for other
characterization.
2.3. Physical measurements
2.3.1. Powder X-ray diffraction (PXRD) and Reitveld refinement
Powder X-ray diffraction patterns were collected using a
Panalytical X’Pert Pro MPD powder X-ray diffractometer operating
2.3.5. Optical spectroscopy
An optical diffuse reflectance spectrum was obtained using a
Varian Cary 5000 UV/Vis/NIR spectrometer. The sample was
ground and loaded into
at 45 kV and 40 mA and using copper K
a
radiation (
l
¼ 1.541871
˚
A). Data were collected as a continuous scan from 10 to 10012
y,
a Harrick Praying Mantis diffuse
with a step width of 0.081 and the time per step of 80 s. The
divergence slit was fixed at 1/41 and the anti-scatter slit at 1/21.
Samples were prepared for analysis by grinding the sample
powder for more than a half hour in an agate mortar and pestle
and then back filling the material into the aluminum sample
holder. Samples were spun during data collection.
reflectance accessory that uses elliptical mirrors. BaSO4 was used
as a 100% reflectance standard. Scans were performed from 2500
to 200 nm at a rate of 600 nm/min. Wavelength data were
converted to electron volts and the percent reflectance data
were converted to absorbance units using the Kubelka–Munk
equation [25].
The Rietveld refinement was carried out using GSAS with an
interface of EXPGUI [21,22]. A Pseudo-Voigt function was used to
model the peak profile and the background was described as a
shifted Chebyschev type. The following parameters were refined:
scale factor, background, peak profile shape, lattice parameters,
atomic coordinates and isotropic displacement parameters (Uiso).
Table 1
Crystallographic data and structure refinement details for EuCu2SnS4
Empirical formula
Formula weight
Temperature
EuCu2SnS4
525.97
273(2) K
˚
Wavelength
0.71073 A
2.3.2. Scanning electron microscopy (SEM) and energy dispersive
spectroscopy (EDS)
Space group
Ama2 (No. 40)
˚
Unit cell dimensions
a ¼ 10.4793(1) A
˚
b ¼ 10.3610(2) A
A CamScan Series 4 scanning electron microscope was used to
image samples and a Princeton Gamma Tech detector was used
for EDS. The working distance was 35 mm and the accelerating
voltage was set to 22.5 kV. Samples were mounted onto double-
sided carbon tape, which was adhered to an aluminum specimen
holder. EDS data were collected for 60 s.
˚
c ¼ 6.4015(1) A
3
˚
Volume
695.04(2) A
Z
4
Calculated density
Absorption coefficient
Crystal size
5.026 g/cm3
19.566 mmꢀ1
0.17 ꢁ 0.08 ꢁ 0.05 mm3
3.74 to 27.081
ꢀ13php12
ꢀ11pkp13
ꢀ8plp7
Theta range for data collection
Limiting indices
2.3.3. Single crystal X-ray diffraction
A dark, red rectangular crystal measuring 0.05 ꢁ 0.08 ꢁ 0.17
mm3 was mounted onto a glass fiber using Krazys glue. Over
a hemisphere of data was collected using 0.31 steps in omega with
a Bruker SMART Apex II diffractometer at room temperature with
Reflections collected
Unique reflections
3369
791 [R(int) ¼ 0.0220]
100.0%
Completeness to 2
y ¼ 27.081
Max and Min transmission
Goodness-of-Fit on F2
0.4412 and 0.1357
1.213
a graphite monochomator, using a CCD detector and Mo K
a
˚
Final R indices [I42
Extinction coefficient
s
(I)]
R1 ¼ 0.99% and wR2 ¼ 2.37%
0.0068(1)
radiation (0.71073 A). 3369 reflections were observed of which
3189 were used after integration using SAINT [23] for the final
cell refinement. An empirical absorption correction was
performed using SADABS. The structure solution and full-matrix
Absolute structure parameter
0.04(1)
3
˚
Peak and hole (e/A )
0.679 and ꢀ0.359