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heated up in place at 5 °C/min (i.e., the sample temperature was
slowly ramped up to 800 °C). The lattice parameters for this
experiment are shown as gray lines in Figure 3. Crystalline ZnO
is ﬁrst observed above 400 °C. Due to the very weak peak
intensities at this stage, the uncertainties are quite large. Once
the sample temperature reached 800 °C, it was then cooled at
15 °C/min. Over the range from 400 to 800 °C the a lattice
parameter increases linearly with temperature. The c lattice
parameter does not appear to be completely reversible; between 400 and 600 °C the c parameter is roughly constant and
then starts to increase as the temperature rises above 600 °C.
21035 dx.doi.org/10.1021/jp207140g |J. Phys. Chem. C 2011, 115, 21034–21040 The Journal of Physical Chemistry C ARTICLE Figure 2. Results from ﬁtting the data shown in Figure 1: lattice
parameters a and c, crystallite size, and scale parameter (providing a
relative measure of the volume of crystalline ZnO). Figure 4. Crystallite size versus time for diﬀerent temperatures
(as indicated in a) for (a) 0% Al, (b) 1% Al, (c) 2% Al, and (d) 4% Al. Figure 3. Final a and c lattice parameters for diﬀerent Al contents as a
function of temperature (symbols) compared with a temperature ramp
experiment with 0% Al (gray line). On the cooling leg, the c parameter decreases linearly with
Superimposed on the heating ramp experiment in Figure 3 are
the a and c lattice parameters averaged from the last 20 min of
data collection for all samples and temperatures studied (where
the hot air blower was ﬁrst heated to temperature and then moved into place beneath the sample). Within the uncertainties,
the lattice parameters of the doped samples show no signiﬁcant
departure from those found for the 0% Al temperature ramp
experiment. This is consistent with earlier ﬁndings for ZnO:Al
calcined powders measured at room temperature using synchrotron X-ray diﬀraction.11
The trend of the scale parameter in Figure 2 is also constant
with time for all samples and temperatures studied. This indicates
that the volume of crystalline ZnO is not changing over time. The
crystallite size in Figure 2, however, increases over time in an
approximately logarithmic or sublinear power law fashion. These
two pieces of information indicate that nucleation of ZnO is rapid
and then grain growth occurs between crystalline regions; no
new ZnO crystallization is occurring at later times.
Comparative plots of crystallite size versus time are shown for
all samples in Figure 4. In general, it was observed that the higher
the temperature, the larger the crystallite size at any given time.
This is consistent with earlier ex situ synchrotron X-ray diﬀraction results.11 Apart from the 1% Al sample calcined at 800 °C,
the crystallite size at a given size and temperature decreases as the
Al content increases, which is consistent with earlier ex situ X-ray
Given the excellent time r...
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This note was uploaded on 06/15/2013 for the course MSE 101 taught by Professor Sen during the Spring '12 term at Indian Institute of Technology, Kharagpur.
- Spring '12