The more commonly used Scherrer formula only concerns
line broadening exclusively due to crystallite size,
and does not take into account microstrain effects. Even
if line broadening is only caused by crystal size effects,
the apparent size parameter is not related simply to the
physical dimensions of the crystallites, but also their volume-
weighted mean column length, requiring the appropriate
Scherrer constant for the actual crystallite shape
[41,42]. However, in reality, the crystallites rarely all have
the same shape and size, and therefore the apparent size
is influenced by this variability in crystallite shape and size,
making the evaluation of the meaning of the apparent size
difficult. TheWH method essentially combines the Scherrer
equation with an expression for the apparent microstrain
obtained by differentiating Bragg’s law [43]. In the WH
method, once the instrumental contribution has been
removed from the observed profiles by measuring a stan-dard, a plot of the integral breadth vs. d provides values
for the volume-weighted mean column length and microstrain
from the intercept and slope, respectively [44]. Here,
the WH method was preferred to other methods (i.e., the
basic Scherrer equation), because microstrain effects were
assumed to be significant. Apparently, this is the first time
that such an approach has been used to qualitatively determine
the microstructure of titania. The Scherrer formula
[45], Fourier analysis on single line broadening [46] or convolution
of profile shape function [47] were used
previously.
The photochromic behaviour of the samples was also
investigated under different UV- and visible-light irradiation
times, with UV–Vis spectroscopy.
The more commonly used Scherrer formula only concerns
line broadening exclusively due to crystallite size,
and does not take into account microstrain effects. Even
if line broadening is only caused by crystal size effects,
the apparent size parameter is not related simply to the
physical dimensions of the crystallites, but also their volume-
weighted mean column length, requiring the appropriate
Scherrer constant for the actual crystallite shape
[41,42]. However, in reality, the crystallites rarely all have
the same shape and size, and therefore the apparent size
is influenced by this variability in crystallite shape and size,
making the evaluation of the meaning of the apparent size
difficult. TheWH method essentially combines the Scherrer
equation with an expression for the apparent microstrain
obtained by differentiating Bragg’s law [43]. In the WH
method, once the instrumental contribution has been
removed from the observed profiles by measuring a stan-dard, a plot of the integral breadth vs. d provides values
for the volume-weighted mean column length and microstrain
from the intercept and slope, respectively [44]. Here,
the WH method was preferred to other methods (i.e., the
basic Scherrer equation), because microstrain effects were
assumed to be significant. Apparently, this is the first time
that such an approach has been used to qualitatively determine
the microstructure of titania. The Scherrer formula
[45], Fourier analysis on single line broadening [46] or convolution
of profile shape function [47] were used
previously.
The photochromic behaviour of the samples was also
investigated under different UV- and visible-light irradiation
times, with UV–Vis spectroscopy.
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