3.3 X-Ray Diffraction (XRD) Results of Lithium Loss
43
nickel nitrate only. There were a number of phases present in these scans with the
strongest peaks being from ammonium nitrate (JCPDS #83-0520), which arose as a
product of the reaction between the metal nitrates and the precipitator. The samples
were then heated for 3 h at 200
◦ C and scanned again. As expected, the ammonium
nitrate decomposed at this temperature [72], and the peaks due to this phase were
not seen beyond this point. The heating step was then repeated at 300, 400 . . . 900
◦ C
and the scattering from each of the samples was measured after each heating step.
Figure 3.6 shows that the x = 0 samples contained NiO only (JCPDS #47-1049) after
being heated at 300
◦ C such that all contaminants are eliminated at this temperature.
Magnesia was selected for this part of the study because it only has three Xray peaks in the range over which scans were taken. These peaks were fit to and
subtracted from the patterns. In practice, the MgO peaks (JCPDS #45-0946) were
shifted from their expected positions because the X-ray machine was aligned to the
top of the samples such that the substrate had a vertical misalignment of up to 1 mm.
This misalignment varied from sample to sample such that an independent zero in
scattering angle was needed for these peaks.
Some samples studied in this way were prepared with the bicarbonate precipitator
heated in oxygen, while others were prepared from ammonium hydroxide heated in
air. In order to help distinguish the effect of the precipitator from the atmosphere,
samples prepared with ammonium hydroxide and heated in oxygen were measured
after heating to 600, 700, 800 and 900
◦ C only. Figure 3.2 (a) and (b) show XRD
scans obtained by this approach, along with the fits and difference plots. The lithium
hydroxide converted to lithium carbonate, and this occurred readily at 300
◦ C while
the stearic acid decomposed. Even the smaller amounts of stearic acid used on alumina (approximately 1.5 mg/cm
2 ) were sufficient to produce enough carbon dioxide
to react with all the lithium in the combinatorial samples. Thus, the synthesis of
lithium nickel oxide in the combinatorial samples involved the reaction of lithium
carbonate with nickel oxide regardless of the precipitator used. The fitting of the
XRD scans therefore required three phases: lithium carbonate (JCPDS #80-1307),
lithium nickel oxide and magnesium oxide.
Figure 3.2 (a) shows that the scattering from samples prepared with ammonium
bicarbonate contained a large peak near 23.5
◦ . The position of this peak varied from
sample to sample, following the magnesia peaks showing that it can be attributed to
the surface of the substrate. Lala et al. [68] found that lithium stearate has a large
peak near 24
◦ and a smaller peak above 40
◦ . Since the peak near 24
◦ was only seen
in samples with lithium, it was most likely lithium stearate, though there may have
been some nickel stearate as well since it also has peaks in this range [73]. The peak
was fit using a pseudo-Voigt function. Figure 3.7 shows that the stearate peak grew as
the samples were heated, especially during the stearic acid decomposition. The peak
disappeared after heating at 600
◦ C in most samples, consistent with the fact that
lithium stearate converts to lithium carbonate at 522
◦ C [68]. The lithium stearate on
the substrate surface results in a lithium deficiency in the sample during heating that
could affect the final lithium content of the samples. The stearate peak was never
seen when ammonium hydroxide was used as the precipitator. It is also possible that
some lithium stearate decomposition also contributed to the lithium loss.
43
nickel nitrate only. There were a number of phases present in these scans with the
strongest peaks being from ammonium nitrate (JCPDS #83-0520), which arose as a
product of the reaction between the metal nitrates and the precipitator. The samples
were then heated for 3 h at 200
◦ C and scanned again. As expected, the ammonium
nitrate decomposed at this temperature [72], and the peaks due to this phase were
not seen beyond this point. The heating step was then repeated at 300, 400 . . . 900
◦ C
and the scattering from each of the samples was measured after each heating step.
Figure 3.6 shows that the x = 0 samples contained NiO only (JCPDS #47-1049) after
being heated at 300
◦ C such that all contaminants are eliminated at this temperature.
Magnesia was selected for this part of the study because it only has three Xray peaks in the range over which scans were taken. These peaks were fit to and
subtracted from the patterns. In practice, the MgO peaks (JCPDS #45-0946) were
shifted from their expected positions because the X-ray machine was aligned to the
top of the samples such that the substrate had a vertical misalignment of up to 1 mm.
This misalignment varied from sample to sample such that an independent zero in
scattering angle was needed for these peaks.
Some samples studied in this way were prepared with the bicarbonate precipitator
heated in oxygen, while others were prepared from ammonium hydroxide heated in
air. In order to help distinguish the effect of the precipitator from the atmosphere,
samples prepared with ammonium hydroxide and heated in oxygen were measured
after heating to 600, 700, 800 and 900
◦ C only. Figure 3.2 (a) and (b) show XRD
scans obtained by this approach, along with the fits and difference plots. The lithium
hydroxide converted to lithium carbonate, and this occurred readily at 300
◦ C while
the stearic acid decomposed. Even the smaller amounts of stearic acid used on alumina (approximately 1.5 mg/cm
2 ) were sufficient to produce enough carbon dioxide
to react with all the lithium in the combinatorial samples. Thus, the synthesis of
lithium nickel oxide in the combinatorial samples involved the reaction of lithium
carbonate with nickel oxide regardless of the precipitator used. The fitting of the
XRD scans therefore required three phases: lithium carbonate (JCPDS #80-1307),
lithium nickel oxide and magnesium oxide.
Figure 3.2 (a) shows that the scattering from samples prepared with ammonium
bicarbonate contained a large peak near 23.5
◦ . The position of this peak varied from
sample to sample, following the magnesia peaks showing that it can be attributed to
the surface of the substrate. Lala et al. [68] found that lithium stearate has a large
peak near 24
◦ and a smaller peak above 40
◦ . Since the peak near 24
◦ was only seen
in samples with lithium, it was most likely lithium stearate, though there may have
been some nickel stearate as well since it also has peaks in this range [73]. The peak
was fit using a pseudo-Voigt function. Figure 3.7 shows that the stearate peak grew as
the samples were heated, especially during the stearic acid decomposition. The peak
disappeared after heating at 600
◦ C in most samples, consistent with the fact that
lithium stearate converts to lithium carbonate at 522
◦ C [68]. The lithium stearate on
the substrate surface results in a lithium deficiency in the sample during heating that
could affect the final lithium content of the samples. The stearate peak was never
seen when ammonium hydroxide was used as the precipitator. It is also possible that
some lithium stearate decomposition also contributed to the lithium loss.