5.5 Spinel–Ordered Rocksalt Coexistence Region
75
Fig. 5.16 The ordered
rocksalt lattice parameter
obtained in the coexistence
region between the spinel and
ordered rocksalt regions as a
function of γ
with an ordered rocksalt structure quite close in composition to the one analyzed
by Rietveld refinement in Sect. 5.3. This phase is previously been referred to as
Li x Ni 1−x O rocksalt [34]. Recognizing that the end of the tie-line is higher up in the
triangle than previously suspected has consequences when one attempts to work out
the stoichiometry of the spinel sample based on the amount of oxygen lost during
synthesis.
The lever rule, described in Sect. 2.4, was used with LiNi 0.5 Mn 1.5 O 4 as the pivot
point (pointA in Fig. 5.13, right) in order to identify the upper boundary of the ordered
rocksalt region. Figure 5.13 (left) shows the points used to define this boundary.
Figure 5.10 shows that once again the boundaries obtained with the lever rule agree
with the phases determined by visual inspection of the XRD scans. Although the
point (0.45, 0.3) lies in the three-phase region of the regular-cooled triangle, it is
close enough to the edge of the region that it appears two-phase and provides a
useful point to obtain the correct curvature of the boundary of the rocksalt solid
solution region.
The position of the boundary at β = 55
◦ is at (0.05, 0.09), the point used in Fig. 5.4
to define the angle γ . Figure 5.16 shows the ordered rocksalt lattice parameter as a
function of γ . Here, the lattice parameter is constant with a value of 8.320 ± 0.001 Å
up to a maximum angle of approximately 54
◦ . This is close to the value of 8.328 ±
0.001 Å obtained for the sample at (0.05, 0.10), but this still represents the greatest
discrepancy seen along tie-lines in this study. Should this region become of greater
interest, it may be necessary to explore this boundary more closely. Nonetheless,
the data suggest that the tie-lines fan out from a point near (0.05, 0.09) up to γ = 54
or 55
◦ beyond which the samples were in the region where tie-lines fan out from
LiNi 0.5 Mn 1.5 O 4 (i.e., β < 55
◦ ). All tie-lines in the region between the spinel and
ordered rocksalt phases were therefore identified and included in Fig. 5.2.
The lever rule was then used with the point (0.05, 0.09) as the pivot in order to
determine the lower spinel boundary to the left of LiNi 0.5 Mn 1.5 O 4 . This was only done
75
Fig. 5.16 The ordered
rocksalt lattice parameter
obtained in the coexistence
region between the spinel and
ordered rocksalt regions as a
function of γ
with an ordered rocksalt structure quite close in composition to the one analyzed
by Rietveld refinement in Sect. 5.3. This phase is previously been referred to as
Li x Ni 1−x O rocksalt [34]. Recognizing that the end of the tie-line is higher up in the
triangle than previously suspected has consequences when one attempts to work out
the stoichiometry of the spinel sample based on the amount of oxygen lost during
synthesis.
The lever rule, described in Sect. 2.4, was used with LiNi 0.5 Mn 1.5 O 4 as the pivot
point (pointA in Fig. 5.13, right) in order to identify the upper boundary of the ordered
rocksalt region. Figure 5.13 (left) shows the points used to define this boundary.
Figure 5.10 shows that once again the boundaries obtained with the lever rule agree
with the phases determined by visual inspection of the XRD scans. Although the
point (0.45, 0.3) lies in the three-phase region of the regular-cooled triangle, it is
close enough to the edge of the region that it appears two-phase and provides a
useful point to obtain the correct curvature of the boundary of the rocksalt solid
solution region.
The position of the boundary at β = 55
◦ is at (0.05, 0.09), the point used in Fig. 5.4
to define the angle γ . Figure 5.16 shows the ordered rocksalt lattice parameter as a
function of γ . Here, the lattice parameter is constant with a value of 8.320 ± 0.001 Å
up to a maximum angle of approximately 54
◦ . This is close to the value of 8.328 ±
0.001 Å obtained for the sample at (0.05, 0.10), but this still represents the greatest
discrepancy seen along tie-lines in this study. Should this region become of greater
interest, it may be necessary to explore this boundary more closely. Nonetheless,
the data suggest that the tie-lines fan out from a point near (0.05, 0.09) up to γ = 54
or 55
◦ beyond which the samples were in the region where tie-lines fan out from
LiNi 0.5 Mn 1.5 O 4 (i.e., β < 55
◦ ). All tie-lines in the region between the spinel and
ordered rocksalt phases were therefore identified and included in Fig. 5.2.
The lever rule was then used with the point (0.05, 0.09) as the pivot in order to
determine the lower spinel boundary to the left of LiNi 0.5 Mn 1.5 O 4 . This was only done