CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

Figure 83 shows the 31 P MAS-NMR spectra of Bi 1-x La PO x 4 (x = 0, 0.3, 0.5, 0.7, 1)
nanomaterials prepared at 185°C. With increase in La 3+
content in BiPO 4 , there is a
significant change in the line shape is observed. The line width of the peak increases
significantly and peak maxima shift towards higher chemical shift (d) values with increase in
La 3+ content in the lattice. This can be understood by considering the difference in the charge
3+ 3+
3+ 3+
to radius ratio (2.46 and 2.56 for La and Bi , respectively) between Bi and La ions. The
lower charge to radius ratio of La 3+ compared to Bi 3+ leads to shifting of peak maxima
3+ 3+
towards higher d values when Bi is replaced by La in BiPO 4 lattice. The sharpening of the
peaks with increase in the La 3+ concentration can be explained based on the environment
3+ 3+
around ‘P’ in the solid solution. It is known that Bi is heavier ion compared to La and
when heavier ions surround the probe nucleus ( 31 P), anisotropy in chemical environment
around ‘P’ will be higher as compared to the situation in which ‘P’ is surrounded by lighter
ions. Higher the anisotropy in chemical environment, greater will be the line width of the
NMR absorption peak. These results further substantiate the solid solution formation between
BiPO and LaPO .
4 4
Intensity (arb.units)
1000
500
0
1000
500
0
800
400
0
600
300
0
LaPO 4
Bi 0.3
La 0.7
PO 4
Bi 0.5
La 0.5
PO 4
Bi 0.7
La 0.3
PO 4
600 BiPO
300
4
0
-20 -10 0 10
Chemical shift (ppm)
Fig.83.
31
P MAS-NMR patterns of Bi 1-x LaxPO4 (x = 0, 0.3, 0.5, 0.7, 1) nanomaterials
prepared at 185°C.
140