It can be seen from the table that both the lattice parameters ((a) and (c)) are found to decrease with increasing dopant concentration and the observed variation may be attributed to the fact that the ionic radius of the dopent ion, La3+ (1.16 A° in 6-coordinated state ) is slightly less that of Bi3+ (1.17 A° in 6-coordinated state) [14].
In fact, the linear variation of the lattice parameters with La content is in conformity with the Vegard’s law [15].