igure 2. Show the results of XRD patterns
of all compositions after calcination in air with an
intermediate grinding. The results indicate they
exhibit a characteristic pattern of a pseudocubic
phase of La2Mo2O9 (JCPDS no. 28-0509). With the
La1.8Sr0.2Mo2O9 composition, the additional peaks
appear around 2θ at 33.3° and 51.8°, indicating the
existing secondary phase of SrMoO4 as pointed by
the arrows. As a consequence, the substitution of
10 mol% Sr into a La site is over the solubility
limit of La2Mo2O9. Moreover, W can substitute
into Mo and form a solid solution upto 15 mol%
for this work. The higher amount of W can be
substituted.(12, 14) possibly due to similar ionic charge
and radius of Mo6+ and W6+, 0.59 and 0.60 Å
respectively.(15) The XRD results after sintering at a
higher temperature are found to be the same as
those of calcined compositions. The pseudocubic
phase of La2Mo2O9 including SrMoO4 in the composition
of La1.8Sr0.2Mo2O9 still exist after firing at 1100°C.