Combustion synthesis and bulk thermal expansion studies of Ba and Sr thorates

Nanocrystalline BaThO3 and SrThO3 powders have been prepared at a relatively low calcination temperature by a gel combustion technique using citric acid as a fuel and the nitrate as an oxidizer. These powders resulted in highly dense (sintered density > 90% of th.d.) pellets on sintering at 1923 K. The orthorhombic lattice parameters of BaThO3 were found to be as a=0.635(1), b=0.6387(9) and c=0.8995(9) nm whereas SrThO3 was monoclinic with a=0.6319(4), b=0.3240(1), c=0.4928(3) nm and β=117.38(5) deg. . It was observed that the average linear thermal expansion coefficients, α-bar, for BaThO3, SrThO3 and ThO2 are 11.09x10-6,10.49x10-6 and 9.10x10-6 K-1, respectively, which are about 21.9% and 15.3%, respectively, higher than that of pure ThO2 between room temperature and 1123 K