Barium crystal ionic radius

No significant modification of the crystal cell structure can be attributed to the substitution of barium (ionic radius 175 pm, coordination number XII) by K that has the same coordination number and a very close ionic radius (178 pm). 

Calcium, strontium and barium each have slightly different impacts on the properties of the perovskite. This is due, in part, to the difference in ionic radii of the ions. Calcium has a radius of 1.36 A, whereas the radii of strontium and barium are 1.44 and 1.65, respectively. Thus barium-containing perovskites have a more open crystal lattice and thus have a higher ionic conductivity compared to strontium- and calcium-based materials. However, barium is more reactive towards C02-containing gas mixtures and forms barium carbonate very readily. 

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