Unprecedented lattice volume expansion on doping stereochemically active Pb(2+) into uniaxially strained structure of CaBa(1−x)Pb(x)Zn(2)Ga(2)O(7)

Lone pair cations like Pb(2+) are extensively utilized to modify and tune physical properties, such as nonlinear optical property and ferroelectricity, of some specific structures owing to their preference to adopt a local distorted coordination environment. Here we report that the incorporation of Pb(2+) into the polar “114”-type structure of CaBaZn(2)Ga(2)O(7) leads to an unexpected cell volume expansion of CaBa(1-x)Pb(x)Zn(2)Ga(2)O(7) (0 ≤ x ≤ 1), which is a unique structural phenomenon in solid state chemistry. Structure refinements against neutron diffraction and total scattering data and theoretical calculations demonstrate that the unusual evolution of the unit cell for CaBa(1-x)Pb(x)Zn(2)Ga(2)O(7) is due to the combination of the high stereochemical activity of Pb(2+) with the extremely strained [Zn(2)Ga(2)O(7)](4−) framework along the c-axis. The unprecedented cell volume expansion of the CaBa(1−x)Pb(x)Zn(2)Ga(2)O(7) solid solution in fact is a macroscopic performance of the release of uniaxial strain along c-axis when Ba(2+) is replaced with smaller Pb(2+).