Reduced cell parameters as a function of the lanthanide cation ionic radius for $\mathrm{CaLn}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}(L n=\mathrm{Pr}, \mathrm{Nd}, \mathrm{Sm})($ black $), \mathrm{CaLn}_{2} \mathrm{ZnTi}_{2} \mathrm{O}_{9}(L n=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd}, \mathrm{Eu})$ (red) [133] orthorhombic phases ( $P b n m$), and $\mathrm{BaLn}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}(\mathrm{Ln}=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd})$ (blue) tetragonal phase ( $4 / \mathrm{mcm}$) at room temperature. The dashed lines are a guide for the eyes.
Reduced cell parameters as a function of the lanthanide cation ionic radius for \mathrm{CaLn}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}(L n=\mathrm{Pr}, \mathrm{Nd}, \mathrm{Sm})( black ), \mathrm{CaLn}_{2} \mathrm{ZnTi}_{2} \mathrm{O}_{9}(L n=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd}, \mathrm{Eu}) (red) [133] orthorhombic phases ( P b n m), and \mathrm{BaLn}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}(\mathrm{Ln}=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd}) (blue) tetragonal phase ( 4 / \mathrm{mcm}) at room temperature. The dashed lines are a guide for the eyes.