X-ray powder diffraction patterns for (a) $\mathrm{CaPr}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}$, (b) $\mathrm{CaNd}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}$, and (c) $\mathrm{CaSm}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}$ at RT, (black) before, and (red) after annealing at 1500 K. The irreversibility of the samples is clearly observed.
X-ray powder diffraction patterns for (a) \mathrm{CaPr}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}, (b) \mathrm{CaNd}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9}, and (c) \mathrm{CaSm}_{2} \mathrm{CuTi}_{2} \mathrm{O}_{9} at RT, (black) before, and (red) after annealing at 1500 K. The irreversibility of the samples is clearly observed.