stacking of two layers of distorted Zr sites plus two layers of octahedral Ti sites alternated along the axis a,
giving rise to a doubling of the parameter a (cell setting: a b c ¼ 9:6 5:3 5:0A˚ ) with respect to the disordered
phase; this ordering scheme is consistent with the formula ZrTiO4 (Zr:Ti ratio ¼ 1:1; XTi ¼ 0:5);