(color online) (a) Schematic view of 2×2×2 orthorhombic unit cells along the crystallographic b zone axis of YAP. The 57 pm Y–Y-atom pair separation is indicated along two directions by the bold lines. Corners of squares give position of O atoms and centers denote positions of Al overlapping with O atoms. (b) Experimental image of YAlO₃:Ce in the [010] projection. Arrows denote examples of Y–Y atom pairs with pair separations given.^[11]