To determine if these films behave as a solid solution, i.e., Ni 2+ and Pb 2+ mix uniformly and randomly, we evaluated the d-spacing of the (110) peak as a function of Ni 2+ concentration (Figure ). Since Ni 2+ (70 ppm) is a smaller ion than Pb 2+ (119 ppm), we expect the d-spacing to decrease with increasing incorporation of Ni 2+ corresponding to a shrinking lattice size.