The synthesis, structure, and physical properties of (\mathrm{La}{3-x}) (M{x} \mathrm{Ni}{2} \mathrm{O}{7-\delta}), with (M=\mathrm{Ca}^{2+}, \mathrm{Sr}^{2+}), or (\mathrm{Ba}^{2+}), and (0<x \leq 0.075), were investigated. These compounds were prepared by a precursor method with tetramethyl ammonium hydroxide and were characterized by room temperature and high-temperature powder X-ray diffraction, TGA, electrical resistivity, and magnetic susceptibility measurements. The substituted compounds form with orthorhombic symmetry in space group Fmmm, similar to the asprepared parent compound, (\mathrm{La}{3} \mathrm{Ni}{2} \mathrm{O}{6.92}). As the amount of divalent alkaline earth metal substitution increases, the (c) cell parameter does not significantly change for (\mathrm{Ca}) and increases significantly for (\mathrm{Sr}) and (\mathrm{Ba}) substitution, while the (a) and (b) cell parameters remain nearly unchanged for all cases. The observed trend in the (c) parameter is due to the increasing (\mathrm{Ni}^{3+}) ion concentration for the case of (\mathrm{Ca}^{2+}) substitution, while for (\mathrm{Sr}^{2+}) and (\mathrm{Ba}^{2+}) substitutions the effective larger size of the divalent cations is dominant. Significant oxygen deficiencies are noted in all of the as-prepared samples. However, upon high-pressure oxygen annealing, stoichiometric oxygen contents can be achieved. The room temperature resistivity of the as-prepared substituted compounds decreases relative to (\mathrm{La}{3} \mathrm{Ni}{2} \mathrm{O}{6.92}), and at (x=0.075) a semiconductor to metal transition is observed for all (M). The high-pressure oxygen annealed samples for all compositions show metallic behavior from room temperature down to (20 \mathrm{~K}). The magnetic susceptibility is nearly temperature independent in the temperature range (100-300 \mathrm{~K}), and paramagnetic behavior is observed below 100 K. 1994 Academic Press, Inc.