Lanthanum-containing perovskites, LaMO3 (M=Al, Sc, Cr, Mn, Fe, Co, Ni, Ga, and In), have been synthesized in molten carbonates from a mixture of lanthanum carbonate and an M-containing oxide or an acetate, or from a co-precipitation mixture of metal (M) and lanthanum. Metal aluminum, chromium, and iron, immersed in a mixture of molten (Li0.52Na0.48)(2)CO3 and lanthanum carbonate at 923 K, were covered, respectively, with LaAlO3, LaCrO3, and LaFeO3. Ceramic and single-crystal alpha-Al2O3, immersed in molten (Li0.52Na0.48)(2)CO3 mixed with lanthanum carbonate, were also covered with LaAlO3. In situ X-ray diffractometry revealed that La2O2CO3 reacted with alpha-LiAlO2 to yield LaAlO3; the reaction proceeded faster under N-2 than under a CO2 atmosphere.