A series of mixed orthovanadates with general formula La1-xCexVO4 (0 < x < 1) were synthesized and characterized using powder XRD and FTIR techniques. The monoclinic phase of LaVO4 was retained for the samples with x < 0.2, while the tetragonal phase of CeVO4 was stabilized in x greater than or equal to 0.5 compositions. On the other hand, the mixed phases of LaVO4 and La0.5Ce0.5VO4 existed for the values of 0.2 < x < 0.5. The lattice parameters, deduced by indexing of XRD patterns, were found to decrease with the increasing cerium content in the case of both the monoclinic and the tetragonal phases of substituted orthovanadates having single-phase compositions. This trend can be attributed to the presence of Ce in +3 oxidation state and to its smaller ionic size compared to that of La3+. The temperature-programmed reduction/oxidation studies showed that, compared to CeVO4 or LaVO4, the single-phase mixed orthovanadates exhibited a better reproducibility during the repeated cycles of reduction/oxidation. (C) 2002 Elsevier Science Ltd. All rights reserved.