LaMnxV1-xO4-delta(0 less than or equal to x less than or equal to 1) samples were characterized using thermogravimetry, thermo-dilatometry, high-temperature X-ray diffraction (HTXRD) and temperature-programmed reduction techniques, with an objective to explore the role of substitution on their thermo-physical properties, which may have a direct bearing on their catalytic behavior. Even though the substituted compositions (x < 0.8) were of a single phase, their reduction occurred in two steps, a lower temperature step corresponding to Mn4+ --> Mn3+/Mn2+ and another higher temperature one related to V5+ --> V3+. The dilatometric measurements gave similar values of linear thermal expansion coefficient (alpha(1)) at temperatures up to 600degreesC, both for LaVO4 and substituted samples. A different behavior was, however, observed at higher temperatures, whereas thermal contraction was observed in case of LaVO4 for measurements at temperatures above 700degreesC, the value of alpha(1) remained almost constant in case of the substituted samples. Furthermore, the HTXRD data revealed expansion in cell volume for all temperatures up to 950degreesC, irrespective of the substitution. These results therefore point to a higher degree of sintering in LaVO4 as compared to Mn-doped samples on heating at temperatures above 700degreesC. It is inferred that the resistance to sintering and the lowering of the reduction temperature are both responsible to the higher catalytic activity of the substituted samples and their compositional stability during the repeated cycles of reduction-reoxidation, as reported earlier [Appl. Catal. A 205 (2001) 295]. (C) 2003 Elsevier B.V. All rights reserved.