Polycrystalline, dense samples of lanthanum gallate doped with strontium on the A and magnesium on the B site, La1-xSrxGa1-yMgyO3-(x+y)/2 (LSGM), were prepared using the Pechini method. Characterisation by X-ray diffraction (XRD) showed that the resulting samples annealed at 1400 degreesC in air are single phase. Using in situ XRD measurements the dissociation and crystallisation of the amorphous precursor powders of the Pechini preparation was followed up to 1100 degreesC. First results for the cation diffusion coefficients of gallium, iron and manganese were obtained by the radiotracer sectioning method. Two different mechanisms (grain boundary and bulk diffusion) were found and ratios of grain boundary to bulk diffusion coefficients were obtained. (C) 2000 Elsevier Science B.V. All rights reserved.