Temperature-stable, high-permittivity (high-dielectric constant) ceramics are used as resonators for microwave telecommunications. Research and development in this area is aimed at increasing the dielectric constant (in order to reduce component size) while maintaining very high quality factor (low dielectric loss). This present work is a synchrotron X-ray powder diffraction study of high quality factor, high permittivity ceramics of the Ti(Al)O-2 and (1-x)Ca2/5Sm2/5TiO3-xLi(1/2)Sm(1/2)TiO(3) families. The synchrotron powder diffraction was used to investigate doping of Al onto the Ti site in Ti(Al)O-2. It was found that the lattice parameters in Ti(AI)02 are not affected by the Al doping. Although this null result does not give any evidence for substitution of Al on the Ti site, it does not exclude the possibility that a small proportion of the Al ions do substitute for Ti in Ti(Al)O-2. In (1-x)Ca2/5Sm2/5TiO3-xLi(1/2)Sm(1/2)TiO(3) the variation of lattice parameters and crystal structure versus x, and the possibility of substitution of Li onto the Ti site were investigated. Single phase samples with the orthorhombic CaTiO3 perovskite structure were obtained for 0.20