The continuing drive towards miniaturization of electronic devices(1) is motivating the search for new materials. Consider, for example, the case of the much-used dynamic random-access memory, The minimum capacitance per cell that can be tolerated is expected(2) to remain at 30-40 fF, but as the cell area decreases, the corresponding reduction in geometric capacitance has to be compensated for. So far, this has been achieved by resorting to complex non-planar structures and/or using much thinner films of the dielectric insulator, amorphous silicon dioxide (a-SiOx), although the latter approach is limited by the electric fields that can be supported by a-SiOx before its insulating properties break down. An alternative strategy is to develop thin-film insulators that have a dielectric constant significantly greater than that of a-SiOx, reducing the size of the fields required for device operation. Here we show that a composition-spread technique allows for the efficient evaluating of materials,vith both a high dielectric constant and a high breakdown field, We apply this approach to the Zr-Sn-Ti-O system, and we find that compositions close to Zr0.15Sn0.3Ti0.55O2-delta are better thin-film dielectrics than high-quality deposited a-SiOx, Although detailed tests of the performance of these materials have not yet been carried out, our initial results suggest that they are likely to be comparable to the best alternatives (such as (Ba, Sr)TiO3) currently being considered for integrated-circuit capacitors.