The present invention includes a method of making a plurality of nanoparticles comprising single crystalline spherical BaZrO.sub.3 particles, cubic BaZrO.sub.3 particles or a mixture of both. The method comprises: providing a mixture of a barium precursor, a zirconium precursor and a hydroxide salt or hydroxide salts; heating the mixture to an isothermic annealing temperature, wherein the annealing temperature is in a range of from about 470.degree. C. to about 800.degree. C.; annealing the mixture at the isothermic annealing temperature for an annealing time of in a range of about 15 minutes to about 280 minutes; and cooling the mixture at a fixed cooling rate to form the plurality of nanoparticles, wherein the cooling rate is in a range of from about 2.degree. C./minute to about 200.degree. C./minute. The ratio of spherical particles to cubic particles in the plurality is greater if the isothermic annealing temperature is at the higher end of the range; the ratio of spherical particles to cubic particles in the plurality is greater if the annealing time is at the higher end of the range; and the ratio of spherical particles to cubic particles in the plurality is greater if the cooling rate is at the lower end of the range.
 This invention was made with government support under grant numbers DMII-0403859 and CAREER award DMR-0348239 awarded by the National Science Foundation., and DE-AC02-98CH10886 awarded by the US Department of Energy. The government has certain rights in the invention.