TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Particle: X-ray diffraction analysis of the zirconium-hafnium mixed oxide powder exhibits the reflexes of monoclinic and tetragonal zirconium dioxide only.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The alcoholate is zirconium(IV) ethylate, zirconium(IV) n-propylate, zirconium(IV) isopropylate, zirconium(IV) n-butylate, zirconium(IV) tert-butylate, hafnium(IV) ethylate, hafnium(IV) n-propylate, hafnium(IV) isopropylate, and/or hafnium(IV) tert-butylate.The carboxylate is zirconium acetate, zirconium propionate, zirconium oxalate, zirconium octoate, zirconium-2-ethyl hexanoate, zirconium neodecanoate and/or zirconium stearate, hafnium acetate, zirconium propionate, hafnium oxalate, hafnium octoate, hafnium-2-ethyl hexanoate and/or hafnium neodecanoate.The organic solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, 2-propanone, 2-butanone, diethyl ether, tert-butyl-methyl ether, tetrahydrofuran, 1-8C carboxylic acids, ethyl acetate, toluene and/or benzene.The solutions containing zirconium and/or hafnium carboxylate also contain the carboxylic acid on which the carboxylate is based and the solutions containing zirconium and/or hafnium alcoholate also contain the alcohol on which the alcoholate is based. EXAMPLE - A solution comprising zirconium octoate (24.4 wt.%), hafnium octoate (0.3 wt.%), octanoic acid (39.6 wt.%), 2-(2-butoxyethoxy)ethanol (3.5 wt.%) and white spirit (32.2 wt.%) was mixed with a solution comprising zirconium n-propanolate (27.8 wt.%), hafnium n-propanolate (0.5 wt.%), n-propanol (30.5 wt.%) and tetra-n-propanolate (41.2 wt.%) in a ration of 90:10 at 50degreesC.    The resulting homogeneous solution (1500 g/h) was atomized with 5 Nm3/h of air using a nozzle having a diameter of 0.8 mm. The resulting aerosol was transferred to a flame formed from hydrogen (5 Nm3/h) and primary air (10 Nm3/h) and burned into a reaction chamber. Secondary air (20 Nm3/h) was introduced into the chamber. The hot gases and the solid products were then cooled in a cooling section. The zirconium-hafnium mixed oxide powder obtained was separated off in filters. The powder had a BET surface area of 63 m2/g; average primary particle diameter of 13 nm; aggregate circumference of 494 nm; and aggregate surface area of 5228 nm2.