TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The precursor solution is a 0.01 M to 0.1 M ethanol solution or acetone solution of cerium nitrate. The high-temperature diffusion flame burner includes five concentric stainless tubes consisting of: an innermost tube through which the carrier gas and the microdroplets are fed; first, second and third intermediate tubes, sequentially surrounding the innermost tube, through which argon, hydrogen and oxygen gases are fed, respectively; and an outermost tube through which air is fed. The carrier gas is an argon gas, a nitrogen gas, an oxygen gas and/or air. The nanopowder is collected by thermophoresis or using a filter, a cyclone and/or an electrostatic collector. Preferred Components: The cerium compound is cerium nitrate, cerium chloride, cerium sulfate and/or cerium carbonate.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The cerium compound is cerium acetate. The organic solvent is methanol, ethanol and/or acetone. EXAMPLE - Cerium nitrate trihydrate was dissolved in ethanol to prepare a precursor solution having a concentration of 0.01 M. After the precursor solution was injected into an ultrasonic atomizer through a syringe pump, it was atomized into micrometer-sized droplets. The droplets were transferred together with an argon gas (Ar, 99.95%) as a carrier gas to a central portion of a diffusion flame burner (outer diameter=36 mm, length=300 mm) including five concentric stainless tubes. The concentric stainless tubes consist of an innermost tube, first, second and third intermediate tubes sequentially surrounding the innermost tube, and an outermost tube. The mixture of droplets and the carrier gas were fed through the innermost tube. The flow rate of the carrier gas was fixed to 2 l/minute. An argon gas was fed at a fixed flow rate of 1 l/min through the first intermediate tube, a hydrogen gas (99.995%) was fed at a fixed flow rate of 5 l/minute through the second intermediate tube, and an oxygen gas (99.95%) was fed at a fixed flow rate of 6 l/minute through the third intermediate tube, and air was fed at a fixed flow rate of 15 l/minute through the outermost tube. The temperature at the central region of flame, where the precursor droplets passed through, was 1300 degrees C to 900 degrees C. A stainless tube having an inner diameter of 38 mm and a length of 100 mm was installed on the burner to protect a stable combustion environment from the ambient air flow. The transferred droplets were pyrolyzed and oxidized into a nanopowder by flame in the central portion of the diffusion flame burner.