A mixed aqueous solution (0.2-0.5 M) of ZrOCl2.8H(2)O and AlCl3.6H(2)O has a controlled forced hydrolysis to form an amorphous Zr1-2xAl2xO(OH)(2-2x).alphaH(2)O precursor on adding NH4OH (in water) dropwise in a controlled manner at room temperature or preferably lower. X-ray diffraction of four halos at 19.2, 28.5, 39.2, and 57.0 nm(-1) wavevectors (x = 0.05) characterizes the amorphous structure of the precursor. It undergoes a self-controlled reconstructive thermal decomposition into stabilized c-ZrO2 of nanoparticles in Fm3m cubic crystal structure at temperature as low as 200degreesC. The process involves a predominant endothermic signal with a total of similar to60% loss in the precursor mass. It controls the local temperature and in turn governs moderate nucleation and grain growth in nanocrystals. The x = 0.02-0.10 Al3+ additives cultivate stabilized c-ZrO2 crystallites in 6-12 nm confined size (d) on heating the precursor at 200-800degreesC for 2-5 h. A reconstructive c --> t/m-ZrO2 phase transformation appears at extended temperature as 1000degreesC as per the Al3+ additives. A pure m-phase, dsimilar to26 nm, results at 1200degreesC (800degreesC otherwise at x = 0). The lattice parameters vary as the x-value. The results of c-ZrO2 formation and its stability and phase transformation are studied with X-ray diffraction, microstructure and thermal analysis of representative specimens. (C) 2063 Elsevier Science B.V. All rights reserved.