Al3+ stabilized tetragonal (t)-ZrO2 of nanoparticles is studied with X-ray photoelectron spectroscopy (XPS) as a function of the Al3+ concentration. The samples, with 2-15 mol% Al3+ additives, are prepared by co-hydrolysis of the two types of the metal cations in an amorphous precursor of oxyhydroxyl Zr1-2xAl2xO(OH)(2-2x).alphaH(2)O gel. Substantially stabile t-ZrO2 occurs with the Al3+ additives on a reconstructive thermal decomposition of gel by heating at 500 degreesC in air. The Al3+ additive inhibits average t-ZrO2 crystallite size to be as small as 6-8 nm (9 nm otherwise in virgin t-ZrO2) depending on the Al3+ concentration. As analyzed with X-ray diffraction, no independent Al2O3 crystallizes, confirming formation of a perfect Al3+:ZrO2 solid solution under these conditions. Six distinct XPS bandgroups lie, in the 0-600 eV range of the binding energy, in excitations of 2p, 2s, 4p, 3d, or 3p core electrons in Al3+ and Zr4+ cations and in Is excitation in O2- anions in Al3+ :t-ZrO2, solid solution. Weak satellite 3d(5/2) and 3d(3/2) bands occur at lowered energies (8-10 eV) of the main bands in trace of part of the metal cations present in the lower Zrq+, q less than or equal to 3, oxidation states. (C) 2003 Elsevier B.V. All rights reserved.