Specimens of yttria fully stabilized zirconia with different amounts of boron oxide have been studied by X-ray diffraction at room temperature and at higher temperatures up to 1250 degreesC. A boron oxide-assisted cubic-to-monoclinic phase transformation was determined in the temperature range 800-1250 degreesC. In situ high temperature X-ray diffraction experiments gave evidences of the dependence of the phase transformation on the heating rate. The possibility of tuning the cubic-monoclinic phase ratio by suitable addition of boron oxide before pressing and sintering is proposed. (C) 2004 Elsevier Ltd. All rights reserved.