INFLUENCE OF CR2O3 ON THE STABILITY OF LOW-TEMPERATURE T-ZRO2

Aqueous solutions containing different molar fractions of Cr(NO3)3 . 9 H(2)O and ZrO(NO3)(2). 2H(2)O salts were dried at 110 degrees C for 24 h and calcinated up to 1100 degrees C. Precise X-ray powder diffracti on measurements of the obtained samples, covering the whole concentrat ion range in the system ZrO2-Cr2O3, were performed. It was found that the solubility of Cr2O3 in ZrO2, as well as the solubility of ZrO2 in Cr2O3, was negligible. Except for the end samples, identified as pure m-ZrO2 and Cr2O3, other samples contained the phases Cr2O3, m-ZrO2 and metastable t-ZrO2. The fraction of the t-ZrO2 phase in the total cont ent of ZrO2 (m-ZrO2 + t-ZrO2) increased with an increase of the initia l content of Cr2O3 but this relation was not linear. The observed stab ilization of metastable t-ZrO2 could not be attributed to the formatio n of a solid solution. It was suggested that the stabilization of t-Zr O2 at room temperature resulted from a very strong surface interaction between chromium oxide and zirconia. This interaction prevented the d iffusion of oxygen from the atmosphere into the ZrO, lattice, which ot herwise triggers the transition t-ZrO2 --> m-ZrO2 on cooling. (C) 1998 Elsevier Science B.V. All rights reserved.