## Abstract

Oxide melt solution calorimetric measurements were made to determine the enthalpy of formation of cubic-yttria-stabilized zirconia (c-YSZ) with respect to the oxides m-ZrO_{2} and C-type YO_{1.5}. The enthalpy of formation can be fit either by a quadratic equation or by two straight line segments about the minimum near x = 0.40. The quadratic fit gives a strongly negative interaction parameter, Ω = -93.7 ± 12.0 kJ/mol, but does not imply regular solution behavior because of extensive short-range order. In this fit, the enthalpy of transition of m-ZrO_{2} to c-ZrO_{2}, 9.7 ± 1.1 kJ/mol, is in reasonable agreement with earlier estimates and that of C-type to cubic fluorite YO_{1.5}, 24.3 ± 14.4 kJ/mol, is consistent with an essentially random distribution of oxide ions and anion vacancies in the high-temperature fluorite phase. The two straight-line segments give 6.1 ± 0.6 kJ/mol and 5.5 ± 2.5 kJ/mol for these transitions, respectively. The latter value would imply strong short-range order in cubic fluorite YO_{1.5}. Clearly more complex solution thermodynamic descriptions need to be developed. The enthalpy of transition from the disordered c-YSZ phase to the ordered δ-phase at 25 °C was also measured and was 0.4 ± 1.6 kJ/mol. No energetic difference between the disordered-c-YSZ phase and the ordered δ-phase underscores the importance of short-range order in c-YSZ. Enthalpy data were combined with Gibbs free energy data to calculate entropies of mixing. Using the quadratic fit, negative excess entropy of mixing in the cubic solid solution, relative to a system with maximum randomness on cation and anion sublattices, was found and was another indication of extensive short-range order in c-YSZ.

Original language | English (US) |
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Pages (from-to) | 908-918 |

Number of pages | 11 |

Journal | Journal of Materials Research |

Volume | 18 |

Issue number | 4 |

DOIs | |

State | Published - Apr 2003 |

Externally published | Yes |

## All Science Journal Classification (ASJC) codes

- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering