E.R. Andrievskaya/ Journal of the European Ceramic Sociery 28(2008)2363-2388 T 十+ ++185t++4"+ Py+A mol Py f F+Ay! Ay ++ M r +++++甘 |,a mo Fig. 1. Phase diagrams of the binary systems with hafnia and lanthanide oxides from lanthana to gadolinia:(a)HfO2-La203, 03(b)HfO2-Pr203, 03(c) HfO2-Nd2O3, (d) HfO2-Sm2O3, (e)HfO2-Eu2O3, (f) HfO2-Gd2O3: (O)DTA in helium: (+)annealing and quenching technique. () thermal analysis in air under solar fumace;(O)single-phase regions, (O hase regions by the data of XRD and annealing and quenching occurs by the way of cation rearrangement, distributed in the wide homogeneity fields, but much narrower ones than fluorite disordered solid solution of the fluorite-type and filling cites type solid solutions. The deviation from stoichiometry in the in the pyrochlore lattice, as well as by the oxygen ion shift- Ln2Hf20, phase appears, when x ions of Hf++ are substituted by ing in the anion sublattice, i.e. by changing of the oxygen xions of Ln+ On substitution, the x/2 additional oxygen vacan- ions coordination and abrupt decreasing of oxygen vacan- cies are formed Ln2+rHf2-O7-(/2). When the 'ions of Ln cies concentration.236 All these pyrochlore-type phases possess are substituted by ions of Hf++ the number of oxygen vacan-E.R. Andrievskaya / Journal of the European Ceramic Society 28 (2008) 2363–2388 2367 Fig. 1. Phase diagrams of the binary systems with hafnia and lanthanide oxides from lanthana to gadolinia: (a) HfO2–La2O3, 103 (b) HfO2–Pr2O3, 103 (c) HfO2–Nd2O3, 103 (d) HfO2–Sm2O3, 122 (e) HfO2–Eu2O3, (f) HfO2–Gd2O3; 122 () DTA in helium; (+) annealing and quenching technique, () thermal analysis in air under solar furnace; () single-phase regions, () two-phase regions by the data of XRD and annealing and quenching. occurs by the way of cation rearrangement, distributed in the disordered solid solution of the fluorite-type and filling cites in the pyrochlore lattice, as well as by the oxygen ion shift￾ing in the anion sublattice, i.e. by changing of the oxygen ion’s coordination and abrupt decreasing of oxygen vacan￾cies concentration.236 All these pyrochlore-type phases possess wide homogeneity fields, but much narrower ones than fluorite￾type solid solutions. The deviation from stoichiometry in the Ln2Hf2O7 phase appears, when x ions of Hf4+ are substituted by x ions of Ln3+. On substitution, the x/2 additional oxygen vacan￾cies are formed Ln2+xHf2−xO7−(x/2). When the ч ions of Ln3+ are substituted by ч ions of Hf4+ the number of oxygen vacan-