E.R. Andrievskaya Journal of the European Ceramic Sociery 28(2008)2363-2388 Table 3 The solubility of components in the systems HfO2-Ln2O3 lonic radius, by Ahrens(nm) Limit of solubility(mol%) 0.114 27-402 T5433 F57 0.095 30-38 5555 83/64 5550 11111 0.092 Er 826702 2.5 0.085 Table 4 Properties of the Ln2Hf20, phases a(nm) △Ht( k/mol) Dmes(g/cm) TEC x LagHf, O7 10776 0960 d?Hf,O7 10648 8010 uhF,07 82-4 Gd Hf, 07 Table 5 Properties of the phases Ln2Zr20758 Phase △H°t(kJ/mol) Tm(K) TEC×10-6 Pr2Zr07 Nd, ZrzO7 00000 8839 11.717 106.8 10.733 1.0554 9.347 Gd Zr?O7 10528 11519 R IMe =/Hf2_Ln,= [(2-x)rHf+XrLnI [(2-x)rLn +x'rHeI RI x1)rHf xrLn R=421.2 (for the pure pyrochlore phases) (2-x1rLn+x/Hf RI =1.2 2rHf where R, is the ratio of average radii for ions taking into account their substitution. The boundary value R1=1.2 responds to two values of x and xr. The results of cal The boundary ratio is Fig8. Calculated scheme for detemination of the homogeneity field size for correct for gadolinium hafnate but wrong for terbium haf the phases of pyrochlore type in the systems HfO2-Ln2O3 2352372 E.R. Andrievskaya / Journal of the European Ceramic Society 28 (2008) 2363–2388 Table 3 The solubility of components in the systems HfO2–Ln2O3 Ln3+ Ionic radius, by Ahrens (nm) Limit of solubility (mol%) Source Py M T F X H A B C La 0.114 27–40 2 5 15 15 12 10 – – 103 Pr 0.107 27–40 2 4 17/65 12 10 8 – – 103 Nd 0.104 27–39 2 3 18/63 11 9 5 – – 103 Sm 0.100 29–39 2 3 27/62 10 8 6 4 – 122 Eu 0.099 30–38 1.5 3 55 10 8 5 4 – 139 Gd 0.095 30–38 1.5 2.5 83/64 10 9 5 3.5 – 122 Tb 0.093 30–38 1.5 2.5 58 8 5 4 3 30 122 Dy 0.092 – 1.5 2.5 62 5 4.5 – 3 32 122 Ho 0.091 – 1 2.0 63 – 4 – 2 30 154 Y 0.092 – 1 2.0 57 – 3 – – 30 154 Er 0.089 – 1 2.0 60 – 3 – – 30 154 Yb 0.086 – 1 2.0 62 – 2.5 – – 35 154 Lu 0.085 – 1 2.0 60 – – – 40 154 Table 4 Properties of the Ln2Hf2O7 phases58 Phase a (nm) −H◦ f (kJ/mol) Tm (K) Dmes (g/cm3) TEC × 10−6/ ◦ La2Hf2O7 1.0776 – 2560 7.84 7.85 Pr2Hf2O7 1.0960 104 2610 7.90 9.13 Nd2Hf2O7 1.0648 85 2730 8.11 9.27 Sm2Hf2O7 1.0568 82 2760 8.20 10.60 Eu2Hf2O7 1.0540 – 2735 8.29 10.82 Gd2Hf2O7 1.0502 41 2790 8.34 – Table 5 Properties of the phases Ln2Zr2O7 58 Phase a (nm) −H◦ f (kJ/mol) Tm (K) Dmes (g/cm3) TEC × 10−6/ ◦ La2Zr2O7 1.0808 126.1 2160 5.89 9.129 Pr2Zr2O7 1.0714 120.3 2220 6.14 5.65 Nd2Zr2O7 1.0668 111.0 2320 6.28 11.717 Sm2Zr2O7 1.0594 106.8 2350 6.48 10.733 Eu2Zr2O7 1.0554 80.0 2350 6.63 9.347 Gd2Zr2O7 1.0528 75.8 2450 6.69 11.519 Fig. 8. Calculated scheme for determination of the homogeneity field size for the phases of pyrochlore type in the systems HfO2–Ln2O3. 235 rMe = rHf2−xLnx = 1 2 [(2 − x)rHf + xrLn] r Me = rLn2−xHfx = 1 2 [(2 − x )rLn + x rHf] Rl = rLn rMe = 2rLn (2 − xl)rHf + xlrLn = 1.2 R = r 3+ Ln r 4+ Hf ≥ 1.2 (for the pure pyrochlore phases) Rl = r Me rHf = (2 − x l )rLn + x l rHf 2rHf = 1.2 where Rl is the ratio of average radii for ions taking into account their substitution. The boundary value Rl = 1.2 responds to two values of xl and x l . The results of cal￾culation are presented in Fig. 8. The boundary ratio is correct for gadolinium hafnate but wrong for terbium haf￾nate.