A.A. Sobol, Y.K. Voronko / Journal of Physics and Chemistry of Solids 65 (2004)1103-1112 (8 mol%)crystals can be repeated using the subsequent low- temperature annealing [17]. By contrast, the particles of e t-phase formed in the diffusion-controlled reaction are retained even after a long-time(20-30 h) annealing at T>T 5. Raman spectroscopy study of the formation of different tetragonal phases in ZrO2-Gd,O3(Eu2O3) solid solutions The above-mentioned two mechanisms of phase for- mation in the ZrO2-Gd2O3(Eu2O3) system are easily 1000 registered by the Raman spectroscopy technique. Fig. 4 displays the Raman spectra at 300 K for a series of rapidl Eu2O3(Gd2O3)-mol% quenched ZrO2-Eu2O3 melts under the variation of the Eu2O3 concentration from 2.5 up to 8 mol%. The Raman t trum of a is also shown in Fig 4. In this figure, all six Raman lines of tetragonal D4, phase are presented in the Raman spectra of the samples. A Fig. 3. Equilibrium ZrO2-Gd2O3(Eu 03)phase diagrams. Ti is the continuous change in the line frequencies is observed with o the cr bet ween turma nd t apd s e egte s nd e i h e temper atse the growth of Eu2O3 concentration, a shift of theRamanline in the experiments. Bottom-the boundaries of the t' and C metastable position within the range 240-270 cm being the most phases at 300K remarkable(Fig. 4). Redistribution of intensities and broadening of the Raman lines followed a growth in the stabilizer concentration. Thus. the most intensive narrow line in the 240-270 cm spectral range for a pure ZrO2 and 9mol% of Gd, 03(Eu,,). This process resulted in the ZrO2-EzO3(2.5 mol% )is registered as the weakest broad formation of large-size t-particles and the milky single band in the spectrum of the ZrO2-Eu2O3(8 mol%)sample crystals. In turn, there is a growth of relative intensities of the two Q The temperature at the point 3 is lower than To of the lines in the ptin o im me srd s ion of 600 cm with increasing Eu2O3 content. These tw merged practically into a unified is similar to the Gd2O3(Eu2O3) cubic phase should nucleate and dominating in the spectrum of the ZrO2-Eu2O3 in the crystal volume as a result of this transformation. (8 mol%)sample(Figs. 4 5). Previously, the band with Diffusion processes at T< To for ZrO2-Gd2O3(Eu2 03) O5 Fluorite structure on the basis of the polarized Raman (8 mol%) was shown to proceed very slowly [17]. They interfere with the nucleation of t-precipitates due to the diffusion-controlled reaction in the case of annealing at t< 242cm265cm To [17]. For the solid solution with Ln2O3 stabilizers of small Ln-ions (Y2O3, Yb2O3, Lu2O3), this phenomenon resulted in the freezing stabilizer concentration in 8-mol% domains. In contrast, the primary concentration of Ln2O oxides with large Ln cations(Gd2O3 and Eu2O3) did not 6-mol%o retain in supersaturated t'-domains even at low-temperature nnealing. gradual decrease in the concentration of Gd,O 4-mol% (Eu?O3) inside the t'-domains occurred, the volume around these domains being fertilized by Gd2O3(Eu2O3) oxides 5-mol% The Gd2O3(Eu2O3)concentration in t'-particles can be reduced to 2-3 mol%o due to long-time low-temperature 人 a pure Zr annealing [22]. The low-temperature phase formation mechanism was reversible for ZrO2-Gd,O3(Eu2O3) (8 mol%) system omposition of the material can be rapidly homogenized by annealing at T> T(point 1 in Raman shift (cm") Fig 3). Then, the process of formation of the low-Gd2O (Eu2O3)t'-domains in the volume of ZrO2-Gd2O3(Eu2O3) Fig 4. Raman spectra at 300 K of the rapidly quenched ZrO2-(Eu203 melts at variation of Eu,O3-conterstabilizer) plus the cubic solid solution containing <9 mol% of Gd2O3 (Eu2O3). This process resulted in the formation of large-size t-particles and the milky single crystals. The temperature at the point 3 is lower than T0 of the C ! t 0 phase transition. The t0 -particles whose composition is similar to the Gd2O3 (Eu2O3) cubic phase should nucleate in the crystal volume as a result of this transformation. Diffusion processes at T , T0 for ZrO2 –Gd2O3 (Eu2O3) (8 mol%) was shown to proceed very slowly [17]. They interfere with the nucleation of t-precipitates due to the diffusion-controlled reaction in the case of annealing at T , T0 [17]. For the solid solution with Ln2O3 stabilizers of small Ln-ions (Y2O3, Yb2O3, Lu2O3), this phenomenon resulted in the freezing stabilizer concentration in t0 domains. In contrast, the primary concentration of Ln2O3 oxides with large Ln cations (Gd2O3 and Eu2O3) did not retain in supersaturated t0 -domains even at low-temperature annealing. Gradual decrease in the concentration of Gd2O3 (Eu2O3) inside the t0 -domains occurred, the volume around these domains being fertilized by Gd2O3 (Eu2O3) oxides. The Gd2O3 (Eu2O3) concentration in t0 -particles can be reduced to 2–3 mol% due to long-time low-temperature annealing [22]. The low-temperature phase formation mechanism was reversible for ZrO2 –Gd2O3 (Eu2O3) (8 mol%) system. The composition of the material can be rapidly homogenized by annealing at T . T1 (point 1 in Fig. 3). Then, the process of formation of the low-Gd2O3 (Eu2O3) t0 -domains in the volume of ZrO2 –Gd2O3 (Eu2O3) (8 mol%) crystals can be repeated using the subsequent low￾temperature annealing [17]. By contrast, the particles of the t-phase formed in the diffusion-controlled reaction are retained even after a long-time (20–30 h) annealing at T . T1: 5. Raman spectroscopy study of the formation of different tetragonal phases in ZrO2 –Gd2O3 (Eu2O3) solid solutions The above-mentioned two mechanisms of phase for￾mation in the ZrO2 –Gd2O3 (Eu2O3) system are easily registered by the Raman spectroscopy technique. Fig. 4 displays the Raman spectra at 300 K for a series of rapidly quenched ZrO2 –Eu2O3 melts under the variation of the Eu2O3 concentration from 2.5 up to 8 mol%. The Raman spectrum of a pure ZrO2 ceramic is also shown in Fig. 4. In this figure, all six Raman lines of tetragonal D15 4h phase are presented in the Raman spectra of the samples. A continuous change in the line frequencies is observed with the growth of Eu2O3 concentration, a shift of the Raman line position within the range 240–270 cm21 being the most remarkable (Fig. 4). Redistribution of intensities and broadening of the Raman lines followed a growth in the stabilizer concentration. Thus, the most intensive narrow line in the 240–270 cm21 spectral range for a pure ZrO2 and ZrO2 –Eu2O3 (2.5 mol%) is registered as the weakest broad band in the spectrum of the ZrO2 –Eu2O3 (8 mol%) sample. In turn, there is a growth of relative intensities of the two lines in the region of 600 cm21 with increasing Eu2O3 content. These two lines merged practically into a unified band dominating in the spectrum of the ZrO2 –Eu2O3 (8 mol%) sample (Figs. 4 and 5). Previously, the band with the frequency of 600 cm21 was assigned to F2g mode of the O5 h fluorite structure on the basis of the polarized Raman Fig. 3. Equilibrium ZrO2 –Gd2O3 (Eu2O3) phase diagrams. T1 is the boundary between cubic and C þ t phases regions and T0 is the temperature of the C ! t 0 transformation. 1,2 and 3 denote the annealing regimes used in the experiments. Bottom—the boundaries of the t0 and C metastable phases at 300 K. Fig. 4. Raman spectra at 300 K of the rapidly quenched ZrO2 –(Eu2O3) melts at variation of Eu2O3-content. 1106 A.A. Sobol, Y.K. Voronko / Journal of Physics and Chemistry of Solids 65 (2004) 1103–1112