l110 A.A. Sobol, Y.K. Voronko / Journal of Physics and Chemistry of Solids 65 (2004)1103-1112 A1g(257cm") (B and >B, D, F columns). Furthermore, an essential decrease in the intensity of the Aig-line in the Raman petra of the zone 2 for the lI-geometry indicated the following relation: axr az between the components of the Alg-mode Raman tensor. Rather interesting results were obtained after repeated annealing at T< To of the ZrO2-Gd,O3(8 mol%)single crystal previously subjected to the deformation. The (1)|(2) ⊥ ample(Fig. 10b) showed that predominant orientation of t domains along the stressed C4 axis was retained after the repeated low-temperature annealing without loading, the 200 400 600 character of the polarized spectra in Figs. 10a and b being the same. The repeated annealing resulted in narrowing A1g(265cm) shift and redistribution of intensities of Raman lines(Fi 10b), which are a result of decreasing the stabilizer concentration in t' domains due to ' low-temperature 2B1 lechanism'of the tetragonal phase formation. The position of the Alg mode(264 cm )in the Raman spectra presented in Fig. 10b evaluates the Gd2O3 content in t' domains as 2.5-3 mol%. Essentially narrowing Raman lines resulted in more noticeable difference in the polarized Raman spectra (1)(2) registered in the zones I and 2 in the crystal subjected to the ⊥ repeated annealing. Thus, the phenomenon of decreasin intensities of the 3Eg modes, when changing exciting-beam positions from the zone l to 2 of the crystal, was registered 200 600800 very distinctly, namely, in the I spectrum of the Raman shift(cm") repeatedly annealed crystal(Fig. 10b) Fig. 10. The polarized Raman spectra at 300 K of ZrO2-Gd2O3( 8 mol%) The assignment of the symmetry of six Raman modes of single crystal for the non-deformed(1)and deformed (2)zones(according the tetragonal form in Zro -based solid solutions, which to Fig. Ib).(a)after annealing at 1800 K and cooling through the C-t were determined in our experiments, is shown in Figs. 5 and phase transformation temperature region under loading, (b) after the 10 and in Table 3 repeated annealing at 1350 K(20 h) without loading. of t' domains with the z axis parallel to the stressed C, cubic 7. Discussion axis. It should be noted that a redistribution of the raman line intensities in 1 and 2 zones allowed us to separate The experiments mentioned above revealed a possibility Raman lines of the B, and Eg modes in the Raman spectra of formation of oriented tetragonal domains in ZrO2-Gd2O3 for the I geometry using the calculation results of Table 2 8 mol%)solid solution because of the stress-induced Table 3 Frequencies(cm )at 300 K and symmetry assignments of the Raman bands of the tetragonal Zro, and ZrO2-based solid solutions Symmetry of the modes Method of assignments Ig [12」 (146,319,469,608,638) ZrO2-3 mol% Eu, O3(sc. This work 323,607 147462,640 ZrO2-3 mol% Gd,O3(.c) This work 150.476.620 ZrO2-8 mol% Gd,O3(sc) 146,458648 ZrOz-undoped (e f) 20 326.616 155476645 ZrO2-undope 14 6206662 266,474645 ZrOz-4.6 mol% Y2O3(sc) 266,474645 PPPPcNccc 18,28 149,269,461 ZrO2-undoped (powder) 27 5,595 257,410,645 ZrO2-undoped (powder) P, polarized study; C, calculated; N, not determined; s.c., single crystal; e f, epitaxial film. Concentration of Ln2O3 in the tetragonal nanodomains was evaluated according to the position of the Alx raman mode (see the textof t0 domains with the z axis parallel to the stressed C4 cubic axis. It should be noted that a redistribution of the Raman line intensities in 1 and 2 zones allowed us to separate Raman lines of the Bg and Eg modes in the Raman spectra for the ’ geometry using the calculation results of Table 2 (B and PB; D; F columns). Furthermore, an essential decrease in the intensity of the A1g-line in the Raman spectra of the zone 2 for the k-geometry indicated the following relation: axx p azz between the components of the A1g-mode Raman tensor. Rather interesting results were obtained after repeated annealing at T , T0 of the ZrO2 –Gd2O3 (8 mol%) single crystal previously subjected to the deformation. The polarized Raman spectra for the zones 1 and 2 of the sample (Fig. 10b) showed that predominant orientation of t0 domains along the stressed C4 axis was retained after the repeated low-temperature annealing without loading, the character of the polarized spectra in Figs. 10a and b being the same. The repeated annealing resulted in narrowing, shift and redistribution of intensities of Raman lines (Fig. 10b), which are a result of decreasing the stabilizer concentration in t0 domains due to ‘low-temperature mechanism’ of the tetragonal phase formation. The position of the A1g mode (264 cm21 ) in the Raman spectra presented in Fig. 10b evaluates the Gd2O3 content in t0 domains as 2.5–3 mol%. Essentially narrowing Raman lines resulted in more noticeable difference in the polarized Raman spectra registered in the zones 1 and 2 in the crystal subjected to the repeated annealing. Thus, the phenomenon of decreasing intensities of the 3Eg modes, when changing exciting-beam positions from the zone 1 to 2 of the crystal, was registered very distinctly, namely, in the ’ spectrum of the repeatedly annealed crystal (Fig. 10b). The assignment of the symmetry of six Raman modes of the tetragonal form in ZrO2-based solid solutions, which were determined in our experiments, is shown in Figs. 5 and 10 and in Table 3. 7. Discussion The experiments mentioned above revealed a possibility of formation of oriented tetragonal domains in ZrO2 –Gd2O3 (8 mol%) solid solution because of the stress-induced Fig. 10. The polarized Raman spectra at 300 K of ZrO2 –Gd2O3 (8 mol%) single crystal for the non-deformed (1) and deformed (2) zones (according to Fig. 1b). (a) after annealing at 1800 K and cooling through the C ! t 0 phase transformation temperature region under loading, (b) after the repeated annealing at 1350 K (20 h) without loading. Table 3 Frequencies (cm21 ) at 300 K and symmetry assignments of the Raman bands of the tetragonal ZrO2 and ZrO2-based solid solutions Ref. Symmetry of the modes Object Method of assignments A1g B1g Eg [12] 262 (146,319,469,608,638) ZrO2 –3 mol% Eu2O3 (s.c.)a P This work 265 323,607 147,462,640 ZrO2 –3 mol% Gd2O3 (s.c.)a P This work 242 343,620 150,476,620 ZrO2 –8 mol% Gd2O3 (s.c.)a P [29] 270 318,602 146,458,648 ZrO2-undoped (e.f.) P [26] 266 326,616 155,476,645 ZrO2-undoped C [14] 616 155,326 266,474,645 ZrO2 –4.6 mol% Y2O3 (s.c.) N [25] 326 155,616 266,474,645 ZrO2-undoped C [18,28] 602 319,648 149,269,461 ZrO2-undoped (powder) C [27] 630 155,595 257,410,645 ZrO2-undoped (powder) C P, polarized study; C, calculated; N, not determined; s.c., single crystal; e.f., epitaxial film. a Concentration of Ln2O3 in the tetragonal nanodomains was evaluated according to the position of the A1g Raman mode (see the text). 1110 A.A. Sobol, Y.K. Voronko / Journal of Physics and Chemistry of Solids 65 (2004) 1103–1112