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Phase relations in the BaO–B2O3–TiO2 system and the crystal structure of BaTi(BO3)2
Materials Research Bulletin 38 (2003) 783–788
Phase relations in the BaO–B2O3–TiO2 system and the crystal structure of BaTi(BO3)2 S.Y. Zhang*, X. Wu, X.L. Chen, M. He, Y.G. Cao, Y.T. Song, D.Q. Ni Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences, P.O. Box 603-50, Beijing 100080, PR China Received 21 June 2002; received in revised form 30 December 2002; accepted 28 February 2003
Abstract In this paper, the subsolidus phase relations in the ternary system BaO–B2O3–TiO2 have been investigated. The phase diagram consists of 15 ternary phase regions. There exist 11 binary compounds and two ternary compounds. The ternary compound, BaTi(BO3)2, is isostructural with CaMg(CO3)2. It crystallizes in a ˚. rhombohedral system with the space group R-3. The lattice parameters are a ¼ 5:0205(2) and c ¼ 16:3844(1) A Final refinement on the diffraction data converge to Rp ¼ 9:09, Rwp ¼ 12:24, and Rexp ¼ 3:75%. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: D. Phase equilibria; D. Crystal structure
1. Introduction Several of the compounds in the high titania portion of the BaO–TiO2 system and some ternary systems BaO–TiO2–MO (MO presents oxide) have properties which make them useful as dielectric materials for microwave applications [1]. Phase equilibria in the BaO–TiO2 system have been extensively studied [2–4]. A series of BaO–TiO2–MO systems, such as BaO–TiO2–V2O5, BaO–TiO2– MoO3, and BaO–TiO2–P2O5, have also been reported [5–7]. Goto and Cross studied the binary system BaTiO3–BaB2O4 [8]. Millet [6] reported the subsystem BaTiO3–TiO2–BaB2O4. However, the BaO–TiO2–B2O3 system has not been studied in detail. In this paper, we report the phase relations in the BaO–B2O3–TiO2 system and the crystal structure of BaTi(BO3)2.
*
Corresponding author. Tel.: þ86-10-82649032; fax: þ86-10-82649531. E-mail address: [email protected] (S.Y. Zhang). 0025-5408/03/$ – see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0025-5408(03)00073-4
784
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788
2. Experimental The specimens were prepared by solid-state reaction at high temperature. After thoroughly mixed and ground, the mixtures of BaCO3 (99.99%), TiO2 (99.99%), and H3BO3 (A.R.) were heated at 400 8C for 2 h to decompose H3BO3, then reground and sintered at 750–1050 8C for 48 h. Thirty-two specimens with different compositions were prepared and their compositions are given in Table 1. Phase analyses were carried out on a Rigaku D/max-2400 diffractometer with Cu Ka radiation at room temperature. The X-ray powder diffraction data used in the structure refinement were collected in a step-scanning mode with step of 0.028. An angular range from 2y ¼ 15 to 1308 and a measuring time of 1 s per step were applied. A total of 5669 points with 770 contributing reflections were observed.
Table 1 List of phase identification for various composition specimens in the BaO–B2O3–TiO2 system No.
B2O3 (at.%)
TiO2 (at.%)
BaO (at.%)
Result
1 2 3 4 5 6 7 8 9 10a 11 12 13 14 15 16 17 18a 19 20 21a 22 23 24 25 26 27 28 29 30 31a 32a
8 8 14 28 20 30 8 20 8 9 9.5 8 17 32 12 20.5 12 13 13.5 14.5 15 25 23 7 15 47 25 47 32 55 35 70
14 28 30 10 35 23 52 40 59 59 59 62 48 25 58 45 61 61 61 61 65 43 43.3 80 65 13 58 25 56 25 60 20
78 64 56 62 45 47 40 40 33 32 31.5 30 35 43 30 34.5 27 26 25.5 24.5 20 32 33.7 13 20 40 17 28 12 20 5 10
BaO þ Ba2TiO4 þ Ba3B2O6 BaTiO3 þ Ba2TiO4 þ Ba3B2O6 BaTiO3 þ BaB2O4 þ Ba3B2O6 BaTiO3 þ BaB2O4 þ Ba3B2O6 BaTiO3 þ BaB2O4 þ Ba2Ti2B2O9 BaTiO3 þ BaB2O4 þ Ba2Ti2B2O9 BaTiO3 þ BaTi2O5 þ Ba2Ti2B2O9 Ba2Ti2B2O9 Ba4Ti13O30 þ BaTi2O5 þ Ba2Ti2B2O9 Ba4Ti13O30 þ Ba2Ti2B2O9 þ (BaTi2O5) Ba4Ti13O30 þ Ba2Ti2B2O9 Ba4Ti13O30 þ Ba2Ti2B2O9 Ba4Ti13O30 þ BaB2O4 þ Ba2Ti2B2O9 Ba4Ti13O30 þ BaB2O4 þ Ba2Ti2B2O9 Ba4Ti13O30 þ BaB2O4 Ba4Ti13O30 þ BaB2O4 BaTi4O9 þ BaB2O4 BaTi4O9 þ BaTi(BO3)2 þ (BaB2O4) BaTi4O9 þ BaTi(BO3)2 Ba2Ti9O20 þ BaTi(BO3)2 Ba2Ti9O20 þ BaTi(BO3)2 þ (TiO2) BaTi4O9 þ BaB2O4 þ BaTi(BO3)2 BaTi4O9 þ BaB2O4 TiO2 þ Ba2Ti9O20 þ BaTi(BO3)2 TiO2 þ Ba2Ti9O20 þ BaTi(BO3)2 BaB4O6 þ BaB2O4 þ BaTi(BO3)2 TiO2 þ BaB4O6 þ BaTi(BO3)2 TiO2 þ BaB4O6 þ BaTi(BO3)2 TiO2 þ BaB4O6 þ BaB8O13 TiO2 þ BaB4O6 þ BaB8O13 TiO2 þ BaB8O13 þ (B2O3) TiO2 þ BaB8O13 þ (B2O3)
a
The diffraction peaks of phases in the bracket could not be observed because of their weak X-ray diffraction intensity.
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788
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3. Results and discussion 3.1. Binary system The phase diagram of the TiO2–B2O3 system has been reported by Pavlikov et al. [9], and no binary compound has been found. In the BaO–B2O3 system, four binary compounds, Ba3B2O6, BaB2O4, BaB4O7, and BaB8O12 have been reported [10–14]. All the compounds have been obtained in our experiments and their diffraction data are consistent with those reported. In the BaO–TiO2 system, seven binary compounds have been reported, namely, Ba2TiO4, BaTiO3, BaTi2O5, Ba6Ti17O40, Ba4Ti13O30, BaTi4O9, and Ba2Ti9O20 [15–21]. However, we did not obtain the single-phase Ba2Ti9O20 in our experiments. Two ternary compounds, BaTi(BO3)2 and Ba2Ti2B2O9, have been reported [6,22–24]. The structure ˚ [22]. The of BaTi(BO3)2 is determined to be the dolomite type, rhombohedral, a ¼ 5:02 and c ¼ 16:4 A ˚ Ba2Ti2B2O9 compound is hexagonal with lattice parameters a ¼ 8:721 and c ¼ 3:933 A [6]. Fig. 1 shows the subsolidus phase relations in the ternary BaO–B2O3–TiO2 system, which consists of 15 ternary phase regions. No new ternary compound has been found. Under our experimental conditions, the pure phase of Ba2Ti2B2O9 compound has not been obtained. We attempted to synthesize it at different temperatures (750–1000 8C) for 1–72 h in air, but failed. The Ba2Ti2B2O9 compound is in equilibrium with BaB2O4, BaTiO3, BaTi2O5, and Ba4Ti13O30. However, the equilibrium with Ba6Ti17O40 has not been observed. 3.2. Crystal structure of BaTi(BO3)2 BaTi(BO3)2 is isostructural with CaMg(CO3)2 [22]. It crystallizes in the rhombohedral system with ˚ . The structure of the space group R-3. Lattice parameters are a ¼ 5:0205(2) and c ¼ 16:3844(1) A
Fig. 1. Subsolidus phase relations in the BaO–B2O3–TiO2 system derived from samples sintered at 750–1050 8C in air: single phase ( ), binary phase (), and (þ) ternary phase.
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Fig. 2. The final Rietveld refinement profile of diffraction data of BaTi(BO3)2. Small crosses (þ) correspond to experimental values and the continuous line corresponds to the calculated spectrum. Vertical bars (|) indicate the positions of Bragg peaks. The bottom trace depicts the difference between the experimental and the calculated intensity values.
BaTi(BO3)2 is refined by the Rietveld method using the DBWS9411 program [25]. The Ba2þ ions are located in the 3(a) sites, the Ti4þ ions are located in the 3(b) sites, the B3þ ions are located in the 6(c) sites and the O2 ions are located in the 18(f) sites. The refinements are stable and finally converge to Rp ¼ 9:09, Rwp ¼ 12:24 and Rexp ¼ 3:75%. If the Ba2þ ions are located in the 3(b) sites and the Ti4þ
Table 2 Crystallographic data Chemical formula Cell setting Space group ˚) a (A ˚) c (A ˚) V (A Z Dx (g/cm3)
BaTi(BO3)2 Rhombohedral R-3 5.0205(2) 16.3844(1) 357.641(1) 3 4.217
Table 3 Positional and thermal parameters for BaTi(BO3)2 Atom
Site
x
y
z
˚ 2) B (A
Ba Ti B O
3(a) 3(b) 6(c) 18(f)
0.0000 0.0000 0.0000 0.3132(3)
0.0000 0.0000 0.0000 0.1271(2)
0.0000 1/2 0.2342(5) 0.2365(4)
1.8001(3) 1.4413(5) 1.5344(1) 1.6129(4)
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788
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Fig. 3. A projection of the structure of BaTi(BO3)2 along (0 1 0). ( ), (*), ( ), and (*) represent Ti, Ba, B, and O atoms, respectively.
˚ , are not ions are located in the 3(a) sites, bond lengths of Ba–O ¼ 1:8511(2) and Ti–O ¼ 2:7402(4) A 2þ 4þ reasonable. If Ba and Ti ions occupy the 3(a) and 3(b) sites at random, the agreement factors are unaccepted large. Final refinement results are presented in Fig. 2. Crystallographic details are summarized in Table 2. The atomic coordinates are listed in Table 3. Bond lengths of Ba–O ¼ 2:7255(4), Ti–O ¼ 1:9213(2), ˚ . The bond angle of O–B–O ¼ 119:9258. Fig. 3 shows a projection of the structure and B–O ¼ 1:3707 A of BaTi(BO3)2 along (0 1 0). An isomorphic structure has been reported [26,27].
Acknowledgements We are thankful to the financial support from National Natural Sciences Foundation of China.
References [1] [2] [3] [4] [5] [6] [7]
H.M. O’Bryan, J. Thomson, J.K. Plourde, J. Am. Ceram. Soc. 57 (10) (1974) 450. T. Negas, R.S. Roth, H.S. Parker, D. Minor, J. Solid State Chem. 9 (1974) 297. H.M. O’Bryan, J. Thomson, J. Am. Ceram. Soc. 57 (12) (1974) 522. J.J. Ritter, R.S. Roth, J. Am. Ceram. Soc. 69 (20) (1986) 155. S. Solacolu, R. Dinescu, Rev. Roum. Chim. 42 (6) (1958) 292. J. Millet, R. Roth, H. Parker, J. Am. Ceram. Soc. 69 (11) (1986) 811. D.E. Harrison, J. Electrochem. Soc. 67 (12) (1960) 619.
788 [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788 Y. Goto, L.E. Cross, Yogyo Kyokaishi 77 (1969) 355. V.N. Pavlikov, V.A. Yurchenko, S.G. Tresvyarskii, Zh. Neorg. Khim. 21 (1) (1976) 233. P. van Vlaanderen, Energineonderzoek Centrum Nederland Petten, The Netherlands, Private Communication, 1993. Hubner, Neues Jahrb. Miner., Monatsh (1969) 335. K. Ito et al., Report Res. Lab. Eng. Mat. Tokyuo. Inst. Technol. 15 (1990) 1. S. Block, A. Perloff, Acta Crystallogr. 19 (1965) 297. J. Krogh-Moe, M. Ihara, Acta Crystallogr. B 25 (1969) 2153. J.R. Guenter, G.B. Jamesom, Acta Crystallogr. C 40 (1984) 207. W. Schildkamp, K. Fischer, Z. Kristallogr. 155 (1981) 217. R. Rog, J. Am. Ceram. Soc. 38 (1955) 108. E. Tillmanns, W.H. Baur, Acta Crystallogr. B 26 (1970) 1645. E. Tillmanns, Cryst. Struct. Commun. 11 (1982) 2087. W. Hofmeister, E. Tillmanns, W.H. Baur, Acta Crystallogr. C 40 (1984) 1510. E. Tillmanns, W. Hofmeister, W.H. Baur, J. Am. Ceram. Soc. 66 (1983) 268. J. Vicat, S. Aleonard, Mater. Res. Bull. 3 (1968) 611. D. Schultze, K.T. Wilke, Ch. Waligora, Z. Anorg. Allg. Chem. 380 (1971) 37. G. Bayer, Z. Kristallogr. 133 (1971) 85. R.A. Young, A. Stakthivel, T.S. Moss, C.O. Paiva-Santors, J. Appl. Crystallogr. 28 (1995) 366. H. Steinfink, F.T. Sans, Am. Miner. 44 (1959) 679. P.L. Althoff, Am. Miner. 62 (1977) 772.
Phase relations in the BaO–B2O3–TiO2 system and the crystal structure of BaTi(BO3)2 S.Y. Zhang*, X. Wu, X.L. Chen, M. He, Y.G. Cao, Y.T. Song, D.Q. Ni Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences, P.O. Box 603-50, Beijing 100080, PR China Received 21 June 2002; received in revised form 30 December 2002; accepted 28 February 2003
Abstract In this paper, the subsolidus phase relations in the ternary system BaO–B2O3–TiO2 have been investigated. The phase diagram consists of 15 ternary phase regions. There exist 11 binary compounds and two ternary compounds. The ternary compound, BaTi(BO3)2, is isostructural with CaMg(CO3)2. It crystallizes in a ˚. rhombohedral system with the space group R-3. The lattice parameters are a ¼ 5:0205(2) and c ¼ 16:3844(1) A Final refinement on the diffraction data converge to Rp ¼ 9:09, Rwp ¼ 12:24, and Rexp ¼ 3:75%. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: D. Phase equilibria; D. Crystal structure
1. Introduction Several of the compounds in the high titania portion of the BaO–TiO2 system and some ternary systems BaO–TiO2–MO (MO presents oxide) have properties which make them useful as dielectric materials for microwave applications [1]. Phase equilibria in the BaO–TiO2 system have been extensively studied [2–4]. A series of BaO–TiO2–MO systems, such as BaO–TiO2–V2O5, BaO–TiO2– MoO3, and BaO–TiO2–P2O5, have also been reported [5–7]. Goto and Cross studied the binary system BaTiO3–BaB2O4 [8]. Millet [6] reported the subsystem BaTiO3–TiO2–BaB2O4. However, the BaO–TiO2–B2O3 system has not been studied in detail. In this paper, we report the phase relations in the BaO–B2O3–TiO2 system and the crystal structure of BaTi(BO3)2.
*
Corresponding author. Tel.: þ86-10-82649032; fax: þ86-10-82649531. E-mail address: [email protected] (S.Y. Zhang). 0025-5408/03/$ – see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0025-5408(03)00073-4
784
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788
2. Experimental The specimens were prepared by solid-state reaction at high temperature. After thoroughly mixed and ground, the mixtures of BaCO3 (99.99%), TiO2 (99.99%), and H3BO3 (A.R.) were heated at 400 8C for 2 h to decompose H3BO3, then reground and sintered at 750–1050 8C for 48 h. Thirty-two specimens with different compositions were prepared and their compositions are given in Table 1. Phase analyses were carried out on a Rigaku D/max-2400 diffractometer with Cu Ka radiation at room temperature. The X-ray powder diffraction data used in the structure refinement were collected in a step-scanning mode with step of 0.028. An angular range from 2y ¼ 15 to 1308 and a measuring time of 1 s per step were applied. A total of 5669 points with 770 contributing reflections were observed.
Table 1 List of phase identification for various composition specimens in the BaO–B2O3–TiO2 system No.
B2O3 (at.%)
TiO2 (at.%)
BaO (at.%)
Result
1 2 3 4 5 6 7 8 9 10a 11 12 13 14 15 16 17 18a 19 20 21a 22 23 24 25 26 27 28 29 30 31a 32a
8 8 14 28 20 30 8 20 8 9 9.5 8 17 32 12 20.5 12 13 13.5 14.5 15 25 23 7 15 47 25 47 32 55 35 70
14 28 30 10 35 23 52 40 59 59 59 62 48 25 58 45 61 61 61 61 65 43 43.3 80 65 13 58 25 56 25 60 20
78 64 56 62 45 47 40 40 33 32 31.5 30 35 43 30 34.5 27 26 25.5 24.5 20 32 33.7 13 20 40 17 28 12 20 5 10
BaO þ Ba2TiO4 þ Ba3B2O6 BaTiO3 þ Ba2TiO4 þ Ba3B2O6 BaTiO3 þ BaB2O4 þ Ba3B2O6 BaTiO3 þ BaB2O4 þ Ba3B2O6 BaTiO3 þ BaB2O4 þ Ba2Ti2B2O9 BaTiO3 þ BaB2O4 þ Ba2Ti2B2O9 BaTiO3 þ BaTi2O5 þ Ba2Ti2B2O9 Ba2Ti2B2O9 Ba4Ti13O30 þ BaTi2O5 þ Ba2Ti2B2O9 Ba4Ti13O30 þ Ba2Ti2B2O9 þ (BaTi2O5) Ba4Ti13O30 þ Ba2Ti2B2O9 Ba4Ti13O30 þ Ba2Ti2B2O9 Ba4Ti13O30 þ BaB2O4 þ Ba2Ti2B2O9 Ba4Ti13O30 þ BaB2O4 þ Ba2Ti2B2O9 Ba4Ti13O30 þ BaB2O4 Ba4Ti13O30 þ BaB2O4 BaTi4O9 þ BaB2O4 BaTi4O9 þ BaTi(BO3)2 þ (BaB2O4) BaTi4O9 þ BaTi(BO3)2 Ba2Ti9O20 þ BaTi(BO3)2 Ba2Ti9O20 þ BaTi(BO3)2 þ (TiO2) BaTi4O9 þ BaB2O4 þ BaTi(BO3)2 BaTi4O9 þ BaB2O4 TiO2 þ Ba2Ti9O20 þ BaTi(BO3)2 TiO2 þ Ba2Ti9O20 þ BaTi(BO3)2 BaB4O6 þ BaB2O4 þ BaTi(BO3)2 TiO2 þ BaB4O6 þ BaTi(BO3)2 TiO2 þ BaB4O6 þ BaTi(BO3)2 TiO2 þ BaB4O6 þ BaB8O13 TiO2 þ BaB4O6 þ BaB8O13 TiO2 þ BaB8O13 þ (B2O3) TiO2 þ BaB8O13 þ (B2O3)
a
The diffraction peaks of phases in the bracket could not be observed because of their weak X-ray diffraction intensity.
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788
785
3. Results and discussion 3.1. Binary system The phase diagram of the TiO2–B2O3 system has been reported by Pavlikov et al. [9], and no binary compound has been found. In the BaO–B2O3 system, four binary compounds, Ba3B2O6, BaB2O4, BaB4O7, and BaB8O12 have been reported [10–14]. All the compounds have been obtained in our experiments and their diffraction data are consistent with those reported. In the BaO–TiO2 system, seven binary compounds have been reported, namely, Ba2TiO4, BaTiO3, BaTi2O5, Ba6Ti17O40, Ba4Ti13O30, BaTi4O9, and Ba2Ti9O20 [15–21]. However, we did not obtain the single-phase Ba2Ti9O20 in our experiments. Two ternary compounds, BaTi(BO3)2 and Ba2Ti2B2O9, have been reported [6,22–24]. The structure ˚ [22]. The of BaTi(BO3)2 is determined to be the dolomite type, rhombohedral, a ¼ 5:02 and c ¼ 16:4 A ˚ Ba2Ti2B2O9 compound is hexagonal with lattice parameters a ¼ 8:721 and c ¼ 3:933 A [6]. Fig. 1 shows the subsolidus phase relations in the ternary BaO–B2O3–TiO2 system, which consists of 15 ternary phase regions. No new ternary compound has been found. Under our experimental conditions, the pure phase of Ba2Ti2B2O9 compound has not been obtained. We attempted to synthesize it at different temperatures (750–1000 8C) for 1–72 h in air, but failed. The Ba2Ti2B2O9 compound is in equilibrium with BaB2O4, BaTiO3, BaTi2O5, and Ba4Ti13O30. However, the equilibrium with Ba6Ti17O40 has not been observed. 3.2. Crystal structure of BaTi(BO3)2 BaTi(BO3)2 is isostructural with CaMg(CO3)2 [22]. It crystallizes in the rhombohedral system with ˚ . The structure of the space group R-3. Lattice parameters are a ¼ 5:0205(2) and c ¼ 16:3844(1) A
Fig. 1. Subsolidus phase relations in the BaO–B2O3–TiO2 system derived from samples sintered at 750–1050 8C in air: single phase ( ), binary phase (), and (þ) ternary phase.
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Fig. 2. The final Rietveld refinement profile of diffraction data of BaTi(BO3)2. Small crosses (þ) correspond to experimental values and the continuous line corresponds to the calculated spectrum. Vertical bars (|) indicate the positions of Bragg peaks. The bottom trace depicts the difference between the experimental and the calculated intensity values.
BaTi(BO3)2 is refined by the Rietveld method using the DBWS9411 program [25]. The Ba2þ ions are located in the 3(a) sites, the Ti4þ ions are located in the 3(b) sites, the B3þ ions are located in the 6(c) sites and the O2 ions are located in the 18(f) sites. The refinements are stable and finally converge to Rp ¼ 9:09, Rwp ¼ 12:24 and Rexp ¼ 3:75%. If the Ba2þ ions are located in the 3(b) sites and the Ti4þ
Table 2 Crystallographic data Chemical formula Cell setting Space group ˚) a (A ˚) c (A ˚) V (A Z Dx (g/cm3)
BaTi(BO3)2 Rhombohedral R-3 5.0205(2) 16.3844(1) 357.641(1) 3 4.217
Table 3 Positional and thermal parameters for BaTi(BO3)2 Atom
Site
x
y
z
˚ 2) B (A
Ba Ti B O
3(a) 3(b) 6(c) 18(f)
0.0000 0.0000 0.0000 0.3132(3)
0.0000 0.0000 0.0000 0.1271(2)
0.0000 1/2 0.2342(5) 0.2365(4)
1.8001(3) 1.4413(5) 1.5344(1) 1.6129(4)
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788
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Fig. 3. A projection of the structure of BaTi(BO3)2 along (0 1 0). ( ), (*), ( ), and (*) represent Ti, Ba, B, and O atoms, respectively.
˚ , are not ions are located in the 3(a) sites, bond lengths of Ba–O ¼ 1:8511(2) and Ti–O ¼ 2:7402(4) A 2þ 4þ reasonable. If Ba and Ti ions occupy the 3(a) and 3(b) sites at random, the agreement factors are unaccepted large. Final refinement results are presented in Fig. 2. Crystallographic details are summarized in Table 2. The atomic coordinates are listed in Table 3. Bond lengths of Ba–O ¼ 2:7255(4), Ti–O ¼ 1:9213(2), ˚ . The bond angle of O–B–O ¼ 119:9258. Fig. 3 shows a projection of the structure and B–O ¼ 1:3707 A of BaTi(BO3)2 along (0 1 0). An isomorphic structure has been reported [26,27].
Acknowledgements We are thankful to the financial support from National Natural Sciences Foundation of China.
References [1] [2] [3] [4] [5] [6] [7]
H.M. O’Bryan, J. Thomson, J.K. Plourde, J. Am. Ceram. Soc. 57 (10) (1974) 450. T. Negas, R.S. Roth, H.S. Parker, D. Minor, J. Solid State Chem. 9 (1974) 297. H.M. O’Bryan, J. Thomson, J. Am. Ceram. Soc. 57 (12) (1974) 522. J.J. Ritter, R.S. Roth, J. Am. Ceram. Soc. 69 (20) (1986) 155. S. Solacolu, R. Dinescu, Rev. Roum. Chim. 42 (6) (1958) 292. J. Millet, R. Roth, H. Parker, J. Am. Ceram. Soc. 69 (11) (1986) 811. D.E. Harrison, J. Electrochem. Soc. 67 (12) (1960) 619.
788 [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]
S.Y. Zhang et al. / Materials Research Bulletin 38 (2003) 783–788 Y. Goto, L.E. Cross, Yogyo Kyokaishi 77 (1969) 355. V.N. Pavlikov, V.A. Yurchenko, S.G. Tresvyarskii, Zh. Neorg. Khim. 21 (1) (1976) 233. P. van Vlaanderen, Energineonderzoek Centrum Nederland Petten, The Netherlands, Private Communication, 1993. Hubner, Neues Jahrb. Miner., Monatsh (1969) 335. K. Ito et al., Report Res. Lab. Eng. Mat. Tokyuo. Inst. Technol. 15 (1990) 1. S. Block, A. Perloff, Acta Crystallogr. 19 (1965) 297. J. Krogh-Moe, M. Ihara, Acta Crystallogr. B 25 (1969) 2153. J.R. Guenter, G.B. Jamesom, Acta Crystallogr. C 40 (1984) 207. W. Schildkamp, K. Fischer, Z. Kristallogr. 155 (1981) 217. R. Rog, J. Am. Ceram. Soc. 38 (1955) 108. E. Tillmanns, W.H. Baur, Acta Crystallogr. B 26 (1970) 1645. E. Tillmanns, Cryst. Struct. Commun. 11 (1982) 2087. W. Hofmeister, E. Tillmanns, W.H. Baur, Acta Crystallogr. C 40 (1984) 1510. E. Tillmanns, W. Hofmeister, W.H. Baur, J. Am. Ceram. Soc. 66 (1983) 268. J. Vicat, S. Aleonard, Mater. Res. Bull. 3 (1968) 611. D. Schultze, K.T. Wilke, Ch. Waligora, Z. Anorg. Allg. Chem. 380 (1971) 37. G. Bayer, Z. Kristallogr. 133 (1971) 85. R.A. Young, A. Stakthivel, T.S. Moss, C.O. Paiva-Santors, J. Appl. Crystallogr. 28 (1995) 366. H. Steinfink, F.T. Sans, Am. Miner. 44 (1959) 679. P.L. Althoff, Am. Miner. 62 (1977) 772.