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Solvothermal synthesis of the complex fluorides KMgF3 and KZnF3 with the Perovskite structures
Materials Research Bulletin 37 (2002) 1189±1195
Solvothermal synthesis of the complex ¯uorides KMgF3 and KZnF3 with the Perovskite structures Ruinian Huaa, Zhihong Jiaa, Demin Xieb, Chunshan Shia,* a
Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China b Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China (Refereed) Received 14 November 2001; accepted 12 February 2002
Abstract The complex ¯uorides KMgF3 and KZnF3 with Perovskite structures were solvothermally synthesised at 150±1808C and characterised by means of X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Fluorides; B. Chemical synthesis; C. X-ray diffraction; C. Electron diffraction
1. Introduction In recent years, complex ¯uorides which show various interesting structures have been extensively studied due to their particular physical properties such as piezoelectric characteristics [1], ferromagnetic [2], nonmagnetic insulator behaviour [3] and photoluminescence host materials [4,5]. Conventional synthesis routes to complex ¯uorides include solid state reactions [6,7] at high-temperature (>4008C), high-pressure (>100 MPa) hydrothermal technique [8±10]. The solid state synthetic apparatus, however, requires a complicated set-up because the corrosive nature of ¯uorides has limited the studies of ¯uorides in the materials chemistry as well as the fact that hightemperature, high-pressure hydrothermal techniques require special devices. Recently, a mild hydrothermal synthesis of the complex ¯uorides at 120±2408C has been reported [11±14]. The oxygen content in the complex ¯uorides synthesised by solid-state *
Corresponding author. Tel.: 86-431-5262-041; fax: 86-431-5685-653. E-mail address: [email protected] (C. Shi).
0025-5408/02/$ ± see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 2 ) 0 0 7 3 2 - 8
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R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
reaction is higher than that of the corresponding complex ¯uorides synthesised by hydrothermal techniques [15]. KMgF3 and KZnF3 are the important complex ¯uorides because they show lasing action [16,17] when they are doped with a proper dopant. Various isomorphous replacements in the framework of complex ¯uorides lead to many controllable properties [18]. In order to explore a new method for the preparation of complex ¯uorides, herein we report a convenient method for the synthesis of KMgF3 and KZnF3 with Perovskite structures using a solvothermal process. 2. Experimental 2.1. Synthesis Solvothermal synthesis of KMgF3 and KZnF3 was carried out in a Te¯on-lined stainless steel autoclave under autogenous pressure. The starting reactants were KF (A.R.), MgF2 (A.R.) and ZnF2 (A.R.). The mole ratios of initial mixtures for the synthesis of KMgF3 and KZnF3 were 1.0KF:1.0MgF2 and 2.0KF:1.0ZnF2, respectively. The typical synthetic procedure for crystalline KMgF3 and KZnF3 were as follows: 0.291 g KF and 0.312 g MgF2, 0.581 g KF and 0.518 g ZnF2 were mixed respectively, and added into a Te¯on-lined autoclave of 20 ml capacity. Then the autoclave was ®lled with ethylene glycol (for the synthesis of KMgF3) and absolute ethanol(for the synthesis of KZnF3) up to 80% of the total volume. The autoclave was sealed into a stainless steel tank and heated in an oven at 1808C for 7 days. After being cooled to room temperature naturally, the ®nal powder product was ®ltered off, washed with absolute ethanol and distilled water, then dried in air at ambient temperature. 2.2. Characterisation All products were characterised by X-ray powder diffraction (XRD), using a Japan Ê ). The XRD Rigaku D/max-IIB diffractometer with Cu Ka1 radiation (l 1:5405 A data for index and cell-parameter calculations were collected by a scanning mode with a step of 0.028 in the 2y range from 10 to 1008 and a scanning rate of 4.08 min 1. Silicon was used as an internal standard. Observation of crystallites by SEM was performed on a JXA-840 scanning electron microscopy. Thermogravimetric analysis (TGA) was conducted using a DT-30 thermogravimetric system. IR spectra were obtained with a Magna 560 spectrometer in the range 400±4000 cm 1. The samples were pressed KBr pellets for the spectral measurements.
3. Results and discussion 3.1. Characterisation Table 1 shows the solvothermal synthesis conditions for KMgF3 and KZnF3. In the synthesis of KMgF3, the K/Mg ratio and the solvents were found to be crucial to the
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
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Table 1 Solvothermal synthesis conditions for KMgF3 and KZnF3 Starting materials
a:b Solvent (mole ratio)
a
b
KF KF KF KF KF KF KF KF KF KF KF KF KF KF KF KF KF
MgF2 MgF2 MgF2 MgF2 MgF2 MgF2 MgF2 MgF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2
1:1 2:1 1:2 1:1 1:1 1:1 1:1 1:1 1:1 2:1 3:1 1:2 2:1 2:1 2:1 2:1 2:1
Ethylene Ethylene Ethylene Ethylene Ethylene Ethylene Ethylene Ethylene Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol
Reaction Reaction Phases in product time (day) temperature (8C)
glycol glycol glycol glycol glycol glycol glycol glycol
7 7 7 4 3 7 6 7 7 7 7 7 1 2 2 3 7
180 180 180 180 180 150 150 120 180 180 180 180 180 180 150 150 120
KMgF3 KMgF3 KMgF3 MgF2 KMgF3 KMgF3 multiphase KMgF3 KMgF3 multiphase KMgF3 multiphase KZnF3 KZnF3 KZnF3 KZnF3 ZnF2 KZnF3 KZnF3 KZnF3 ZnF2 KZnF3 KZnF3 ZnF2
formation, crystallisation and purity of the products. When the mole ratio K/Mg of mixture was 1 or 2, and ethylene glycol or pyridine was used as solvent, the pure and well-crystallised product was prepared. However, when the mole ratio K/Mg was 0.5, impurity phases appeared. In the synthesis of KZnF3, the K/Zn ratio is a dominating factor. Although when the mole ratio K/Zn was from 1 to 3, KZnF3 was formed. A large K/Zn ratio was favourable for crystallisation and purity of the products, and when K/Zn ratio <1 an impurity phase of ZnF2 was obtained. Crystallisation temperature and reaction times were also important factors for an effective synthesis. Although KMgF3 and KZnF3 can be crystallised at temperature below 1808C, however, lower temperatures require longer reaction times. For instance, in the KF±MgF2±ethylene glycol system, KMgF3 is obtained after 4 days at 1808C, but at 1508C, 7 days are required. In the KF±ZnF2±ethanol system, KZnF3 is obtained after 1 day at 1808C, but at 1508C, 3 days are needed. The possible reaction mechanism can be formulated as follows: H2 O
KF K F ; a trace of water is coming from the solvents MF2 nRMF2 nR MF2 nR K F KMF3 nR (M Mg or Zn, R ethylene glycol, ethanol, n 1 and 4)
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R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
Fig. 1. XRD patterns of KMgF3 (a) and KZnF3 (b).
3.2. X-ray diffraction patterns The XRD patterns of the KMgF3 and KZnF3 are shown in Fig. 1 (see Tables 2 and 3 for the XRD data of KMgF3 and KZnF3 ) and can be indexed in the primitive cubic Ê and for system. The unit-cell parameter [19] for KMgF3 is a 3:9919 0:0027 A Ê KZnF3 is a 4:0563 0:0007 A. The value for KMgF3 is slightly bigger than that of Ê) the corresponding KMgF3 synthesised by solid-state reaction (a 3:9889 A [JCPDS Card 18-1033]. The value for KZnF3 is similar to that of the corresponding Ê ) [JCPDS Card 6-0439]. The KZnF3 synthesised by solid-state reaction (a 4:056 A powder XRD patterns show that the samples are single phase. 3.3. SEM observation The scanning electron micrographs of the complex ¯uorides KMgF3 and KZnF3 are shown in Fig. 2. As Fig. 2 clearly indicates, the crystallites have regular
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
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Table 2 XRD data for KMgF3 h
k
l
Ê) dobs (A
Ê) dJCPDS (A
(I/I0)obs
1 1 2 2 2 3 3 2 3
1 1 0 1 2 1 1 2 2
0 1 0 1 0 0 1 2 1
2.8255 2.3064 1.9976 1.6295 1.4112 1.2638 1.2036 1.1516 1.0665
2.819 2.302 1.994 1.628 1.410 1.261 1.202 1.151 1.066
84 70 100 24 42 9 11 11 10
Table 3 XRD data for KZnF3 h
k
l
Ê) dobs (A
Ê) dJCPDS (A
(I/I0)obs
1 1 1 2 2 2 2 3 3 2 3 3 4
0 1 1 0 1 1 2 0 1 2 2 2 0
0 0 1 0 0 1 0 0 0 2 0 1 0
4.0551 2.8679 2.3422 2.0282 1.8138 1.6565 1.4340 1.3523 1.2823 1.1712 1.1250 1.0840 1.0141
4.055 2.869 2.343 2.029 1.814 1.656 1.434 1.352 1.283 1.171 1.125 1.084 1.014
30 100 5 70 15 39 29 5 14 8 2 14 4
morphology and implying that the samples are single phase. The two complex ¯uorides KMgF3 and KZnF3 have the same cubic of morphology, and the average grain sizes are ca. 17 and 1 mm, respectively.
Fig. 2. SEM photographs of KMgF3 (left) and KZnF3 (right).
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R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
3.4. Thermal analysis The thermal stability of the as-prepared KMgF3 and KZnF3 were studied by TGDTA analysis in air. Neither KMgF3 is decomposed up to 8308C nor KZnF3 up to 8708C. A small mass of ca. 3.5% surface water was evident for KMgF3 and ca. 1% for KZnF3 between 50±1108C. The presence of water is con®rmed by IR at 3420.8 and 1643.4 cm 1, 3436.1 and 1642.7 cm 1, respectively. Upon increasing the temperature, the surface water is removed. 4. Conclusion A new method for the synthesis of KMgF3 and KZnF3 by solvothermal crystallisation at 150±1808C is presented. Both KMgF3 and KZnF3 crystallise in cubic systems with Perovskite structure. All the products have uniform grain shapes and sizes. The mole ratios and solvents are effective for the synthesis. Compared with traditional high temperature solid-state methods, high-temperature, high-pressure hydrothermal synthesis method and mild hydrothermal synthesis method, the solvothermal synthesis method to complex ¯uorides appears advantageous in terms of lower synthesis temperature, simple operation, single phase and well-crystallisation. Acknowledgments This work was supported by the State Key Project of Foundation Research (G1998061306) and National Nature Science Foundation of China (50072031). References [1] M. Eibschutz, H.J. Guggenheim, S.H. Wemple, I. Camlibel, M. Didomenico, Phys. Lett. 29A (1969) 409. [2] A.H. Cooke, D.A. Jones, J.F.A. Silva, M.R. Weils, J. Phys. C: Solid State Phys. 8 (1975) 4083. [3] R.A. Heaton, C. Lin, Phys. Rev. B. 25 (1982) 3538. [4] A. Meijerink, J. Lumin. 55 (1993) 125. [5] Y. Tan, C. Shi, J. Solid State Chem. 150 (2000) 178. [6] G.D. Dzik, I. Sokolska, S. Golab, M. Baluka, J. Alloys Comp. 300±301 (2000) 254. [7] J. Dexpert-Ghys, S.J.L. Ribeiro, P. Dugat, D. Avignant, M.D. Faucher, Spectrochim. Acta A. 56 (2000) 475. [8] P.M. Bridenbaugh, J.O. Eckert, G. Nykolak, G. Thomas, W. Wilson, L.M. Demianets, R. Riman, R.A. Laudise, J. Crystal Growth 144 (1994) 243. [9] L.N. Demianets, Prog. Crystal Growth Charact. 21 (1990) 299. [10] S. Somiya, S.I. Hirano, M. Yoshimura, K. Yanagisawa, J. Mater. Sci. 16 (1981) 813. [11] C. Zhao, S. Feng, Z. Chao, C. Shi, R. Xu, J. Ni, Chem. Commun. (1996) 1641. [12] C. Zhao, S. Feng, R. Xu, C. Shi, J. Ni, Chem. Commun. (1997) 945. [13] X. Xun, S. Feng, R. Xu, Mater. Res. Bull. 33 (1998) 369. [14] X. Xu, S. Feng, J. Wang, R. Xu, Chem. Mater. 9 (1997) 2966.
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195 [15] [16] [17] [18] [19]
H. Li, Z. Jia, S. Feng, C. Shi, Chem. J. Chinese U. 12 (2000) 1805. G. Horsch, H. Paus, J. Opt. Commun. 60 (1986) 69. O. Pillo, P.T.C. Freire, V. Lemos, Phys. Rev. B: Condens. Matter 52 (1995) 177. K. Somaiah, M.V. Narayana, Mater. Chem. Phys. 24 (1990) 353. Y. Takaki, T. Taniguchi, H. Yamaguchi, T. Ogura, J. Ceram. Soc. Jpn. 95 (1987) 565.
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Solvothermal synthesis of the complex ¯uorides KMgF3 and KZnF3 with the Perovskite structures Ruinian Huaa, Zhihong Jiaa, Demin Xieb, Chunshan Shia,* a
Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China b Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China (Refereed) Received 14 November 2001; accepted 12 February 2002
Abstract The complex ¯uorides KMgF3 and KZnF3 with Perovskite structures were solvothermally synthesised at 150±1808C and characterised by means of X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Fluorides; B. Chemical synthesis; C. X-ray diffraction; C. Electron diffraction
1. Introduction In recent years, complex ¯uorides which show various interesting structures have been extensively studied due to their particular physical properties such as piezoelectric characteristics [1], ferromagnetic [2], nonmagnetic insulator behaviour [3] and photoluminescence host materials [4,5]. Conventional synthesis routes to complex ¯uorides include solid state reactions [6,7] at high-temperature (>4008C), high-pressure (>100 MPa) hydrothermal technique [8±10]. The solid state synthetic apparatus, however, requires a complicated set-up because the corrosive nature of ¯uorides has limited the studies of ¯uorides in the materials chemistry as well as the fact that hightemperature, high-pressure hydrothermal techniques require special devices. Recently, a mild hydrothermal synthesis of the complex ¯uorides at 120±2408C has been reported [11±14]. The oxygen content in the complex ¯uorides synthesised by solid-state *
Corresponding author. Tel.: 86-431-5262-041; fax: 86-431-5685-653. E-mail address: [email protected] (C. Shi).
0025-5408/02/$ ± see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 2 ) 0 0 7 3 2 - 8
1190
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
reaction is higher than that of the corresponding complex ¯uorides synthesised by hydrothermal techniques [15]. KMgF3 and KZnF3 are the important complex ¯uorides because they show lasing action [16,17] when they are doped with a proper dopant. Various isomorphous replacements in the framework of complex ¯uorides lead to many controllable properties [18]. In order to explore a new method for the preparation of complex ¯uorides, herein we report a convenient method for the synthesis of KMgF3 and KZnF3 with Perovskite structures using a solvothermal process. 2. Experimental 2.1. Synthesis Solvothermal synthesis of KMgF3 and KZnF3 was carried out in a Te¯on-lined stainless steel autoclave under autogenous pressure. The starting reactants were KF (A.R.), MgF2 (A.R.) and ZnF2 (A.R.). The mole ratios of initial mixtures for the synthesis of KMgF3 and KZnF3 were 1.0KF:1.0MgF2 and 2.0KF:1.0ZnF2, respectively. The typical synthetic procedure for crystalline KMgF3 and KZnF3 were as follows: 0.291 g KF and 0.312 g MgF2, 0.581 g KF and 0.518 g ZnF2 were mixed respectively, and added into a Te¯on-lined autoclave of 20 ml capacity. Then the autoclave was ®lled with ethylene glycol (for the synthesis of KMgF3) and absolute ethanol(for the synthesis of KZnF3) up to 80% of the total volume. The autoclave was sealed into a stainless steel tank and heated in an oven at 1808C for 7 days. After being cooled to room temperature naturally, the ®nal powder product was ®ltered off, washed with absolute ethanol and distilled water, then dried in air at ambient temperature. 2.2. Characterisation All products were characterised by X-ray powder diffraction (XRD), using a Japan Ê ). The XRD Rigaku D/max-IIB diffractometer with Cu Ka1 radiation (l 1:5405 A data for index and cell-parameter calculations were collected by a scanning mode with a step of 0.028 in the 2y range from 10 to 1008 and a scanning rate of 4.08 min 1. Silicon was used as an internal standard. Observation of crystallites by SEM was performed on a JXA-840 scanning electron microscopy. Thermogravimetric analysis (TGA) was conducted using a DT-30 thermogravimetric system. IR spectra were obtained with a Magna 560 spectrometer in the range 400±4000 cm 1. The samples were pressed KBr pellets for the spectral measurements.
3. Results and discussion 3.1. Characterisation Table 1 shows the solvothermal synthesis conditions for KMgF3 and KZnF3. In the synthesis of KMgF3, the K/Mg ratio and the solvents were found to be crucial to the
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
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Table 1 Solvothermal synthesis conditions for KMgF3 and KZnF3 Starting materials
a:b Solvent (mole ratio)
a
b
KF KF KF KF KF KF KF KF KF KF KF KF KF KF KF KF KF
MgF2 MgF2 MgF2 MgF2 MgF2 MgF2 MgF2 MgF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2 ZnF2
1:1 2:1 1:2 1:1 1:1 1:1 1:1 1:1 1:1 2:1 3:1 1:2 2:1 2:1 2:1 2:1 2:1
Ethylene Ethylene Ethylene Ethylene Ethylene Ethylene Ethylene Ethylene Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol
Reaction Reaction Phases in product time (day) temperature (8C)
glycol glycol glycol glycol glycol glycol glycol glycol
7 7 7 4 3 7 6 7 7 7 7 7 1 2 2 3 7
180 180 180 180 180 150 150 120 180 180 180 180 180 180 150 150 120
KMgF3 KMgF3 KMgF3 MgF2 KMgF3 KMgF3 multiphase KMgF3 KMgF3 multiphase KMgF3 multiphase KZnF3 KZnF3 KZnF3 KZnF3 ZnF2 KZnF3 KZnF3 KZnF3 ZnF2 KZnF3 KZnF3 ZnF2
formation, crystallisation and purity of the products. When the mole ratio K/Mg of mixture was 1 or 2, and ethylene glycol or pyridine was used as solvent, the pure and well-crystallised product was prepared. However, when the mole ratio K/Mg was 0.5, impurity phases appeared. In the synthesis of KZnF3, the K/Zn ratio is a dominating factor. Although when the mole ratio K/Zn was from 1 to 3, KZnF3 was formed. A large K/Zn ratio was favourable for crystallisation and purity of the products, and when K/Zn ratio <1 an impurity phase of ZnF2 was obtained. Crystallisation temperature and reaction times were also important factors for an effective synthesis. Although KMgF3 and KZnF3 can be crystallised at temperature below 1808C, however, lower temperatures require longer reaction times. For instance, in the KF±MgF2±ethylene glycol system, KMgF3 is obtained after 4 days at 1808C, but at 1508C, 7 days are required. In the KF±ZnF2±ethanol system, KZnF3 is obtained after 1 day at 1808C, but at 1508C, 3 days are needed. The possible reaction mechanism can be formulated as follows: H2 O
KF K F ; a trace of water is coming from the solvents MF2 nRMF2 nR MF2 nR K F KMF3 nR (M Mg or Zn, R ethylene glycol, ethanol, n 1 and 4)
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Fig. 1. XRD patterns of KMgF3 (a) and KZnF3 (b).
3.2. X-ray diffraction patterns The XRD patterns of the KMgF3 and KZnF3 are shown in Fig. 1 (see Tables 2 and 3 for the XRD data of KMgF3 and KZnF3 ) and can be indexed in the primitive cubic Ê and for system. The unit-cell parameter [19] for KMgF3 is a 3:9919 0:0027 A Ê KZnF3 is a 4:0563 0:0007 A. The value for KMgF3 is slightly bigger than that of Ê) the corresponding KMgF3 synthesised by solid-state reaction (a 3:9889 A [JCPDS Card 18-1033]. The value for KZnF3 is similar to that of the corresponding Ê ) [JCPDS Card 6-0439]. The KZnF3 synthesised by solid-state reaction (a 4:056 A powder XRD patterns show that the samples are single phase. 3.3. SEM observation The scanning electron micrographs of the complex ¯uorides KMgF3 and KZnF3 are shown in Fig. 2. As Fig. 2 clearly indicates, the crystallites have regular
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
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Table 2 XRD data for KMgF3 h
k
l
Ê) dobs (A
Ê) dJCPDS (A
(I/I0)obs
1 1 2 2 2 3 3 2 3
1 1 0 1 2 1 1 2 2
0 1 0 1 0 0 1 2 1
2.8255 2.3064 1.9976 1.6295 1.4112 1.2638 1.2036 1.1516 1.0665
2.819 2.302 1.994 1.628 1.410 1.261 1.202 1.151 1.066
84 70 100 24 42 9 11 11 10
Table 3 XRD data for KZnF3 h
k
l
Ê) dobs (A
Ê) dJCPDS (A
(I/I0)obs
1 1 1 2 2 2 2 3 3 2 3 3 4
0 1 1 0 1 1 2 0 1 2 2 2 0
0 0 1 0 0 1 0 0 0 2 0 1 0
4.0551 2.8679 2.3422 2.0282 1.8138 1.6565 1.4340 1.3523 1.2823 1.1712 1.1250 1.0840 1.0141
4.055 2.869 2.343 2.029 1.814 1.656 1.434 1.352 1.283 1.171 1.125 1.084 1.014
30 100 5 70 15 39 29 5 14 8 2 14 4
morphology and implying that the samples are single phase. The two complex ¯uorides KMgF3 and KZnF3 have the same cubic of morphology, and the average grain sizes are ca. 17 and 1 mm, respectively.
Fig. 2. SEM photographs of KMgF3 (left) and KZnF3 (right).
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R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195
3.4. Thermal analysis The thermal stability of the as-prepared KMgF3 and KZnF3 were studied by TGDTA analysis in air. Neither KMgF3 is decomposed up to 8308C nor KZnF3 up to 8708C. A small mass of ca. 3.5% surface water was evident for KMgF3 and ca. 1% for KZnF3 between 50±1108C. The presence of water is con®rmed by IR at 3420.8 and 1643.4 cm 1, 3436.1 and 1642.7 cm 1, respectively. Upon increasing the temperature, the surface water is removed. 4. Conclusion A new method for the synthesis of KMgF3 and KZnF3 by solvothermal crystallisation at 150±1808C is presented. Both KMgF3 and KZnF3 crystallise in cubic systems with Perovskite structure. All the products have uniform grain shapes and sizes. The mole ratios and solvents are effective for the synthesis. Compared with traditional high temperature solid-state methods, high-temperature, high-pressure hydrothermal synthesis method and mild hydrothermal synthesis method, the solvothermal synthesis method to complex ¯uorides appears advantageous in terms of lower synthesis temperature, simple operation, single phase and well-crystallisation. Acknowledgments This work was supported by the State Key Project of Foundation Research (G1998061306) and National Nature Science Foundation of China (50072031). References [1] M. Eibschutz, H.J. Guggenheim, S.H. Wemple, I. Camlibel, M. Didomenico, Phys. Lett. 29A (1969) 409. [2] A.H. Cooke, D.A. Jones, J.F.A. Silva, M.R. Weils, J. Phys. C: Solid State Phys. 8 (1975) 4083. [3] R.A. Heaton, C. Lin, Phys. Rev. B. 25 (1982) 3538. [4] A. Meijerink, J. Lumin. 55 (1993) 125. [5] Y. Tan, C. Shi, J. Solid State Chem. 150 (2000) 178. [6] G.D. Dzik, I. Sokolska, S. Golab, M. Baluka, J. Alloys Comp. 300±301 (2000) 254. [7] J. Dexpert-Ghys, S.J.L. Ribeiro, P. Dugat, D. Avignant, M.D. Faucher, Spectrochim. Acta A. 56 (2000) 475. [8] P.M. Bridenbaugh, J.O. Eckert, G. Nykolak, G. Thomas, W. Wilson, L.M. Demianets, R. Riman, R.A. Laudise, J. Crystal Growth 144 (1994) 243. [9] L.N. Demianets, Prog. Crystal Growth Charact. 21 (1990) 299. [10] S. Somiya, S.I. Hirano, M. Yoshimura, K. Yanagisawa, J. Mater. Sci. 16 (1981) 813. [11] C. Zhao, S. Feng, Z. Chao, C. Shi, R. Xu, J. Ni, Chem. Commun. (1996) 1641. [12] C. Zhao, S. Feng, R. Xu, C. Shi, J. Ni, Chem. Commun. (1997) 945. [13] X. Xun, S. Feng, R. Xu, Mater. Res. Bull. 33 (1998) 369. [14] X. Xu, S. Feng, J. Wang, R. Xu, Chem. Mater. 9 (1997) 2966.
R. Hua et al. / Materials Research Bulletin 37 (2002) 1189±1195 [15] [16] [17] [18] [19]
H. Li, Z. Jia, S. Feng, C. Shi, Chem. J. Chinese U. 12 (2000) 1805. G. Horsch, H. Paus, J. Opt. Commun. 60 (1986) 69. O. Pillo, P.T.C. Freire, V. Lemos, Phys. Rev. B: Condens. Matter 52 (1995) 177. K. Somaiah, M.V. Narayana, Mater. Chem. Phys. 24 (1990) 353. Y. Takaki, T. Taniguchi, H. Yamaguchi, T. Ogura, J. Ceram. Soc. Jpn. 95 (1987) 565.
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