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Preparation of single crystals of binary and ternary transition metal and uranium arsenides and antimonides from reactive-fluxes
Journal of Crystal Growth 217 (2000) 250}254
Preparation of single crystals of binary and ternary transition metal and uranium arsenides and antimonides from reactive-#uxes Thomas E. Albrecht-Schmitt *, Philip M. Almond , Andreas J. Illies , Casey C. Raymond, Catherine E. Talley Department of Chemistry, Auburn University, 179 Chemistry Building, Auburn, AL 36849, USA Department of Chemistry, Kent State University, Kent, OH 44242, USA Received 1 January 2000; accepted 14 April 2000 Communicated by A.A. Chernov
Abstract Single crystals as large as 2 mm of binary transition metal and uranium arsenides and antimonides can be grown from the reactions of titanium, chromium, zirconium, hafnium, tantalum, rhenium, or uranium with alkali metal arsenides and antimonides from 5003C to 9503C. Single crystals of the ternary uranium copper arsenide phases UCuAs and U Cu As can also be grown from the reaction of uranium and copper with Cs As . The resulting crystals were analyzed by electron dispersive analysis by X-rays (EDX) and single crystal X-ray di!raction. 2000 Elsevier Science B.V. All rights reserved. PACS: 81.10.Fq Keywords: Reactive-#ux technique; Single-crystal growth; Arsenides; Antimonides
1. Introduction Transition metal and uranium pnictides, particularly those containing arsenic and antimony, exhibit a number of intriguing properties including magnetic transitions [1}4], semi-conductivity [5,6], superconductivity [7], and thermoelectricity [8}12]. Many of these properties can be ascribed to
* Corresponding author. Tel.: #1-334-844-6948; fax: #1334-844-6959. E-mail address: [email protected] (T.E. AlbrechtSchmitt).
the atypical structures that these compounds can adopt owing to their ability to form homoatomic bonds and interactions [13}15]. The preparation of single crystals of known and new pnictides is critical for both structural determinations and for physical property measurements, particularly where anisotropy is predicted [16]. Tin and lead #uxes have proven to be important crystal growth media for pnictides [17}28]. This is clearly demonstrated in the synthesis of rhenium phosphides, where a number of pure phases can be prepared in 1 week at 9003C in a tin #ux [17]. In the absence of such #ux, the reactions fail to reach equilibrium, even after several months [17].
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 4 7 5 - 9
T.E. Albrecht-Schmitt et al. / Journal of Crystal Growth 217 (2000) 250}254
The reactive-#ux technique has developed over the past decade as a focal point for the syntheses of ternary and quaternary chalcogenides [29}39]. In these preparations, molten alkali metal sul"des, selenides, and tellurides mix and partially dissolve additional reaction components, and serve as reactants, as they are incorporated into the "nal products. These reactions yield single crystals from the melts that allow for X-ray structural determinations. As in alkali metal chalcogenides, low-melting potassium, rubidium, and cesium pnictides also exist, which leads one to speculate as to whether these too can be used as reactive-#uxes for preparative chemistry, particularly for the growth of single crystals of known and new compounds [40]. While the reactive-#ux technique has not been formally applied to the synthesis of pnictides, ternary alkali metal arsenides and antimonides have been prepared either through the direct reaction of the elements, or in a few cases, through the use of mixtures of alkali metal arsenides [41}46]. In these reactions, it is highly probable that molten alkali metal pnictides form. We have found that rubidium and cesium arsenides and antimonides readily react with a variety of transition metals and uranium to form high-quality single crystals of binary and ternary arsenides and antimonides where the alkali metals are not incorporated.
2. Experimental section 2.1. Preparation of alkali metal arsenides and antimonides Alkali metal arsenides and antimonides can be prepared by either the direct reaction of the elements, or by "rst mixing the components in liquid ammonia followed by annealing in sealed tubes [47}49]. The direct method is carried out in sealed quartz or niobium tubes or in alumina boats inside quartz tubes. The former method has its advantage in that it is a one-step preparation. However, great care should be taken in that alkali metals react with main group elements in a highly exothermic fashion and can result in explosions. By "rst dissolving the alkali metals in liquid ammonia, violent reactions can be avoided. This method
251
requires stringent removal of ammonia from the resulting powders under high vacuum and mild heating.
2.2. Synthesis and growth of binary transition metal and uranium arsenides and antimonides In a typical synthesis Cs As , Rb Sb , or Cs Sb are ground together in an argon "lled glovebox in a 1 : 1 ratio with Ti (Alfa} Aesar, 99.99%), Cr (Alfa}Aesar, 99%), Zr (Alfa}Aesar, 98.5%), Hf (Alfa}Aesar, 99.6%), Ta (Alfa}Aesar, 99.9%), Re (Alfa}Aesar, 99.997%) or U (Alfa}Aesar, 99.7%) in a total amount of 250 mg. The mixtures are then placed in quartz tubes and sealed under high vacuum (10\ Torr). The tubes are heated in a single zone, horizontal tube furnace at 103C/min to the desired temperature where they are held for 3}7 days. Finally, the tubes are cooled at 0.53C/min to room temperature. The tubes are then scored and broken, with care being taken not to crush the product mixtures. In many cases the crystals grow directly out of the top of the melt and can be easily isolated. If the crystals are embedded in excess #ux, water can be added to the product mixture, which rapidly decomposes alkali metal pnictides. The transition metal pnictides are typically stable towards water and simply fall out of the matrix as it decomposes. Crystals of these compounds usually grow as long needles, 1}2 mm in size. UAs does not form needles and instead ad opts a wide variety of crystal habits that seem to be determined by the location of crystal growth relative to the #ux/quartz interface. Truncated tetragonal bipyramidal plates grow at the edge of the #ux/quartz tube boundary; whereas crystals that grow within the melt adopted a wide variety of polyhedral habits. Re As forms small rhombicuboctahedra, as shown in Fig. 1 [50,51]. Compounds prepared by this method are listed along with the #uxes, temperatures, and the reaction duration utilized in Table 1. In all cases, the composition of the single crystals were determined by electron dispersive analysis by X-rays and the unit cells were measured using single crystal X-ray di!raction techniques.
252
T.E. Albrecht-Schmitt et al. / Journal of Crystal Growth 217 (2000) 250}254
Fig. 1. SEM micrograph of a single crystal of Re As at 20.0 kV and X430.
Table 1 Compounds, #uxes, temperatures, and durations used for the syntheses of single crystals of transition metal and uranium arsenides and antimonides Compound
Flux
Temperature (3C)
Reaction duration (days)
TiAs CrAs HfAs TaAs Re As UAs UCuAs U Cu As TiSb TiSb HfSb
Cs As Cs As Cs As Cs As Cs As Cs As Cs As Cs As Rb Sb Cs Sb Rb Sb
900 900 900 950 900 900 900 900 650 500 900
7 7 5 5 7 7 7 7 3 7 5
2.3. Synthesis and growth of UCuAs2 and U2 Cu4 As5 Cs As (151 mg, 0.164 mmol), Cu (Alfa}Aesar, 99.9%, 21 mg, 0.330 mmol), and U (78 mg, 0.328 mmol) were reacted in a quartz tube using the same procedure as listed in Section 2.2. The resulting product mixture contained unreacted #ux, columnar crystals, and truncated tetragonal pyramidal crystals, the last appears to be square plates without close examination. The columnar crystals were examined by EDX, and shown to
contain U, Cu, and As in a 1 : 1 : 2 ratio. Subsequent analysis by single crystal X-ray di!raction identi"ed these crystals as UCuAs [2]. We were unable to visually distinguish between crystals of UAs and U Cu As as both crystallized as truncated tetragonal pyramids [3]. Crystallographic Studies. Data were collected from single crystals using either a Nicolet R3M single crystal X-ray di!ractometer, or a Siemens SMART 1000 di!ractometer with an area detector. Intensity data sets for HfAs and UCuAs were collected and the structures re"ned as a method for determining the quality of these crystals. These structures re"ned to "nal R values of 0.0424 (wR2"0.1131) and 0.0221 (wR2"0.0461), respectively. SEM/EDX. EDX data were collected on a JEOL 840 scanning electronmicroscope equipped with an Oxford Instruments microanalysis system (Link Isis).
3. Discussion and conclusions The use of alkali metal pnictides as reactive-#uxes for the growth of transition metal and uranium pnictides is a general method that allows for reaction temperatures as low as 5003C and reaction times as short as 3 days. This method is an alternative to the use of tin #uxes, where the resulting products are not always unreactive towards hydrochloric acid, which is required to remove excess tin. Crystals resulting from the use of alkali metal pnictides can be easily isolated from excess #ux through the addition of water, which decomposes alkali metal pnictides. Furthermore, this method also eliminates secondary crystal growth steps, such as the use of chemical transport methods [2,3]. While crystals of TiSb and HfSb can be grown directly from reactions of the elements, large single crystals of the corresponding arsenides are more di$cult to prepare without the aid of the reactive-#uxes described herein. Furthermore, in order to prepare pure phases, the synthesis of transition metal pnictides directly from the elements often requires reaction lengths as long as 3 weeks. In the case of Re As substantial attack of the quartz tubes takes place during this period and
T.E. Albrecht-Schmitt et al. / Journal of Crystal Growth 217 (2000) 250}254
silicate impurities are present in large amounts at the end of this reaction. By using Cs As as a react ive-#ux, the reaction duration can be shortened to 1 week and attack of the quartz tubes is greatly reduced. Our X-ray di!raction data indicates that the crystals prepared from these reactive-#uxes are of high quality as indicated by peak pro"les and structural re"nements. As we were unable to detect appreciable amounts of alkali metal contaminants, with the caveat that EDX is not particularly good tool for quantitative analysis, these crystals are suitable for physical property measurements. Furthermore, alkali metal pnictide #uxes should also be useful for the preparation of new pnictides, which is the subject of one of our current investigations.
Acknowledgements This work was supported by NASA (Alabama Space Grant Consortium), NASA/EPSCoR, Auburn University in the form of start-up funds, a competitive research grant, a Dean's Research Initiative Grant, and start-up funds provided by Kent State University to C.C. Raymond. We thank our reviewers for helpful comments, some of which have been incorporated into this paper.
References [1] P.A. Ole`s, J. Phys. 26 (1965) 561. [2] J. Stepien-Damm, D. Kaczorowski, R. Troc, J. Less-Common Met. 132 (1987) 15. [3] D. Kaczorowski, H. NoeK l, R. Troc, J. Less-Common Met. 170 (1991) 263. [4] H. Boller, A. Kallel, J. Solid State Chem. 9 (1971) 1699. [5] F. Hulliger, Nature 209 (1966) 500. [6] G.A. Slack, V.G. Tsoukala, J. Appl. Phys. 76 (1994) 1665. [7] D. Jung, M.H. Whangbo, S. Alvarez, Inorg. Chem. 29 (1990) 2252. [8] J.W. Sharp, E.C. Jones, R.K. Williams, P.M. Martin, B.C. Sales, J. Appl. Phys. 78 (1995) 1013. [9] D.T. Morelli, T. Caillat, J.P. Fleurial, A. Borshchevsky, A. Vandersande, B. Chen, C. Uher, Phys. Rev. B 51 (1995) 9622. [10] D. Mandrus, A. Migliori, T.W. Darling, M.F. Hundley, E.J. Peterson, J.D. Thompson, Phys. Rev. B 52 (1995) 4926.
253
[11] B.C. Sales, D. Mandrus, R.K. Williams, Science 272 (1996) 1325. [12] G.D. Mahan, Solid State Physics, Vol. 51, Academic Press, New York, 1998, pp. 81}157. [13] S.M. Kauzlarich (Ed.), Chemistry, Structure, and Bonding of Zintl Phases and Ions, VCH Publishers, New York, 1996. [14] J.D. Corbett, Chem. Rev. 85 (1985) 383. [15] H.G. von Schnering, Angew. Chem. Int. Ed. Engl. 20 (1981) 33. [16] M.J. Fergusson, R.E. Ellenwood, A. Mar, Inorg. Chem. 38 (1999) 4503. [17] R. RuK hl, U. FloK rke, W. Jeitschko, J. Solid State Chem. 53 (1984) 55. [18] M.V. Dewalsky, W. Jeitschko, U. Wortmann, Chem. Mater. 3 (1991) 316. [19] M.V. Dewalsky, W. Jeitschko, Acta Chem. Scand. 45 (1991) 828. [20] J.H. Albering, W. Jeitschko, Z. Naturforsch. B 49 (1994) 1074. [21] M. Brylak, W. Jeitschko, Z. Naturforsch. B 49 (1994) 747. [22] J.H. Albering, W. Jeitschko, J. Alloys Compounds 241 (1996) 44. [23] M.J. Ferguson, R.W. Hushagen, A. Mar, Inorg. Chem. 35 (1996) 4505. [24] R. Lam, A. Mar, Inorg. Chem. 35 (1996) 6959. [25] M.J. Ferguson, R.W. Hushagen, A. Mar, J. Alloys Compounds 249 (1997) 191. [26] D.T. Chow, R. McDonald, A. Mar, Inorg. Chem. 36 (1997) 3750. [27] R. Lam, A. Mar, Inorg. Chem. 37 (1998) 5364. [28] A. Wurth, A. Mewis, Z. Anorg. Allg. Chem. 625 (1999) 1486. [29] S.A. Sunshine, D. Kang, J.A. Ibers, J. Am. Chem. Soc. 109 (1987) 6202. [30] M.G. Kanatzidis, Y. Park, J. Am. Chem. Soc. 111 (1989) 3767. [31] M.G. Kanatzidis, Y. Park, Chem. Mater. 2 (1990) 99. [32] Y. Park, M.G. Kanatzidis, Angew. Chem. Int. Ed. Engl. 29 (1990) 914. [33] P.M. Keane, J.A. Ibers, Inorg. Chem. 30 (1991) 1327. [34] M.G. Kanatzidis, Chem. Mater. 2 (1990) 353. [35] M.F. Mansuetto, P.M. Keane, J.A. Ibers, J. Solid State Chem. 101 (1992) 257. [36] T.J. McCarthy, S.-P. Ngeyi, J.-H. Liao, D.C. DeGroot, J. Schindler, C.R. Kannewurf, M.G. Kanatzidis, Chem. Mater. 5 (1993) 331. [37] M.F. Mansuetto, P.M. Keane, J.A. Ibers, J. Solid State Chem. 105 (1993) 580. [38] J.A. Cody, J.A. Ibers, Inorg. Chem. 34 (1995) 3165. [39] J.A. Cody, J.A. Ibers, Inorg. Chem. 35 (1996) 3836. [40] T.B. Massalski (Ed.), Binary Alloy Phase Diagrams, 2nd edition, ASM International, Materials Park, OH, 1990. [41] A. Adam, H.U. Schuster, Z. Naturforsch. B 45 (1990) 559. [42] J. Nuss, R.H.C. Gil, W. HoK nle, K. Peters, H.G. von Schnering, Z. Anorg. Allg. Chem. 622 (1996) 1854. [43] P. Wenz, H.-U. Schuster, Z. Naturforsch. B 39 (1984) 1816.
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[44] C. Schnabel, H.-U. Schuster, Z. Anorg. Allg. Chem. 584 (1990) 138. [45] W. Weise, H.-U. Schuster, Z. Anorg. Allg. Chem. 535 (1986) 143. [46] J. Stuhrmann, A. Adam, H.-U. Schuster, Z. Naturforsch. B 48 (1993) 898. [47] M. Somer, M. Hartweg, K. Peters, H.G. von Schnering, Z. Kristallogr. 195 (1991) 103.
[48] A. Rehr, F. Guerra, S. Parkin, H. Hope, S.M. Kauzlarich, Inorg. Chem. 34 (1995) 6218. [49] H.-G. von Schnering, J. Wolf, D. Weber, R. Ramirez, T. Meyer, Angew. Chem. Int. Ed. Engl. 25 (1986) 353. [50] M. Klein, H.-G. von Schnering, J. Less-Common Met. 11 (1966) 298. [51] K.P. Jensen, A. Kjekshus, T. Skansen, J. Less-Common Met. 17 (1969) 455.
Preparation of single crystals of binary and ternary transition metal and uranium arsenides and antimonides from reactive-#uxes Thomas E. Albrecht-Schmitt *, Philip M. Almond , Andreas J. Illies , Casey C. Raymond, Catherine E. Talley Department of Chemistry, Auburn University, 179 Chemistry Building, Auburn, AL 36849, USA Department of Chemistry, Kent State University, Kent, OH 44242, USA Received 1 January 2000; accepted 14 April 2000 Communicated by A.A. Chernov
Abstract Single crystals as large as 2 mm of binary transition metal and uranium arsenides and antimonides can be grown from the reactions of titanium, chromium, zirconium, hafnium, tantalum, rhenium, or uranium with alkali metal arsenides and antimonides from 5003C to 9503C. Single crystals of the ternary uranium copper arsenide phases UCuAs and U Cu As can also be grown from the reaction of uranium and copper with Cs As . The resulting crystals were analyzed by electron dispersive analysis by X-rays (EDX) and single crystal X-ray di!raction. 2000 Elsevier Science B.V. All rights reserved. PACS: 81.10.Fq Keywords: Reactive-#ux technique; Single-crystal growth; Arsenides; Antimonides
1. Introduction Transition metal and uranium pnictides, particularly those containing arsenic and antimony, exhibit a number of intriguing properties including magnetic transitions [1}4], semi-conductivity [5,6], superconductivity [7], and thermoelectricity [8}12]. Many of these properties can be ascribed to
* Corresponding author. Tel.: #1-334-844-6948; fax: #1334-844-6959. E-mail address: [email protected] (T.E. AlbrechtSchmitt).
the atypical structures that these compounds can adopt owing to their ability to form homoatomic bonds and interactions [13}15]. The preparation of single crystals of known and new pnictides is critical for both structural determinations and for physical property measurements, particularly where anisotropy is predicted [16]. Tin and lead #uxes have proven to be important crystal growth media for pnictides [17}28]. This is clearly demonstrated in the synthesis of rhenium phosphides, where a number of pure phases can be prepared in 1 week at 9003C in a tin #ux [17]. In the absence of such #ux, the reactions fail to reach equilibrium, even after several months [17].
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 4 7 5 - 9
T.E. Albrecht-Schmitt et al. / Journal of Crystal Growth 217 (2000) 250}254
The reactive-#ux technique has developed over the past decade as a focal point for the syntheses of ternary and quaternary chalcogenides [29}39]. In these preparations, molten alkali metal sul"des, selenides, and tellurides mix and partially dissolve additional reaction components, and serve as reactants, as they are incorporated into the "nal products. These reactions yield single crystals from the melts that allow for X-ray structural determinations. As in alkali metal chalcogenides, low-melting potassium, rubidium, and cesium pnictides also exist, which leads one to speculate as to whether these too can be used as reactive-#uxes for preparative chemistry, particularly for the growth of single crystals of known and new compounds [40]. While the reactive-#ux technique has not been formally applied to the synthesis of pnictides, ternary alkali metal arsenides and antimonides have been prepared either through the direct reaction of the elements, or in a few cases, through the use of mixtures of alkali metal arsenides [41}46]. In these reactions, it is highly probable that molten alkali metal pnictides form. We have found that rubidium and cesium arsenides and antimonides readily react with a variety of transition metals and uranium to form high-quality single crystals of binary and ternary arsenides and antimonides where the alkali metals are not incorporated.
2. Experimental section 2.1. Preparation of alkali metal arsenides and antimonides Alkali metal arsenides and antimonides can be prepared by either the direct reaction of the elements, or by "rst mixing the components in liquid ammonia followed by annealing in sealed tubes [47}49]. The direct method is carried out in sealed quartz or niobium tubes or in alumina boats inside quartz tubes. The former method has its advantage in that it is a one-step preparation. However, great care should be taken in that alkali metals react with main group elements in a highly exothermic fashion and can result in explosions. By "rst dissolving the alkali metals in liquid ammonia, violent reactions can be avoided. This method
251
requires stringent removal of ammonia from the resulting powders under high vacuum and mild heating.
2.2. Synthesis and growth of binary transition metal and uranium arsenides and antimonides In a typical synthesis Cs As , Rb Sb , or Cs Sb are ground together in an argon "lled glovebox in a 1 : 1 ratio with Ti (Alfa} Aesar, 99.99%), Cr (Alfa}Aesar, 99%), Zr (Alfa}Aesar, 98.5%), Hf (Alfa}Aesar, 99.6%), Ta (Alfa}Aesar, 99.9%), Re (Alfa}Aesar, 99.997%) or U (Alfa}Aesar, 99.7%) in a total amount of 250 mg. The mixtures are then placed in quartz tubes and sealed under high vacuum (10\ Torr). The tubes are heated in a single zone, horizontal tube furnace at 103C/min to the desired temperature where they are held for 3}7 days. Finally, the tubes are cooled at 0.53C/min to room temperature. The tubes are then scored and broken, with care being taken not to crush the product mixtures. In many cases the crystals grow directly out of the top of the melt and can be easily isolated. If the crystals are embedded in excess #ux, water can be added to the product mixture, which rapidly decomposes alkali metal pnictides. The transition metal pnictides are typically stable towards water and simply fall out of the matrix as it decomposes. Crystals of these compounds usually grow as long needles, 1}2 mm in size. UAs does not form needles and instead ad opts a wide variety of crystal habits that seem to be determined by the location of crystal growth relative to the #ux/quartz interface. Truncated tetragonal bipyramidal plates grow at the edge of the #ux/quartz tube boundary; whereas crystals that grow within the melt adopted a wide variety of polyhedral habits. Re As forms small rhombicuboctahedra, as shown in Fig. 1 [50,51]. Compounds prepared by this method are listed along with the #uxes, temperatures, and the reaction duration utilized in Table 1. In all cases, the composition of the single crystals were determined by electron dispersive analysis by X-rays and the unit cells were measured using single crystal X-ray di!raction techniques.
252
T.E. Albrecht-Schmitt et al. / Journal of Crystal Growth 217 (2000) 250}254
Fig. 1. SEM micrograph of a single crystal of Re As at 20.0 kV and X430.
Table 1 Compounds, #uxes, temperatures, and durations used for the syntheses of single crystals of transition metal and uranium arsenides and antimonides Compound
Flux
Temperature (3C)
Reaction duration (days)
TiAs CrAs HfAs TaAs Re As UAs UCuAs U Cu As TiSb TiSb HfSb
Cs As Cs As Cs As Cs As Cs As Cs As Cs As Cs As Rb Sb Cs Sb Rb Sb
900 900 900 950 900 900 900 900 650 500 900
7 7 5 5 7 7 7 7 3 7 5
2.3. Synthesis and growth of UCuAs2 and U2 Cu4 As5 Cs As (151 mg, 0.164 mmol), Cu (Alfa}Aesar, 99.9%, 21 mg, 0.330 mmol), and U (78 mg, 0.328 mmol) were reacted in a quartz tube using the same procedure as listed in Section 2.2. The resulting product mixture contained unreacted #ux, columnar crystals, and truncated tetragonal pyramidal crystals, the last appears to be square plates without close examination. The columnar crystals were examined by EDX, and shown to
contain U, Cu, and As in a 1 : 1 : 2 ratio. Subsequent analysis by single crystal X-ray di!raction identi"ed these crystals as UCuAs [2]. We were unable to visually distinguish between crystals of UAs and U Cu As as both crystallized as truncated tetragonal pyramids [3]. Crystallographic Studies. Data were collected from single crystals using either a Nicolet R3M single crystal X-ray di!ractometer, or a Siemens SMART 1000 di!ractometer with an area detector. Intensity data sets for HfAs and UCuAs were collected and the structures re"ned as a method for determining the quality of these crystals. These structures re"ned to "nal R values of 0.0424 (wR2"0.1131) and 0.0221 (wR2"0.0461), respectively. SEM/EDX. EDX data were collected on a JEOL 840 scanning electronmicroscope equipped with an Oxford Instruments microanalysis system (Link Isis).
3. Discussion and conclusions The use of alkali metal pnictides as reactive-#uxes for the growth of transition metal and uranium pnictides is a general method that allows for reaction temperatures as low as 5003C and reaction times as short as 3 days. This method is an alternative to the use of tin #uxes, where the resulting products are not always unreactive towards hydrochloric acid, which is required to remove excess tin. Crystals resulting from the use of alkali metal pnictides can be easily isolated from excess #ux through the addition of water, which decomposes alkali metal pnictides. Furthermore, this method also eliminates secondary crystal growth steps, such as the use of chemical transport methods [2,3]. While crystals of TiSb and HfSb can be grown directly from reactions of the elements, large single crystals of the corresponding arsenides are more di$cult to prepare without the aid of the reactive-#uxes described herein. Furthermore, in order to prepare pure phases, the synthesis of transition metal pnictides directly from the elements often requires reaction lengths as long as 3 weeks. In the case of Re As substantial attack of the quartz tubes takes place during this period and
T.E. Albrecht-Schmitt et al. / Journal of Crystal Growth 217 (2000) 250}254
silicate impurities are present in large amounts at the end of this reaction. By using Cs As as a react ive-#ux, the reaction duration can be shortened to 1 week and attack of the quartz tubes is greatly reduced. Our X-ray di!raction data indicates that the crystals prepared from these reactive-#uxes are of high quality as indicated by peak pro"les and structural re"nements. As we were unable to detect appreciable amounts of alkali metal contaminants, with the caveat that EDX is not particularly good tool for quantitative analysis, these crystals are suitable for physical property measurements. Furthermore, alkali metal pnictide #uxes should also be useful for the preparation of new pnictides, which is the subject of one of our current investigations.
Acknowledgements This work was supported by NASA (Alabama Space Grant Consortium), NASA/EPSCoR, Auburn University in the form of start-up funds, a competitive research grant, a Dean's Research Initiative Grant, and start-up funds provided by Kent State University to C.C. Raymond. We thank our reviewers for helpful comments, some of which have been incorporated into this paper.
References [1] P.A. Ole`s, J. Phys. 26 (1965) 561. [2] J. Stepien-Damm, D. Kaczorowski, R. Troc, J. Less-Common Met. 132 (1987) 15. [3] D. Kaczorowski, H. NoeK l, R. Troc, J. Less-Common Met. 170 (1991) 263. [4] H. Boller, A. Kallel, J. Solid State Chem. 9 (1971) 1699. [5] F. Hulliger, Nature 209 (1966) 500. [6] G.A. Slack, V.G. Tsoukala, J. Appl. Phys. 76 (1994) 1665. [7] D. Jung, M.H. Whangbo, S. Alvarez, Inorg. Chem. 29 (1990) 2252. [8] J.W. Sharp, E.C. Jones, R.K. Williams, P.M. Martin, B.C. Sales, J. Appl. Phys. 78 (1995) 1013. [9] D.T. Morelli, T. Caillat, J.P. Fleurial, A. Borshchevsky, A. Vandersande, B. Chen, C. Uher, Phys. Rev. B 51 (1995) 9622. [10] D. Mandrus, A. Migliori, T.W. Darling, M.F. Hundley, E.J. Peterson, J.D. Thompson, Phys. Rev. B 52 (1995) 4926.
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