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Single-crystal growth of some neptunium arsenides
Journal
of the Less-Common
SINGLE-CRYSTAL
Metals. 83 (1982)
GROWTH
263
263
- 26’7
OF SOME NEPTUNIUM
ARSENIDES
A. WOJAKOWSKI* DPpartement de GPnie Radioactif. aux-Roses (France)
Centre
d ‘Etudes
NuclPaires.
B.P. 6. 92 260
Fontenay-
D. DAMIEN Dc’partement d’Etude des Combustibles ci Base de Plutonium, B.P. 6, 92 260 Fontenay-aus-Roses (France) (Received
August
26,
Centre
d ‘Etudes
Nuclkaires,
1951)
Summary Single crystals of neptunium arsenides (NpsAs, and NpAsa) were prepared by chemical transport using iodine as the transporting agent. The neptunium arsenides were transported from 720 to 760 “C and from 800 to 850 “C for NpsAs, and NpXs, respectively. The single-crystal size is in the millimetre range.
1. Introduction Much work has been performed on the preparation, structure and physical properties of actinide pnictides and chalcogenides. Most of these compounds have been obtained and studied in polycrystalline form. For solid state investigations such as neutron diffraction or optical properties studies, good-quality single crystals with suitable dimensions are often required. No information about the preparation of single crystals of neptunium pnictides and chalcogenides, with the exception of NpO, [l] , has been reported. However, it is well known that some of the thorium, protactinium and uranium pnictides or chalcogenides can be grown by the chemical transport reaction method [2 - 61 . Extending this method to the Np-As system we examined the possibility of single-crystal growth of some neptunium arsenides. Three binary compounds were found in the Np-As system: NpAs, Np3As4 and NpAs2, with NaCl-, Th3P,- and anti-Fez&-type crystal structures respectively [7,8]. Only a very limited amount of information about the electronic structure of these compounds is available. The most intensive-
*Permanent address: Institute for Low Academy of Sciences, 50950 Wrocfaw, P.O. 0002-5088/62/0000-OOOO/$O2.i5
Temperature and Box 937. Poland.
@ Elsevier
Structure
Sequoia/Printed
Research,
in The
Polish
Netherlands
264
ly studied compound of this group is NpAs. Magnetic investigations have shown that NpAs exhibits complex magnetic ordering below TN = 175 K [9]. So far no experimental data have been reported on NpsAs,. Magnetic susceptibility results on polycrystalline samples of NpAsa have shown that it orders magnetically at low temperatures with several magnetic phases
[lOI In this paper we describe the details of preparation of NpsAs, and NpAsz single crystals and present some data on growth conditions and morphology.
2. Experimental
details
The appropriate compounds were used in powder form as starting materials. NpAss was prepared by the reaction of neptunium (23’Np) hydride with an excess of arsenic at approximately 700 “C in an evacuated and sealed silica tube. Np3As4 in powder form was prepared by the thermal decomposition of NpAs2 under an argon atmosphere at about 780 “C. The details of the preparation and characterization of polycrystalline samples have been reported previously [ 7,8] . The transport reaction process was carried out in sealed quartz tubes (12 - 15 mm in diameter and 100 - 150 mm long) in a temperature gradient furnace installed in a glove-box. The choice of iodine as a transporting agent was suggested by the good results of single-crystal growth of uranium phosphides and arsenides [2] . The substrate and the iodine enclosed in a capillary were introduced into the quartz tube which had been carefully cleaned with an equimolar HN03:HF mixture, rinsed with water and preheated under vacuum at about 1000 “C. For the preliminary experiments, not more than 200 mg of each compound was involved. After determination of the thermal conditions of the transport the final experiments were performed using 1 or 2 g of each neptunium arsenide. Figure 1 shows the details of the quartz tube arrangement as well as the temperature profile during the growth of neptunium arsenide single crystals. First the tube was sealed under a vacuum of about 10e6 Tot-r (Fig. 1, l), and then iodine was introduced. The small capillary was broken open by rotating element 2 (Fig. 1) and iodine vapour was condensed in the main tube by freezing it. The tube was finally sealed at 3 (Fig. 1).
3. Results and discussion The results of the growth experiments with both NpAs2 and Np,As, single crystals are summarized in Table 1. No substantial change in the growth conditions was observed when the concentration of the transporting agent was varied from 3 to 6 mg cmW3. The number of nucleation centres in the crystal growth zone was not controlled,
265
CRYSTAL
FEED
GROWTH
ZONE
Fig. 1. Experimental arrangement of the preparation growth, and the temperature profile in the furnace
TABLE Results
of the quartz tube during single-crystal
for single-crystal growth.
1 of growth
experiments
Feed quantity (g) Tube volume (cm”) Transporting agent Concentration (mg cme3) Time (days) Crystal growth zone temperature Feed zone temperature (‘C) Crystal dimensions (mm) Crystal habit Lattice parameters (A) Measured Literature [ 7, 8) Symmetry Space group
1
2 * 20 I
x 15
*, 5 10 760 720
;’ (“C)
10 X50 so0 1 x 1 x 0.5 Platelets 0
=
(I
=
3.956( t 2), c = 8.098(? 3.962( f 1). c = 8.115(.
Tetragonal I’-I/nmrn
1X1X1
Polyhedra 2)
a = 8.51.57(
‘2) (I = 8.5153(
I 7)
f 7)
B.c.c. li3d
and rather a large number of small crystals were obtained with typical dimensions of 1 mm X 1 mm X 0.5 mm and 1 mm X 1 mm X 1 mm for Np As, and Np,As4 respectively. In Figs. 2 and 3, scanning electron micrographs of typical single crystals of NpAs2 and Np,As4 are presented. NpAs.,_ single crystals are platelets with the c axis perpendicular to the plates. NprSAs., single crystals are polyhedra with no particular preferred orientation. Neptunium arsenide single crystals are much more stable in air than the corresponding powder sample is. Even after esposure for a few days in air they are still bright. NpAs, crystals are brown-gold in colour and show a
266
(a)
(b)
Fig. 2. Scanning (b) 48x .)
electron
micrograph
of NpAsz silogle crystals.
Fig. 3. Scanning (b) 48x .)
electron
micrograph
of NpsAsq
single crystals.
(Magnifications:
(Magnifications:
(a) 16x ;
(a) 16x ;
tendency to cleave in layers perpendicular to the c axis, while Np3As4 crystals are black and rather harder. The lattice parameters of ~\pAs~ and Np3As, measured by X-ray diffraction are in good agreement with the published data [7,8] (see Table 1).
267
Recently, single crystals of NpAsp have been used for a study of magnetic properties using neutron diffraction, magnetic susceptibility and Ussbauer measurements [ 11 - 131. NpAsa orders ma~etic~ly at 2?, = 54 K and shows a first-order transition to a ferromagnetic state at T, = 18 K. X very strong magnetic anisotropy has been found in the ferromagnetic state with the easy direction along the c axis. The lattice parameters and the atomic position parameters of NpAsa at liquid helium temperature are a = 3.930(5) A, c = 8.137(S) A, z(Xp) = 0.281(3) and z(As) = 0.639(3) [lZ] . Investigations of the physical properties (magnetic susceptibility and neutron diffraction) of single crystals of Np,As, are now in progress.
Acknowiedgment The authors wish to thank Mr. P. Parmentier preparation of the scanning electron micrographs.
for his assistance
in the
References I. Ray and W. illtiller, J. Phys. (Paris). Colloq. C4, 40 1 J. C. Spirlet, E. Bednarczyk, (1979) 108. ‘2 Z. Henkie, Rocz. Clre~rr.. 42 (1968) 363. 3 G. Calestani, J. C. Spirlet and W. Sliiller, J. f%ys. (f’aris), Colloq. C4, 40 (1979) 106. -1 A. Wojnkowski, Z. Henkie and Z. liletowski, Phys. Stolus Sotidi .-I, 14 (1972) 517. 5 Z. Henkie and P. J. Markowski, J. Cryst. Groats, 41 (1977) 303. 6 J. C. Spirlet, J. Phys. (Purist, Colfog. C4, 40 (1979) 87. 7 J. P. Charvillat anti D. Dam&, fnorg. N~ci. Chem. Lett.. 9 (1973) 337. 8 J. P. Charvillat, ‘I’&% de Doctorat en Sciences, University of Clermont-Ferrand, 1977. 9 D. J. Lam, B. D. Dunlap, A. T. Aldred and I. Nowik, AIP Conf. Proc.. 10 (1973) 83. 10 J. M. Fournier, A. Blaise and P. Salmon, in Froc. Int. Conf. OR Magnetism. Vol. 6, Nauka. Moscow, 1974, p. 65. I1 P. Burlct, S. Quezel, J. Root-Mignod, A. Blaise. J. M. Fournier, D. Damien and A. Wojakowski, A neutron diffraction study of the magnetic ordering in NpAsl. in Actinides-1981, Abstracts, September 10 - 15, 1981, Lawrence Berkeley Laboratory, University of California, 1981, p. 133. 12 A. Delapalme, A. Blaise. J. M. Fournier, J. Mulak, J. Charviilat, D. Damien and A. Wojakowski, NpAsz : magnetic form factor of Np and tentative crystal field model, in Actinides-1981. Abstracts, September LO - 15, 1981, Lawrence Berkeley Laboratory, University of California, 1981, p. 139. 13 M. Boge, J. Chappert, L. Asch, G. M. Kalvius, A. Blaise, J. M. Fournier, D. Damien and A. Wojakowski, 237Np Mossbauer spectroscopy in binary compounds, in Actinides-198 1, Abstracts, September 10 - 15, 1981. Lawrence Berkeley Laboratory, University of California, 1981. p. 165.
of the Less-Common
SINGLE-CRYSTAL
Metals. 83 (1982)
GROWTH
263
263
- 26’7
OF SOME NEPTUNIUM
ARSENIDES
A. WOJAKOWSKI* DPpartement de GPnie Radioactif. aux-Roses (France)
Centre
d ‘Etudes
NuclPaires.
B.P. 6. 92 260
Fontenay-
D. DAMIEN Dc’partement d’Etude des Combustibles ci Base de Plutonium, B.P. 6, 92 260 Fontenay-aus-Roses (France) (Received
August
26,
Centre
d ‘Etudes
Nuclkaires,
1951)
Summary Single crystals of neptunium arsenides (NpsAs, and NpAsa) were prepared by chemical transport using iodine as the transporting agent. The neptunium arsenides were transported from 720 to 760 “C and from 800 to 850 “C for NpsAs, and NpXs, respectively. The single-crystal size is in the millimetre range.
1. Introduction Much work has been performed on the preparation, structure and physical properties of actinide pnictides and chalcogenides. Most of these compounds have been obtained and studied in polycrystalline form. For solid state investigations such as neutron diffraction or optical properties studies, good-quality single crystals with suitable dimensions are often required. No information about the preparation of single crystals of neptunium pnictides and chalcogenides, with the exception of NpO, [l] , has been reported. However, it is well known that some of the thorium, protactinium and uranium pnictides or chalcogenides can be grown by the chemical transport reaction method [2 - 61 . Extending this method to the Np-As system we examined the possibility of single-crystal growth of some neptunium arsenides. Three binary compounds were found in the Np-As system: NpAs, Np3As4 and NpAs2, with NaCl-, Th3P,- and anti-Fez&-type crystal structures respectively [7,8]. Only a very limited amount of information about the electronic structure of these compounds is available. The most intensive-
*Permanent address: Institute for Low Academy of Sciences, 50950 Wrocfaw, P.O. 0002-5088/62/0000-OOOO/$O2.i5
Temperature and Box 937. Poland.
@ Elsevier
Structure
Sequoia/Printed
Research,
in The
Polish
Netherlands
264
ly studied compound of this group is NpAs. Magnetic investigations have shown that NpAs exhibits complex magnetic ordering below TN = 175 K [9]. So far no experimental data have been reported on NpsAs,. Magnetic susceptibility results on polycrystalline samples of NpAsa have shown that it orders magnetically at low temperatures with several magnetic phases
[lOI In this paper we describe the details of preparation of NpsAs, and NpAsz single crystals and present some data on growth conditions and morphology.
2. Experimental
details
The appropriate compounds were used in powder form as starting materials. NpAss was prepared by the reaction of neptunium (23’Np) hydride with an excess of arsenic at approximately 700 “C in an evacuated and sealed silica tube. Np3As4 in powder form was prepared by the thermal decomposition of NpAs2 under an argon atmosphere at about 780 “C. The details of the preparation and characterization of polycrystalline samples have been reported previously [ 7,8] . The transport reaction process was carried out in sealed quartz tubes (12 - 15 mm in diameter and 100 - 150 mm long) in a temperature gradient furnace installed in a glove-box. The choice of iodine as a transporting agent was suggested by the good results of single-crystal growth of uranium phosphides and arsenides [2] . The substrate and the iodine enclosed in a capillary were introduced into the quartz tube which had been carefully cleaned with an equimolar HN03:HF mixture, rinsed with water and preheated under vacuum at about 1000 “C. For the preliminary experiments, not more than 200 mg of each compound was involved. After determination of the thermal conditions of the transport the final experiments were performed using 1 or 2 g of each neptunium arsenide. Figure 1 shows the details of the quartz tube arrangement as well as the temperature profile during the growth of neptunium arsenide single crystals. First the tube was sealed under a vacuum of about 10e6 Tot-r (Fig. 1, l), and then iodine was introduced. The small capillary was broken open by rotating element 2 (Fig. 1) and iodine vapour was condensed in the main tube by freezing it. The tube was finally sealed at 3 (Fig. 1).
3. Results and discussion The results of the growth experiments with both NpAs2 and Np,As, single crystals are summarized in Table 1. No substantial change in the growth conditions was observed when the concentration of the transporting agent was varied from 3 to 6 mg cmW3. The number of nucleation centres in the crystal growth zone was not controlled,
265
CRYSTAL
FEED
GROWTH
ZONE
Fig. 1. Experimental arrangement of the preparation growth, and the temperature profile in the furnace
TABLE Results
of the quartz tube during single-crystal
for single-crystal growth.
1 of growth
experiments
Feed quantity (g) Tube volume (cm”) Transporting agent Concentration (mg cme3) Time (days) Crystal growth zone temperature Feed zone temperature (‘C) Crystal dimensions (mm) Crystal habit Lattice parameters (A) Measured Literature [ 7, 8) Symmetry Space group
1
2 * 20 I
x 15
*, 5 10 760 720
;’ (“C)
10 X50 so0 1 x 1 x 0.5 Platelets 0
=
(I
=
3.956( t 2), c = 8.098(? 3.962( f 1). c = 8.115(.
Tetragonal I’-I/nmrn
1X1X1
Polyhedra 2)
a = 8.51.57(
‘2) (I = 8.5153(
I 7)
f 7)
B.c.c. li3d
and rather a large number of small crystals were obtained with typical dimensions of 1 mm X 1 mm X 0.5 mm and 1 mm X 1 mm X 1 mm for Np As, and Np,As4 respectively. In Figs. 2 and 3, scanning electron micrographs of typical single crystals of NpAs2 and Np,As4 are presented. NpAs.,_ single crystals are platelets with the c axis perpendicular to the plates. NprSAs., single crystals are polyhedra with no particular preferred orientation. Neptunium arsenide single crystals are much more stable in air than the corresponding powder sample is. Even after esposure for a few days in air they are still bright. NpAs, crystals are brown-gold in colour and show a
266
(a)
(b)
Fig. 2. Scanning (b) 48x .)
electron
micrograph
of NpAsz silogle crystals.
Fig. 3. Scanning (b) 48x .)
electron
micrograph
of NpsAsq
single crystals.
(Magnifications:
(Magnifications:
(a) 16x ;
(a) 16x ;
tendency to cleave in layers perpendicular to the c axis, while Np3As4 crystals are black and rather harder. The lattice parameters of ~\pAs~ and Np3As, measured by X-ray diffraction are in good agreement with the published data [7,8] (see Table 1).
267
Recently, single crystals of NpAsp have been used for a study of magnetic properties using neutron diffraction, magnetic susceptibility and Ussbauer measurements [ 11 - 131. NpAsa orders ma~etic~ly at 2?, = 54 K and shows a first-order transition to a ferromagnetic state at T, = 18 K. X very strong magnetic anisotropy has been found in the ferromagnetic state with the easy direction along the c axis. The lattice parameters and the atomic position parameters of NpAsa at liquid helium temperature are a = 3.930(5) A, c = 8.137(S) A, z(Xp) = 0.281(3) and z(As) = 0.639(3) [lZ] . Investigations of the physical properties (magnetic susceptibility and neutron diffraction) of single crystals of Np,As, are now in progress.
Acknowiedgment The authors wish to thank Mr. P. Parmentier preparation of the scanning electron micrographs.
for his assistance
in the
References I. Ray and W. illtiller, J. Phys. (Paris). Colloq. C4, 40 1 J. C. Spirlet, E. Bednarczyk, (1979) 108. ‘2 Z. Henkie, Rocz. Clre~rr.. 42 (1968) 363. 3 G. Calestani, J. C. Spirlet and W. Sliiller, J. f%ys. (f’aris), Colloq. C4, 40 (1979) 106. -1 A. Wojnkowski, Z. Henkie and Z. liletowski, Phys. Stolus Sotidi .-I, 14 (1972) 517. 5 Z. Henkie and P. J. Markowski, J. Cryst. Groats, 41 (1977) 303. 6 J. C. Spirlet, J. Phys. (Purist, Colfog. C4, 40 (1979) 87. 7 J. P. Charvillat anti D. Dam&, fnorg. N~ci. Chem. Lett.. 9 (1973) 337. 8 J. P. Charvillat, ‘I’&% de Doctorat en Sciences, University of Clermont-Ferrand, 1977. 9 D. J. Lam, B. D. Dunlap, A. T. Aldred and I. Nowik, AIP Conf. Proc.. 10 (1973) 83. 10 J. M. Fournier, A. Blaise and P. Salmon, in Froc. Int. Conf. OR Magnetism. Vol. 6, Nauka. Moscow, 1974, p. 65. I1 P. Burlct, S. Quezel, J. Root-Mignod, A. Blaise. J. M. Fournier, D. Damien and A. Wojakowski, A neutron diffraction study of the magnetic ordering in NpAsl. in Actinides-1981, Abstracts, September 10 - 15, 1981, Lawrence Berkeley Laboratory, University of California, 1981, p. 133. 12 A. Delapalme, A. Blaise. J. M. Fournier, J. Mulak, J. Charviilat, D. Damien and A. Wojakowski, NpAsz : magnetic form factor of Np and tentative crystal field model, in Actinides-1981. Abstracts, September LO - 15, 1981, Lawrence Berkeley Laboratory, University of California, 1981, p. 139. 13 M. Boge, J. Chappert, L. Asch, G. M. Kalvius, A. Blaise, J. M. Fournier, D. Damien and A. Wojakowski, 237Np Mossbauer spectroscopy in binary compounds, in Actinides-198 1, Abstracts, September 10 - 15, 1981. Lawrence Berkeley Laboratory, University of California, 1981. p. 165.