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Tm4B3C4: Preparation, crystal structure and physical properties
Solid State Communications 152 (2012) 1531–1534
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Tm4B3C4: Preparation, crystal structure and physical properties Volodymyr Babizhetskyy a,n, Kurt Hiebl b, Arndt Simon c a b c
Department of Inorganic Chemistry, Ivan Franko National University of Lviv, Kyryla & Mefodiya Str. 6, UA-79005 Lviv, Ukraine Arbeitsgruppe Neue Materialien, Universit¨ at Wien, W¨ ahringerstrasse 42, A-1090 Wien, Austria Max-Planck-Institut f¨ ur Festk¨ orperforschung, Heisenbergstrasse 1, Postfach 800665, D-70569 Stuttgart, Germany
a r t i c l e i n f o
abstract
Article history: Received 29 February 2012 Received in revised form 2 May 2012 Accepted 4 June 2012 Available online 13 June 2012
Tm4B3C4 crystallizes in the triclinic Gd4B3C4 structure type, space group P1 , a¼ 3.4850(2), b ¼ 3.5220(2), c ¼11.6972(6), a ¼ 92.86(1), b ¼ 96.43(1), g ¼ 90.14(1) according to X-ray powder diffraction. The magnetic properties of the compound Tm4B3C4 have been measured in the temperature range 2 K o To 300 K and in various external fields up to B ¼ 7 T. The sample undergoes an anti-ferromagnetic transition at TN ¼ 3 K, and in fields B 40.1 T a meta-magnetic transition is encountered. The measurements of the temperature dependence of the electrical resistivity proves a poor metallic state of this compound. & 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Ternary thulium–boride–carbide compound D. Electrical resistivity D. Magnetic behavior
1. Introduction The structures of the ternary rare earth (RE) boride carbides display a variety of different arrangements with boron–carbon substructures. They extend from zero-dimensional units to chains and two-dimensional nets embedded in the metal atom sublattices as well as interconnected boron icosahedra [1]. The substructures can be divided into three groups. In the first group the finite (0-D) quasi-molecular entities fill voids of the metal atom matrix and can have different lengths ranging from 2 to 13 nonmetal atoms. Linear units of different sizes as well as isolated C atoms can coexist. In the second category, the non-metal atoms form infinite one-dimensional planar or nearly planar ribbons (BC)N of zigzag chains of boron atoms to which carbon atoms are attached. In the third family, the boron and carbon atoms form infinite, planar (2-D) nets which alternate with sheets of metal atoms. From the second category four structures, UBC, ThBC, Th3B2C3 and Gd4B3C4, up to now have been characterized [2–5]. In all of them, the metal atoms form trigonal prisms which condense in one direction via square faces, resulting in infinite channels filled with (BC)N ribbons. Gd4B3C4 was the first characterized member of the rare earth metal borocarbide family in which both 1-D and 0-D non-metal atom systems are coexisting [5]. Tb10B7C10 is the second structurally characterized member of this family [6]. In contrast to the structure of Gd4B3C4, the non-linear CBC units as well as (BC)N chains in Tb10B7C10 are oriented in a non-parallel manner to each other in different slabs. The CBC units in the same
n
Corresponding author. Tel.: þ38 032 260 0388; fax: þ38 032 261 6048. E-mail address: [email protected] (V. Babizhetskyy).
0038-1098/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ssc.2012.06.002
slab exhibit different angles to the c axis, although the (BC)N ribbons lie parallel in the slab. The metal atom environment for the (BC)N ribbons in Tb10B7C10 is almost identical to that in Gd4B3C4. Recently we have synthesized the new series of ternary rare earth metal boride carbides with composition RE4B3C4 (RE¼Tb, Dy, Ho, Er, Tm, Yb, Lu) belonging to the Gd4B3C4 type structure with no detailed characterization [6]. A closer inspection of the crystal structure of Tm4B3C4 as well as physical properties of this compound is the subject of the present work.
2. Experimental section 2.1. Synthesis The samples of composition Tm4B3C4 were prepared from commercially available pure elements: rare earth metal with a claimed purity of 99.99 at%, Alfa—Aesar, Johnson Matthey Company, sublimed bulk pieces; crystalline boron powder, purity 99.99 at%, H.C. Starck, Germany; graphite powder, purity 99.98 at%, Aldrich. Before use, the graphite and boron powders were outgased overnight at 950 1C, po10 5 mbar. Stoichiometric mixtures of the constituents were compacted in stainless steel dies. The pellets were arc-melted under purified argon atmosphere [7] on a watercooled copper hearth. The buttons of 1 g were turned over and remelted typically three times to improve homogeneity. Finally, the samples were wrapped in molybdenum foil, annealed in evacuated silica tubes for one month at 1000 1C and subsequently quenched in cold water. All handling was carried out under argon atmosphere in a glove box or through the Schlenk technique.
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2.2. X-ray diffraction and sample characterization X-ray powder diffraction patterns of Tm4B3C4 samples sealed in capillaries under dry argon for the full profile refinement were collected on a powder diffractometer STOE STADI P with monochromated Mo-Ka1 radiation (51r2y r701, step size 0.11, measurement time per step: 220 s). For metallographic inspection and electron probe microanalysis, the samples were embedded in Woods metal (melting point 75 1C, Fluka Chemie, Switzerland). The samples were polished on ¨ a nylon cloth using chromium oxide (Buhler Isomet) with grain sizes 1–5 mm under dry petroleum. Energy dispersive X-ray spectroscopy analysis (EDX) of the polished samples by a scanning electron microscope (TESCAN 5130MM with Oxford Si-detector) confirmed the presence of only thulium, boron and carbon. The density measurement of Tm4B3C4 was performed under argon atmosphere in a pycnometer AccuPyc 1330 (Micrometrics GmbH, Germany) and was found to be 8.76(2) g/cm3 (rcalc ¼ 8.81 g/cm3) in good agreement with calculated X-ray densities. 2.3. Magnetic and electric resistivity measurements
Table 1 Crystal data of the structure refinement for the Tm4B3C4. Space group Composition from refinement Lattice parameters a/A˚
P1 (no. 2) Tm4B3C4 3.4850(2)
b/A˚ c/A˚
3.5220(2)
a/1
92.86(1) 96.43(1) 90.14(1) 142.49(3)
11.6972(6)
b/1
g/1 Unit cell volume/A˚ 3 Number of atoms in cell Calculated density (g/cm3) Diffractometer Radiation Mode of refinement Number of atom sites Number of free parameters 2W limits, (siny/l)max RBragg, Rp, Rwp,
11 8.812(2) STOE STADI P Mo-Ka1 Full matrix full profile data refinement 6 22 5–70, 0.808 0.078, 0.158, 0.149,
Table 2 Atomic coordinates and isotropic displacement parameters (in A˚ 2) or Tm4B3C4.
The magnetic properties were studied in the temperature interval 1.8–330 K by use of a MPMS XL-7 SQUID magnetometer (Quantum Design, Inc.) in external fields up to 7 T. Measurements of the electrical resistivity were carried out applying a common four-probe technique in the temperature range 5–300 K.
3. Results and discussion
Atom
Site
x
y
z
Biso
Tm1 Tm2 C1 C2 B1 B2
2i 2i 2i 2i 1a 2i
0.1887(1) 0.6081(1) 0.122(4) 0.693(5) 0 0.729(6)
0.9718(2) 0.4414(2) 0.933(6) 0.480(7) 0 0.493(6)
0.3509(2) 0.1405(2) 0.124(5) 0.333(4) 0 0.455(5)
0.48(1) 0.55(1) 0.7(1) 0.7(1) 0.9(1) 0.9(1)
3.1. Structural characterization The X-ray powder pattern of the ternary compound Tm4B3C4 was indexed on the basis of the Gd4B3C4 type structure [5], triclinic unit cell and space group P1 (no. 2). All our attempts to obtain a single crystal of good quality failed. In order to check the homogeneity of the sample a Rietveld profile refinement of the X-ray powder pattern was performed using the programs WinPLOTR and Fullprof [8,9]. Fig. 1 compares the final calculated with the observed pattern. Details of the refinement are summarized in Table 1. The starting atom parameters were chosen from the single crystal structure of Lu4B3C4 [6]; the refined values are given in Table 2. The crystal structure of Tm4B3C4 is shown in Fig. 2. It contains linear CBC units, as well as one-dimensional planar
Tm
C B
Fig. 2. (Color online) Crystal structure of Tm4B3C4.
Fig. 1. (Color online) Comparison of observed and calculated X-ray powder profiles for Tm4B3C4.
ribbons (BC)N formed from zigzag chains of boron atoms to which carbon atoms are attached. The boron atoms in the ribbon exhibit a slight bond alternation with two crystallographically ˚ Owing to the different B2–B2 distances, 2.00(5) and 2.06(5) A. associated standard deviations, these distances are not significantly different from common B–B single bond distances observed in Tb2B2C3 [10] or UBC [2], which exhibit B–B separa˚ respectively. In contrast, in ThBC a strong tions of 1.93 and 1.90 A, ˚ With two BBC bond B–B alternation is observed (1.77 and 2.47 A).
V. Babizhetskyy et al. / Solid State Communications 152 (2012) 1531–1534
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1.0
Table 3 Selected interatomic distances/A˚ for Tm4B3C4. Distance
Atoms
Distance
Atom
Distance
Tm1–2Tm2 Tm2 2Tm1 Tm2 2Tm1 Tm1 Tm2
3.471(2) 3.484(3) 3.485(1) 3.493(2) 3.522(1) 3.859(3) 3.892(3)
C1–Tm1 Tm2 Tm2 Tm2 Tm2
2.631(7) 2.55(2) 2.52(2) 2.45(2) 2.43(2)
B1–2Tm2 2Tm2
2.690(1) 2.925(4)
B2–2Tm1 2Tm1 2Tm1
2.75(3) 2.77(3) 2.85(8)
C2–Tm1 2Tm1 Tm1 Tm2
2.43(2) 2.49(2) 2.54(2) 2.23(4)
B12C1
1.499(8)
B2–C2 B2 B2
1.45(7) 2.00(5) 2.06(5)
Tm2–Tm2 2Tm2 2Tm2
3.334(3) 3.471(2) 3.484(3)
0.8 M (Am2/kg)
Atoms
0.6 0.4 0.2 0.0
20
0
40
60
80
100
T (K) Fig. 4. Magnetization vs. temperature for Tm4B3C4 in a magnetic field B¼ 0.01 T.
60
M (Am2/kg)
40
20
0
80
40
0
0
50
100
150 T (K)
200
250
300
Fig. 3. Reciprocal susceptibility vs. temperature for Tm4B3C4 in a magnetic field B¼ 7 T.
angles of 123.0(8)1, 118.8(7)1, and the BBB bond angle of 118.0(7)1. The C2 atoms of the (BC)N ribbon in Tm4B3C4 lie in the bases of square pyramids of Tm atoms which cap distorted trigonal prisms centered by B atoms. The B2 atoms are surrounded by trigonal prisms of Tm atoms, forming layers. These layers are connected by a layer of distorted cubes centered by the B atoms of the CBC units. The linear CBC unit formed from B1 and C1 atoms has short B–C distances of 1.499(8) A˚ indicative of double bond character (Table 3). 3.2. Magnetism The plot of reciprocal susceptibility versus temperature for Tm4B3C4 in an external field of B ¼7 T as presented in Fig. 3 shows a linear dependence above 150 K. The paramagnetic data were derived from a least squares refinement according to the Curie– Weiss law and resulted in an effective moment meff ¼7.8 mB together with a paramagnetic Curie temperature yp ¼11.2 K. From the magnetization versus temperature plots at various applied magnetic fields, B, we conclude the following: In the low field, B ¼0.01 T, a maximum in the M(T) plot is revealed at Neel temperature, TN ¼3 K (see Fig. 4), which is attributed to an antiferromagnetic ordering of the thulium atoms. However in elevated fields, B 40.1 T a saturization of the magnetization is observed below To10 K (Fig. 5). This is due to a metamagnetic transition, which is the result of a nearly parallel spin alignment of the Tm moments. The isothermal magnetization curve versus external field (see Fig. 6) corroborates the ferromagnetic behavior. The inset of Fig. 6 represents the magnetization data measured in low external fields (Bo0.1 T). The linear behavior of M(B) in the vicinity of the ordering temperature
0
50
100
150 T (K)
200
250
300
Fig. 5. Magnetization vs. temperature for Tm4B3C4 in a magnetic field B¼ 7 T.
Tm4B3C4
120 M (Am2/kg)
1/χ (103 kg/m3)
120
T=2K T=3K
80
T=5K
20 15 10
T = 10 K
40
5 0 0.00 0.02 0.04 0.06 0.08 0.10
0
0
1
2
3
B (T)
4
5
6
7
Fig. 6. Isothermal magnetization vs. applied fields for Tm4B3C4 at various temperatures. Inset: M(B) plots for Bo0.1 T (same symbols as above).
proves the antiferromagnetism as well as the metamagnetic behavior. No hysteresis was observed in decreasing fields. The calculated saturation moment mS ¼4.5 mB is smaller than the expected theoretical value mS ¼gJ¼ 7 mB indicating an imperfect spin structure. 3.3. Electrical transport properties The results of the normalized resistivity data versus temperature are presented in Fig. 7. The compound reveals the typical shape of a ‘‘bad’’ metal. A rough estimate of the room temperature resistivity leads to a rather large value of r300 K 1 10 mO cm, only, compared to 100 mO cm for Tm metal or 1.5 mO cm for Cu metal. The values of the measured resistivities decrease only
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V. Babizhetskyy et al. / Solid State Communications 152 (2012) 1531–1534
increase of the resistivity stemming from the ‘‘super zone’’ effects (Brillouin scattering) close to TN [12], however was not reached at, due to the limited temperature interval of the used apparatus.
1.0
/300
0.8 0.6
4. Conclusions
0.4 0.2 0.0
0
50
100
150 T (K)
200
250
300
Fig. 7. Normalized resistivity vs. temperature for Tm4B3C4.
slightly with falling temperatures down to T 7 K stemming from a weak reduction of the electron–phonon scattering. Furthermore a tendency of an increase of the resistivity below 50 K is indicated. A temperature gradient close to zero is usually attributed to a high degree of disorder (defects) of the metal atoms (a-radiation damaged rare-earth transition metal borides etc.) [11]. The distortion of the Tm polyhedra, see Section 3.1, above in this low symmetric (triclinic structure type) compound could be the reason for the poor metallic state. Additionally, the altering boron–carbon environments of the Tm atoms should have a ‘‘negative’’ influence on the mean free path of the conduction electrons in order to increase the resistivity at lower temperatures. The Neel temperature TN ¼3 K, in order to encounter an
We have shown that the compound Tm4B3C4 crystallizes in the triclinic Gd4B3C4 structure type. The compound undergoes an anti-ferromagnetic transition at TN ¼3 K, and in fields B40.1 T a meta-magnetic transition is encountered. The measurement of the temperature dependence of the electrical resistivity proves a poor metallic state of this compound.
References [1] J. Bauer, J.-F. Halet, J.-Y. Saillard, Coord. Chem. Rev. 178–180 (1998) 723–753. [2] L. Toth, H. Nowotny, F. Benesovsky, E. Rudy., Monatsh. Chem. 92 (1961) 794–802. [3] P. Rogl, J. Nucl. Mater. 73 (1978) 198–203. [4] P. Rogl, J. Nucl. Mater. 79 (1979) 154–158. [5] C. Jardin, O. Oeckler, Hj. Mattausch, A. Simon, J.-F. Halet, J.-Y. Saillard, J. Bauer., Inorg. Chem. 33 (2000) 5895–5900. [6] V. Babizhetskyy, Hj. Mattausch, A. Simon, Z. Anorg. Allg. Chem. 635 (2009) 737–742. [7] B. Horvath, J. Strutz, J. Geyer-Lippmann, G. Horvath, Z. Anorg. Allg. Chem. 483 (1981) 205–218. [8] T. Roisnel, J. Rodrı´guez-Carvajal, Proceedings of the 7th European Powder Diffraction Conference (EPDIC 7), R. Delhez, E. J. Mittemeijer (Eds.), 2000, 118. [9] J. Rodriguez-Carvajal, Phys. B. 192 (1993) 55. [10] V. Babizhetskyy, Hj. Mattausch, A. Simon, Z. Naturforsch 63b (2008) 929–933. [11] J.M. Rowell, R.C. Dynes, Proceedings of the International Conference Ternary Superconductivity, G.K. Shenoy, B.D. Dunlap, F.Y. Fradin (Eds.), 1981, 186. [12] G.T. Meaden, Contemp. Phys. 12 (1971) 313–337.
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Solid State Communications journal homepage: www.elsevier.com/locate/ssc
Tm4B3C4: Preparation, crystal structure and physical properties Volodymyr Babizhetskyy a,n, Kurt Hiebl b, Arndt Simon c a b c
Department of Inorganic Chemistry, Ivan Franko National University of Lviv, Kyryla & Mefodiya Str. 6, UA-79005 Lviv, Ukraine Arbeitsgruppe Neue Materialien, Universit¨ at Wien, W¨ ahringerstrasse 42, A-1090 Wien, Austria Max-Planck-Institut f¨ ur Festk¨ orperforschung, Heisenbergstrasse 1, Postfach 800665, D-70569 Stuttgart, Germany
a r t i c l e i n f o
abstract
Article history: Received 29 February 2012 Received in revised form 2 May 2012 Accepted 4 June 2012 Available online 13 June 2012
Tm4B3C4 crystallizes in the triclinic Gd4B3C4 structure type, space group P1 , a¼ 3.4850(2), b ¼ 3.5220(2), c ¼11.6972(6), a ¼ 92.86(1), b ¼ 96.43(1), g ¼ 90.14(1) according to X-ray powder diffraction. The magnetic properties of the compound Tm4B3C4 have been measured in the temperature range 2 K o To 300 K and in various external fields up to B ¼ 7 T. The sample undergoes an anti-ferromagnetic transition at TN ¼ 3 K, and in fields B 40.1 T a meta-magnetic transition is encountered. The measurements of the temperature dependence of the electrical resistivity proves a poor metallic state of this compound. & 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Ternary thulium–boride–carbide compound D. Electrical resistivity D. Magnetic behavior
1. Introduction The structures of the ternary rare earth (RE) boride carbides display a variety of different arrangements with boron–carbon substructures. They extend from zero-dimensional units to chains and two-dimensional nets embedded in the metal atom sublattices as well as interconnected boron icosahedra [1]. The substructures can be divided into three groups. In the first group the finite (0-D) quasi-molecular entities fill voids of the metal atom matrix and can have different lengths ranging from 2 to 13 nonmetal atoms. Linear units of different sizes as well as isolated C atoms can coexist. In the second category, the non-metal atoms form infinite one-dimensional planar or nearly planar ribbons (BC)N of zigzag chains of boron atoms to which carbon atoms are attached. In the third family, the boron and carbon atoms form infinite, planar (2-D) nets which alternate with sheets of metal atoms. From the second category four structures, UBC, ThBC, Th3B2C3 and Gd4B3C4, up to now have been characterized [2–5]. In all of them, the metal atoms form trigonal prisms which condense in one direction via square faces, resulting in infinite channels filled with (BC)N ribbons. Gd4B3C4 was the first characterized member of the rare earth metal borocarbide family in which both 1-D and 0-D non-metal atom systems are coexisting [5]. Tb10B7C10 is the second structurally characterized member of this family [6]. In contrast to the structure of Gd4B3C4, the non-linear CBC units as well as (BC)N chains in Tb10B7C10 are oriented in a non-parallel manner to each other in different slabs. The CBC units in the same
n
Corresponding author. Tel.: þ38 032 260 0388; fax: þ38 032 261 6048. E-mail address: [email protected] (V. Babizhetskyy).
0038-1098/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ssc.2012.06.002
slab exhibit different angles to the c axis, although the (BC)N ribbons lie parallel in the slab. The metal atom environment for the (BC)N ribbons in Tb10B7C10 is almost identical to that in Gd4B3C4. Recently we have synthesized the new series of ternary rare earth metal boride carbides with composition RE4B3C4 (RE¼Tb, Dy, Ho, Er, Tm, Yb, Lu) belonging to the Gd4B3C4 type structure with no detailed characterization [6]. A closer inspection of the crystal structure of Tm4B3C4 as well as physical properties of this compound is the subject of the present work.
2. Experimental section 2.1. Synthesis The samples of composition Tm4B3C4 were prepared from commercially available pure elements: rare earth metal with a claimed purity of 99.99 at%, Alfa—Aesar, Johnson Matthey Company, sublimed bulk pieces; crystalline boron powder, purity 99.99 at%, H.C. Starck, Germany; graphite powder, purity 99.98 at%, Aldrich. Before use, the graphite and boron powders were outgased overnight at 950 1C, po10 5 mbar. Stoichiometric mixtures of the constituents were compacted in stainless steel dies. The pellets were arc-melted under purified argon atmosphere [7] on a watercooled copper hearth. The buttons of 1 g were turned over and remelted typically three times to improve homogeneity. Finally, the samples were wrapped in molybdenum foil, annealed in evacuated silica tubes for one month at 1000 1C and subsequently quenched in cold water. All handling was carried out under argon atmosphere in a glove box or through the Schlenk technique.
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V. Babizhetskyy et al. / Solid State Communications 152 (2012) 1531–1534
2.2. X-ray diffraction and sample characterization X-ray powder diffraction patterns of Tm4B3C4 samples sealed in capillaries under dry argon for the full profile refinement were collected on a powder diffractometer STOE STADI P with monochromated Mo-Ka1 radiation (51r2y r701, step size 0.11, measurement time per step: 220 s). For metallographic inspection and electron probe microanalysis, the samples were embedded in Woods metal (melting point 75 1C, Fluka Chemie, Switzerland). The samples were polished on ¨ a nylon cloth using chromium oxide (Buhler Isomet) with grain sizes 1–5 mm under dry petroleum. Energy dispersive X-ray spectroscopy analysis (EDX) of the polished samples by a scanning electron microscope (TESCAN 5130MM with Oxford Si-detector) confirmed the presence of only thulium, boron and carbon. The density measurement of Tm4B3C4 was performed under argon atmosphere in a pycnometer AccuPyc 1330 (Micrometrics GmbH, Germany) and was found to be 8.76(2) g/cm3 (rcalc ¼ 8.81 g/cm3) in good agreement with calculated X-ray densities. 2.3. Magnetic and electric resistivity measurements
Table 1 Crystal data of the structure refinement for the Tm4B3C4. Space group Composition from refinement Lattice parameters a/A˚
P1 (no. 2) Tm4B3C4 3.4850(2)
b/A˚ c/A˚
3.5220(2)
a/1
92.86(1) 96.43(1) 90.14(1) 142.49(3)
11.6972(6)
b/1
g/1 Unit cell volume/A˚ 3 Number of atoms in cell Calculated density (g/cm3) Diffractometer Radiation Mode of refinement Number of atom sites Number of free parameters 2W limits, (siny/l)max RBragg, Rp, Rwp,
11 8.812(2) STOE STADI P Mo-Ka1 Full matrix full profile data refinement 6 22 5–70, 0.808 0.078, 0.158, 0.149,
Table 2 Atomic coordinates and isotropic displacement parameters (in A˚ 2) or Tm4B3C4.
The magnetic properties were studied in the temperature interval 1.8–330 K by use of a MPMS XL-7 SQUID magnetometer (Quantum Design, Inc.) in external fields up to 7 T. Measurements of the electrical resistivity were carried out applying a common four-probe technique in the temperature range 5–300 K.
3. Results and discussion
Atom
Site
x
y
z
Biso
Tm1 Tm2 C1 C2 B1 B2
2i 2i 2i 2i 1a 2i
0.1887(1) 0.6081(1) 0.122(4) 0.693(5) 0 0.729(6)
0.9718(2) 0.4414(2) 0.933(6) 0.480(7) 0 0.493(6)
0.3509(2) 0.1405(2) 0.124(5) 0.333(4) 0 0.455(5)
0.48(1) 0.55(1) 0.7(1) 0.7(1) 0.9(1) 0.9(1)
3.1. Structural characterization The X-ray powder pattern of the ternary compound Tm4B3C4 was indexed on the basis of the Gd4B3C4 type structure [5], triclinic unit cell and space group P1 (no. 2). All our attempts to obtain a single crystal of good quality failed. In order to check the homogeneity of the sample a Rietveld profile refinement of the X-ray powder pattern was performed using the programs WinPLOTR and Fullprof [8,9]. Fig. 1 compares the final calculated with the observed pattern. Details of the refinement are summarized in Table 1. The starting atom parameters were chosen from the single crystal structure of Lu4B3C4 [6]; the refined values are given in Table 2. The crystal structure of Tm4B3C4 is shown in Fig. 2. It contains linear CBC units, as well as one-dimensional planar
Tm
C B
Fig. 2. (Color online) Crystal structure of Tm4B3C4.
Fig. 1. (Color online) Comparison of observed and calculated X-ray powder profiles for Tm4B3C4.
ribbons (BC)N formed from zigzag chains of boron atoms to which carbon atoms are attached. The boron atoms in the ribbon exhibit a slight bond alternation with two crystallographically ˚ Owing to the different B2–B2 distances, 2.00(5) and 2.06(5) A. associated standard deviations, these distances are not significantly different from common B–B single bond distances observed in Tb2B2C3 [10] or UBC [2], which exhibit B–B separa˚ respectively. In contrast, in ThBC a strong tions of 1.93 and 1.90 A, ˚ With two BBC bond B–B alternation is observed (1.77 and 2.47 A).
V. Babizhetskyy et al. / Solid State Communications 152 (2012) 1531–1534
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1.0
Table 3 Selected interatomic distances/A˚ for Tm4B3C4. Distance
Atoms
Distance
Atom
Distance
Tm1–2Tm2 Tm2 2Tm1 Tm2 2Tm1 Tm1 Tm2
3.471(2) 3.484(3) 3.485(1) 3.493(2) 3.522(1) 3.859(3) 3.892(3)
C1–Tm1 Tm2 Tm2 Tm2 Tm2
2.631(7) 2.55(2) 2.52(2) 2.45(2) 2.43(2)
B1–2Tm2 2Tm2
2.690(1) 2.925(4)
B2–2Tm1 2Tm1 2Tm1
2.75(3) 2.77(3) 2.85(8)
C2–Tm1 2Tm1 Tm1 Tm2
2.43(2) 2.49(2) 2.54(2) 2.23(4)
B12C1
1.499(8)
B2–C2 B2 B2
1.45(7) 2.00(5) 2.06(5)
Tm2–Tm2 2Tm2 2Tm2
3.334(3) 3.471(2) 3.484(3)
0.8 M (Am2/kg)
Atoms
0.6 0.4 0.2 0.0
20
0
40
60
80
100
T (K) Fig. 4. Magnetization vs. temperature for Tm4B3C4 in a magnetic field B¼ 0.01 T.
60
M (Am2/kg)
40
20
0
80
40
0
0
50
100
150 T (K)
200
250
300
Fig. 3. Reciprocal susceptibility vs. temperature for Tm4B3C4 in a magnetic field B¼ 7 T.
angles of 123.0(8)1, 118.8(7)1, and the BBB bond angle of 118.0(7)1. The C2 atoms of the (BC)N ribbon in Tm4B3C4 lie in the bases of square pyramids of Tm atoms which cap distorted trigonal prisms centered by B atoms. The B2 atoms are surrounded by trigonal prisms of Tm atoms, forming layers. These layers are connected by a layer of distorted cubes centered by the B atoms of the CBC units. The linear CBC unit formed from B1 and C1 atoms has short B–C distances of 1.499(8) A˚ indicative of double bond character (Table 3). 3.2. Magnetism The plot of reciprocal susceptibility versus temperature for Tm4B3C4 in an external field of B ¼7 T as presented in Fig. 3 shows a linear dependence above 150 K. The paramagnetic data were derived from a least squares refinement according to the Curie– Weiss law and resulted in an effective moment meff ¼7.8 mB together with a paramagnetic Curie temperature yp ¼11.2 K. From the magnetization versus temperature plots at various applied magnetic fields, B, we conclude the following: In the low field, B ¼0.01 T, a maximum in the M(T) plot is revealed at Neel temperature, TN ¼3 K (see Fig. 4), which is attributed to an antiferromagnetic ordering of the thulium atoms. However in elevated fields, B 40.1 T a saturization of the magnetization is observed below To10 K (Fig. 5). This is due to a metamagnetic transition, which is the result of a nearly parallel spin alignment of the Tm moments. The isothermal magnetization curve versus external field (see Fig. 6) corroborates the ferromagnetic behavior. The inset of Fig. 6 represents the magnetization data measured in low external fields (Bo0.1 T). The linear behavior of M(B) in the vicinity of the ordering temperature
0
50
100
150 T (K)
200
250
300
Fig. 5. Magnetization vs. temperature for Tm4B3C4 in a magnetic field B¼ 7 T.
Tm4B3C4
120 M (Am2/kg)
1/χ (103 kg/m3)
120
T=2K T=3K
80
T=5K
20 15 10
T = 10 K
40
5 0 0.00 0.02 0.04 0.06 0.08 0.10
0
0
1
2
3
B (T)
4
5
6
7
Fig. 6. Isothermal magnetization vs. applied fields for Tm4B3C4 at various temperatures. Inset: M(B) plots for Bo0.1 T (same symbols as above).
proves the antiferromagnetism as well as the metamagnetic behavior. No hysteresis was observed in decreasing fields. The calculated saturation moment mS ¼4.5 mB is smaller than the expected theoretical value mS ¼gJ¼ 7 mB indicating an imperfect spin structure. 3.3. Electrical transport properties The results of the normalized resistivity data versus temperature are presented in Fig. 7. The compound reveals the typical shape of a ‘‘bad’’ metal. A rough estimate of the room temperature resistivity leads to a rather large value of r300 K 1 10 mO cm, only, compared to 100 mO cm for Tm metal or 1.5 mO cm for Cu metal. The values of the measured resistivities decrease only
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increase of the resistivity stemming from the ‘‘super zone’’ effects (Brillouin scattering) close to TN [12], however was not reached at, due to the limited temperature interval of the used apparatus.
1.0
/300
0.8 0.6
4. Conclusions
0.4 0.2 0.0
0
50
100
150 T (K)
200
250
300
Fig. 7. Normalized resistivity vs. temperature for Tm4B3C4.
slightly with falling temperatures down to T 7 K stemming from a weak reduction of the electron–phonon scattering. Furthermore a tendency of an increase of the resistivity below 50 K is indicated. A temperature gradient close to zero is usually attributed to a high degree of disorder (defects) of the metal atoms (a-radiation damaged rare-earth transition metal borides etc.) [11]. The distortion of the Tm polyhedra, see Section 3.1, above in this low symmetric (triclinic structure type) compound could be the reason for the poor metallic state. Additionally, the altering boron–carbon environments of the Tm atoms should have a ‘‘negative’’ influence on the mean free path of the conduction electrons in order to increase the resistivity at lower temperatures. The Neel temperature TN ¼3 K, in order to encounter an
We have shown that the compound Tm4B3C4 crystallizes in the triclinic Gd4B3C4 structure type. The compound undergoes an anti-ferromagnetic transition at TN ¼3 K, and in fields B40.1 T a meta-magnetic transition is encountered. The measurement of the temperature dependence of the electrical resistivity proves a poor metallic state of this compound.
References [1] J. Bauer, J.-F. Halet, J.-Y. Saillard, Coord. Chem. Rev. 178–180 (1998) 723–753. [2] L. Toth, H. Nowotny, F. Benesovsky, E. Rudy., Monatsh. Chem. 92 (1961) 794–802. [3] P. Rogl, J. Nucl. Mater. 73 (1978) 198–203. [4] P. Rogl, J. Nucl. Mater. 79 (1979) 154–158. [5] C. Jardin, O. Oeckler, Hj. Mattausch, A. Simon, J.-F. Halet, J.-Y. Saillard, J. Bauer., Inorg. Chem. 33 (2000) 5895–5900. [6] V. Babizhetskyy, Hj. Mattausch, A. Simon, Z. Anorg. Allg. Chem. 635 (2009) 737–742. [7] B. Horvath, J. Strutz, J. Geyer-Lippmann, G. Horvath, Z. Anorg. Allg. Chem. 483 (1981) 205–218. [8] T. Roisnel, J. Rodrı´guez-Carvajal, Proceedings of the 7th European Powder Diffraction Conference (EPDIC 7), R. Delhez, E. J. Mittemeijer (Eds.), 2000, 118. [9] J. Rodriguez-Carvajal, Phys. B. 192 (1993) 55. [10] V. Babizhetskyy, Hj. Mattausch, A. Simon, Z. Naturforsch 63b (2008) 929–933. [11] J.M. Rowell, R.C. Dynes, Proceedings of the International Conference Ternary Superconductivity, G.K. Shenoy, B.D. Dunlap, F.Y. Fradin (Eds.), 1981, 186. [12] G.T. Meaden, Contemp. Phys. 12 (1971) 313–337.