Crystal structure and physical properties of the new intermetallics REPt4In4 (RE = Gd – Lu, Y)

Intermetallics 32 (2013) 194e199

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Crystal structure and physical properties of the new intermetallics REPt4In4 (RE ¼ Gd e Lu, Y) A. Tursina a, *, S. Nesterenko a, Y. Seropegin a, D. Kaczorowski b a b

Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroclaw, Poland

a r t i c l e i n f o

a b s t r a c t

Article history: Received 27 June 2012 Received in revised form 10 September 2012 Accepted 11 September 2012 Available online 9 October 2012

A new compound ErPt4In4 was synthesized by arc melting and its crystal structure was determined from A, c ¼ 19.807(13)  A, Pearson the single crystal X-ray diffraction data: space group P63/mmc, a ¼ 4.5321(9)  symbol hP18. The new structure type is composed of condensed via side edges Er-centered polyhedra [Pt8In6] and the corrugated slabs of In atoms alternating in the c-direction. A few isostructural compounds were found to form with GdeLu, and Y. The low-temperature physical properties of TbPt4In4, DyPt4In4 and YbPt4In4 were characterized by means of magnetic susceptibility and electrical resistivity measurements. All three compounds exhibit CurieeWeiss paramagnetism, due to the presence of well localized magnetic moments carried on trivalent rare-earth atoms, and metallic character of their electrical conductivity. The compounds TbPt4In4 and DyPt4In4 order magnetically below 8 and 5 K, respectively, whereas YbPt4In4 remains paramagnetic down to 1.7 K. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: A. Rare-earth intermetallics B. Crystal chemistry of intermetallics B. Electrical resistance and other electrical properties B. Magnetic properties

1. Introduction In contrast to the well studied crystal chemistry of light rareearths (RE) platinum indides, characterized by multitude of crystal structure types, the related field of late RE based compounds seems much less recognized. Fragmentary investigations into the ternary phase diagrams REePteIn have yielded the following phases and structure types: RE6Pt12In23 (RE ¼ Nd, Sm, Gd) [1,2], REPtIn (RE ¼ EueTm, Lu) [3e5], R12Pt7In (R ¼ Ce, Pr, Nd, Gd, Ho) [6], YbPtIn4 [7], Dy2Pt7In16 [2], Gd(Tb)3Pt4In12 [8], GdPt2In [9], RE5Pt2In4 (RE ¼ Sc, Y, LaeNd, Sm, GdeTm, Lu) [10]. Herein, we report on the new series of the late rare-earth indides REPt4In4 (RE ¼ Gd e Lu, Y), which crystallize with a new structure type. A few representatives of this novel family of compounds have been characterized regarding their magnetic and electrical transport properties. 2. Experimental The metals used for the sample preparation were rare-earths (GdeLu) and yttrium, platinum and indium ingots of the purity 99.8 and 99.8, 99.99 and 99.999 wt%, respectively. The elemental components were taken in the 1:4:4 and 1:4:5 atomic ratios and arc * Corresponding author. E-mail address: [email protected] (A. Tursina). 0966-9795/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.intermet.2012.09.006

melted several times under purified argon atmosphere. To compensate for the weight losses due to possible volatilization of rare-earth metals the masses were adjusted beforehand for the appropriate extra amounts of rare-earths. The total weight losses after final melting were always smaller than 1 wt%. The products were annealed in evacuated quartz ampoules at 1073 K for one month, and subsequently quenched in cold water. All the materials were stable against air and moisture. The polycrystalline sample compositions were investigated by means of energy dispersive X-ray (EDX) spectroscopy using a scanning electron microscope Carl Zeiss LEO EVO 50XVP equipped with an EDX-spectrometer INCA Energy 450 (Oxford Instruments). For the REPt4In4 samples the EDX data revealed the composition RE11(2)Pt44(2)In45(2), while for the REPt4In5 it was RE10(2)Pt41(2)In49(2). The X-ray examination of the obtained samples was carried out by both powder and single crystal methods. The powder data were collected with a Stoe Stadi-P transmission diffractometer (Cu Ka1radiation), equipped with curved Ge(111) primary beam monochromator and a linear PSD. Single crystals suitable for the data collection were obtained from the crashed samples of DyPt4In4, ErPt4In4 and HoPt4In4. The X-ray intensity data were collected on a CAD4 Enraf Nonius diffractometer (Ag Ka radiation, u/q-scan). An empirical absorption correction was done on the basis of J-scan data [11].

A. Tursina et al. / Intermetallics 32 (2013) 194e199 Table 1 Crystallographic data for REPt4In4 (RE ¼ Dy, Ho, Er) (single crystal data). Empirical formula Space group a ( A) c ( A) V ( A3) Z D (calc) (g/cm3) Abs coeff m (mm1) Extinction coef Range q Range h k l

Reflns collected/ unique/Rint Parameters/reflections with I > 2s(I) GooF on F2 R[F2 > 2s(F2)] wR(F2)

DyPt4In4 P63/mmc 4.5364(18) 19.792(11) 352.7(3) 2 13.202 55.187 e 1.62 e19.99 4  h  5 5  k  0 0  l  24 725/168/0.0656

HoPt4In4 P63/mmc 4.5350(12) 19.800(4) 352.66(15) 2 13.227 55.510 0.0053(3) 1.62 e24.96 6  h  6 6  k  6 29  l  29 2210/289/0.0503

ErPt4In4 P63/mmc 4.5321(9) 19.807(13) 352.3(3) 2 13.261 55.959 0.0089(3) 1.62 e29.93 0h8 8  k  6 0  l  35 2084/452/0.0613

15/131

19/232

18/308

1.270 0.0490 0.1240

1.355 0.0224 0.0425

1.067 0.0219 0.0492

Some attempts to synthesize isotypic REPt4In4 compounds with light rare-earths (LaeSm) appeared unsuccessful. The magnetic properties of TbPt4In4, DyPt4In4 and YbPt4In4 were studied on polycrystalline specimens in the temperature range 1.7e400 K and in external magnetic field up to 5 T using a Quantum Design MPMS-5 SQUID magnetometer. The electrical resistivity was measured on parallelepiped-shaped samples over the temperature interval 5e300 K employing a home-made setup and DC four-point technique. Current and voltage leads were attached to the specimens using silver epoxy paste. 3. Structure refinement Details on the data collection and structure refinement made for the single crystal of ErPt4In4 are presented in Table 1. The obtained crystallographic data are gathered in Table 2 (the positional and thermal displacement parameters) and Table 3 (the interatomic distances). The starting atomic parameters in the structure determination were deduced by direct methods using

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SHELXS-97 [12] and were refined using SHELXL-97 [12] (fullmatrix least-squares on F2) with anisotropic displacement parameters for all atoms. As a check for correct composition and site assignment, the occupancy parameters were refined in a separate series of least squares cycles along with the displacement parameters. All sites were fully occupied within two standard deviations and in the final cycles the ideal occupancies were assumed. The final difference Fourier syntheses revealed a residual peak of 8.8 e/ A3, located at (0, 0, 0). A refinement with indium on this position (In3) resulted in an occupancy of 2.6(7) at.% and led to the composition ErPt4In4.013. In spite of rather short In3eIn1 distances of 2.7418(6)  A, we consider the refinement with the In atom on the 2a (In3) position as the most reliable one. This is because: (i) the coordination environment of the 2a position (CN ¼ 14) would be unusual for Pt atom, and (ii) the presence of extra Er atom is not possible in view of the chemical composition revealed by the EDX analysis. On the other hand, the existence of a compound with the hypothetical composition ErPt4In5 was suggested by the EDX data, and such a phase could be formed if the 2a site is fully filled up by indium. The positional parameters derived for ErPt4In4 were used in the refinements of the single-crystal X-ray diffraction data collected for DyPt4In4 and HoPt4In4 (see Table 1 and Table 2). The results indicated some In occupancy at the 2a site in the latter crystal, while in the former one this position was empty within the experimental accuracy. Because in each case the amount of the extra indium content was found very small (if finite), in the following, the ideal compositions REPt4In4 were assumed to label the investigated samples. Precise determination of the actual homogeneity range in the particular REPt4In4þx compounds might become a subject of separate investigation. For the other REPt4In4 compounds synthesized in this work (RE ¼ Gd, Tb, Tm, Yb, Lu and Y), the lattice parameters were refined from the powder X-ray diffraction data (see Table 4). For the sake of completeness, the table comprises also the results obtained for powder samples of DyPt4In4, HoPt4In4 and ErPt4In4. Apparently, the unit cell volume systematically decreases on passing from the Gdbased to the Lu-based indide. No deviation from the lanthanide contraction is observed for YbPt4In4, hence suggesting that the Yb ions in this compound are trivalent. The volume of YPt4In4 fits between those of TbPt4In4 and DyPt4In4.

Table 2 Atomic coordinates and isotropic-equivalent displacement parameters ( A2) for REPt4In4 (RE ¼ Dy, Ho, Er). Atom DyPt4In4 Dy Pt1 Pt2 In1 In2 HoPt4In4 Ho Pt1 Pt2 In1 In2 In3 ErPt4In4 Er Pt1 Pt2 In1 In2 In3

Wyckoff position

x

y

z

Ueq

Occupancy

2c 4f 4f 4f 4e

1/3 1/3 1/3 1/3 0

2/3 2/3 2/3 2/3 0

1/4 0.09555(11) 0.67971(10) 0.54132(18) 0.1419(2)

0.0025(9) 0.0024(7) 0.0018(7) 0.0029(10) 0.0025(9)

1.0 1.0 1.0 1.0 1.0

2c 4f 4f 4f 4e 2a

1/3 1/3 1/3 1/3 0 0

2/3 2/3 2/3 2/3 0 0

1/4 0.09584(3) 0.67973(2) 0.54148(5) 0.14221(5) 0

0.00412(18) 0.00563(15) 0.00467 0.0064(2) 0.0058(2) 0.010(7)

1.0 1.0 1.0 1.0 1.0 0.060(8)

2c 4f 4f 4f 4e 2a

1/3 1/3 1/3 1/3 0 0

2/3 2/3 2/3 2/3 0 0

1/4 0.09613(2) 0.67989(2) 0.54134(4) 0.14247(4) 0

0.00195(13) 0.00280(10) 0.00219(9) 0.00361(13) 0.00337(14) 0.005(11)

1.0 1.0 1.0 1.0 1.0 0.026(7)

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Table 3 Interatomic distances in the structure of ErPt4In4, d ( A). Atom

To atom

d

Er

6 Pt2 2 Pt1 6 In2 In1 3 In2 3 In1 Er 3 Pt2 3 In2 In1 Pt2 3 Er 3 Pt1 Pt1 3 In3a Pt2 3 Pt1 3 In1 3 In2 3 Pt2 3 Pt1 In3a 3 In1 3 Er In2 6 In1 2 In2 6 Pt1

2.9623(7) 3.048(2) 3.3738(11) 2.723(2) 2.7729(6) 2.8327(7) 3.048(2) 3.0982(8) 2.7195(6) 2.744(2) 2.778(2) 2.9623(7) 3.0982(8) 2.723(2) 2.7418(2) 2.744(2) 2.8327(7) 3.0869(12) 3.2952(12) 2.7195(6) 2.7729(6) 2.822(2) 3.2952(12) 3.3738(11) 4.282(2) 2.7418(6) 2.822(2) 3.2361(9)

Pt1

Pt2

In1

In2

In3a

a

Occupancy of In3 position is equal to 2.6%.

4. Crystal chemistry The rare-earth platinum indides REPt4In4 (RE ¼ Gd e Lu, Y) crystallize with a structure of own type (space group P63/mmc, Pearson symbol hP18). The detailed description of the key features of this new structure will be presented for ErPt4In4 that can be considered as a prototype compound. The crystal lattice of ErPt4In4 is composed of condensed via side edges Er-centered polyhedra [Pt8In6] and the corrugated slabs of In atoms alternating in the c-direction (see Fig. 1). Basically, in the unit cell there are one erbium site (2c), two platinum sites (both 4f), and two indium sites (In1 4f and In2 4e). In the crystal investigated, an additional In3 site (2a) was occupied by 2.6(7) %. The coordination polyhedra of all the atoms are presented in Fig. 2. The Er atom is coordinated by six platinum atoms with interatomic distances of 2.9623(7)  A, two platinum atoms with distances of 3.048(2)  A, and six indium atoms with interatomic distances of 3.3738(11)  A. The Pt1 and Pt2 atoms have identical coordination environment of distorted cube centered on three neighbor faces by three additional platinum atoms: Pt1[ErIn7Pt3] and Pt2[Er3PtIn4Pt3]. The ranges of interatomic distances in these two polyhedra are very

Table 4 Cell parameters of REPt4In4 (RE ¼ Gd e Lu, Y) from powder X-ray data. Compound

a,  A

c,  A

V,  A3

GdPt4In4 TbPt4In4 DyPt4In4 HoPt4In4 ErPt4In4 TmPt4In4 YbPt4In4 LuPt4In4 YPt4In4

4.5538(13) 4.5502(10) 4.5492(13) 4.5479(13) 4.5442(11) 4.5412(14) 4.5354(10) 4.5324(9) 4.5486(16)

19.905(4) 19.889(4) 19.879(5) 19.861(4) 19.838(4) 19.818(5) 19.800(4) 19.776(3) 19.900(5)

359.48(13) 356.63(10) 356.28(13) 355.76(12) 354.76(11) 353.94(14) 352.73(10) 351.82(8) 356.57(15)

Fig. 1. View of the crystal structure of ErPt4In4. Erbium atoms are drawn as big green circles, platinum atoms as blue circles, and indium atoms as pink circles. For the sake of clarity the In3 atoms were omitted. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

close (from 2.723(2)  A to 3.0982(8)  A for Pt1 and from 2.7195(6)  A to 3.0982(8)  A for Pt2) with Pt1ePt2 separation being equal to 3.0982(8)  A. The latter distance is the shortest PtePt spacing for the Pt1 atom. In turn, Pt2 has a shorter Pt2ePt2 distance of 2.778(2)  A that is nearly equal to the PtePt distance in fcc platinum (2.773  A) [13]. Interestingly, fairly similar difference in the interatomic distances, which involve two noble-metal sites was found before in the crystal lattice of EuAu3In3, where gold zigezag chains are formed due to Au1eAu1spacing of 2.79  A [14]. Coordination environment of the atoms In1, In2, and In3 can be presented as polyhedra with 11, 12, and 14 apexes, respectively (Fig. 2). In3 with low occupancy of 2.6(7)% was not included in coordination polyhedra for In1 and In2. The values of interatomic distances within the three indium polyhedra fall into the range from 2.7195(6)  A to 3.3738(11)  A (Table 3). As can be inferred from Fig. 3, the crystal structure of ErPt4In4 can be described as an ordered stacking of two types of building blocks. The proposed structural model consists of two ErPt2 layers denoted as A, and four PtIn2 layers denoted as B, arranged within the unit cell in the sequence [BeA0 eB00 eB000 eAeB0 ]. Building slabs B000 and B00 are generated from slabs B0 and B by mirror plane m at z ¼ 1/4 and 3/4, respectively, whereas slabs A, B and B00 are inverted with respect to slabs A0 , B0 and B000 , respectively. Interestingly, the layer A is of the CaIn2-type [15], while the layer B is similar to that observed in the NiAs-type [16] structure.

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Fig. 2. Coordination polyhedra of all the atoms in the crystal structure of ErPt4In4. Erbium atoms are drawn as big green circles, platinum atoms as blue circles, and indium atoms as pink circles. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

5. Physical behavior The magnetic properties of polycrystalline samples of TbPt4In4, DyPt4In4 and YbPt4In4 are summarized in Fig. 4. For all three compounds the inverse magnetic susceptibility is a linear function of temperature over extended temperature ranges below 400 K. The CurieeWeiss law applied to the experimental data above 50 K

yielded the effective magnetic moment meff ¼ 11.08, 9.94 and 4.49 mB for the Tb-, Dy- and Yb-based indide, respectively. These values are fairly close to the theoretical values of meff calculated in the frame of the Russell-Saunders LS coupling scenario for free trivalent rare-earth ions (10.65, 9.72 and 4.54 mB, respectively). The result obtained for YbPt4In4 corroborates thus the valence state indicated by the adherence of the unit cell volume of this compound to the

Fig. 3. (a) Projection of the crystal structure of ErPt4In4 along the crystallographic a axis. (b) and (c) Projection of the structures of CaIn2 and NiAs along the b axis, respectively. Erbium and calcium atoms are drawn as big green circles, platinum and nickel atoms as blue circles, indium and arsenic atoms as pink circles. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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lanthanide contraction (see above). The paramagnetic Curie temperatures derived from the CurieeWeiss fits are equal to 3.1, 0.6 and 1.9 K for TbPt4In4, DyPt4In4 and YbPt4In4, respectively. As displayed in the upper insets to Fig. 4, the low-temperature dependencies of the magnetization in TbPt4In4 and DyPt4In4 exhibit pronounced anomalies manifesting the onsets of longrange magnetically-ordered state. Characteristic shape of these s(T) variations suggests that the magnetic order has predominantly a ferromagnetic-like nature. The critical temperatures, defined here as singularities in the temperature derivative of the magnetization ds/dT(T), amount to 8 and 5 K for the Tb- and Dy-based compound, respectively. The presumption on the ferromagnetic-like ordering finds strong support in the behavior of the magnetization isotherm measured deeply in the ordered state (see lower insets to Fig. 4). The s(B) variations are distinctly curvilinear, with a very rapid rise in weak magnetic fields, clear tendency for saturation around 0.5 T, followed by an inflection in stronger fields (about 1 and 2.5 T for TbPt4In4 and DyPt4In4, respectively), and then another region of saturation. For both compounds the magnetization measured in 5 T is nearly twice that observed below the inflection point. Its maximum magnitude corresponds to the magnetic moment of 5.1 and 3.3 mB for the Tb- and Dy-based compound, respectively. These values are distinctly smaller than the free ion ordered magnetic moments (10 and 9 mB, respectively), presumably due to crystal field effect. Fig. 5 presents the temperature dependencies of the electrical resistivity of TbPt4In4, DyPt4In4 and YbPt4In4. All these compounds exhibit metallic character of electronic conduction with the resistivity being nearly a linear function of temperature over extended regions below the room temperature. Some curvature in r(T) arises from a combined effect of scattering the conduction electrons on phonons and crystalline electric field excitations. For each compound, the r(T) curve shows a low-temperature plateau at a value that is a sum of residual scattering on static defects (crystal lattice imperfections) and contribution due to spin disorder. The ratio of the resistivity measured at 300 K (42, 22 and 33 mU cm for TbPt4In4, DyPt4In4 and YbPt4In4, respectively) to that observed at the lowest temperatures (18, 6 and 7 mU cm for TbPt4In4, DyPt4In4 and YbPt4In4, respectively) spans from about 2e5, as usually derived for good-quality polycrystalline metallic samples. In the case of TbPt4In4, the r(T) variation shows an anomaly at the

Fig. 4. Temperature dependencies of the inverse molar magnetic susceptibility of (a) TbPt4In4, (b) DyPt4In4 and (c) YbPt4In4. The solid straight lines represent the leastsquares fits of the CurieeWeiss formula to the experimental data. Lower insets: magnetic field variations of the isothermal magnetization taken at 1.72 K with increasing (full circles) and decreasing (open circles) field strength. Upper insets: lowtemperature variations of the magnetization (magnetic susceptibility for YbPt4In4) measured in a field of 0.1 T upon cooling the specimen in zero field. Fig. 5. Temperature dependencies of the electrical resistivity of TbPt4In4, DyPt4In4 and YbPt4In4. Inset: low-temperature behavior of the resistivity of TbPt4In4.

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magnetic phase transition at 8 K that has a shape characteristic of ferromagnets (see the inset to Fig. 5), in line with the magnetic data. For DyPt4In4 the onset of the magnetic ordering at 5 K is slightly beyond the range of the performed electrical measurements, thus its r(T) is featureless down to the lowest temperature reached in this study.

6. Conclusions The compound ErPt4In4 crystallizes with a novel structure type composed of condensed via side edges Er-centered polyhedra [Pt8In6] and the corrugated slabs of In atoms alternating in the cdirection. Large cavities with the center at (0, 0, 0) within the Inslabs can be filled by extra indium atoms providing the composition of ErPt4In5, which likely corresponds to the edge of the possible solid solution region. Several isostructural compounds were found with GdeLu, and Y, whereas REPt4In4 compounds with light rareearths didn’t form. The compounds TbPt4In4, DyPt4In4 and YbPt4In4 are Curiee Weiss paramagnets, due to the presence of well localized magnetic moments carried on trivalent rare-earth atoms. The Tband Dy-based indides order magnetically below 8 and 5 K, respectively, while YbPt4In4 does not undergo any magnetic phase transition down to 1.7 K. All three ternaries studied exhibit metallic character of electrical conductivity.

Acknowledgment This work was supported by the RFBR projects 11-03-00957a and 11-03-01191a.

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