Journal of Alloys and Compounds 587 (2014) 783–789

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Journal of Alloys and Compounds

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Systematics and anomalies in formation and crystal structures of RScSband R3Sc2Sb3 rare earth compounds

0925-8388/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.jallcom.2013.10.197

⇑ Corresponding author at: Department of Chemistry, University of Genova, ViaDodecaneso 31, 16146 Genova, Italy. Tel.: +39 010 3536081; fax: +39 010 3536102.

E-mail address: chimfis@chimica.unige.it (P. Manfrinetti).

A. Provino a,b, D. Paudyal b, A.V. Morozkin c, P. Manfrinetti a,b,⇑, K.A. Gschneidner Jr. b,d

a Department of Chemistry, University of Genova, Via Dodecaneso 31, 16146 Genova, Italyb The Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, IA 50011-3020, USAc Department of Chemistry, Moscow State University, Leninskie Gory, Moscow GSP-2 119992, Russiad Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011-2300, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 3 October 2013Received in revised form 23 October 2013Accepted 25 October 2013Available online 4 November 2013

Keywords:Rare earth ternary compoundsRare earth scandium antimonidesCrystal structuresFirst principles calculations

A systematic study of RScSb (R = rare earth) ternary alloys has been carried out by X-ray diffraction, opti-cal and electron microscopy and microprobe analysis. As a result, the new equiatomic RScSb (R = La–Nd,Sm, Gd–Tm, Lu, Y) compounds have been identified. No formation of equiatomic 1:1:1 phases has beenobserved for Eu and Yb. It has been found the RScSb compounds crystallize in two different crystal struc-tures. The phases formed by the lighter R (La–Nd, Sm) adopt the CeScSi-type (tetragonal tI12, I4/mmm, anordered variant of the La2Sb-type), while the ones containing the heavier R (R = Gd–Tm, Lu, Y) crystallizewith the CeFeSi-type (tetragonal tP6, P4/nmm, an ordered derivative of the Cu2Sb-type). The latter phaseswere expected to be dimorphic, thus suggesting they might be polymorphic having the CeScSi-type as thelow-temperature form; however, no proof of this was found in the course of the present study.

Besides the equiatomic compounds, the R3Sc2Sb3 phases have also been identified. They form fromGd-Tm, Lu, included Y, and crystallize in the b-Yb5Sb3-type (orthorhombic oP32, Pnma). The observed lat-tice parameters, unit cell volume and volume contraction, for both the series of compounds, decrease ongoing from La to Lu following the lanthanide contraction trend. First principles calculations pinpoint thatthe differences in the electronic structure are directly related to the differences in the crystal structures ofthese compounds.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

The ternary intermetallic systems R–T–X (where R = rare earth,T = transition metal, X = p-block element) are among the mostinvestigated for the search of new and useful magnetic materials[1]. In these systems, the most common phases present are theequiatomic compounds RTX [2,3]. Among them, the ternary inter-metallic RScSi, RScGe [4–8], RTiGe [9,10], R(Ti1�xTx)Ge [11] andRZrSb [12,13] have been found to show high or relatively highmagnetic-ordering temperatures, in some cases even higher thanthe Curie temperature of Gd metal (TC = 293 K) [14], often with fer-romagnetic ordering and large coercive fields. In particular, thephases formed by Nd, Sm, Gd and Tb, such as SmScSi and SmScGe[15], GdScSi and GdScGe [6,7], and the two dimorphic forms ofGdTiGe [16] have shown the highest transition temperatures. Thetransition temperatures TC/TN of some of these compounds arelisted in Table 1. Strong doubt remains about the existence of theGdTiSb compound, reported with a CeFeSi-type structure with

anomalously large lattice parameters and a TC = 268 K [17]; for thisreason this data is not added in Table 1. All these phases are knownto crystallize mainly with the tetragonal CeScSi-type (tI12, I4/mmm, ordered variant of the La2Sb-type). The magnetic structuresof some RScGe (R = Pr, Nd, Tb) [18], RTiGe (Pr, Nd, Tb, Ho, Er)[19,20], RTi0.85Mo0.15Ge (R = Tb, Er) [21], RZrSb (R = Tb, Ho, Er)[22] in the magnetically ordered state(s), have been more recentlystudied by neutron diffraction.

In the present investigation a study on the R–Sc–Sb ternary sys-tems has been carried out; as a result, the new equiatomic com-pounds RScSb (R = La–Nd, Sm, Gd-Lu, Y), have been discovered.During this work, besides the above equiatomic compounds anew series of phases has also been identified: the R3Sc2Sb3

(R = Gd–Tm, Lu, Y) compounds. Here we present the results ob-tained on the determination of their crystal structure. In addition,first principles electronic structure calculations have also been per-formed for some representative compounds to correlate electronicstructure and crystal structure to better understand the thermody-namic stability and physics of these phases. Preliminary data havebeen recently presented at the TMS2011 annual conference [23].Measurements of some of the physical and magnetic propertiesof these compounds are still in progress; the results will be

Table 1Magnetic ordering temperature(s) TC/TN of some RTX compounds.

RTX Transition temperature (K) References

SmScSi TC = 270 [15]GdScSi TC = 318 [8]

PrScGe TN = 140 [18]NdScGe TC = 200 [18]SmScGe TC = 270 [15]GdScGe TC = 350 [6]TbScGe TC = 216 [18]

GdTiGe TN = 412 [16]GdTiGe TC = 376 [16]

GdZrSb TC = 37 [14]

Fig. 1. A sketch of the CeScSi and CeFeSi structure types of the RScSb compounds. For both5 Sb atoms, are highlighted.

Table 2Atomic coordinates, equivalent isotropic displacement parameters and anisotropic disc = 16.541(5) Å, space group I4/mmm (wR2 = 0.094, R1 = 0.039).

Atom Site Atomic coordinates

x y z

Ce 4e 0 0 0.32437(5)Sca 8j 0.0701(11) 1/2 0Sb 4e 0 0 0.12451(7)

a occ = 0.5.

Table 3Atomic coordinates, equivalent isotropic displacement parameters and anisotropic dispc = 16.344(5) Å, space group I4/mmm (wR2 = 0.091, R1 = 0.035).

Atom Site Atomic coordinates

x y z

Nd 4e 0 0 0.32348(9)Sca 8j 0.0834(15) 1/2 0Sb 4e 0 0 0.12765(9)

a occ = 0.5.

784 A. Provino et al. / Journal of Alloys and Compounds 587 (2014) 783–789

reported later. Neutron diffraction studies of the magnetic struc-ture of the RScSb phases, with R = Ce, Pr, Nd and Tb, are also nowunderway.

2. Experimental

The samples (except the ones containing the volatile Sm, Eu and Yb) were pre-pared by arc melting the elements under a pure Argon atmosphere. The rare earthmetals and antimony were commercial products; stated purities were 99.9% for therare earths (with respect to the other rare earths only, interstitial impurities andnon-rare earth metals concentrations were not given) and 99.999 wt.% for Sb. TheR elements were however considered as 99.0 wt.% [24], while 1.5 wt.% excess ofSb (referred to the weight of element) was added to compensate for the averageweight loss observed during melting of the first alloys, due to the volatility of thiselement. The light R metals were weighed and handled in a glove box under an inert

the structures the square pyramid polyhedra formed by R atoms, coordinating with

placement parameters (U23 = U13 = U12 = 0) of CeScSb (CeScSi-type); a = 4.466(1) Å,

Ueq (Å) U11 U22 U33

0.0069(4) 0.0055(5) U11 0.0099(5)0.0099(13) 0.014(3) 0.002(2) 0.0136(15)0.0071(4) 0.0052(5) U11 0.0109(7)

lacement parameters (U23 = U13 = U12 = 0) of NdScSb (CeScSi-type); a = 4.392(1) Å,

Ueq (Å) U11 U22 U33

0.0096(4) 0.0100(5) U11 0.0089(6)0.0075(13) 0.011(3) 0.006(3) 0.006(2)0.0056(4) 0.0059(5) U11 0.0050(7)

Fig. 2. Rietveld refinement of GdScSb (CeFeSi-type, tP6 – P4/nmm); observed andcalculated X-ray powder patterns (Cu Ka1) (Rwp = 9.36%, RB = 0.63%, v2 = 0.96%).

Table 4Fractional atomic coordinates of GdScSb (CeFeSi-type, tP6 – P4/nmm) obtained fromRietveld refinement (Rwp = 9.36%, RB = 0.63%, v2 = 0.96%).

Atoms Wyckoff notation Atomic coordinates Occupation

x y z

Gd 2c 1/4 1/4 0.6564(3) 1Sc 2a 3/4 1/4 0 1Sb 2c 1/4 1/4 0.2664(4) 1

a = 4.3402(1) Å, c = 8.2154(1) Å.

Fig. 3. The lattice parameters (a, c) (a) and observed unit cell volume (Vobs) (b)versus the R3+ ionic radius for both the CeFeSi and CeScSi structure types formed bythe RScSb compounds.

A. Provino et al. / Journal of Alloys and Compounds 587 (2014) 783–789 785

atmosphere. The total mass of samples was � 2–3 g. The buttons were melted threetimes, turning them upside down each time. They were then wrapped in Ta foil,sealed under vacuum in quartz ampoules and annealed at 900–1000 �C for 1–2 weeks; then slowly cooled down to room temperature. The alloys with nominalcomposition SmScSb, EuScSb and YbScSb were synthesized by high-frequencyinduction melting. The elements were sealed in an outgassed Ta crucible under aHe atmosphere, slowly heated up to � 1500 �C, kept 10 min at this temperature,then slowly cooled down. The resulting samples appeared crystalline, brittle, witha dark-grey color, and having a metallic and lustrous appearance.

The alloys were examined by optical (LOM) and electron microscopy (SEM) andthe phase composition determined by electron probe microanalysis (EDS). Micro-graphic specimens were prepared by standard techniques; no etching agent wasnecessary to reveal the phases, because the samples were moisture sensitive. TheX-ray analyses were performed by powder diffractometric methods. For the singlecrystal work, some crystals have been isolated from the Ce and Nd samples and,after being checked by Laue method, a data collection was performed by aBruker–Nonius MACH3 diffractometer (graphite monochromated Mo Ka radiation).

Table 5Lattice parameters (a, c), unit cell volume (Vobs) and volume contraction (DV%) for the RS

RScSb Crystallographic data

Prototype Pearson Symbol Space group

LaScSb CeScSi tI12 I4/mmmCeScSb CeScSi tI12 I4/mmmPrScSb CeScSi tI12 I4/mmmNdScSb CeScSi tI12 I4/mmmSmScSb CeScSi tI12 I4/mmmGdScSb CeFeSi tP6 P4/nmmTbScSb CeFeSi tP6 P4/nmmDyScSb CeFeSi tP6 P4/nmmHoScSb CeFeSi tP6 P4/nmmErScSb CeFeSi tP6 P4/nmmTmScSb CeFeSi tP6 P4/nmmLuScSb CeFeSi tP6 P4/nmmYScSb CeFeSi tP6 P4/nmm

Both a Guinier–Stoe camera (Cu Ka1 radiation, Si as internal standard, a = 5.4308 Å)and a X’Pert PANalytical diffractometer (Cu Ka1 radiation, Si monocrystal as sampleholder) were used for the powder diffraction investigation.

cSb compounds (R = La–Nd, Sm, Gd–Tm, Lu, Y).

Lattice parameters Vcell (Å3) DV (%)

a (Å) c (Å)

4.508(1) 16.643(3) 338.2(1) 8.54.468(1) 16.503(2) 329.4(1) 8.24.438(1) 16.427(2) 323.6(1) 9.64.420(1) 16.420(5) 320.8(1) 10.04.379(1) 16.285(2) 312.3(1) 11.44.338(1) 8.202(2) 154.4(1) 12.44.326(1) 8.159(4) 152.7(1) 12.44.299(1) 8.114(5) 150.0(1) 13.34.288(1) 8.088(4) 148.7(1) 13.64.281(2) 8.064(6) 147.8(2) 13.74.283(1) 8.056(4) 147.8(1) 13.24.266(1) 8.002(5) 145.6(1) 13.84.294(1) 8.105(5) 149.4(1) 15.2

Fig. 4. The contraction volume (DV) versus the R3+ ionic radius for all the RScSbcompounds; the dashed line is a fit (quadratic function) of the data except for Laand Y (a). The observed unit cell volume divided by the contraction volume plottedversus the R3+ ionic radius divided by the contraction volume, for the RScSbcompounds; the dashed lines are linear fits (b).

Table 6Atomic coordinates of Gd3Sc2Sb3 (b-Yb5Sb3-type oP32, Pnma) obtained from Rietveld refin

Gd3Sc2Sb3a Wyckoff notation Atomic coordinate

x

Gd1 4c 0.2265(5)Gd2 4c 0.2874(3)M1 4c 0.007(2)M2 8d 0.0656(5)Sb1 8d 0.3339(3)Sb1 4c 0.4756(5)

a = 11.6425(5) Å, b = 9.0338(4) Å, c = 7.8951(4) Å.M1 = Gd0.2Sc0.8, M2 = Gd0.4Sc0.6.

a Crystallographic data used with permission of JCPDS – International Centre for Diffr

Table 7Lattice parameters (a, b, c), unit cell volume (Vcell) and formation volume (DV%) for the R3

R3Sc2Sb3 Crystallographic data

Prototype Pearson symbol Space group

Gd3Sc2Sb3 Yb5Sb3 oP32 PnmaTb3Sc2Sb3 Yb5Sb3 oP32 PnmaDy3Sc2Sb3 Yb5Sb3 oP32 PnmaHo3Sc2Sb3 Yb5Sb3 oP32 PnmaEr3Sc2Sb3 Yb5Sb3 oP32 PnmaTm3Sc2Sb3 Yb5Sb3 oP32 PnmaLu3Sc2Sb3 Yb5Sb3 oP32 PnmaY3Sc2Sb3 Yb5Sb3 oP32 Pnma

786 A. Provino et al. / Journal of Alloys and Compounds 587 (2014) 783–789

3. Results and discussion

3.1. Crystal structure

3.1.1. RScSbThe X-ray powder patterns have been indexed by comparing

them with patterns calculated by the LAZY PULVERIX program[25]; the lattice parameters have been calculated by means ofleast-square methods (handmade software). These analysesshowed that RScSb compounds crystallize in two different crystalstructures. The compounds formed by the light R (La–Nd, Sm)adopt the CeScSi-type, an ordered variant of the La2Sb-type (tI12,I4/mmm), while the ones containing the heavier R (Gd-Tm, Lu, Y)crystallize in the CeFeSi-type, an ordered derivative of the Cu2Sb-type (tP6, P4/nmm). The formation of the two different crystalstructures is likely due both to a difference in the rare earth atomicdimension and a change in the electronegativity (slightly increas-ing from the lighter rare earths to the heavier ones). In the caseof Eu and Yb we did not observe formation of equiatomic ‘EuScSb’and ‘YbScSb’ phases, possibly because of the divalent character ofthese two metals. These two well known crystal structures are verysimilar; they can be considered as built up by one layer of Sc alter-nating with two layers of R–Sb along the c-axis. An evaluation ofthe interatomic distances shows the shortest distances are be-tween R�Sb, Sc�Sb and Sc�Sc atoms (in NdScSb they are3.207 Å, 3.029 Å and 3.106 Å, respectively; in GdScSb they are3.126 Å, 3.106 Å and 3.069 Å, respectively), while there are notR�R, R�Sc and Sb�Sb bonds. A schematic of both these two crystalstructures is shown in Fig. 1, where the coordination polyhedra (asquare pyramid) formed by 5 Sb atoms around the R atoms arehighlighted. Single crystal investigations performed on both theCeScSb (Table 2) and NdScSb (Table 3) compounds have confirmedthe CeScSi-type for the RScSb phases formed by the light rareearths. However, from this work neither good nor conclusive re-sults could be obtained: refinement of these data apparently leadsto satisfactory results only after permitting the Sc atom to slightlymove from the 4c position (0, 1/2, 0) to the 8j one (x, 1/2, 0) with an

ement (Rwp = 0.14, RB = 0.04, GoF = 2.33).

s Occupation

y z

1/4 0.8227(7) 11/4 0.3366(7) 11/4 0.516(2) 10.0547(6) 0.1956(8) 10.0070(6) 0.0646(5) 11/4 0.5941(7) 1

action Data.

Sc2Sb3 compounds (R = Gd–Tm, Lu, Y).

Lattice parameters Vcell (Å3) DV (%)

a (Å) b (Å) c (Å)

11.626(4) 9.042(3) 7.911(3) 831.6(1) 13.111.598(2) 9.023(2) 7.888(2) 825.5(3) 12.711.515(3) 8.965(2) 7.842(2) 809.5(3) 13.711.476(2) 8.941(2) 7.826(2) 803.0(3) 13.911.432(2) 8.920(2) 7.810(2) 796.4(2) 14.111.401(4) 8.901(3) 7.794(3) 790.9(5) 14.111.311(2) 8.857(2) 7.761(2) 777.5(3) 14.911.532(3) 8.939(2) 7.846(2) 808.8(3) 15.6

Fig. 5. The lattice parameters (a, b, c) (a) and observed unit cell volume (Vobs)(b) versus the R3+ ionic radius for the R3Sc2Sb3 compounds forming in theYb5Sb3 structure type.

A. Provino et al. / Journal of Alloys and Compounds 587 (2014) 783–789 787

occupational factor of 0.5 (Tables 2 and 3). Further details aboutthe crystal structure will be reported in future work along withthe results obtained by a neutron diffraction investigation carriedout both to refine the crystal and magnetic structures of thesephases.

It is worthy to recall that powder patterns of the two crystaltypes are similar to each other and in the patterns of the heavy Ronly the appearance of the [102] reflection, and of a few morereflections pertaining to a primitive lattice, and the quasi absenceof the [105] one, lead to the CeFeSi structure type. A Rietveldrefinement performed for the GdScSb compound confirmed thiscrystal structure (Fig. 2); the positional parameters are given inTable 4. It is also valid to mention that since the Gd compoundwas the first member of the series crystallizing with the primitivetetragonal lattice of the CeFeSi-type, and in view of the dimor-phism reported for GdTiGe [17], GdScSb could also have adoptedthe body-centered CeScSi-type cell. Therefore, three differentheat-treatment attempts were performed on one sample: afterannealing it at 1000 �C for 3 days + water-quench, two parts of itwere then also retreated at 700 �C for 7 days + air cooled and at500 �C for 14 days + slow cooling, respectively, in order to see ifit was possible to retain this low-temperature form, but all of themgave negative results.

The lattice parameters, a and c, observed unit cell volume, Vobs,and volume contraction, DV% {defined as DV = [(Vcalc � Vobs)/Vcalc]� 100, where Vcalc is the volume of the compound calculated fromthe atomic volumes of the individual atoms [26]} for all the RScSbcompounds are listed in Table 5; the plots in Fig. 3a and b show thetrend of the lattice parameters and unit cell volume, respectively,for the RScSb compounds versus the R3+ ionic radius [27,28]. Boththe lattice parameters and unit cell volume decrease on going fromLaScSb to LuScSb, accordingly with the lanthanide contraction. Aplot of the volume contraction, DV, versus the R3+ ionic radius isshown in Fig. 4a. The DV values increase on going from the lightR to the heavier ones by following a curved trend (quadratic fit);similar trends were also observed for other series of binary and ter-nary R compounds (RZnSn [29], RZnGe, [30], RMgSn [31] andRMgPb [32], as some examples). A DV increasing on going fromthe light R compounds to the heavier ones suggests a higher freeenergy of formation for the late (heavy) lanthanide compounds[33]. Fig. 4b shows a plot of the observed unit cell volume dividedby volume of formation (Vobs/DV%) plotted versus the R3+ ionic ra-dius divided by percent volume of formation (R3+/DV%) for all theRScSb phases. As already observed for RMgSn and RMgPb com-pounds [31,32], the data points fall on a straight line, but this timefollowing two different trends depending on the crystal structureadopted; this is because the CeScSi-type compounds have 4 formu-lae per cell, while the CeFeSi-type compounds have 2 formulae percell. However, the slopes of the two linear trends are noticeablydifferent; if the slope of these plots is directly connected to thethermodynamic stability of the compounds, and on how fast itchanges on going through the series of isostructural compounds,we could suppose the stability of the CeScSi-type phases (fromLa to Sm) decreases faster than that of the CeFeSi-type phases(from Gd to Lu and Y).

3.1.2. R3Sc2Sb3

While the equiatomic samples prepared for the light R resultedin a nearly single phase, containing only a few percent of the binaryR4Sb3 (anti-Th3P4 structure type) as separate grains, in the alloysfrom Gd through Lu and Y, even after annealing, large and increas-ing amounts of a secondary phase were observed. For this lattermicroprobe results have indicated a composition of aboutR33–35Sc27–30Sb37–38, i.e. a stoichiometry very close to (R1�xScx)5Sb3.The existence of the known Yb5Sb3, with its own structure (ortho-rhombic b-Yb5Sb3 structure type, also anti-Y2HfS5-type, oP32,

Pnma; Z = 4), suggested for these new phases this crystal structure;X-ray intensity calculations well agreed with this hypothesis.These new ternary compounds have been found to form from Gdto Lu, including Y, with an estimated compositional range x, overthe stoichiometry R1�xScx, of about ± 1.5 at.%; they are hereaftercalled R3Sc2Sb3 phase. All of them crystallize in the Yb5Sb3 struc-ture type. This was further confirmed by a Rietveld refinement per-formed on the compound Gd3Sc2Sb3; the atomic positions asobtained for this phase are collected in Table 6. The cell parameters(a, b, c), unit cell volume (Vobs) and volume contraction (DV), forthe R3Sc2Sb3 phases are listed in Table 7. They decrease on goingfrom La to Lu, again well following the lanthanide contraction trend(Fig. 5a and b). The formation of homologous ‘3:2:3’ compounds forthe light R and Yb will be investigated in a near future. A largenumber of new ternary phases adopting this structural prototypehave been identified in the last decade, like the hydrogen stabilizedA5(Sb,Bi)3H (A = Ca, Sr, Sm, Eu, Yb) phases [34,35], the R5Tx

(Sb,Bi)3�x (T = transition metal) [36,37] and R5XBi2 (X = Si, Ge)[38] compounds, to cite some.

0

2

4

6

8

10

12

-10 -8 -6 -4 -2 0

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tate

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E - EF (eV)

0

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CeScSi−type LaScSb

LSDA

CeScSi−type GdScSb

LSDA+U

CeFeSi−type GdScSb

LSDA+ULuScSbCeFeSi−type

LSDA

(c)

(a)

La

GdLu

Sc

ScSc

Sb

SbSb

GdScSb

(d)

(b)

Fig. 6. The atom projected density of states (DOS) of LaScSb (a), GdScSb (b and c), and LuScSb (d) compounds.

0

2

4

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14

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15

20

25

30

35

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tate

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ll)

E - EF (eV)

YScSb

YScSb

YScSb Y3 Sc2 Sb3

Fig. 7. The atom projected density of states (DOS) of YScSb (left panel) and Y3Sc2Sb3 (right panel) compounds.

788 A. Provino et al. / Journal of Alloys and Compounds 587 (2014) 783–789

3.2. Theoretical investigations

Local spin density approximation (LSDA) for LaScSb, LuScSb, andY3Sc2Sb3 and LSDA including Hubbard U, LSDA + U [39]calculationsfor GdScSb have been performed in conjunction with the tight-binding linear muffin tin orbital band structure method [40]. Theconventional von Barth and Hedin exchange correlation potentialshave been used; the k-space integration being performed with32 � 32 � 32 Brillouin zone mesh. This large Brillouin zone meshwas used to make sure the convergence of total energy and totalcharge in the studied systems. It should also be noted that the tightbinding linear muffin tin orbital method is accurate enough for thecompact crystal structure systems including the systems reportedhere compared to the open structure systems where one needs touse full potential methods.

For GdScSb, we have used LSDA + U which shifts occupied 4fstates below the Fermi level (��8.5 eV) and unoccupied 4f statesabove the Fermi level. For the La compound there are no occupied4f states but for Lu compound the 4f states are positioned slightly

below �5 eV. Since 4f states are unoccupied in the La and fullyoccupied in the Lu compounds, the LSDA approach works fine.On the other hand, since the 4f states are half filled in Gd com-pounds, the LSDA + U (with U = 6.7 eV and J = 0.7 eV) is consideredto be the best approach for the correct positioning of occupied andunoccupied 4f states.

In these calculations, the actual experimental CeScSi-typecrystal structure for LaScSb and CeFeSi-type crystal structure forLuScSb have been used. On the other hand, for GdScSb both hypo-thetical CeScSi-type and actual CeFeSi-type have been used forcomparison. The CeFeSi-type GdScSb has lower total energycompared to CeScSi-type GdScSb indicating CeFeSi-type as thestable crystal structure as found from the experiment, see Fig. 6.However the small energy difference (�5.6 eV/cell) between CeFe-Si-type and CeScSi-type in GdScSb indicates that GdScSb is indeedon the borderline in the formation of these structures in thecompounds containing light and heavy rare earths. The unstableCeScSi-type structure may be attributed to the Fermi level lyingat the narrow density of states peak, while the density of states

A. Provino et al. / Journal of Alloys and Compounds 587 (2014) 783–789 789

are pushed towards lower energy for stable CeFeSi-type phase. InFig. 7, the atom projected density of states of Y3Sc2Sb3 and YScSbare shown. Y3Sc2Sb3 has delocalized (broad) bands at and belowthe Fermi level compared to the localized (narrow) bands in thedifferent energy locations of YScSb. The differences in the bandstructure in these compounds reflect the differences in the crystalstructure. Compared to GdScSb within the CeFeSi-type structure,the conduction electron (spd) bands of YScSb and LuScSb becomemore localized. This indicates that the lanthanide contractiondrives the spd bands to become more localized in YScSb and LuScSbcompounds.

Acknowledgments

Part of this work was performed at the Ames Laboratory. TheAmes Laboratory is operated by Iowa State University of Scienceand Technology for the U S Department of Energy; the work wassupported by the Office of Basic Energy Sciences, Materials Scienceand Engineering Division of the Office of Science under ContractNo. DE-AC02-07CH11358. Crystallographic data of Gd3Sc2Sb3 wereused with permission of JCPDS – International Centre for Diffrac-tion Data (ICDD Grant No. 05-07). A. P. and P. M. would like tothank E. Caltvedt for carefully reading the manuscript.

References

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