lable at ScienceDirect

Intermetallics 43 (2013) 103e109

Contents lists avai

Intermetallics

journal homepage: www.elsevier .com/locate/ intermet

Contribution to the investigation of the ternary EueAgeAl system

Yuriy Verbovytskyy*, António Pereira GonçalvesCampus Tecnológico e Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa/CFMC-UL, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal

a r t i c l e i n f o

Article history:Received 23 June 2013Received in revised form16 July 2013Accepted 19 July 2013Available online

Keywords:A. Ternary alloy systemsB. Phase diagramsB. Phase identificationF. DiffractionF. Electron microscopy, scanning

* Corresponding author. Tel.: þ351 219946184; fax:E-mail address: yuryvv@bigmir.net (Y. Verbovytsk

0966-9795/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.intermet.2013.07.013

a b s t r a c t

The interaction of the components from the EueAgeAl system at 500 �C, in the concentration region of0e33.3 at.% Eu, was investigated by X-ray diffraction, metallographic and microprobe analysis. Besidesthe known ternary intermetallic phases (EuAg3þxAl8�x and EuAg4þxAl7�x), six new ones (EuAg6þxAl7�x,Eu2Ag15�xAl2þx, Eu3Ag13�xAl8þx, EuAg1�xAl2þx, EuAg1þxAl2�x and EuAg1�xAl1þx) were revealed to bestable at the temperature investigated. Furthermore, extended solid solutions based on the binaryEuAl4, EuAl2, EuAg5 and EuAg2 compounds were also found. The crystal structures of selected phaseswere studied by means of powder X-ray diffraction techniques and are briefly discussed.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The systematic oriented studies of the phase diagrams provideimportant information on the condition of the compounds forma-tion (stability, composition, structure transformation etc.). The rareearth based alloy systems and compounds are one example amongthem. They are known to exhibit a number of interesting propertiessuch as heavy-fermion ground state, superconductivity, Kondobehaviour, anomalous magnetism, and/or intermediate valence.The europium containing compounds are of particular interest:besides the divalent Eu2þ (magnetic) and trivalent Eu3þ (nonmag-netic) states in solids, fluctuations between these configurationsfrequently occur. Intermediate valence characteristics of europiumatoms are known for EuCu2Si2 [1] and EuNi2P2 [2] phases. TheEu4As3 [3], EuPtP [4], EuPdAs [5] and EuPdP [6] compounds areexamples with inhomogeneous mixed valence (simultaneouspresence of both Eu2þ and Eu3þ states). However, the systemati-zation of the crystal structure and properties among europiumbased compounds were not performed up to now, just onemonograph work on the selected equiatomic ternary Eu e d-metale p-metal compounds was published by the authors [7].

The Eu e d-metal e aluminium are poorly studied system: threeisothermal sections of the Eue{Mn, Cu, Zn}eAl phase diagramswereconstructed and the crystal structure of 31 ternary EuxTyAlz phases

þ351 219941455.yy).

All rights reserved.

are known up to now [8e18]: BaAl4-type (EuAg0.88Al3.12 and EuZn1e

2Al3e2), BaCd11-type (EuAg5e6Al6e5), BaFe2Al9-type (EuCo2Al9),BaHg11-type (EuAg4Al7), BaNiSn3-type (EuAuAl3), CaBe2Ge2-type(EuAu2Al2), CeCr2Al20-type (EuT2Al20, T¼ Ti, V, Nb, Ta, Cr,MoandW),CaCu0.83Al1.27-type (EuCu0.83Al1.27), CeFe2Al8-type (EuFe2Al8),Ce3Zn22-type (Eu3Zn18Al4), Co2Si-type (EuAuAl), Eu2Re6S11-type(Eu2Mn5Al12), MgNi2-type (EuCu0.6Al1.4), NaZn13-type (EuCu6.2e9.1Al6.8e3.9), PrNi2Al3-type (EuCu2Al3 and EuAg2.5Al2.5), ThMn12-type(EuMn2.3e3.6Al9.7e8.4, EuFe4e6Al8e6 and EuCu4Al8), Th2Zn17-type(Eu2Mn5Al12 and Eu2Zn13.9e14.3Al3.1e2.7), YNi2Al3-type (EuPd2Al3)and ZrNiAl-type (EuNiAl).

The binary EueAg, EueAl and AgeAl systems were wellexplored [8e10]. Five binary compounds are known from the EueAg system: EuAg5 (CaCu5-type), EuAg4 (unknown type), EuAg2(CeCu2-type), EuAg (FeB-type) and Eu3Ag2 (U3Si2-type). The EueAlsystem is characterized by the existence of three compounds (EuAl4with BaAl4-type, EuAl2 with MgCu2-type and EuAl with own type).Three intermediate binary phases with extended homogeneityranges, ht-Ag3Al (20e30 at.% Al, W-type), rt-Ag3Al (21e25 at.% Al,Mn-type) and Ag2Al (23e42 at.% Al, Mg-type), are formed in theAgeAl system.

Up to our best knowledge, only four alloys from the EueAgeAlsystem have their crystal structures refined: EuAg0.88Al3.12 (BaAl4-type) [14], EuAg2.5Al2.5 (PrNi2Al3-type) [15], EuAg5e6Al6e5 (BaCd11-type) [16,17] and EuAg4Al7 (BaHg11-type) [18]. Magnetic studiesperformed by the authors [17,18] on the EuAg5e6Al6e5 and EuAg4Al7phases indicated a paramagnetic behaviour above 5 K and 20 K,respectively, and a divalent state of europium.

Fig. 1. Isothermal section of the EueAgeAl system at 500 �C.

Fig. 2. Volume of the unit cell from various EuAg5�xAlx alloys versus Al content.

Y. Verbovytskyy, A.P. Gonçalves / Intermetallics 43 (2013) 103e109104

This work is the continuation of a systematic research of theeuropium based systems and compounds and presents results onthe phase relations in the EueAgeAl systems at 500 �C in theconcentration region of 0e33.3 at.% Eu, identification of the ternaryphases and the structure refinement of selected compounds.

2. Experimental details

Metals with nominal purities better than 99.95 wt.% (europiumingots, silver plates and aluminium rods) were used as a startingmaterials. A total of 74 binary and ternary samples with a weight�1.0 g were prepared by arc-melting the elements under argonatmosphere. Due to the partial evaporation of the europium metalduring synthesis, up to 0.5 at.% Eu was added over the nominalcomposition in each sample. The products were re-melted at leastthree times in order to ensure homogeneity. Finally, the alloys werecut into small pieces, sealed in evacuated quartz tubes under vac-uum (10�5 Torr) and annealed at 500 �C for oneetwo months. Afterthe heat treatments, the samples were quenched, by submergingthe quartz tubes in cold water, and analysed.

The polycrystalline products were crushed, powdered andexamined by X-ray diffraction. X-ray phase and structural analysiswere performedusing a PANalytical X’Pert Pro diffractometer (CuKa-radiation). The scans were taken in the q/2qmodewith the followingparameters: 2q region 15e120�; step scan 0.03e0.05�; counting timeper step 5e20 s. The theoretical powder patterns were calculatedwith the help of the PowderCell program [19]. The lattice parameterswere obtainedby least-squaresfitting, using the Latconprogram[20].The FullProf [21] programwasused for Rietveld refinements. Pseudo-Voigt profile shape function was used. The background was refinedwith a polynomial function. The microstructure of the selectedsamples was studied on polished and etched surfaces, by using anoptical microscope Olympus OM150 and/or observed by electronmicroscopy, byusing a JEOL JSM-T330Ascanningelectronmicroscope(SEM), complemented with energy dispersive X-ray spectroscopy(EDS). X-raydiffractionpatterns aswell asmicrostructures of selectedEueAgeAl alloys are shown in Supplementary data (Fig. S1 and S2).Results of X-ray phase analysis of selected multiphase annealedEueAgeAl alloys are also listed in Supplementary data (Table S1).

3. Results and discussion

The isothermal section of the EueAgeAl system at 500 �C with0e33.3 at.% Eu is presented in Fig. 1.

Three binary AgeAl phases are stable at 500 �C: two solid so-lutions, namely, Ag0.79e1Al0.21e0 and Ag0e0.1Al1e0.9, both with Cu-type structure, and Ag0.59e0.77Al0.41e0.23 with Mg-type. The EuAl4(BaAl4-type) and EuAl2 (MgCu2-type) compounds have beenconfirmed to exist at 500 �C. Moreover, they dissolve about 15 and20 at.% Ag, respectively. The EuAg5e6 (CaCu5/TbCu7-type), EuAg4(unknown type) and EuAg2 (CeCu2-type) are usually detected in theAg-rich region of the EueAgeAl system in the annealed alloys. TheEuAg2 dissolves up to 13 at.% Al, while EuAg2Al3 is the limitcomposition of the solid solution based on the EuAg5e6 phase (theevolution of the volume cell versus Al content in the EuAg5exAlx isshown in Fig. 2). Therefore, the reported EuAg2.5Al2.5 [15] is not anindividual compound, but it is a part of this solid solution. Thesolubility of aluminium on the binary EuAg4 compound is negli-gible. Calculated lattice parameters for the annealed binary EueAland EueAg compounds as well as selected alloys from their solidsolutions are presented in Table 1.

Two early reported and six new ternary phases has been foundto exist in the EueAgeAl system at 500 �C: (s1) EuAg6e7.29Al7e5.71(NaZn13-type), (s2) EuAg3.56e3.68Al7.44e7.32 (BaHg11-type), (s3)EuAg4.08e7Al6.92e4 (BaCd11-type), (s4) Eu2Ag12.07e14.98Al4.93e2.02

(Th2Zn17-type), (s5) Eu3Ag12.12e12.98Al8.88e7.98 (Ba3Ag14.6Al6.4-type),(s6) EuAg0.68e0.8Al2.32e2.2 (PuNi3-type), (s7) EuAg1.12e1.24Al1.88e1.76(CeNi3-type) and (s8) EuAg0.86e1.02Al1.14e0.98 (MgZn2-type). Itshould be also noted that in the as-cast Al-rich alloys onemore newphase, with composition close to Eu2Ag5Al12 (Th2Ni17-type), hasbeen identified. Calculated lattice parameters obtained from pow-der X-ray diffraction data for the phases mentioned above can beseen in Table 1. Results of the Rietveld refinement of selected EueAgeAl phases are shown in Table 2. Briefly discussion of the crystalstructures of the EuxAgyAlz ternary phases and comparison withstructures from related ReAgeAl systems (see Table 3) [8e10,22e30] is given below. Unit cell and coordination polyhedra of theatoms in the structures of selected EueAgeAl phases are shown inSupplementary data (Fig. S3).

3.1. EuAg6þxAl7�x phase (NaZn13 type)

The EuAg6þxAl7�x phase exists at 500 �C over the 40.8e50 at.% Alrange and it is the first representative of the NaZn13-type amongthe ReAgeAl systems (Table 3). The crystal structure of the Ag-richcontent phase is characterized by a full occupation of all crystal-lographic sites: the Eu atoms are located in 8a site, while a

Table 1Solid phases from the EueAgeAl system.

Phase Structure type Space group Lattice parameters (�A) x

a b c V

EuAgxAl4�x BaAl4 I4/mmm 4.3995(3) e 11.1521(8) 215.86(3) 04.3397(2) e 11.3625(7) 213.99(2) 0.254.3186(2) e 11.4396(7) 213.35(2) 0.54.3109(2) e 11.4729(8) 213.22(2) 0.75

EuAgxAl2�x MgCu2 Fd3m 8.1208(4) e e 535.55(4) 08.1322(4) e e 537.81(5) 0.258.1360(4) e e 538.55(4) 0.48.1425(5) e e 539.86(6) 0.6

EuAg2�xAlx CeCu2 Imma 4.7862(5) 7.5402(8) 8.2154(8) 296.48(5) 04.7818(5) 7.5730(7) 8.1784(7) 296.17(5) 0.244.7709(3) 7.5951(5) 8.1318(5) 294.66(3) 0.4

EuAg5�xAlx CaCu5 P6/mmm 5.6227(5) e 4.6410(5) 127.07(2) 05.6266(5) e 4.6177(5) 126.61(2) 0.245.6220(5) e 4.6028(5) 125.99(2) 0.55.6073(5) e 4.5949(5) 125.11(2) 0.785.5935(5) e 4.5941(5) 124.48(2) 15.5907(4) e 4.5571(4) 123.35(2) 1.55.5833(4) e 4.5170(4) 121.95(2) 25.5840(4) e 4.4618(3) 120.49(1) 2.55.5905(3) e 4.4095(3) 119.35(1) 3

EuAg6þxAl7�x (s1) NaZn13 Fd3c 12.5057(2) e e 1955.81(5) w012.6240(2) e e 2011.81(5) 0.4612.6942(2) e e 2045.57(6) 1.2412.6952(3) e e 2046.04(9) 1.29

EuAg3þxAl8�x (s2) BaHg11 Pm3m 8.7080(2) e e 660.32(3) 0.6

EuAg4þxAl7�x (s3) BaCd11 I41/amd 11.0656(6) e 7.1179(4) 871.57(8) 0.811.0592(6) e 7.1379(4) 873.01(8) 111.0983(4) e 7.1249(3) 877.59(5) 211.1077(6) e 7.1425(4) 881.25(8) 2.511.1148(6) e 7.1522(4) 883.56(8) 3

Eu2Ag15�xAl2þx (s4) Th2Zn17 R3m 9.5455(4) e 13.9578(6) 1101.40(8) 0.029.5329(3) e 13.9254(5) 1095.94(7) 0.749.5133(2) e 13.8406(3) 1084.80(4) 1.929.5032(2) e 13.7926(4) 1078.72(5) 2.519.5012(4) e 13.7613(6) 1075.83(8) 2.93

Eu2Ag5þxAl12�x (s04) Th2Ni17 P63/mmc 9.4241(3) e 9.1264(4) 701.96(4) w09.4144(2) e 9.1328(2) 701.01(3) w0.5

Eu3Ag13�xAl8þx (s5) Ba3Ag14.6Al6.4 P62m 8.7254(4) e 7.1549(3) 471.74(3) w08.7187(2) e 7.1370(2) 469.84(2) 0.648.7154(4) e 7.1316(3) 469.13(3) 0.88

EuAg1�xAl2þx (s6) PuNi3 R3m 5.6982(2) e 27.0900(9) 761.76(4) 0.23

EuAg1þxAl2�x (s7) CeNi3 P63/mmc 5.7159(2) e 18.0870(9) 511.76(4) 0.24

EuAg1�xAl1þx (s8) MgZn2 P63/mmc 5.8409(1) e 9.2293(2) 272.69(1) 05.8404(1) e 9.2178(2) 272.30(1) 0.095.8402(1) e 9.2085(3) 272.00(1) 0.16

Y. Verbovytskyy, A.P. Gonçalves / Intermetallics 43 (2013) 103e109 105

statistical mixture of Ag and Al atoms are distributed over 8b and96i sites. This structure type was also found earlier in the SrAg5.5e6.5Al7.5e6.5 and BaAg5.8e6Al7.2e7 phases [31], from the SeAgeAlsystems (S e large alkaline earth metal), which have similar crystalchemical behaviour as the europium systems. In contrast to thementioned above, a partial occupation of the 8b position by Alatoms was found in Al-rich part of this EuAg6þxAl7�x solid solution,giving a slightly defected composition. A partial occupation of the8b position in the NaZn13 structure type is known for many binaryas well as ternary phases [10]. Among the ternary europium basedcompounds, a defected EuCu6.3Ga6.5 one [32] can be noted as anexample. Nearest neighbours of the Eu atoms form distortedpseudo FrankeKasper polyhedra (coordination number 24). TheM1 andM2 atoms are located inside icosahedra (CN 12) and pseudoFrankeKasper polyhedra (CN 13).

3.2. EuAgxAl11�x phases (BaHg11 and BaCd11 types)

Single crystal studies as well as magnetic properties for theEuAgxAl11�x phases with BaHg11 and BaCd11 structure types, whichwere confirmed to exist at 500�C, were already reported by theauthors [17,18]. The homogeneity ranges for these phases wereestablished along 8.3 at.% Eu, with 61e62 and 33.3e51.7 at.% Al,respectively. Structural studies were not performed in this work,only calculated lattice parameters are given here, and they arecompatible with the early published results. Among the ReAgeAlsystems, eight RAgxAl11�x representives are known up to now withBaHg11-type, for R ¼ Ce, Eu and Yb, and with BaCd11-type, forR ¼ La, Ce, Pr, Eu and Yb, respectively. Concerning the SeAgeAlsystems, only one compound, CaAg4Al7, is described in literature[32].

Table 2Results of the Rietveld refinements of selected EueAgeAl phases.

Atom Site x y z Biso (�A2) G

EuAg5.69Al6.61 (NaZn13-type)Eu 8a 1/4 1/4 1/4 0.96(8) 1EuM1 8b 0 0 0 1.50(�) 0.305(21)AlM2 96i 0 0.12182(10) 0.17733(10) 1.01(4) 0.474(7)Ag þ 0.546(7)AlReliability factors: RB ¼ 5.75%, RF ¼ 5.00%

EuAg6.46Al6.54 (NaZn13-type)Eu 8a 1/4 1/4 1/4 1.00(11) 1EuM1 8b 0 0 0 1.16(34) 0.164(13)Ag þ 0.836(13)AlM2 96i 0 0.12320(10) 0.18063(11) 0.91(5) 0.525(9)Ag þ 0.475(9)AlReliability factors: RB ¼ 6.73%, RF ¼ 6.58%

EuAg7.29Al5.71 (NaZn13-type)Eu 8a 1/4 1/4 1/4 1.14(8) 1EuM1 8b 0 0 0 1.17(16) 0.362(8)Ag þ 0.638(8)AlM2 96i 0 0.12294(10) 0.18224(10) 0.98(4) 0.577(6)Ag þ 0.423(6)AlReliability factors: RB ¼ 4.70%, RF ¼ 4.01%

Eu2Ag13.08Al3.92 (Th2Zn17-type)Eu 6c 0 0 0.34823(24) 0.96(10) 1EuM1 6c 0 0 0.10173(22) 0.98(8) 0.93(e)Ag þ 0.07(e)AlM2 9d 1/2 0 1/2 0.93(18) 0.04(e)Ag þ 0.96(e)AlM3 18f 0.29615(18) 0 0 0.97(6) 0.94(e)Ag þ 0.06(e)AlM4 18h 0.50410(13) 1�x 0.15021(14) 1.00(6) 0.91(e)Ag þ 0.09(e)AlReliability factors: RB ¼ 7.28%, RF ¼ 4.20%

Eu2Ag12.49Al4.51 (Th2Zn17-type)Eu 6c 0 0 0.34629(22) 1.06(10) 1EuM1 6c 0 0 0.10242(20) 1.00(8) 1AgM2 9d 1/2 0 1/2 0.91(18) 0.05(e)Ag þ 0.95(e)AlM3 18f 0.29584(17) 0 0 0.93(6) 0.89(e)Ag þ 0.11(e)AlM4 18h 0.50286(12) 1ex 0.15038(14) 0.93(6) 0.83(e)Ag þ 0.17(e)AlReliability factors: RB ¼ 7.22%, RF ¼ 4.15%

Eu3Ag13.02Al7.98 (Ba3Ag14.6Al6.4-type)Eu1 1a 0 0 0 1.19(9) 1EuEu2 2d 1/3 2/3 1/2 1.19(9) 1EuM1 3g 0.1913(27) 0 0 0.97(5) 1AlM2 6i 0.7021(4) 0 0.2985(9) 0.97(5) 1AgM3 6i 0.3713(4) 0 0.2065(8) 0.97(5) 1AgM4 6j 0.3055(10) 0.4837(13) 0 0.97(5) 0.17(1)Ag þ 0.83(1)AlReliability factors: RB ¼ 4.87%, RF ¼ 3.46%

Eu3Ag12.36Al8.64 (Ba3Ag14.6Al6.4-type)Eu1 1a 0 0 0 1.28(8) 1EuEu2 2d 1/3 2/3 1/2 1.28(8) 1EuM1 3g 0.1908(26) 0 0 0.88(5) 1AlM2 6i 0.7031(4) 0 0.3015(6) 0.88(5) 1AgM3 6i 0.3709(4) 0 0.2085(6) 0.88(5) 1AgM4 6j 0.3053(13) 0.4813(17) 0 0.88(5) 0.06(1)Ag þ 0.94(1)AlReliability factors: RB ¼ 5.90%, RF ¼ 4.67%

EuAg0.77Al2.23 (PuNi3-type)Eu1 3a 0 0 0 0.96(10) 1EuEu2 6c 0 0 0.14319(8) 0.82(6) 1EuM1 3b 0 0 1/2 1.00(31) 0.05(e)Ag þ 0.95(e)AlM2 6c 0 0 0.33610(11) 0.98(7) 0.98(e)Ag þ 0.02(e)AlM3 18h 0.5026(7) 1�x 0.08198(21) 0.99(12) 0.05(e)Ag þ 0.95(e)AlReliability factors: RB ¼ 4.17%, RF ¼ 2.51%

EuAg1.24Al1.76 (CeNi3-type)Eu1 2d 1/3 2/3 3/4 0.55(11) 1EuEu2 4f 1/3 2/3 0.53415(13) 1.02(8) 1EuM1 2a 0 0 0 1.03(34) 0.21(e)Ag þ 0.79(e)AlM2 2b 0 0 1/4 1.06(13) 0.98(e)Ag þ 0.02(e)AlM3 2c 1/3 2/3 1/4 1.06(13) 0.94(e)Ag þ 0.06(e)AlM4 12k 0.1688(11) 2x 0.12664(21) 1.11(10) 0.27(e)Ag þ 0.73(e)AlReliability factors: RB ¼ 5.17%, RF ¼ 3.57%

EuAg0.91Al1.09 (MgZn2-type)Eu 4f 1/3 2/3 0.55785(21) 1.12(5) 1EuM1 2a 0 0 0 0.58(13) 0.34(e)Ag þ 0.66(e)AlM2 6h 0.16688(63) 2x 1/4 0.61(7) 0.49(e)Ag þ 0.51(e)AlReliability factors: RB ¼ 4.65%, RF ¼ 4.66%

(e) e Means value was fixed in the final refinement.

Y. Verbovytskyy, A.P. Gonçalves / Intermetallics 43 (2013) 103e109106

Table 3Structure types of the ternary compounds in the ReAgeAl systems.

Structure type Sc Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

NaZn13 e e e e e e e þ e e e e e e e e

ThMn12 e þ e e e e e e þ þ þ þ e e e e

BaHg11 e e e þ e e e þ e e e e e e þ e

BaCd11 e e þ þ þ e e þ e e e e e e þ e

Th2Zn17 e e þ þ þ þ þ þ e e e e e e þ e

Th2Ni17 e þ þ þ þ þ þ þ þ þ þ þ þ þ þ e

Yb8Cu17Al49 e þ e e e e e e þ þ þ þ þ þ þ e

Ba3Ag14.6Al6.4 e e e e e e e þ e e e e e e e e

CaCu5 e e þ þ þ þ e e e e e e e e e e

SmAg3.5Al1.5 e þ e e þ þ þ e þ þ e e e e e e

DyAg2.4Al2.6 e þ e e þ þ þ e þ þ þ þ þ þ þ þBaAl4 e e þ þ þ þ e e e e e e e e e e

Th6Mn23 e e e e þ e e e e e e e e e e e

La3Al11 e þ e e e e e e þ þ þ þ e e e e

PuNi3 e þ þ þ þ þ þ þ þ þ e e e e þ e

CeNi3 e e e e e e e þ e e e e e e þ e

BiF3 þ e e e e e e e e e e e e e e e

AlB2 e e e e þ e e e e e e e e e e e

CeCu2 e þ e e e e þ e þ þ þ e e e e e

MgZn2 e e e e e e e þ e e e e e e þ e

System e D D D : : : D D D : e e e e e

Compound exists with this structure type (þ). Lack of a symbol means the compounds has not been identified. Phase equilibrium is investigated in the whole concentrationregion (:) or in part of it (D). No data or system was not studied (e).

Y. Verbovytskyy, A.P. Gonçalves / Intermetallics 43 (2013) 103e109 107

3.3. Eu2Ag17�xAlx phases (Th2Zn17 and Th2Ni17 types)

In the as-cast Al-rich and annealed Ag-rich alloys along 10.5 at.%Eu (general composition Eu2Ag17�xAlx) two newphases,with Th2Ni17and Th2Zn17 structure types, respectively (both related to the well-knownCaCu5-type), were established. The phase stability and crystalstructure determination for the as-cast Al-rich phase with Th2Ni17structure type will be given in a separate publication. The singlephase region of the Eu2Ag17�xAlx phase (with Th2Zn17 type) is limitedby 11 and 26 at.% Al. Crystal structure studies were performed forx ¼ 3.92 and 4.51. The Eu atoms occupy the 6c site, a preference ofoccupation by the Ag atoms can be seen in the 6c, 18f and 18h po-sitions, while almost full Al occupancy can be seen in the 9d site. TheEu atoms have a distorted pseudo FrankeKasper polyhedra (19)environment. TheM1 andM3 atoms are located inside 14-vertex andpseudo 13-vertex FrankeKasper polyhedra. Icosahedral environ-ments (CN 12) can be seen for the M2 and M4 atoms. The RxAgyAlzintermetallic phaseswith Th2Zn17 structure type aremainly know forthe big rare earth metals (LaeNd, Sm and Yb), while the ReAgeAlphases with Th2Ni17-type are formedwith all rare earthmetals, withthe exception of smallest Sc and Lu. It should be noted that RxAgyAlzstructures with, or related to, the CaCu5-type (as ThMn12 and SmA-g3.5Al1.5 types) are also known for many ReAgeAl systems.

3.4. Eu3Ag13�xAl8þx (Ba3Ag14.6Al6.4 type)

The hexagonal phase, Eu3Ag13�xAl8þx, was identified in theannealed samples, and its homogeneity extends from 33 to 37 at. %Al at 500 �C. To our knowledge, this phase is the second examplewith Ba3Ag14.6Al6.4-type structure among all studied ternary in-termetallics. In this structure two independent sites (1a and 2d) areoccupied by europium atoms. The Ag atoms are located in two 6ipositions. Pure Al and its richmixturewith Ag are situated in 3g and6j sites, respectively. Coordination polyhedra for the Eu1 and Eu2atoms are 24-vertex and 21-vertex spheres, respectively. Distortedor defected icosahedra are the coordination polyhedra for the M1(CN 12), M2 (CN 11), M3 (CN 12) and M4 (CN 12) atoms.

The structure of this phase can be considered as layer like one(Fig. 3). Composition of three different layers of the atoms A, B andC in the sequence ABCB’C along z axis forms the Eu3Ag13�xAl8þx

structure. The A layer, with R0.5M3 composition, is composed by flat

3535 and 353,535 nets. A slightly deformed hexagonal layer 63

forms the B one (M6). The 53 and 353 nets can be seen in the C layer,with composition R2M3. The relation of the atoms for this structure,R/M ¼ 3/21, can be easy calculated taking into account thecomposition of the layers: 2R0.5M3þ 2M6þ R2M3¼ R3M21. It is easyto find that above mentioned nets have some similar features withthose from the AlB2-type, CaCu5-type ones and Laves phases.

3.5. EuAgxAl3�x phases (CeNi3 and PuNi3 types)

The ternary EuAgxAl3�x phases with CeNi3 and PuNi3 structuretypes were recognized in the as-cast as well as annealed Al-rich EueAgeAl alloys. Homogeneity ranges at 500 �Cwere established as 17e20 and 28e31 at.% Al, respectively. Rietveld refinement for theEuAgxAl3�x phases were performed for x ¼ 0.77 (PuNi3-type) andx ¼ 1.24 (CeNi3-type). In the EuAg0.77Al2.23 structure the Eu atomsoccupy the 3a and 6c sites; statisticalmixturesM (Ag/Al), with visibletendency of occupation of the Ag or Al atoms, are located in threepositions (3b, 6c and 18h). The PuNi3 structures from the ReAgeAlsystems are known for all light rare earth metals (LaeSm); with theheavy rare earth metals they form in the systems with R ¼ Y, Gd, Tband Yb. In the case of R ¼ Y, Gd and Ca, an ordered structure with acomposition R3Ag2Al7 (¼RAg0.67Al2.33) and with Ca3Cu2Al7 structuretype (superstructure of PuNi3) were suggested by the authors[22,28,32]. Two independent (2d and 4f) Eu sites and four positions(2a, 2b, 2c and 12k) of the Ag/Al atoms are observed in the structureof the EuAg1.24Al1.76 phase (CeNi3-type). A predominant content ofthe Ag atoms is situated in the 2b and 2c sites. The CaAg1.3Al1.7 andYbAg0.7Al2.3 compounds [32] also crystallize with CeNi3 structuretype. It should be also noted that the PuNi3 and CeNi3 structures arewell described in the literature, belonging to the block stacking ones:simple MgZn2 and CaCu5 like slabs are the construction units forthese types. The coordination polyhedra for the phases with PuNi3and CeNi3 are similar: the big europium atoms are located inside 16-vertex or pseudo 20-vertex FrankeKasper polyhedra; coordinationspheres for the small Ag/Al atoms are icosahedra (CN 12).

3.6. EuAg1exAl1þx (MgZn2 type)

Similarly to the CaeAgeAl and YbeAgeAl systems [32], theEuAg1�xAl1þx phase, with MgZn2 structure type, was revealed to

Fig. 3. Projection of the Eu3Ag13�xAl8þx structure along [110] direction emphasizing the A, B and C layers (europium: big blue balls; Ag/Al atoms: smaller cyan and green balls). (Forinterpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Y. Verbovytskyy, A.P. Gonçalves / Intermetallics 43 (2013) 103e109108

exist at 500 �C in the alloys along the EuAl2eEuAg2 cross-sectionwith 28.5e34 at.% Al. Structural studies of the EuAg1�xAl1þx phasewere conducted for x ¼ 0.09. Taking into account results of thestructure refinement for this composition, two different statisticalmixtures of the Ag and Al atomswere observed, i.e. 1/3Agþ 2/3Al in2a site and 1/2Ag þ 1/2Al in 6h site; the Eu atoms occupy one crys-tallographic position, 4h. 16-vertex FrankeKasper polyhedra areformed around the Eu atoms. The M1 and M2 atoms are situatedinside icosahedra (CN 12). In general, besides the formation of thephase with MgZn2-type, other Laves phase (EuAgxAl2�x solid solu-tion with MgCu2-type) and orthorhombic structure (EuAg2�xAlxsolid solution with CeCu2-type) expand into the ternary system.Thus, the alteration of the structure type in the sequenceMgCu2 / MgZn2 / CeCu2 along 33.3 at. % Eu exists in the studiedEueAgeAl system. Other structural transformations, likeMgCu2/CeCu2 andMgCu2/CeCu2/MoSi2 along theRAl2eRAg2cross-section, are also known for light (R ¼ LaeSm) [23e27] andheavy (R ¼ Y, Gd, Tb, Dy) [22,28e30] rare earth metals, respectively.

4. Conclusion

The isothermal section of the EueAgeAl (0e33.3 at.% Eu) phasediagram has been constructed at 500 �C by means of X-ray diffrac-tion, optical microscopy and scanning electronic microscopy. Theinteraction of the components in these systems leads to the for-mation of eight ternary phases (six of them reported here for thefirst time): (s1) EuAg6e7.29Al7e5.71, (s2) EuAg3.56e3.68Al7.44e7.32, (s3)EuAg4.08e7Al6.92e4, (s4) Eu2Ag12.07e14.98Al4.93e2.02, (s5) Eu3Ag12.12e

12.98Al8.88e7.98, (s6) EuAg0.68e0.8Al2.32e2.2, (s7) EuAg1.12e1.24Al1.88e1.76and (s8) EuAg0.86e1.02Al1.14e0.98. Binary EuAl4, EuAl2, EuAg5 andEuAg2 compounds formsolid solutions by theAg/Al substitutions. Inthe partial isothermal section of the EueAgeAl phase diagramtwenty one ternary phase fields have been identified, those arelisted below in order of increasing of silver contents:(1) s1 þ Al1�xAgx þ Ag2�xAl1þx; (2) s1 þ s3 þ Al1�xAgx;(3) s2 þ s3 þ Al1�xAgx; (4) s2 þ Al þ EuAgxAl4�x;(5) s2 þ s3 þ EuAgxAl4�x; (6) s3 þ EuAgxAl4�x þ EuAg5�xAlx;(7) s6þ EuAgxAl4�xþ EuAg5�xAlx; (8) s6þ EuAgxAl4�xþ EuAgxAl2�x;(9) s6 þ s7 þ EuAg5�xAlx; (10) s6 þ s7 þ EuAgxAl2�x;(11) s7 þ s8 þ EuAgxAl2�x; (12) s7 þ s8 þ EuAg5�xAlx;(13) s3 þ s5 þ EuAg5�xAlx; (14) s1 þ s3 þ Ag2�xAl1þx;(15) s8 þ EuAg5�xAlx þ EuAg2�xAlx; (16) s3 þ s4 þ s5;(17) s3 þ Ag2�xAl1þx þ Ag1�xAlx; (18) s4 þ s5 þ EuAg5�xAlx;(19) s3 þ s4 þ Ag1�xAlx; (20) s4 þ EuAg5�xAlx þ Ag1�xAlx;(21) EuAg2�xAlx þ EuAg4 þ EuAg5�xAlx. The available data on theEueAgeAl systems point to the possibility of identification of newternary phases in the yet unexplored systems with rare earth andalkaline earth metals.

Acknowledgements

This work was partially supported by FCT, Portugal, under thecontract No. PTDC/CTM/102766/2008. The FCT Grant No. SFRH/BPD/34840/2007 for the research work of Y.V. at CTN, Bobadela,Portugal is highly appreciated. The authors would like to express

Y. Verbovytskyy, A.P. Gonçalves / Intermetallics 43 (2013) 103e109 109

their gratitude to Dr. Nuno Leal from Universidade Nova de Lisboa(Caparica, Portugal) for the help during the SEM/EDS studies.

Appendix A. Supplementary data

Supplementary data related to this article can be found athttp://dx.doi.org/10.1016/j.intermet.2013.07.013.

References

[1] Bauminger ER, Froindlich D, Nowik I, Ofer S, Felner I, Mayer I. Charge fluc-tuations in europium in metallic EuCu2Si2. Phys Rev Lett 1973;30:1053e6.

[2] Nagarajan R, Sampathkumaran EV, Gupta LC, Vijayaraghavan R,Prabhawalkar V, Haktdarshan B, et al. Mössbauer and X-ray absorptionspectroscopic measurements on the new mixed-valence system EuNi2P2. PhysLett A 1981;84A:275e7.

[3] Wortmann G, Sampathkumaran EV, Kaindl G. Verwey transition in Eu4As3.J Magn Magn Mater 1986;54e57:338e40.

[4] Lossau N, Kierspel H, Langen J, Schlabitz W, Wohlleben D, Mewis A, et al.EuPtP: a new mixed valent europium-system. J Phys B Condens Matter1989;74:227e32.

[5] Michels G, Junk S, Lossau N, Schlabitz W, Wohlleben D, Johrendt D, et al.Mixed valency and first order phase transition in EuPdAs. J Phys B CondensMatter 1992;86:53e8.

[6] Felser C, Cramm S, Johrendt D, Mewis A, Jepsen O, Hohlneicher G, et al. A newview of valence instabilities in europium compounds: van Hove singularity inEuPdP. Europhys Lett 1997;40:85e91.

[7] Pöttgen R, Johrendt D. Equiatomic intermetallic europium compounds: syn-theses, crystal chemistry, chemical bonding, and physical properties. ChemMater 2000;12:875e97.

[8] Villars P, editor. Pearson’s handbook, crystallographic data for intermetallicphases (desk ed.). ASM Materials Park, OH: 1997.

[9] Villars P, Cenzual K. Pearson’s crystal data e crystal database for inorganiccompounds: ASM International. Material Park, OH: Release 2010/2011.

[10] Springer Materials. The LandolteBörnstein database. http://www.springermaterials.com; 2013.

[11] Manyako MB, Yanson TI, Zarechnyuk OS. Isothermal section at 770 K throughternary phase diagrams of systems Eu (Ca, Sr, Ba) e Mn e Al. Izv Akad NaukSSSR Met 1988:212e5 [in Russian].

[12] Yanson TI, Manyako MB, Zarechnyuk OS. Features of component interaction inthe ternary (Ca, Eu, Sr) e Cu e Al systems. Metally 1992:175e9 [in Russian].

[13] Verbovytskyy Yu, Alves LC, Gonçalves AP. Phase relations of the EueZneAlsystem at 400 �C from 0 to 33.3 at.% Eu. J Alloys Compd 2010;495:39e44.

[14] Denysyuk OV, Stel’makhovych BM, Kuz’ma YuB. New compound NdAg0.6Al3.4and it’s crystal structure. Visn L’viv Derzh Univ Ser Khim 1994:24e33 [inUkranian].

[15] Denysyuk OV, Stel’makhovych BM, Kuz’ma YuB. Crystal structures of newcompounds Ln(Ag0.5Al0.5)5, Ln e Y, LaeLu). Metally 1993:213e5 [in Russian].

[16] Denysyuk OV, Stel’makhovych BM, Kuz’ma YuB. Crystal structure ofnew compounds in the REeAgeAl systems. J Solid State Chem 1994;109:172e4.

[17] Wang F, Pearson KN, Miller GJ. EuAgxAl11�x with the BaCd11-type struc-ture: phase width, coloring and electronic structure. Chem Mater 2009;21:230e6.

[18] Wang F, Pearson KN, Straszheim WE, Miller GJ. EuAgxAl11�x with the BaHg11-type structure: composition, coloring, and competition with the BaCd11-typestructure. Chem Mater 2010;22:1798e806.

[19] Nolze G, Kraus W. Powder cell for Windows (Version 2.3). Berlin: FederalInstitute for Materials Research and Testing; 1999.

[20] Schwarzenbach D. Program LATCON. Switzerland: University of Lausanne;1975.

[21] Rodriguez-Carvajal J, Roisnel T. FullProf.98 and WinPLOTR: new Windows 95/NT applications for diffraction commission for powder diffraction: Interna-tional Union for Crystallography, Newsletter N� 20 (MayeAugust), Summer,1998.

[22] Gumenyuk RM, Kuz’ma YuB, Stel’makhovych BM. The YeAgeAl system.J Alloys Compd 2000;299:213e6.

[23] Kuzma YuB, Zhak OV, Shkolyk SYu. The Lanthanumesilverealuminum sys-tem. Dop Akad Nauk Ukr 1995;3:101e4 [in Ukranian].

[24] Zhak OV, Stel’makhovich BM, Kuz’ma YuB. Phase equilibria in the CeeAgeAlsystem in the field ranging from 0 to 50 mole fraction of cerium. Iz Ros AkadNauk Metally 1995;6:158e61 [in Russian].

[25] Zhak OV, Kuz’ma YuB. The PreAgeAl system. J Alloys Compd 1999;291:175e80.

[26] Kuzma YuB, Zhak OV, Sarapina OS. X-ray diffraction study of the NdeAgeAlsystem. Metally 1997;2:166e73 [in Russian].

[27] Zhak OV, Stel’makhovych BM, Kuz’ma YuB. The SmeAgeA1 system. J AlloysCompd 1996;237:144e9.

[28] Stel’makhovych BM, Zhak OV, Bilas NR, Kuz’ma YuV. The GdeAgeAl system.J Alloys Compd 2004;363:243e8.

[29] Gumeniuk RV, Stel’makhovych BM, Kuz’ma YuB. The TbeAgeAl system.J Alloys Compd 2001;321:132e7.

[30] Stelmakhovych BM, Kuzma YuB. Diagram of the phase equilibrium in thesystem DyeAgeAl at 870 K. Dop Akad Nauk Ukr 1994;3:86e9 [in Ukrainian].

[31] Crystmet e the metals database (Version 1.1), Toth Information System, Inc.;2000.

[32] Cho JY, Thomas EL, Nambu Y, Capan C, Karki AB, Young DP, et al. Crystalgrowth, structure, and physical properties of Ln(Cu, Ga)13�x (Ln ¼ LaeNd, Eu;x z 0.2). Chem Mater 2009;21:3072e8.