Pr1.33Pt4Ga10: Superstructure and magnetism

Sau Doan Nguyen a, Kevin Ryan a, Ping Chai b, Michael Shatruk b,c, Yan Xin c,Karena W. Chapman d, Peter J. Chupas d, Frank R. Fronczek e, Robin T. Macaluso a,n

a Department of Chemistry and Biochemistry, University of Northern Colorado, Greeley, CO 80639, United Statesb Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, United Statesc National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United Statesd X-Ray Science Division, The Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, United Statese Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, United States

a r t i c l e i n f o

Article history:Received 4 June 2014Received in revised form21 July 2014Accepted 23 July 2014Available online 1 August 2014

Keywords:Pr1.33Pt4Ga10SuperstructureIntermetallicPair distribution functionTransmission electron microscopyMagnetism

a b s t r a c t

Pr1.33Pt4Ga10 crystals were prepared by Ga-flux method. The superstructure of this compound wasstudied by single-crystal X-ray diffraction (XRD), transmission electron microscopy (TEM), and diffuseX-ray scattering. Pr1.33Pt4Ga10 adopts the P63/mmc space group with a¼b¼4.3227(5) Å, c¼16.485(3) Å:the structure features Pr2Ga3 layers alternating with Pt2Ga4 layers along the c-axis. TEM studies and pairdistribution function (PDF) analysis of X-ray total scattering data show that Pr2Ga3 layers possess anordered superstructure (of dimension a0 ¼ a

ffiffiffi

3p

) in which Pr vacancies and Ga atoms are ordered withinthe ab-plane but disordered along the c-direction. PDF analysis also shows temperature-dependentstructural features local to the Pr3þ ion. Magnetic measurements reveal that Pr3þ ions orderferrimagnetically below 12.5(2) K.

& 2014 Elsevier Inc. All rights reserved.

1. Introduction

Intermetallic compounds containing f-elements are among themost active research topics in the exploratory synthesis of corre-lated electron materials. Among them stands out a class ofcompounds known as heavy-fermions where strong hybridizationbetween conduction electrons and f-electrons generates quasipar-ticles with effective masses several order of magnitudes largerthan that of a free electron. This behavior results in a very largeSommerfeld coefficient of specific heat, γ, typically Z400 mJ/(mol K2). The instability of localized f-electrons under chemicaldoping, high pressure, and applied magnetic field also contributesto interplay of physical properties of these materials, such assuperconductivity and magnetism [1].

Layered structures are a common characteristic of many super-conducting materials, and theoretical calculations show that themagnetic pairing is more robust in quasi two-dimensional struc-tures than in three-dimensional structures [2,3]. Therefore, thesynthesis of new rare-earth intermetallic compounds with layeredstructures has attracted attention in the area of heavy-fermionsuperconductors. In this respect, ternary transition metal rare-earth intermetallics with high content of triel elements (Al, Ga, In)

are especially appealing because they exhibit a variety of layeredstructures. For example, the tetragonal crystal structure ofCenMIn3nþ2 (M¼Co, Ir, Rh) can be viewed in terms of n-fold layersof CeIn3 separated by layers of MIn2 [4]. CeCoIn5 and CeIrIn5 (n¼1)are superconducting at 2.3 K and 0.4 K, respectively, while Ce2R-hIn8 (n¼2) becomes superconducting at 2 K under pressure of25 kbar [5–7].

Many ternary compounds of the general composition LnxTyXz

(Ln¼ lanthanide, T¼transition metal and X¼Al, Ga) with a high Xcontent possess layered ABAB structures [3,8–15]. Typically, the Alayer consists of Ln and Xmetals, and the B layer consists of T and Xmetals. For example, in Er4Pt9Al24, Y2Co3Ga9, and Ce1.33Pt4Ga10, Aand B layers have the composition Er2Al3, Y2Ga3, Ce2Ga3 and PtAl2,CoGa2, Pt2Ga4, respectively.

Ce1.33Pt4Ga10 consists of hexagonal Ce2Ga3 layers alternatingwith Pt2Ga4 layers along the crystallographic c-axis. It belongs to aseries Ln2�xPt4Ga8þy (xE0.66, yE2.0; Ln¼La, Ce, Pr, Nd, Sm, Gd,Er, Yb, and Y), which was first reported by Lacerda et al. [13].Ce1.33Pt4Ga10 is a heavy-fermion compound that does not exhibitany signs of magnetic ordering down to 2 K [13,16]. Pr1.33Pt4Ga10,on the other hand, exhibits a low-temperature, field-dependentmagnetic transition [13]. We have successfully grown large repre-sentative single crystals of Pr1.33Pt4Ga10 and characterized the localstructure and physical properties. Single crystal X-ray diffraction(XRD), transmission electron microscopy (TEM), and atomic pairdistribution function (PDF) analysis have been used to provide, for

Contents lists available at ScienceDirect

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

Journal of Solid State Chemistry

http://dx.doi.org/10.1016/j.jssc.2014.07.0330022-4596/& 2014 Elsevier Inc. All rights reserved.

n Corresponding author . Tel.: þ1 970 351 1282.E-mail address: robin.macaluso@unco.edu (R.T. Macaluso).

Journal of Solid State Chemistry 220 (2014) 9–16

the first time, a detailed description of the structural disorderobserved in this compound. In addition, magnetic measurementsconfirm the results obtained earlier by Lacerda et al. and demon-strate significant magnetic anisotropy of Pr1.33Pt4Ga10.

2. Materials and methods

2.1. Synthesis

Single crystals of Pr1.33Pt4Ga10 were prepared using Ga-flux. Amixture of 0.327 g Pr (2.32 mmol), 0.343 g Pt (1.77 mmol), and2.47 g Ga (35.4 mmol) was placed in an alumina crucible. Thecrucible and its contents were sealed under vacuum in a fusedsilica ampoule, and then heated to 1150 1C in the box furnace for4 h before cooling down to 350 1C at a rate of 8 1C/h. The ampoulewas removed from the furnace at 350 1C and immediately invertedand placed into a centrifuge. The excess liquid Ga was removed bycentrifugation of the inverted ampoule for 10 min. The productcontained hexagonal rod crystals of Pr1.33Pt4Ga10 (E10% yieldwith respect to Pr). The residual Ga flux remaining on thePr1.33Pt4Ga10 crystal surface was removed by placing the crystalsin a 3 M solution of I2 in DMF. Crystals of Pr1.33Pt4Ga10 are stable inair for several months. Wavelength-dispersive microprobe analysisof multiple crystals resulted in a chemical formula of Pr1.508(6)Pt3.8(1)Ga10.0(1), which is in agreement with single-crystal XRD results.

2.2. Single crystal X-ray diffraction

A fragment (approximately 0.01 mm�0.01 mm�0.03 mm) cutfrom a larger single crystal was mounted onto the goniometer of aBruker KappaCCD diffractometer equipped with MoKα(λ¼0.71073 Å) radiation. Data collection and structure solutionwere performed with SIR97 [17]. Structural refinements andextinction corrections were performed using SHELXL suite [18].Further crystallographic details are included in Table 1; atomicpositions and displacement parameters are provided in Table 2.Select interatomic distances are listed in Table 3.

2.2.1. Transmission electron microscopy and electron diffractionTEM analysis was carried out on a probe aberration corrected

sub-Å resolution JEOL JEM-ARM200cF microscope operated at200 kV. The TEM sample was prepared by crushing a small pieceof a single crystal with a mortar and pestle in methanol, anddropping the suspension onto a carbon/formvar coated 200 meshCu TEM grid. The TEM data was obtained from selected thinelectron transparent single crystal pieces. Atomic resolutionimages along the major axis were obtained using scanningtransmission electron microscopy high angle annular dark fieldimaging techniques (STEM HAADF). STEM images were taken withthe JEOL HAADF detector using the following experimental con-ditions: probe size 7c, CL aperture 30 mm, scan speed 32 ms/pixel,and camera length 8 cm. The STEM resolution of the microscope is0.78 Å. The inner detector collection angle is 76 mrad. Electrondiffraction patterns were obtained by tilting the crystal pieces toalign along the major axis.

2.3. High energy X-ray total scattering measurement

A pulverized sample of Pr1.33Pt4Ga10 was loaded in a polyimidecapillary of 0.0435″ outer diameter (Cole-Parmer EW-95820-09). TheX-rays (58.26 keV, 0.2128 Å) available at the 11-ID-B beamline at theAdvanced Photon Source at Argonne National Laboratory were used tocollect X-ray total scattering data, in the range of 80–298 K at regular1.5 K intervals. Sample temperature was controlled using an OxfordCryostream 700 plus. Raw images were reduced with Fit-2D [19].

2.4. Magnetization and resistivity

Magnetic measurements were performed on a polycrystalline or asingle-crystal sample with a Quantum Design SQUID magnetometerMPMS-XL. Field-cooled (FC) and zero-field cooled (ZFC) magnetizationmeasurements were carried out in an applied field of 0.100 T in the1.8–300 K temperature range. Hysteresis was measured with themagnetic field varying from �7 to 7 T.

Table 1Crystallographic data for Pr1.33Pt4Ga10.

Formula Pr1.33Pt4Ga10Space group P63/mmc (No. 194)Crystal system Hexagonala¼b (Å) 4.3227(5)c (Å) 16.485(3)V (Å3) 266.77(7)Z 1FW (g/mol) 1672.8ρcalcd (g/cm3) 10.413T (K) 293(2)λ (Å) 0.71073Completeness to θ¼251 99.2%θmaximum 45.24Number unique reflections 484Number reflections I42σ(I) 430Number of refined parameters 19Extinction coefficient 0.0121(9)μ (mm�1) 83.083R(int) 0.0501R(F)a 0.0332Rw(Fo2)b 0.0776GOF (F2)c 1.144Δρmin, Δρmax �5.42, 7.23

a R(F)¼Σ||Fo|� |Fc||/Σ|Fo|.b Rw(Fo2)¼[Σw(Fo2�Fc

2)2/Σw(Fo2)2]1/2.c Goodness of fit (GOF)¼fð∑jw=jF2o�F2c j2jÞ=ðn�pÞg1=2 where n¼number of

reflections used and p¼number of refined parameters.

Table 2Atomic coordinates and isotropic displacement parameters of Pr1.33Pt4Ga10.

Atom Wyckoff site x y z Occupancy Ueq (Å2)a

Pr 2d 1/3 2/3 1/4 0.708(7) 0.005(1)Pt 4f 2/3 1/3 0.10806(2) 1 0.007(1)

Ga(1) 4e 0 0 0.13682(9) 1 0.008(1)Ga(2) 2d 1/3 2/3 0.04613(8) 1 0.008(1)Ga(3) 6h 0.5348(5) 0.0696(9) 1/4 0.322(7) 0.007(1)

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

Table 3Selected interatomic distances (Å) for Pr1.33Pt4Ga10.

Atom Pair Distance (Å)

Pt–Ga(1) 2.5405(4)Pt–Ga(2) 2.541(1)Pt–Ga(2) 2.6956(6)Pt–Ga(3) 2.541(2)Pt–Pr 3.4223(4)Pr–Ga(1) 3.1166(9)Pr–Ga(3) 3.109(3)Ga(1)–Ga(2) 2.909(1)Ga(2)–Ga(2) 2.923(1)Ga(1)–Ga(3) 2.868(1)Ga(3)–Ga(3) 2.613(6)

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–1610

3. Results and discussion

3.1. Crystal structure

Pr1.33Pt4Ga10 is isostructural with Ce1.33Pt4Ga10 and Gd1.33Pt4Al10.The material crystallizes in hexagonal space group P63/mmc andcontains five atoms in the asymmetric unit. Of these, Pt, Ga(1), andGa(2) atoms are at fully occupied 4f, 4e, and 4f Wyckoff sites,respectively, and form a Pt2Ga4 double layer perpendicular to the c-axis. The other two atoms, Pr and Ga(3), are at partially occupied 2cand 6h Wyckoff sites with occupancies of 0.708(7) and 0.322(7),respectively. The Pr and Ga(3) atoms form a hexagonal Pr2Ga3 layerperpendicular to the c-axis. The Pt2Ga4 and Pr2Ga3 layers stackalternatively along the c-axis direction with an ABAB… stackingsequence (Fig. 1).

The Pt2Ga4 double layer can be constructed by positioning twoPtGa2 single layers parallel to each other and binding Ga(2) atomsof one layer to Pt atoms of the other layer along the c-axis (Fig. 1).Each PtGa2 single layer is comprised of a hexagonal net of Pt atomssandwiched between a hexagonal net of Ga(1) atoms and ahexagonal net of Ga(2) atoms (Fig. 2). Within the PtGa2 layer, thePt–Ga(1) and Pt–Ga(2) distances are 2.5405(4) Å and 2.6956(6) Å,respectively, while the interlayer Pt–Ga(2) distances between twoPtGa2 layers are 2.541(1) Å, which are shorter than the intralayerPt–Ga(2) distances.

The Pr2Ga3 layers consists of partially occupied Pr and Ga(3) atoms with site occupancies of 0.708(7) and 0.322(7), respec-tively, which deviate slightly from the 2/3 and 1/3 values that arerequired to obtain the composition of Pr1.33Pt4Ga10. These devia-tions have been seen in other Ln1.33Pt4� 10 compounds (X¼Al, Ga),where the occupancies of Ln and X sites have been observed to beas low as 0.5 and as high as 0.37, respectively [10,14,15,20,21].These site occupancy deviations further contribute to the disorderof Ln2X3 layers and their superstructure. A fully-occupied rare-earth layer would result in a Pr3Ga9 stoichiometry and Pr–Ga(3) and Ga(3)–Ga(3) distances of 1.508(4) Å and 1.710(6) Å, respec-tively. However, these atomic distances are much shorter thansums of Pr (1.85 Å) and Ga (1.30 Å) atomic radii [22], which wouldlead to a chemically unreasonable structure. By removing approxi-mately 1/3 of Pr atoms and 2/3 of Ga(3) atoms, as reflected by theexperimental site occupancies, the composition of the layerchanges to Pr2Ga3, with reasonable Pr–Ga(3) and Ga(3)–Ga(3) dis-tances of 3.109(3) Å and 2.613(6) Å, respectively. In this model, thecoordination environment of the Pr site is represented by a

penta-capped trigonal prism (Fig. 3). Six Ga(1) atoms form thetrigonal prism while three Ga(3) atoms cap the three rectangularfaces and 2 Ga(2) atoms caps the two trigonal faces.

Given the experimental site occupancies (obtained from single-crystal XRD) and the layered structure, the chemical formula of thetitle compound can be rewritten as (Pr0.67Ga)2(Pt2Ga4)2. The Pt–Pr,Pt–Ga(3), and Pr–Ga(1) distances between Pr2Ga3 layers andPt2Ga4 double layers are 3.4223(4) Å, 2.541(2) Å, and 3.117(1) Å,respectively.

3.1.1. Disorder and superstructure of Ln2X3 layersThe disorder of Ln and X (Al, Ga) atoms and the superstructure

of the Ln2X3 layer in compounds related to Pr1.33Pt4Ga10 have beenextensively studied by X-ray and neutron diffraction. Interestingly,all these compounds contain Ln2X3 layers with hexagonal sym-metry, but they crystallize in different crystal systems, includingtriclinic (Ln4Pt9Al24) [11], orthorhombic (Y2Co3Ga9) [23], trigonal(LnNi3Al9) [24], and hexagonal (Ln1.33Pt4Al10) [15]. Besides trielides(X¼Al, Ga), this layered structure is also found in transition-metaliron silicides, e.g., Sc1.2Fe4Si9.9 which has been recently extendedto Ln2�xFe4Si14�y [25]. For compounds containing Al and Ga, thereexists a consensus that the Ln2Ga(Al)3 layer has a honeycombsuperstructure of Ln atoms with Ga3 (Al3) triangles located in thecenter of each rare-earth hexagonal unit. Ga3 triangles have also

Fig. 1. Ball-and-stick representation of Pr1.33Pt4Ga10 shows Pt2Ga4 double layersand Pr2Ga3 layers along the c-axis. Interlayer Pr–Ga and Pt–Ga bonds betweenPt2Ga4 double layers and Pr2Ga3 layers have been omitted for clarity. Blue, gray, andorange spheres represent Pr, Pt, and Ga atoms, respectively. Dashed lines outlinethe unit cell. (For interpretation of the references to color in this figure legend, thereader is referred to the web version of this article.)

Fig. 2. Ball-and-stick representation of the PtGa2 single layer (top) and an orderedstructure of Pr2Ga3 (bottom). In the PtGa2 single layer, Ga(2) atoms connected to Ptatoms represented by dash bonds whereas Pt–Ga(1) bonds are solid lines. In thePr2Ga3 layer, orange triangles are Ga(3)3 trimers centered inside Pr-hexagons,shown as blue spheres and dashed lines. (For interpretation of the references tocolor in this figure legend, the reader is referred to the web version of this article.)

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–16 11

been recently observed in Sr2Au6Ga3 [26]. Perhaps the mostconvincing evidence for ordered Ga3 triangles in the title com-pound is that diffraction spots in the [h k 0] zone can be indexed toa larger supercell with dimensions of a

ffiffiffi

3p

� affiffiffi

3p

[15,20,21].Streaks extending along the reciprocal cn-axis in single crystalX-ray and neutron diffraction patterns have been observed forLn4Pt9Al24, Ln1.33Pt4Al10, and LnNi3Al9, but the superstructure alongthe c-direction has yet to be determined because of the weak anddiffuse nature of these streaks [11,15,24]. All these considerationsincited us to further investigate the disorder and superstructure ofPr2Ga3 layers in Pr1.33Pt4Ga10 by TEM and PDF methods.

3.2. Transmission electron microscopy and electron diffraction

Atomic resolution STEM HAADF Z-contrast images and electrondiffraction (ED) pattern of Pr1.33Pt4Ga10 are provided in Fig. 4.Fig. 4a shows well-ordered diffraction spots in the [1–100] zonedirection. Two sharp streak lines observed in the ED pattern(labeled S1 and S2 in Fig. 4a) have d-spacing values of 6.45 Åand 3.20 Å; their shape indicates disorder along the c axis. Theorigin of the diffraction streaks will be discussed later.

Intensities observed in STEM HAADF images are proportional tothe atomic number Zn (where n is close to 2).[27,28] Fig. 4b is anatomic resolution STEM Z-contrast image of Pr1.33Pt4Ga10 pro-jected along the [1–100] direction. Because of the large differencesin Z of Pt, Pr, and Ga (Z¼78, 59, and 31, respectively), the Pt atomsappear as the brightest intensity in the image while Pr atoms areobserved as less intense rows sandwiched between the brighter Ptspots. Upon close inspection, it is obvious that the intensities ofthe Pr atoms vary such that for every two brighter Pr spots, onedarker Pr spot follows along the [11–20] direction. This pattern (ofbright Pr/bright Pr/dark Pr) is shown in Fig. 4c. In addition todependence upon the atomic number, Z, atom intensities in STEMHAADF Z-contrast images also have a linear relationship with thenumber of atoms. Thus, these darker Pr spots correspond to Prvacancies in that column.

The images show Ga(3) atoms with similar intensity as Ga(1) atoms beside Pr vacancies, and that there are no Ga(3) atomsbetween occupied Pr atoms. Fig. 4d has a high magnification,which clearly shows each atom. The smaller atoms above andbelow the Pr vacancy are the Ga(3) atoms. The bottom inset showsthat not all Pr vacancy positions are aligned along the c-axis,rather, they are shifted relative to the adjacent ab-plane. Each Pr

vacancy in the [1–100] direction is separated by two occupied Prsites, which is consistent with the occupancy of 0.708(7) obtainedfrom single-crystal XRD.

The fast Fourier transformation (FFT) of Fig. 4b is shown inFig. 4e. The two sharp diffraction streaks show up in the FFTimage, the same as those observed in the ED pattern. The inverseFFT images obtained from each of the streak features are shown inFig. 4f, where the top image is the original experimental image, themiddle image is the inverse FFT from the 6.45 Å diffraction streak,and the lower image is the inverse FFT from the 3.20 Å diffractionstreak. These three images are aligned to show that the periodi-cities in intensities derive from the Pr/Ga(3) columns.

The pattern of black and white intensities in the inverse FFTimage from streak 1 reveals that the periodicity of Pr-vacancies is6.45 Å, which agrees well with the calculated distance of 6.48 Åbetween two Pr-vacancy lines in the Pr2Ga3 layer, confirming theordering of the Pr-vacancies within each layer. However, Pr-vacancies are not ordered along the c axis, as the positions ofthe Pr-vacancies are shifted within the ab-plane with respect to anadjacent Pr2Ga3 layer. This observation agrees with the previousstudies on stacking of Ln2X3 layers in Ln4Pt9Al24, Ln1.33Pt4Al10, andGd1.33Pt4Ga10 [11,15,20], as well as with the superstructure modelof the Pr2Ga3 layer obtained from single-crystal XRD (Fig. 5).According to the single-crystal XRD model, the distances betweenGa(3)-vacancy columns and Pr-vacancy columns is one-half of theperiodicity of Pr-vacancy columns (3.24 Å), which is consistentwith the periodicity of vacancies in the inverse FFT image fromstreak 2 (3.2 Å) along the [1–100] direction.

3.3. Pair distribution function analysis

PDF analysis was based on variable temperature X-ray totalscattering data collected at beamline 11-ID-B at the AdvancedPhoton Source at Argonne National Laboratory. Our initial modelwas based on the crystal structure obtained from single-crystalXRD experiments. In refinements using PDFGUI, the lattice para-meters, atomic positions, and isotropic thermal parameters of allatoms were allowed to refine while keeping site occupanciesof all atoms fixed. No structural transitions were observed forPr1.33Pt4Ga10 between 80 K and 298 K. Weighted Rw for refine-ments performed in PDFGUI range between 25.4% and 20.7% for alldata between 80 K to 298 K. Fig. 6a shows a good fit between the

Fig. 3. Polyhedral representations of Ga-coordination environments of Pr and Pt atoms. Blue, gray, and orange spheres represent Pr, Pt and Ga, respectively. (Forinterpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–1612

experimental PDF data and the calculated PDF (from the single-crystal XRD) model, indicating that the structural model ofPr1.33Pt4Ga10 obtained from single crystal XRD fairly describes

the local crystal structure. However, there is one peak at �3.2 Åthat is not described well by the single-crystal XRD model. Thelocal structure associated with this peak will be discussed infurther detail.

The partial PDFs of each atomic pair (which were calculated fromthe single-crystal model) and observed and calculated G(r) plots in therange 2oro4.0 Å are presented in Fig. 6b. The highest residual peak,which occurs at �3.2 Å, corresponds to neither the 3.4223(4) Å Pr–Ptdistance nor the �3.11 Å Pr–Ga distances determined from single-crystal XRD. This mismatch can be easily visualized in Fig. 6b where allpeaks in the G(r), except for the peak at �3.2 Å, can be assigned tointeratomic pairs based on calculated partial PDFs.

None of the atomic displacement parameters from single-crystaldiffraction were significantly elongated; however, to assess the possi-bility that the peak in the residual at 3.2 Å reflected disorder in the Gaposition, a single-crystal refinement with a split-Ga(1) site wasattempted. The Ga(1) site was chosen for further investigation fortwo reasons. In the original single-crystal XRD refinement, the Ga(1) site had the least spherical thermal ellipsoid. In addition, thelargest Q-peak in our original single-crystal XRD refinements corre-sponded to a Pr–Ga distance of �3.2 Å. The refinement of the split Ga(1) model proved to be worse than the original model; Rwp(¼0.0349)for the split Ga(1) model did not improve and the thermal ellipsoid ofthe newly formed Ga site became unusually oblong (U11¼0.00840,

Fig. 4. (a) ED pattern of Pr1.33Pt4Ga10 along [1–100]; (b) Atomic resolution STEM HAADF Z-contrast image of the crystal projected down [1–100] showing the ordering of Prvacancies along [11–20]. (c) Enlarged image with Pr vacancies highlighted with white circles. (d) Higher magnification image showing Pt, Pr and Ga atoms. (e) FFT of (b);(f) Top: Experimental inverse FFT image; inverse FFT image Middle: inverse FFT from the 6.45 Å diffraction streak, and the lower image is the inverse FFT from the 3.20 Ådiffraction streak.

Fig. 5. Pr and Ga(3) vacancies of ordered structure of Pr2Ga3 layers from the singlecrystal data and TEM data. Stacking of Pr2Ga3 layers along the c-axis contribute tothe observed superstructure of Pr2Ga3 layers. Blue, gray, and orange spheresrepresent Pr, Pt and Ga, respectively, while red pentagons and red squaresrepresent Pr and Ga(3) vacancies, respectively. (For interpretation of the referencesto color in this figure legend, the reader is referred to the web version of thisarticle.)

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–16 13

U22¼U33¼0.00376). Therefore, disorder of the Ga site is not a reason-able explanation for the �3.2 Å peak in the PDF data.

Another interesting observation was made in the temperature-dependent PDF data shown in Fig. 6c. With increasing tempera-ture, the Pr–Ga vacancy peak shifts to larger r; this peak clearlybroadens and shifts from �3.16(1) Å at 80 K to �3.20(1) Å at298 K. The Pr–Pt peak also broadens but continuously shifts withincreasing temperature to smaller r until it reaches �3.38(1) Å by298 K. These peak positions were obtained from fitting the firstfour peaks of Pr1.33Pt4Ga10 PDF data using Gaussian peak shapefunctions.[29] Neither the Pt–Ga nor the Ga–Ga peak shifts withtemperature (besides a slight increase due to thermal motion).These opposing trends in the Pr–Ga vacancy and Pr–Pt peaks maybe the result of the Pr and Ga(3) vacancies, for which evidence wasobserved in TEM data. Vacancy ordering in intermetallics canresult in a supercell and hence, be observed via X-ray diffraction.Recent examples of such experimental evidence have beenobserved for β-Fe1�xSe [30], SmGe2�x [31], and type-I clathrate,Rb8Sn44□2 intermetallics (□¼vacancy) [32]. Fässler et al. proposeda model of local structural relaxation for ordered vacancies inRb8Sn44□2 where Sn-□ distances are shorter than typical Sn–Snbonds and nearest-neighbor Sn–Sn contacts are elongated tocompensate for the vacancies. We postulate that a similar localstructural relaxation due to the Pr and Ga(3) vacancies can beobserved in PDF data. This is most clearly seen at 80 K where thePr–Ga vacancy distance is at its shortest (at 3.16(1) Å) while thePr–Pt distance is at its longest (at �3.40(1) Å).

It should also be noted that analogous Ce–Ga and Ce–Pt peaksshow no temperature dependence within the same temperaturerange of 80–298 K. Temperature-dependent G(r) plots forCe1.33Pt4Ga10 are provided in Supplementary Information. SinceCe1.33Pt4Ga10 does not exhibit magnetic ordering [33] in contrastto the ferrimagnetism of Pr1.33Pt4Ga10, it would be interesting tolearn how the local structural environment around the Ln3þ ioninfluences the magnetic behavior. Because current cooling cap-abilities were limited to 80 K, PDF data could not be used tocorrelate the ferrimagnetic transition in Pr1.33Pt4Ga10 with thelocal environment, but we do not exclude the possibilities of suchstudies in the future.

3.4. Magnetism

Fig. 7 shows the magnetization of a microcrystalline powdersample of Pr1.33Pt4Ga10 as a function of temperature. A Curie–Weiss fit to the linear part of the temperature-dependent portionof the data gives a Weiss constant θ¼–20.8 K, which indicatesnearest-neighbor antiferromagnetic correlations. The Curie con-stant was determined to be 6.99 emu K/mol per formula unit,which corresponds to an effective moment of 3.74 μB per Pr atom.This value is close to the expected value of 3.58 μB for a Pr3þ ion,indicating nearly a free-ion behavior at moderate temperatures.Upon cooling, the magnetization curve increases rapidly around15 K and saturates below 8 K. This observation, along with thenegative value of the Weiss constant, suggests Pr1.33Pt4Ga10behaves as a weak ferromagnet (canted antiferromagnet). Theantiferromagnetic coupling can be suppressed by applied mag-netic field; as shown by field-dependent magnetization measure-ments (Fig. 8), a metamagnetic transition takes place at H�2 T.This findings agrees with the earlier observations by Lacerda et al.[13]. At 7 T, the magnetization saturates at �1.5 μB per Pr3þ ion,which is much lower than the theoretical expectation value of3.20 μB. Thus, a significant antiferromagnetic exchange componentis still present at 7 T, the highest field available in our experiment,

Fig. 6. (a) Compares experimental PDF data with the structural model derived fromsingle crystal X-ray diffraction. Inset: Feature at 3.2 Å that does not agree with thesingle-crystal model. (b) Compares calculated partial PDFs of Ga–Pt, Ga–Ga, Pr–Ga,and Pr–Pt with experimental PDF data. (c) Shows temperature-dependent PDF dataof Pr1.33Pt4Ga10.

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–1614

suggesting that another metamagnetic transition to a ferromag-netically ordered state might be possible at higher fields.

The magnetic behavior was also studied on an oriented singlecrystal of Pr1.33Pt4Ga10. The measurements of the field-cooled (FC) andzero-field-cooled (ZFC) magnetic response revealed a significantlyhigher magnetization value when the applied magnetic field wasparallel to the c axis (Fig. 9), indicating the preferred alignment of thePr moments in this direction. At both field orientations, the divergenceof the FC and ZFC curves was observed at TC¼12.5(2) K, the tempera-ture of magnetic phase transition.

4. Conclusion

The structural properties of Pr1.33Pt4Ga10 have been analyzedusing single-crystal X-ray diffraction, TEM, and PDF analysis.Single-crystal X-ray diffraction and TEM results support a super-structure model with partially occupied (�2/3) Pr sites. The

periodicity of the Pr-vacancies measures 6.45 Å and confirms thatPr vacancies occur within the plane and not along the c-axis. ThePDF analysis showed that the single crystal model provided agenerally good fit with experimental data. A peak at �3.20 Å wasobserved, but not yet explained. Temperature-dependent PDF datashow that Pr–Pt distances increase with temperature, but that Pr–Ga distances decrease with temperature. These trends may suggeststructural relaxation about the Pr and Ga3 vacancies.

Magnetization studies show that the Pr3þ ion exhibits ametamagnetic transition at �2 T and that studies regarding apossible second metmagnetic transition to a ferromagnetic stateoccurs with applied fields greater than 7 T. These studies arecurrently underway in our laboratories.

Acknowledgments

Support of this research via the National Science FoundationCAREER Award (DMR-1056515 to R.M. and DMR-0955353 to M.S.)and ANL Project #20130011 are gratefully acknowledged. RTM andSDN also thank R. Osborn, O. J. Borkiewicz and K. A. Beyer forassistance and useful discussions. Work done at Argonne NationalLaboratory and the use of the Advanced Photon Source (APS) wassupported by the U.S. DOE under Contract no. DE-AC02-06CH11357.The TEM work was carried out at FSU TEM facility, which is fundedand supported by the Florida State University Research Foundation,and the National High Magnetic Field Laboratory, which was sup-ported in part by the National Science Foundation CooperativeAgreement DMR-1157490, the State of Florida, the U.S. Departmentof Energy, and Florida State University.

Appendix A. Supporting information

Supplementary data associated with this article can be found inthe online version at http://dx.doi.org/10.1016/j.jssc.2014.07.033.

References

[1] C. Pfleiderer, Rev. Mod. Phys. 81 (2009) 1551.[2] P. Monthoux, G.G. Lonzarich, Phys. Rev. B: Condens. Matter 63 (2001) 054529.

Fig. 8. Hysteresis curve measured on a polycrystalline sample of Pr1.33Pt4Ga10 at1.8 K. Inset: The magnified (low-field) section of the plot.

Fig. 9. Temperature dependence of FC (closed symbols) and ZFC (open symbols)magnetization measured under applied field parallel of 0.100 T (red circles) andperpendicular (black triangles) to crystallographic c-axis on single crystals ofPr1.33Pt4Ga10. (For interpretation of the references to color in this figure legend,the reader is referred to the web version of this article.)

Fig. 7. Temperature dependence of FC (red circles) and ZFC (black circles)magnetization measured on a polycrystalline sample of Pr1.33Pt4Ga10 in an appliedfield of 0.100 T. Inset: Temperature dependence of inverse magnetic susceptibility.The red line corresponds to the Curie–Weiss fit. (For interpretation of thereferences to color in this figure legend, the reader is referred to the web versionof this article.)

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–16 15

[3] R.E. Gladyshevskii, K. Cenzual, H.D. Flack, E. Parthe, Acta Crystallogr., Sect. B:Struct. Sci. 49 (1993) 468.

[4] J.L. Sarrao, J.D. Thompson, J. Phys. Soc. Jpn. 76 (2007) 051013.[5] C. Petrovic, P.G. Pagliuso, M.F. Hundley, R. Movshovich, J.L. Sarrao, J.

D. Thompson, Z. Fisk, P. Monthoux, J. Phys.: Condens. Matter 13 (2001) L337.[6] C. Petrovic, R. Movshovich, M. Jaime, P.G. Pagliuso, M.F. Hundley, J.L. Sarrao,

Z. Fisk, J.D. Thompson, Europhys. Lett. 53 (2001) 354.[7] M. Nicklas, V.A. Sidorov, H.A. Borges, P.G. Pagliuso, C. Petrovic, Z. Fisk, J.

L. Sarrao, J.D. Thompson, Phys. Rev. B: Condens. Matter 67 (2003) 020506.[8] O. Sichevych, W. Schnelle, Y. Prots, U. Burkhardt, Y. Grin, Z. Naturforsch., B:

Chem. Sci 61 (2006) 904.[9] Y.N. Grin, P. Rogl, Izv. Akad. Nauk SSSR 25 (1989) 593.[10] G.H. Kwei, A.C. Lawson, A.C. Larson, B. Morosin, E.M. Larson, P.C. Canfield, Acta

Crystallogr., Sect. B: Struct. Sci. 52 (1996) 580.[11] V. Thiede, B. Fehrmann, W. Jeitschko, Z. Anorg. Allg. Chem. 625 (1999) 1417.[12] M.A. Zhuravleva, X. Wang, A.J. Schultz, T. Bakas, M.G. Kanatzidis, Inorg. Chem.

41 (2002) 6056.[13] A. Lacerda, P.C. Canfield, W.P. Beyermann, M.F. Hundley, J.D. Thompson,

G. Sparn, Z. Fisk, C. Burns, D. Barnhart, A.D. Lawson, G.H. Kwei, J. Goldstone,J. Alloys Compd 181 (1992) 191.

[14] E.V. Murashova, A.I. Tursina, N.G. Bukhan’ko, A.V. Gribanov, I.V. Chernyshev, Y.D. Seropegin, J. Alloys Compd 398 (2005) 100.

[15] J. Niermann, W. Jeitschko, Z. Anorg. Allg. Chem. 630 (2004) 361.[16] T. Yamashita, S. Ohara, J. Phys.: Conf. Ser 400 (2012) 04274.[17] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giacovazzo,

A. Guagliardi, A.G.G. Molitemi, G. Polidor, R. Spagna, J. Appl. Crystallogr. 32(1999) 115.

[18] G.M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 64 (2008) 112.

[19] A.P. Hammersley, ESRF Internal Report, ESRF98HA01T, FIT2D V9.129 ReferenceManual V3 (1998) 1.

[20] S.E. Latturner, M.G. Kanatzidis, Inorg. Chem. 41 (2002) 5479.[21] M. Zhuravleva, X.Z. Chen, X. Wang, A.J. Schultz, J. Ireland, C.K. Kannewurf, M.

G. Kanatzidis, Chem. Mater. 14 (2002) 3066.[22] N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, second ed.,

Butterworth-Heinemann, Oxford, 1997.[23] Y.N. Grin, R.E. Gladyshevskii, O.M. Sichevich, V.E. Zavodnik, Y.P. Yarmolyuk, I.

V. Rozhdestvenskaya, Sov. Phys. Crystallogr 29 (1984) 528.[24] R.E. Gladyshevskii, K. Cenzual, H.D. Flack, E. Parthe, Acta Crystallogr., Sect. B:

Struct. Sci. 49 (1993) 468.[25] M.-K. Han, Y.-Q. Wu, M. Kramer, B. Vatovez, F. Grandjean, G.J. Long, G.J. Miller,

Inorg. Chem. 45 (2006) 10503.[26] B. Gerke, R.-D. Hoffmann, R. Pöttgen, Z. Anorg. Allg. Chem. 639 (2013) 2444.[27] S.J. Pennycook, L.A. Boatner, Nature 336 (1988) 565.[28] R.F. Loane, P. Xu, J. Silcox, Acta Crystallogr., Sect. A: Found. Crystallogr. 47

(1991) 267.[29] M. Wojdyr, J. Appl. Crystallogr. 43 (2010) 1126.[30] T.-K. Chen, C.-C. Chang, A.-H. Fang, W.-H. Chao, C.-M. Tseng, Y.-C. Lee, M.-

H. Wen, F.-R. Chen, M.-J. Wang, M.-K. Wu, D.V. Dyck, Proc. Nat. Acad. Sci. U.S.A.111 (2014) 63.

[31] P.H. Tobash, S. Bobev, N. Hur, J.D. Thompson, J.L. Sarrao, Inorg. Chem. 45(2006) 7286.

[32] F. Dubois, T.F. Fässler, J. Am. Chem. Soc. 127 (2005) 3264.[33] R.T. Macaluso, M. Shatruk, P. Chai, H. Hong, C. Wangeline, K. Ryan, P. Holton,

J. Allaz, G. Morrison, B. Fulfer, F.R. Fronczek, J.Y. Chan, J. Alloys Compd 600(2014) 193.

S. Doan Nguyen et al. / Journal of Solid State Chemistry 220 (2014) 9–1616