Magnetic, Structural and Morphological Characterization of Sr<sub>2</sub>GdRuO<sub>6</sub> Double Perovskite

doi:10.4236/jmp.2011.23023

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Journal of Modern Physics, 2011, 2, 154-157

doi:10.4236/jmp.2011.23023 Published Online March 2011 (http://www.SciRP.org/journal/jmp)

Magnetic, Structural and Morphological Characterization

of Sr2GdRuO6 Double Perovskite

L. T. Corredor1, D. A. Landínez Téllez1, J. L. Pimentel Jr2, P. Pureur2, J. Roa-Rojas1

1Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, Bogotá

DC,Colombia

2Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil

E-mail: [email protected].

Received October 6, 2010; revised December 8, 2010; accepted December 15, 2010

Abstract

We report structural, morphological and magnetic properties of the Sr2GdRuO6 compound, which is used as

precursor oxide in the production process of RuSr2GdCu2O8 superconducting ruthenocuprates. The crystal-

line structure was studied by X-ray diffraction and Rietveld refinement. Results reveal that material crystal-

lizes in a monoclinic double perovskite, space group P21/n (#14). Scanning Electron Microscopy experi-

ments on samples show homogeneous granular morphology with grain size from 3 up to 7 μm. Semiquanti-

tative analysis of composition was performed by the Energy Dispersive X-ray technique. Experimental re-

sults are 98% in agreement with the theoretical stoichiometry. Curves of magnetization as a function of tem-

perature exhibit an antiferromagnetic-like behaviour, with Néel temperature TN=15.3 K and magnetic effec-

tive moment 8.72 μB.

Keywords: Complex Perovskite, Structure, Magnetic Properties

1. Introduction

The RuSr2GdCu2O8 ruthenocuprate oxide was synthe-

sized for the first time in 1995 [1]. It belongs to the

RuSr2RECu2O8 (Ru-1212RE) family, where RE repre-

sents rare earth elements. The main characteristic of

these compounds is the presence of magnetic and super-

conductor properties in a simultaneous way, with mag-

netic transition temperature higher than the supercon-

ductor critical temperature, which make them unique

respect to the other magnetic superconductors. Initially,

ruthenocuprates were obtained by the solid state reaction

with CuO and Sr2RERuO6 as precursor oxides [2-4]. The

superconductor properties are determined by the Cu-O

bonds in the CuO2 conduction planes, which give rise to

critical temperature values between 15 and 50 K [5].

Magnetic properties are associated with Ru-O bonds

(RuO2), even when actually there is no consensus about

the magnetic ordering between Ru atoms [6]. Muon Spin

Rotation measurements (μSR) point a ferromagnetic or-

dering normal to c crystallographic axis [7], while neu-

tron diffraction experiments indicate an antiferromag-

netic response [8]. The main obstacle to define the nature

of the superconductor-magnetic mechanisms in this kind

of materials is the lack of high purity samples. In order to

enhance the knowledge about the synthesis method of

RuSr2GdCu2O8, we report the high quality production

process, a carefully structural Rietveld analysis of X-ray

diffraction data, morphologic and compositional studies

of the Sr2GdRuO6 material. Measurements of magnetic

susceptibility as a function of temperature were also

performed to observe the possible effects of this precursor

material on the magnetic characteristics of the

RuSr2GdCu2O8 superconductor.

2. Experimental

The Sr2GdRuO6 ceramic was obtained by the standard

solid state reaction method, from stoichiometric quanti-

ties of SrCO3 (Chemi 99.7%), Gd2O3 (Aldrich 99.9%)

and RuO2 (Aldrich 99.9%). In order to extract possible

humidity, the oxide powders were heated to 200oC for

24h. Then they were weighted, grounded in an agatha

mortar, and pressed to form pellets of 9.8 ± 0.1 mm di-

ameter and 1.0 ± 0.1 mm thickness. These pellets were

calcined at 930oC for 12 h, cooled up to ambient tem-

perature, regrounded and twice heated in a sinterization

process at 1230oC for 16 h. Structural characterization

L. T. CORREDOR ET AL.

155

was performed by the X ray diffraction technique (XRD)

through a Panalytical Xpert Pro diffractometer with

CuK = 1,5406 Å radiation. The morphological charac-

terization was carried out by using a FEI Quanta 200

Scanning Electron Microscope SEM, and the semiquan-

titative analysis of composition was performed by means

Energy Dispersive X-ray (EDX) experiments, with an

EDAX microanalysis accessory for the SEM. Magneti-

zation and susceptibility versus temperature measure-

ments were performed through a Quantum Design 2000

MPMS SQUID. Rietveld refinement of experimental

XRD data was performed by using the GSAS code [9].

Refinement results were compared with characteristic

values predicted by the Structure Prediction Diagnostic

Software (SPuDs), which was created for perovskite-like

materials [10].

3. Results and Discussion

Figure 1 shows the powder x-ray diffraction pattern for

Sr2GdRuO6 material. Rietveld refinement of these ex-

perimental data is shown too. The continuous curve cor-

responds to the pattern calculated for Sr2GdRuO6 and the

symbols represent the experimental diffractogram. In the

same graph, locations of Bragg peaks are shown as ver-

tical lines. Curve in bottom of Figure 1 represents the

difference between experimental pattern and the calcu-

lated one. From Rietveld refinement we determined that

this diffraction pattern is characteristic of a monoclinic

perovskite structure, space group P21/n (#14).

The discrepancy factor of refinement was χ2 = 1.063.

The final cell parameters found were a = 5.8019(0) Å,

B = 5.8296(5) Å, c = 8.2223(7) Å, and Tilt Angle

 = 90.258o. The atomic coordinates and relative occu-

Figure 1. XRD pattern for Sr2GdRuO6 complex perovskite.

Symbols correspond to the experimental data and continu-

ous one is the obtained by Rietveld refinement. Bottom

curve represents the difference between experimental and

calculated patterns.

pancy of each site are shown in Table 1.

Results are 99 % in agreement with the SPuDs [10],

which predicts P21/n (#14) space group as very probable.

The SPuDs program also predicts the lattice parameters a

= 5.7537 Å, b = 5.9634 Å, c = 8.2760 Å, tolerance factor

0.9170 and tilt angle  = 89.9546o. The presence of the

(002), (114) and (116) peaks in the diffractogram of Fig-

ure 1 confirms the existence of the superstructure that

characterizes the A2BB’O6 complex perovskites [11].

The values for the bond distances of cations (relative

to the oxygen anion) and occupancy were obtained from

the Rietveld refinement. These are shown in Table 2.

In this double perovskite the explanation of distortion

from the ideal cubic perovskite structure is clear because

the Sr2GdRu O 6 complex perovskite have the generic

formula A2BB’O6, and for this type of material the toler-

ance factor t, is calculated by the ratio:

BB'

rr r















where rA, rM’, rM’’ and ro are the ionic radii of the A, B,

B’, and O ions, respectively. If t is equal to unity, there is

ideal cubic perovskite structure, and if t < 1 the struc-

tures is distorted from the cubic symmetry, and in

agreement to the SPuDs prediction [10], the value of

tolerance factor by Sr2GdRuO6 complex perovskite is

0.9170. The distortion from the ideal cubic perovskite

structure is a consequence of the inclination of the

Gd-O6/2 and Ru-O6/2 octahedra; in the mean time support

their corner connectivity. Then, the Ru5+ and Gd3+

cations occupy two crystallographic independent octahe-

dral sites, namely 2d and 2c [12]. Our crystallographic

results are in accordance with other reports, but there is

no an enhanced characterization about atomic positions

and the inter-atomic distances [13].

The alternating distribution between Ru+5 and Gd+3,

ions on the six coordinate B sites of the double

perovskite is in agreement with the results obtained from

the refinement of experimental diffraction pattern. On

the other hand, the Sr2+ is located in the A crystal-

lographicsite, as shown the Figure 2.

The surface morphology of Sr2GdRuO6 samples was

Table 1. Structural parameters of Sr2GdRuO6 found by

Rietveld analysis of XRD data.

Atom Site x y z

Sr 4e 0.5054 0.5309 0.2511

Ru 2c 0.0000 0.5000 0.0000

Gd 2d 0.5000 0.0000 0.5000

O 4e 0.2333 0.2084 0.9773

O 4e 0.2675 0.7408 0.9357

O 4e 0.3856 0.9806 0.2281

156 L. T. CORREDOR ET AL.

Table 2. Inter-atomic distance and occupancy calculated

through Rietveld refinement of experimental data.

Cation Anion & Multipl. Distance (Å) Occupancy

Ru(2c) O(4e) × 2 1.9681 1.00

Ru(2c) O(4e) × 2 1.9666 1.00

Ru(2c) O(4e) × 2 1.9677 1.00

Gd(2d) O(4e) × 2 2.2823 1.00

Gd(2d) O(4e) × 2 2.2805 1.00

Gd(2d) O(4e) × 2 2.2821 1.00

Sr(4e) O(4e) × 1 3.6412 1.00

Sr(4e) O(4e) × 1 2.8741 1.00

Sr(4e) O(4e) × 1 2.7532 1.00

Sr(4e) O(4e) × 1 2.5319 1.00

Sr(4e) O(4e) × 1 2.9295 1.00

Sr(4e) O(4e) × 1 3.6321 1.00

Sr(4e) O(4e) × 1 2.5176 1.00

Sr(4e) O(4e) × 1 3.7147 1.00

Sr(4e) O(4e) × 1 3.3141 1.00

Sr(4e) O(4e) × 1 2.4884 1.00

Sr(4e) O(4e) × 1 3.4116 1.00

Sr(4e) O(4e) × 1 2.6425 1.00

studied by SEM images as shown in Figure 3. Per-

formed analysis reveals the occurrence of granular to-

pology with size grain between 2 up to 7 µm. As ob-

served in microphotography, grains are strongly diffused

between them. It is important to notice that sample evi-

dences a single type of grain.

Through semiquantitative EDX analysis, we obtain

that composition of material are 98 % in agreement with

theoretical values calculated from stoichiometry of

Sr2GdRuO6 material. Results are shown in Table 3.

It is known that the light characteristic of oxygen on

the application of X-ray radiation produces a subestima-

tion of its concentration in material when EDX technique

is applied to study composition. From structural, mor-

phologic and compositional characterizations we de-

duced that no other crystallographic phases or impurities

are present in the sample.

The magnetic character of material was analyzed from

dc-susceptibility experiments as a function of tempera-

ture. The results are shown in the Figure 4, where the

magnetic susceptibility reveal an anomaly close to T =

15.3 K. This behavior is usually related with the occur-

rence of a magnetic ordering transition. Fitting of sus-

ceptibility with the Curie-Weiss relation 0









CTT reveals that Sr2GdRuO6 behaves as an anti-

ferromagnetic material below a Néel temperature TN =

15.3 K.

In addition, the Curie-Weiss adjust permitted to de-

termine the temperature independent susceptibility



o =

0.0181 emu/mol and the effective magnetic moment

PeffµB = 8.72 µB. Theoretical calculations by the Hund’s

Figure 2. Crystal structure of Sr2GdRuO6. The continuous

black lines indicate the primitive perovskite unit c ell.

Figure 3. SEM micrograph for Sr2GdRuO6 double

perovskite obtained from ETD detector (secondary elec-

trons).

Figure 4. Measurements of dc Susceptibility for Sr2GdRuO6

on the application of H = 0.1 T. In picture, circles are the

experimental data and the line represents the Curie-Weiss

fitting.

L. T. CORREDOR ET AL.

157

6. References

Table 3. Results of semi quantitative EDX analysis for the

Sr2GdRuO6 sample.

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Atom Theoretical %Wt Experimental %Wt

Sr 33.09 33.82

Ru 29.69 30.05

Gd 19.09 19.78

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

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PgJJ

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moments of the isolated ions Gd3+ and Ru5+ must be

µGd3+ = 7.94µB and µRu5+= 3.87µB, respectively [14].

The effective magnetic moment of Sr2GdRuO6 is ob-

tained to be µeff= 8.83µB, where we have used

ef fGd Ru



.This result corresponds to 98.3% of

agreement between experimental and theoretical values.

Below TN, it is observed that the antiferromagnetic or-

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4. Conclusions

We have performed an experimental study on crystalline

structure, surface morphology, composition and mag-

netic response of Sr2GdRuO6 oxide ceramic. Rietveld

refinement of X-ray diffraction pattern showed that ma-

terial crystallizes in a monoclinic complex perovskite

structure with space group P21/n (#14), with an alternat-

ing distribution between Ru+5 and Gd+3 ions on the six

coordinate B sites of the complex perovskite. The pres-

ence of the crystallographic peaks (002), (114) and (116)

in the diffractogram confirms the existence of the super-

structure that characterizes the A2BB’O6, Complex

perovskites. The image of scanning electron microscopy

reveals the strongly compact characteristic of grains with

sizes from 2 up to 7 µm. The results of Energy Disper-

sive X-ray experiments show that the composition of the

material corresponds in a 98% to the expected

stoichiometry of Sr2GdRuO6 complex perovskite. Mag-

netic susceptibility experiments permitted to determine

the occurrence of a paramagnetic-antiferromagnetic tran-

sition with a Néel temperature of 15.3 K. From the

analysis of susceptibility curves we found the effective

magnetic moment to be 8.72µB. In the dc susceptibility

curve it is possible to observe a tendency to the anti-

ferromagnetic ordering below the Néel temperature.

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5. Acknowledgements

This work was partially supported by the Colombian

agencies Colciencias, the Division of Investigations,

Universidad Nacional de Colombia (DIB - Bogotá), and

Brazilian CNPq.