vibrationel spectroscopy of sr2znteo6

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Research Article

Received: 25 May 2009 Accepted: 18 August 2009 Published online i n Wiley Interscience: 13 November 2009

(www.interscience.wiley.com) DOI 10.1002/jrs.2494

Vibrational spectroscopic study of Sr2ZnTeO6

double perovskitesAnderson Dias,a∗ Ganesanpotti Subodh,b Mailadil T. Sebastianb

and Roberto L. Moreirac

Sr2ZnTeO6 ceramics were prepared by thesolid-staterouteand their vibrational phononmodes were investigatedusingopticalspectroscopic techniques, for the first time. X-ray diffraction (XRD) and Raman and infrared spectroscopies were employed toinvestigate the structures of these perovskite materials and the results analysed together with group-theoretical predictions.The number and behaviour of the first-order modes observed in both spectroscopic techniques are in agreement with thecalculations for a tetragonal I 4/m space group.The complete setof theoptical phononmodes wasdetermined,and theintrinsicdielectric properties of the materials were evaluated, allowing us to discuss their potential application in microwave (MW)circuitry. Copyright c 2009 John Wiley & Sons, Ltd.

Keywords: double perovskites; Raman spectroscopy; infrared spectroscopy; ceramics; microwave dielectrics; crystal structure

Introduction

From the materials chemistry point of view, ceramics with

the perovskite structure present an incredibly wide array of

structures and phases with totally different functions, which are

directly related to the combination of chemical elements in the

basic formula ABX3, X being usually oxygen. The multiple ion

substitutionin theperovskitelatticein eitherthe A orB position,or

in both, creates the so-called complex perovskites, which present

pairs of unlike valence cations in proportions depending on their

oxidation states and ionic radii.[1] It is well known that the finalproperties of any perovskite material are highly dependent on

the nature of its constituent cations, as well as on its structural

features, including ordering and defects.[2,3] In particular, because

of their adequate dielectric responses at high frequencies, ceramic

materials such as A2BBO6, known as ‘double perovskites,’ can

be used as dielectric resonators and filters in microwave (MW)

circuitry. Therefore, these compounds have been investigated

in the past years by many research groups in an attempt to

understand their crystal structure and dielectric behaviour as

functions of chemical substitution and physical behaviour, which

are intimately related to their performance in service.[3–5] More

recently, studies have been performed on double perovskites

containing B-site hexavalent cations, such as Mo, Re, U, W and Te.[6–12]

According to Augsburger etal .,[9] p-elements like tellurium can

be successfully stabilized in the B sites of the perovskite structure,

once they show the required spherical symmetry and adequate

ionicsizes.Also, previousworkson Te-basedcompositions showed

excellent MW properties with very low sintering temperatures

(<700 ◦C).[9,13] Although a number Te-based new materials have

been reported, to the best of our knowledge, no investigation

has been carried out to explore the vibrational properties of

complex perovskites with simultaneous presence of Zn and Te

sharing their B positions. In particular, ceramics with the formula

Sr2ZnTeO6 have not yet been investigated from the perspectives

of the behaviour of their optical phonon modes either from their

crystalline structure. In order to study the potential of a given

material to MW applications (resonators or filters), the knowledge

of its polar phonon features is mandatory, since these infrared

active phonons determine the intrinsic dielectric response of

the system in the intermediate terahertz region. Recently, Dias

etal .[11] and Ayalaetal .[14] studied the characteristics of the optical

phononsinSr2MgTeO6 andSr2CoTeO6 based on Raman scattering

data and found correlations between the crystalline structures

and thevibrational modes fortheseceramics. In the present work,

Raman and infrared reflectivity spectra of Sr2ZnTeO6 ceramics are

investigated in detail togetherwith group theory calculations. Theresults allow us to contribute to the debate on the crystalline

structure and MW dielectric properties of this ceramic system.

Experimental

Sr2ZnTeO6 ceramics were prepared by a solid-state ceramic route.

High-purity SrCO3 and TeO2 (99 + %, Aldrich Chemical Co.) were

used as starting materials. Stoichiometric amounts of the powder

mixtures were ball-milledin distilledwater as medium usingyttria-

stabilized zirconia balls in a plastic container for 24 h. The slurry

was dried, ground well, heated at a rate of 2.5 ◦C/min and kept

at 700 ◦C for 4 h. A slow heating rate was given for the oxidation

of Te4+ to Te6+, which occurs under specific thermodynamic

∗ Correspondenceto: Anderson Dias,Departamento de Química, ICEBII, Sala67,

UFOP, OuroPreto, MG 35400-000, Brazil.

E-mail: anderson [email protected]

a Departamento de Química, Universidade Federal de Ouro Preto-UFOP, Ouro

Preto, MG 35400-000, Brazil

b Materials and MineralsDivision,NationalInstitutefor Interdisciplinary Science

and Technology, Trivandrum695 019, India

c Departamento de Física, Universidade Federal de Minas Gerais-UFMG, C. P.

702, BeloHorizonte, MG 30123-970, Brazil

J. Raman Spectrosc. 2010, 41, 702–706 Copyright c 2009 John Wiley & Sons, Ltd.




conditions.[15] The mixed powders were calcined at 1000 ◦C for

4 h,groundintofinepowdersanddividedintodifferentbatchesfor

optimizing the sinteringtemperature. Dueto the poorsinterability

of Sr2ZnTeO6, 0.2 wt% B2O3 (Aldrich Chemical Co.) was added as

sintering aid and mixed thoroughly to the powders in distilled

water and dried. They were subsequently mixed with 4 wt% of

polyvinyl alcohol (molecular weight ≈22 000, BDH Lab Suppliers,

England) and again dried and ground well. Cylindrical pucks of

about 10–11 mm height and ca 20 mm diameter were made by

applying 150 MPa pressure. These compacts were then fired at

600 ◦C for 30 min to expel the binder before sintering at 1125 ◦C

for2 h. Thedensities of thesintered materials were determined by

the Archimedes method.

The crystalstructure and thephase purityof thesinteredsamples

were studied by X-ray diffraction (XRD) using Cu K α radiation

(λ = 0.15418 nm) in a Rigaku-Geigerflex 2037 diffractometer,

with the Bragg–Brentano geometry, in the 2θ range 10–140◦

(step 0.05◦ 2θ , 1 s/step). Besides, higher resolution data for using

in investigations concerning deviations from cubic symmetry

were collected at 4 s/step of 0.02◦

2θ , in special ranges around

chosen peaks. In these measurements, because of imperfect

monochromaticity, the data contain the contribution of theK α2 line, which was then considered in the data analysis. The

sintered samples were thermally etchedfor 20 min at 1100 ◦C, and

the microstructures were analysed by using a scanning electron

microscope (SEM: JSM 5600 LV, Tokyo, Japan).

Micro-Raman scattering spectra were collected in backscat-

tering configuration by using an Olympus confocal microscope

attachedtoaHoriba/Jobin-YvonLABRAM-HRspectrometer(objec-

tive 100×), equipped with 600 and 1800 grooves/mm diffraction

gratings. The 632.8 nm line of a He–Ne laser (effective power of

6 mW at the sample surface) was used as the exciting line and

a Peltier-cooled charge-coupled device (CCD) as detector of the

scattered light. An edge filter was employed for stray light re-

jection, i.e. Rayleigh scattered light. The wavenumber resolution

was better than 2 cm−1 and the accumulation times were typi-cally ten collections of 20 s. The obtained spectra were divided

out by the Bose–Einstein thermal factor[16] before being fitted

by a sum of Lorentzian lines. Infrared reflectivity measurements

were performed in a Fourier transform spectrometer (Bomem DA

8-02) equipped with a fixed-angle specular reflectance accessory

(external incidence angle of 11.5◦). In the mid-infrared region

(500– 4000 cm−1), we used an SiC glowbar lamp as the infrared

source, a Ge-coated KBr beamsplitter and an LN2-cooled HgCdTe

detector. In the far-infrared range (50–600 cm−1), we used the

same source, but a 6-µm coated Mylar hypersplitter and a liquid-

He-cooled Si bolometer. The sample’s surfaceswere polishedto an

optical grade (0.25 µm) prior to the measurements. A gold mirror

was used as reference. The data were collected under vacuum(10−4 bar) with a spectral resolution of 2 cm−1. The reflectivity

spectra were evaluated by means of standard Kramers–Kronig

analysis and adjusted by an oscillator model. A generalized four-

parameter oscillator model was used rather than the classical

model to achieve a good fit with minimum number of physically

meaningful oscillators.

Results and Discussion

Crystalline, single-phase Sr2ZnTeO6 perovskites were produced

after conventional solid-state processing at 1125 ◦C without any

secondary phases or impurities. The XRD results are displayed in

20 40 60 80 100 120 140

74.4 75.0 75.6 76.2 76.8

2θ /degrees

(620)

44.8 45.2 45.6 46.0 46.4

(400)

2θ /degrees

6 2 0

5 3 1

4 4 0

5 1 1

4 2 2

4 2 0

3 3 1

4 0 0

2 2 2

3 1 1

2 2 0

2 0 0

1 1 1

I n t e n s i t y

2θ /degrees

Figure 1. XRD pattern for the Sr2ZnTeO6 ceramics sintered at 1125 ◦C for2 h. Insets: high-resolution data for the peaks (400) and (620). Notice thecomplex structure of the peaks (fitted by Gaussian curves), owing to thelowering of symmetry besides K α1 and K α2 reflections.

Figure 2. Microstructure (SEM) of the Sr2ZnTeO6 samples sintered at1125 ◦C for 2 h.

Fig. 1andweretentativelyindexedonthebasisoftheInternational

Centre for Diffraction Data (ICDD) file #16-0549, assuming a

cubic structure, as previously made in other similar Te-based

ceramic systems.[11] The bulk density of Sr2ZnTeO6 ceramics with

additions of B2O3 was greatly enhanced and attained a maximum

at 1125 ◦C (96.1% of the theoretical density). Figure 2 presents

the microstructure of 0.2 wt% B2O3 added Sr2ZnTeO6 material

sintered at 1125 ◦C for 2 h. As can be observed, the materials

have uniform distribution of grains with sizes varying from 1 to

4 µm. The stability of complex perovskite structures can be well

explained with the use of tolerance factors (t ).[1] For the materials

studied here, the tolerance factors can be determined by:

t = RSr + RO

√ 2

RZn + R Te

2

+ RO

(1)

J. Raman Spectrosc. 2010, 41, 702 –706 Copyright c 2009 John Wiley & Sons, Ltd. www.interscience.wiley.com/journal/jrs



A. Dias etal .

where RSr, RZn, R Te and RO are the ionic radii of Sr, Zn, Te and

O ions, respectively.[1,11,17] Shannon’s ionic radii[17] are frequently

employed to determine the tolerance factors. For Sr2ZnTeO6,

the tolerance factor is 0.985, which is at the borderline between

cubic (untilted) and distorted pseudo-cubic (tilted) structures.

Based on previous results of Dias etal .,[11] which showed how to

distinguish between cubic or pseudo-cubic symmetries in similar

Sr-containing double perovskites, high-resolution XRD analyses

were then carried out around the particular peaks (400) and

(620). The corresponding diffractograms are displayed in the

insets of Fig. 1, where characteristic splittings of the XRD peaks

are seen after peak deconvolution (the experimental data were

fitted by Gaussian curves for easier visualization), demonstrating

unequivocally a lowering of symmetry in these ceramics. The

observed peak splitting together the high tolerance factor (close

to 1) suggests a slight tetragonal distortion of the cubic lattices

for our materials, as has been verified in other double perovskites

containing tellurium or indium.[11,18] As will be shown later, these

observations are confirmed by the analysis of our spectroscopic

data. TheMW dielectric propertiesof theSr2ZnTeO6 ceramics were

investigated using the resonance method at 5 GHz (details on the

experimental setup are described in Ref. [11]). The material hasdielectric constant of 16.5, quality factor of 8500 and temperature

coefficient of the resonant frequency of −77 ppm/◦C at the

optimized sintering conditions of 1125 ◦C/4 h.

Room-temperatureRamananalysiswascarriedoutinSr2ZnTeO6

materials, and the results are displayed in Fig. 3 (open squares).

As can be seen, the spectrum is dominated by four strong bands

centred at 147, 430, 573 and 767 cm−1, together with other

weaker though well-defined bands which will be discussed later.

Such a profile with four intense Raman bands is characteristic

of ordered 1 : 1 complex perovskites with cubic or pseudo-cubic

structures.[19,20] Compared to their MgTe analogues, the bands

of the Sr2ZnTeO6 ceramics are slightly downshifted.[11] This is

as a consequence of the larger Zn ions compared to Mg ions,

which leads to an expanded unit cell with larger ionic distances

150 300 450 600 750 900

390 420 450Wavenumber/cm-1

105 140 175 210

Wavenumber/cm-1

R a m a n I n t e n s i t y

Wavenumber/cm-1

Figure 3. Micro-Raman spectrum for the Sr2ZnTeO6 complex perovskitesinthe spectral region40– 900 cm−1.Experimentaldataareinopensquares,while the fitted curve is the black line. Grey lines represent the phononmodes adjusted by Lorentzian curves.

and, therefore, to general weaker ionic bonds. Completing the

spectroscopic analysis, infrared reflectivity spectrumof Sr2ZnTeO6

materialsis presented inFig. 4 (open squares). Thevisualinspection

of the spectra shows at least six well-defined bands for these

samples, indicating an average non-cubic symmetry for the

Sr2ZnTeO6 materials, as will be discussed below. A careful

analysis of Fig. 4 reveals the presence of other weaker bands

and shoulders in the reflectivity spectrum, which can be revealed

only after adequate fitting procedures. In view of that, a group

theoretical investigation was undertaken in order to get a better

understanding of thecrystal structureand its consequenceon the

samples’ vibrational features.

The ideal simple perovskite is cubic, belonging to the Pm3m

spacegroup, but tilting of the oxygen octahedra occurs veryoften,

owing to structural instabilities linked to a mismatch in the sizes

of the cations. It is worth mentioning that there are no active

first-order Raman phonons and only three infrared active modes

for the ideal Pm3m group. Concerning the complex perovskites of

the general formula A2BBO6, cubic structures will be presented

by materials with tolerance factors close to or greater than 1.

In such cases, the ideal cubic structure can still be assumed by

totally disordered systems (B site with average occupation of twocations). However, the most interesting and frequent cases are

shown by ordered, yet untilted lattices with Fm3m symmetry (O5h,

No. 225, Glazer’s notation a0a0a0).[21] This configuration allows a

classification of the normal modes at the Brillouin zone centre as

= Ag+E g+F 1g+2F 2g+5F1u+F2u. Thesymmetry analysis of the

irreducible representations above indicates that four modes are

Raman active ( Ag, E g, 2F 2g), and another four modes are infrared

active (4F 1u).[22] For our Sr2ZnTeO6 ceramics, XRD data showed

that an Fm3m structure is not adequate to describe its structure,

because it is not compatible either with the splitting of the (400)

and (620) XRD peaks or with the number of observed modes in

Raman and infrared spectra. Indeed, a lower symmetry structure

with a small distortion from the cubic one appears to be more

Figure 4. Measured (closedsquares)and adjusted (solidblack line)infraredreflectivity spectra for the Sr2ZnTeO6 ceramics.

www.interscience.wiley.com/journal/jrs Copyright c 2009 John Wiley & Sons, Ltd. J. RamanSpectrosc. 2010, 41, 702–706




plausible to describe the XRD and spectroscopic data. A2BBO6

double perovskites withtetragonal distortion belong veryoften to

the I 4/m space group.[23] In the present case, we believe that this

structure could describe our data, since it holds for other similar

materials. [11,18,19]

Assuming this tetragonal structure, Sr2ZnTeO6 materials could

be described as belonging to the I 4/m space group (C 54h, No. 87,

Glazer’s notation a0a0c−).[21] This tetragonal symmetry is derived

from the prototype Fm3m cubic structure by an antiphase tilt

of ZnO6 and TeO6 octahedra in the basal plane along the [001]

direction of the cubic cell. In this structure, Sr atoms occupy 4 d

sites of S4 symmetry, Zn and Te ions occupy 2a and 2b sites of C 4h

symmetry and the oxygen atoms are in 4e and 8h sites (C 4 and C ssymmetries, respectively). Then, by usingthe site group method of

Rousseau etal .,[22] one obtains the followingdecomposition of the

phonon modes in terms of the irreducible representations of the

C 4h point group: = 3 Ag+5 Au+ 3Bg+ Bu+ 3E g+ 6E u. Excluding

theacoustic ( Au + E u) and silent modes (Bu), we wouldexpect nine

Raman active(3 Ag, 3Bg, 3E g) and nine infrared modes (4 Au, 5E u) for

this structure. Bearing in mindthe above factor group calculations,

careful fitting of the Raman spectra of Sr2ZnTeO6 samples were

carried out. The theoretical curves are displayed in Fig. 3 as solidblacklines,besidesnineLorentziangreylines,inperfectagreement

with the theoretical predictions. Table 1 presents the adjustment

parameterstothebestfitoftheRamanspectrum,i.e.wavenumbers

(cm−1) and full width at half-maxima (cm−1). This result presents

strong evidence that Sr2ZnTeO6 perovskite would belong to the

tetragonal I 4/m (C 54h) space group.

Now, the results from infrared reflectivity measurements will be

discussed. The spectrum displayedin Fig. 4 was analysed by using

the four-parameter semi-quantum model,[24] with a nonlinear

least-squares program.[25] Within this model, the infrared phonon

contributions to the complex dielectric function ε(ω) can be

described by:

ε(ω) = ε∞N

j =1

2 j ,LO − ω2 + i ωγ j ,LO

2 j ,TO − ω2 + i ωγ j ,TO

(2)

where ε∞ is the electronic polarization contribution, and

j ,LO( j ,TO) and γ j ,LO(γ j ,TO) are the frequency and damping of

the j th longitudinal (transverse) optical polar modes, respectively.

N is the number of polar phonons. At quasi-normal incidence, the

dielectric function is related to the optical reflectivity R by the

Table 1. Observed Raman modes for the Sr2ZnTeO6 ceramics

Band γ

1 114.2 15.5

2 141.8 4.3

3 155.6 10.2

4 166.4 19.5

5 413.9 7.3

6 422.4 6.9

7 432.1 6.6

8 568.5 20.3

9 765.9 23.8

Positions (, cm−1) and full width at half-maxima (γ , cm−1) wereobtained from the adjustment of the experimental data by Lorentzianlines.

Fresnel formula:

R =

ε(ω)− 1 ε(ω)+ 1

2

(3)

The best fit of our experimental reflectivity data by Eqns (1) and (2)

are presented in Fig. 4 as the solid black curve, and the obtained

dispersion parameters (positions and widths of the TO and LO

infrared branches) are listed in Table 2. We note that nine infrared

modes were discerned for the Sr2ZnTeO6 ceramics, in perfectagreement with the predicted number of modes for materials

with the assumed tetragonal structure.

Once the dispersion parameters for the polar phonons are

determined, we can calculate the intrinsic phonon contribution to

theMW dielectric properties of thematerial. First, we calculate the

oscillator strengths of the individual j th TO modes (Table 2) by:

ε j =ε∞

2 j ,TO

×

k

(2k ,LO −2

j ,TO)

k = j

(2k ,TO −2

j ,TO)(4)

From these values, the ‘static’ dielectric constant in the MW limit( j ,TO ω) is obtained by adding the oscillator strengths over all

modes according to the equation:

εr = ε∞ +N

j =i

ε j (5)

The values of εr and ε∞ for the double perovskite are given in

Table 2, together with the phonon dispersion parameters. Now,

the intrinsic unloaded quality factor Qu extrapolated to the MW

region ( j ,TO ω) can be calculated as the reciprocal of the

dielectric loss tangent (tan δ), i.e.

tan δ =

j

tan δ j =

j

ω ε j γ j ,TO

εr 2 j ,TO

(6)

The obtained values for the individual and overall losses are also

presented in Table 2. At 10 GHz, Sr2ZnTeO6 ceramics presented

intrinsic Qu × f of 85 THz and εr = 14.1. These values are

quite adequate for applications as MW devices – relatively high

quality factor (high selectivity) and high dielectric constant – and

Table 2. Dispersionparameters calculated from thefit of theinfraredreflectance spectrum of Sr2ZnTeO6

j ,TO

γ j ,TO

j ,LO

γ j ,LO

ε j

105 tan δ j

/ω

147.2 12.5 161.7 9.7 4.342 17.863

187.7 18.4 197.0 65.1 3.458 12.826

198.0 36.7 237.3 67.3 0.329 2.188

243.6 48.2 255.2 57.6 0.105 0.606

258.4 79.2 260.0 15.5 0.007 0.063

372.7 13.4 440.6 53.3 1.760 1.208

441.0 41.3 460.1 20.5 0.002 0.003

668.3 30.2 701.2 37.6 0.628 0.301

705.3 44.1 760.3 14.6 0.046 0.029

ε∞ = 3.41 εr = 14.1 tan δ j /ω = 35.0× 10−5

The positions () and damping constants (γ ) are given in cm−1.

J. Raman Spectrosc. 2010, 41, 702 –706 Copyright c 2009 John Wiley & Sons, Ltd. www.interscience.wiley.com/journal/jrs



A. Dias etal .

are in good agreement with the dielectric response of other

double perovskites.[11,18,19] However, we should remember that

for ceramic materials the intrinsic Qu × f values are usually higher

than the actual MW ones, because some important dielectric

losses of extrinsic origin (impurities, polar species, microstructural

defects, etc.) must be added up to the phonon ones. [26] Despite

this, the intrinsic quality factor value allows a good evaluation

of the processing conditions for a ceramic material once single

crystals have very low extrinsic contributions.

Let us now discuss the tetragonal structure proposed for

our Sr2ZnTeO6 ceramics. Howard etal .[27] have applied group

theoretical tools to study ordereddouble-perovskite structures by

considering different combinations of octahedral tilting, starting

from the cubic Fm3m structure. This structure is a result of the

doubling of the ideal perovskite by imposition of rocksalt 1 : 1

ordering. FromthisFm3m spacegroup,tiltingoftheBO 6 octahedra

are allowed, resulting in eleven structures of lower symmetry, as a

result of the cation orderingin combination withthe corner-linked

tilting of theoctahedralunits. Group– subgrouprelationships were

established, which could be applied to explain the experimentally

observed results of the present work, as discussed below.

Sr2ZnTeO6 perovskites present a tolerance factor nearly unity,which means that a cubic phase would be expected. Many

other complex perovskites with tolerance factors near unity

(or traditionally considered cubic) were recently revisited, and

distorted structures were determined.[11,14,18,19,28] Indeed, in some

recent works, Dias etal .[11,14,19] and Ayala etal .[14] showed that

although XRD and other techniques indicate cubic or nearly

cubic structures for a number of double perovskites, Raman

spectroscopic analysis wasable to resolvethe structures as actually

tetragonal. Within the framework of the Glazer[21] description,

the I 4/m structure derives from Fm3m (a0a0a0) by a single

rotation of the BO6 octahedra about one of the four-fold axes,

lowering the symmetry to tetragonal (a0a0c−). This structure

presents nine Raman active and another nine infrared active

phonon modes,[19] in complete agreement with our findings forthe Sr2ZnTeO6 ceramics. We believe that the small tetragonal

distortion in these materials is similar to that observed in

Sr2MgTeO6,[11] Ba2MgTeO6,[11] Sr2CoWO6[14] and Ba2YNbO6 ,[19]

i.e. the octahedral tilting is too small to be detected by XRD

or even more sophisticated techniques such as neutron and

electron diffraction. However, the anti-phase distortions appear

to be sufficiently large to be detected by Raman and infrared

spectroscopies, giving rise to the degeneracy and breaking of the

symmetries of the normal modes and leading to a larger number

of observed fundamentals.

ConclusionsSr2ZnTeO6 ceramics were prepared as single-phase materials, and

their vibrational features are reported for the first time beside

structural and microstructural characterizations. XRD as well as

Raman andinfrared dataallowedus to resolvethe correctstructure

of Sr2ZnTeO6 ceramics in the light of group theoretical models.

Besides, our results contributed to understand and explain small

lattice distortions in perovskite materials with tolerance factors

closeto unity (usually considered cubic). The materials present the

tetragonal I 4/m structure with small deviations fromthe common

cubic Fm3m structure, which occursvery often in perovskites with

ordered lattice arrangements with 1 : 1 ratio.

Acknowledgements

The Brazilian authors acknowledge the financial support from

CNPq (Conselho Nacional de Desenvolvimento Científico e Tec-nologico), FINEP (Agencia de Inovacao) and FAPEMIG (Fundacao

de Amparo a Pesquisa do Estado de Minas Gerais). G. Subodh

is grateful to CSIR (Council of Scientific and Industrial Research),

India for a junior research fellowship. We also thank Alexandre M.

Moreira for his help in XRD experiments.

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vibrationel spectroscopy of sr2znteo6

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