Structural order, magnetic and intrinsic dielectric properties of magnetoelectric La2CoMnO6

Accepted Manuscript Structural order, magnetic and intrinsic dielectric properties of magnetoelectric La2CoMnO6 Rosivaldo X. Silva, Alan S. de Menezes, Rafael M. Almeida, Roberto L. Moreira, R. Paniago, Xavi Marti, Helena Reichlova, Miroslav Maryško, Marcos Vinicius S. Rezende, Carlos William A. Paschoal PII:

S0925-8388(15)31654-6

DOI:

10.1016/j.jallcom.2015.11.097

Reference:

JALCOM 35952

To appear in:

Journal of Alloys and Compounds

Received Date: 27 August 2015 Revised Date:

6 November 2015

Accepted Date: 17 November 2015

Please cite this article as: R.X. Silva, A.S. de Menezes, R.M. Almeida, R.L. Moreira, R. Paniago, X. Marti, H. Reichlova, M. Maryško, M.V.S. Rezende, C.W.A. Paschoal, Structural order, magnetic and intrinsic dielectric properties of magnetoelectric La2CoMnO6, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.11.097. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Structural order, magnetic and intrinsic dielectric properties of magnetoelectric La2CoMnO6

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Rosivaldo X. Silva1,2,3, Alan S. de Menezes1, Rafael M. Almeida3,4, Roberto L. Moreira3, R. Paniago3, Xavi Marti5, Helena Reichlova5, Miroslav Maryško5, Marcos Vinicius S. Rezende6 and Carlos William A. Paschoal7, * 1

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Departamento de Física, Universidade Federal do Maranhão, Campos VII, 65400-000, Codó-MA, Brazil 2 Departamento de Física, Universidade Federal do Maranhão, Campus do Bacanga, 65085-580, São Luis-MA, Brazil 3 Departamento de Física, Universidade Federal de Minas Gerais, ICEx, 31270-901 Belo HorizonteMG, Brazil 4 Instituto Federal de Educação, Ciência e Tecnologia do Maranhão, Campus Imperatriz, 65919-050, Imperatriz-MA, Brazil 5

Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic Departamento de Física, Universidade Federal de Sergipe, 49500-000, Itabaiana-SE, Brazil 7 Departamento de Física, Universidade Federal do Ceará, Campus do Pici, 65455-900, Fortaleza-CE, Brazil

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Abstract

Rare-earth manganites with a double perovskite structure play an important role in the field of multiferroics and magnetoelectrics as they encompass remarkable dielectric properties, semiconductivi-

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ty and ferromagnetism near room temperature. In this family, La2CoMnO6 is one of the most investigated compounds partially due to its ferromagnetic Curie temperature reaching up to 235 K. Since their magnetic and dielectric properties are strongly influenced by the B-site ordering of Co and Mn ions,

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understanding and mitigating the sources of structural disorder becomes a crucial task in order to produce functional materials. In this paper, we present a series of La2CoMnO6 ceramics covering a broad spectrum of B-site orderings obtained by employing different calcination temperatures and synthesis conditions. Consequently, the magnetic and intrinsic dielectric properties, which depend on the ordering, change accordingly. Next, we show that the intrinsic dielectric constant of La2CoMnO6 is weakly dependent on the calcination temperature and we argue that the early observed colossal dielectric constant is of an extrinsic origin. Finally, we report reduced dielectric losses upon changing the calcination temperatures thus enabling a tool for enhancing the unloaded quality factor as demanded by dielectric resonator at microwave frequencies applications. 1

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Keywords: La2CoMnO6, double perovskite, structural order, magnetodielectric, Raman spectroscopy, infrared spectroscopy

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1. Introduction Cationic structural order-disorder transitions drive the crystal structure, the phase stability and

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the properties of many oxides with complex perovskite structure. Changes in the structural order induce critical changes in magnetic and electric properties as well as in the electronic and ionic conductivities [1]. B-site substitutions in simple ABX3 perovskites originate mainly A2B’B’’X6 and A3B’B’’2X9 complex perovskites which correspond to 1:1 and 1:2 substitutions, respectively. Triple complex perovskites A3B’B’’2X9 have properties that are fully controlled by B-site structural ordering: from ionic properties,

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with the order defining high ionic conductivity [2,3], up to dielectric properties where the ordering drives the dielectric properties thus enabling their application in dielectric resonators [4–6]. B-site struc-

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tural order plays an important role in double complex perovskites A2B’B’’X6, since B’ and B’’ ions can order alternately along the three crystalline axes, as NaCl-type ordering. This structural ordering governs dielectric [7–13], magnetic [14–18], vibrational [19–23] and ionic [24] properties. Particularly, La2NiMnO6 (LNMO), La2CoMnO6 (LCMO) and related RE2MeMnO6 compounds (RE is a rare-earth ion and Me is Ni or Co) have been intensively investigated due to their peculiar magnetic [18,24–30], electric [31,32], magnetoelectric [13,29,33–35], magnetoresistance [36] and multiferroic [37,38] proper-

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ties. This plethora of different and coupled electric and magnetic properties has enabled the application of these compounds into new devices and spintronics [39–41]. In LCMO, the B-site structural order rules the magnetic properties because the ferromagnetism  in this compound comes from the super-exchange interaction between Co2+ (
  ,  = 3⁄2) and Mn4+

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(
  ,  = 3⁄2) ions, which is maximum at Co—O—Mn bond angle of 180°. In this case, the struc-

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tural disorder in the B-site influences the magnetism through the generation of antiferromagnetic clusters of the types Co—O—Co and Mn—O—Mn. Usually, as it is well known in solid-state inorganic chemistry, high temperatures combined with calcination or sintering times induce B-site structural order in complex perovskites. Tôru Kyômen et al. [42] have investigated polycrystalline samples obtained under air for several heat treatment conditions and suggested that at high temperatures the Mn3+/Co3+ state is in thermal equilibrium with Mn4+/ Co2+ state. However, LCMO tends to be deficient in oxygen at high temperatures. For example, LCMO synthesized by solid state reaction in air at 1320 °C showed a disordered crystalline orthorhombic structure ( or space group #62) as probed by neutron diffraction measurements [43]. Also, LCMO samples annealed at 1370 °C showed lower critical temperatures (Tc ~150 K), which are characteristic of low site ordering (estimated 47.6% [44]). Recently, Ming Lin 3

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and Chen [13] obtained a LCMO ceramic that was calcined at 1200 °C and sintered at high temperature (1500 °C) under air. This sample showed multiple magnetic transitions with Tc around 210 K, 150 K and 80 K, a phenomenon that is commonly associated to disordered samples and mixed Co and Mn valence states. It is worth noting that LCMO ceramic samples that exhibited double magnetic transitions were

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generally obtained by heat treatments under air [18,19,45]. The charge compensation mechanism therein demands oxygen vacancies formation. This vacancy generation, and consequent disordering, is circumvented by synthesizing LCMO under oxygen rich atmosphere, which prevents vacancy increasing and consequent structural disordering [11,46]. For instance, ordered samples were obtained at high tempera-

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tures, around 1300 °C, and under oxygen atmosphere [11,12,18]. Nevertheless, for samples synthesized at low temperatures, one can also get order: Viswanathan et al. [44] calcined samples at 790 °C in air

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which displayed a high Tc value (~ 230 K) and a B-site order around 81%. The cooling rate is also a parameter that influences the B-site structural order. For example, Barón-González et al. [11] investigated two LCMO ceramic samples annealed at 1400 °C under oxygen-rich atmosphere, but cooled at different rates. They showed, using neutron diffraction and synchrotron X-ray diffraction of high resolution, that the samples had different B-site structural order degrees: 95% and 74% (while the complete random distribution of Co and Mn in the sublattice of the perovskite B would drive to 50%). Both sam-

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ples exhibited a single transition at about the magnetic points Tc = 235 and 225 K, respectively. Besides the magnetic properties, synthesis conditions strongly bias the electrical properties of LCMO ceramics. The synthesis conditions in conventional electronic materials change the electrical properties by modifying the microstructure but in complex perovskites they also work by modifying the

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B-site structural order. Regarding the dielectric properties of LCMO, Yáñez-Vilar et al. [12] observed that at room temperature, for frequencies lower than 104 Hz and for polycrystalline samples, the dielec-

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tric constant increases by two orders of magnitude from ordered to disordered specimens. In addition, at 106 Hz and 100 K, the dielectric constant observed was ε’ ̴ 15 for ordered samples but ε’ ̴ 30 for disordered ones. On the other hand, Lin and Chen [13] showed that LCMO exhibits a colossal dielectric constant (CDC) of about 105, at low frequencies (10 Hz), and 102 at high frequencies (107 Hz), within the temperature range of 123 K ≤ T ≤ 223 K. Moreover, they attributed the relaxor-type behavior combined with the CDC effect to cationic spatial ordering of Co2+ and Mn4+ in B-sites of LCMO. Finally, Sayed et al. [47] observed that different atmospheres lead to important differences in the dielectric and magnetic properties of LCMO.

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Therefore, literature tends to agree that, in LCMO, the calcination at temperatures lower than 1100 °C minimizes the deficiencies of oxygen and favours the long range B-site structural ordering thus improving its electrical and magnetic properties. Hence, by tuning the synthesis conditions, it is possible to control the B-site structural order in manganites with double perovskite structure, which is the pre-

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ponderant parameter to define the actual potential for of these compounds in devices and applications. Here, we report a way to control the B-site disorder in LCMO ceramics obtained by polymeric precursors method. We present exhaustive X-ray, X-ray photoelectron spectroscopy (XPS), vibrational, magnetic and dielectric characterizations of a series of samples in which we systematically scanned the cal-

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cination temperature while keeping constant other synthesis parameters such as calcination time and cooling rate. We argue the role of the selected synthesis parameters and its concomitant impact on the B-

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site order as well as the intrinsic dielectric and magnetic properties of LCMO. 2. Experimental 2.1 Synthesis procedure

We obtained polycrystalline samples of La2CoMnO6 by a modified polymeric precursors (MPP) route based in Pechini’s method [48], using cobalt acetate tetrahydrate (C4H6CoO4·4H2O, Sigma Aldrich

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Co.), manganese nitrate hydrate (MnN2O6·xH2O, Sigma Aldrich) and high purity lanthanum oxide (La2O3, Sigma, Aldrich) as metal sources to obtain the precursors. The correct amount of precursors to get the correct metal stoichiometry to form La2CoMnO6 perovskite was determined by gravimetric analysis at 900°C for 1h. The three precursors were mixed and heated at 85°C to form the polyester res-

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in, which was viscous and glassy. The resin was subsequently annealed at 400°C for 2h. This treatment converted the resin in a black porous powder (hereafter called “LCMO puff”) that was lightly grounded

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using an agate mortar and then divided into four different samples to be annealed for 16 hours at several temperatures: 700 (LCMO700), 800 (LCMO800), 900 (LCMO900) and 1000 °C (LCMO1000). All four samples were cooled at 1°C min-1. 2.2 Structural characterization The samples’ crystalline structure were studied by powder X-ray diffraction using a Bruker D8 Advance. We performed a continuous scanning using Cu-Kα1 radiation (40 kV, 40 mA), in the range between 15° and 90° (0.02/step with 0.5 s/step). The X-ray powder diffraction (XRPD) patterns were compared with data from ICSD (Inorganic Crystal Structure Database, FIZ Karlsruhe and NIST) international diffraction database (ICSD# 98240) [49]. The structure was refined using the GSAS software 5

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[50]. XPS measurements were performed in a VG ESCALAB 220i-XL system, using Al-Kα radiation and base pressure of 2 x 10-10 mbar. Survey XPS spectra were collected with pass energy of 50 eV and detailed spectra around the Co 2p and Mn 2p regions were taken with 20 eV pass energy. Sample’s microstructure were examined by using a JEOL-JSM 6510 LV scanning electron microscopy (SEM) at

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Centro Multiusuário de Nanotecnologia, CMnano/UFS (Aracaju, Brazil). The calcined samples were directly cut into pieces and then gold sputtered coated before being examined by scanning electron microscopy.

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2.3 Magnetic measurements

Magnetic measurements were carried out in a Quantum Design superconducting quantum interference device (SQUID). Magnetization loops were collected at 10K and up to 40 kOe. Temperature

ciprocating Sample Option scans.

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sweeps were collected between 300K and 10K. All measurements were done using with 4 cm long Re-

2.4 Vibrational and intrinsic dielectric measuremets

Raman spectroscopic measurements were performed using an iHR550 Horiba scientific spec-

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trometer coupled to an Olympus microscope (model BX-41) configured in a backscattering geometry. A He-Ne laser (632.8 nm) operating at 17 mW was used as excitation source. The scattered light was collected in a Peltier-cooled Synapse CCD system. All slits were set up to get spectral resolution lower than 2 cm-1. Infrared reflectance spectra were collected in a Fourier-transform spectrometer (Bomem DA 8-

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02) combined with a fixed-angle specular reflectance accessory (external incidence angle of 11.5 °). In the mid-infrared region (500 – 4000 cm-1) we used a SiC glow-bar lamp as infrared source, a Ge-coated KBr beamsplitter and LN2-cooled HgCdTe detector. In the far-infrared range (50 – 600 cm-1), we em-

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ployed a mercury-arc lamp, a 6 mm coated Mylar hypersplitter®, and LHe-cooled Si bolometer. For obtaining the reference spectra, we used one region of the ceramic face slightly covered with a thin gold coating acting as a ‘‘rough’’ mirror. This method helps improving the reflectivity spectra since the mirror surface mimics the sample one thus reducing the losses by diffuse reflections at the sample surface. 3. Results and discussions Fig. 1 shows the XRPD pattern obtained for the synthesized LCMO samples. All samples were indexed according to a monoclinic structure lattice that belongs to the space group P21/n, in agreement with ICSD no. 98240. Fig. 2 shows the XRPD pattern Rietveld refinements obtained for all samples. The structural parameters obtained from the refinements are summarized in Table 1. The sample cal6

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cined at a lower temperature (700 °C) shows additional diffraction peaks corresponding to secondary phases of lanthanum oxide La2O3 (~1.8%) and manganese-cobalt spinel MnCo2O4 (~3.3%), which were marked with asterisk symbols in Fig. 2. For the sample calcined at 800°C, there is a small fraction

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of MnCo2O4 (~2.0%). No secondary phases are observed in samples calcined at 900 and 1000 °C.

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Fig. 1. XRPD pattern of LCMO puff (calcined at 400°C) and samples calcined at 700, 800, 900, and 1000 °C for 16 h.

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Fig. 2. From top to bottom panel it is presented the XRPD pattern Rietveld refinements of LCMO samples calcined at 700, 800, 900 and 1000ºC, using the monoclinic space group 2 /.

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Table 1. Structural parameters of LCMO powders after using X-ray powder diffraction data refinements. Parameters

LCMO700

LCMO800

LCMO900

LCMO1000

Space Group

2 /

2 /

2 /

2 /

5.5248(4)

5.5239(2)

5.5256(1)

5.5255(1)

5.4730(4)

5.4807(2)

5.4846(1)

5.4847(1)

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a (Å)

b (Å) c (Å)

7.7741(7)

7.7750(4)

7.7773(2)

7.7771(2)

 (deg)

89.921(25)

89.923(11)

89.933 (10)

89.926(5)

V, Å3

235.047(29)

235.394(17)

235.704(6)

235.710(5)

La x

0.0037(2)

0.0026(2)

0.0077(7)

0.0021(7)

y

0.0214(4)

0.0180(4)

0.0189(2)

0.0209(2)

z

0.2453(6)

0.2544(2)

0.2516(8)

0.2520(4)

Uiso(Å2)

0.024(2)

0.022(2)

0.025(1)

0.016(4)

Co (x, y, z)

0, 0.5, 0

0, 0.5, 0

0, 0.5, 0

0, 0.5, 0

Uiso(Å2)

0.026(8)

0.038(1)

0.036(3)

0.034(2)

Mn (x, y, z)

0.5, 0, 0

0.5, 0, 0

0.5, 0, 0

0.5, 0, 0

Uiso(Å2)

0.052(3)

0.035(1)

0.036(3)

0.029(2)

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0.296(26)

0.287(9)

0.269(6)

0.273(8)

y

0.259(24)

0.236(12)

0.211(12)

0.225(9)

z

0.034(44)

0.035(7)

0.033(14)

0.033(6)

Uiso(Å2)

0.050(1)

0.028(5)

0.033(2)

0.026(8)

O2 x

0.274(13)

0.280(9)

0.260(5)

0.274(4)

y

0.265(18)

0.275(6)

0.267(3)

z

0.458(11)

0.463(7)

0.455(3)

Uiso(Å2)

0.028(1)

0.028(5)

0.018(8)

O3 x

0.561(8)

0.564(3)

0.554(4)

y

-0.000(4)

0.015(3)

0.010(2)

0.220(22)

0.229(8)

0.235(4)

0.247(6)

Uiso(Å )

0.032(5)

0.029(5)

0.031(4)

0.024(3)

Density, g/cm3

6.890

6.880

6.871

6.871

D, nm

40.16

 x (%)

11.47

Rp (%)

5.01

wRp (%)

6.57

Cagglioti parameters: Gaussian (U; P) Lorentz (X; Y)

(88.0; 39.4) (12.2; 25.7)



0.017(8)

0.568(2)

-0.003(1)

168.93

326.08

428.57

18.11

16.52

13.02

4.76

5.05

5.23

6.10

6.41

6.53

(246.4; 6.0) (4.99; 17.5)

(217.8; 1.9) (3.65; 12.1)

(130.3; 4.7) (0.13; 14.7)

1.759

1.946

1.888

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2.142

0.472(3)

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2

0.303(4)

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O1 x

Fig. 3 shows the calcination temperature dependence of the structural parameters obtained from

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the Rietveld refinement. We can observe that the lattice parameters ! and " are almost temperature in-

dependent (see Fig. 3a), while the  parameter increases until saturation after 900 °C (see Fig. 3c),

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which also leads to a saturation in the unit cell volume at the same temperature (see Fig. 3b). This behavior is similar to that obtained by Dass and Goodenough [18] for LCMO samples with different B-site structural ordering thus suggesting an enhanced ordering under increasing calcination temperature .

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Fig. 3. Calcination temperature dependence of the (a) lattice parameters, (b) unit cell volume, (c) lattice parameter b. The lines are guide for the eyes.

As the MPP route usually produces nanopowders, we calculated the crystallite size (D) and the microstrain (ε) of the samples using the Williamson-Hall (WH) analysis [51], in which these parameters are calculated using the following relation: #$%& ' (

=

)

*

+

,(

sin 1 ,

(1)

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where 2 is the wavelength of incident radiation, 3 a dimensionless shape factor which assumes a typical

value of ~0.9, and β the full width at half maximum (FWHM) of the diffraction peaks, corrected for the

β = 5  6789 −   ;<=9 .

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instrumental broadening by: (2)

In this method,  expt is the measured broadening and  inst is the instrumental broadening using the parameters (U, P, X, Y). The instrumental broadening was obtained through refinement of a corundum

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(Al2O3) reference. This analysis is presented in Fig. 4. The data show that the sample produced at 700 °C is nanometric with crystallite size around 40 nm. Inspection of the remaining samples reveals that the crystallite size increased with calcination temperature and reaching up to ~430 nm for the sample cal-

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cined at 1000 °C. The obtained crystallite sizes (D) and microstrains (ε) are listed in Table II. The significant straight lines in the WH plotting indicate no dispersion in particle size and microstrain thus suggesting that the samples display homogeneous particle size distributions and microstrains [52]. This result falls within the expectations of the employed synthesis method which tends to form homogenous

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nanopowders.

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Fig. 4. (a-d) Williamson–Hall analyses for LCMO powders calcined at different temperatures. (e) Evolution of crystallite size under calcination temperature increasing.

The microstructures of the calcined samples were investigated by scanning electronic microsco-

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py, and their micrographs are shown in Fig. 5. The increasing calcination temperature leads to particle agglomeration and size increasing due to the formation of “necks” and blocks. The particle size distributions obtained from the SEM micrographs are shown in Fig. 6 and their respective mean sizes (L) are listed in Table 2. The average particle size changes from a more uniform size distribution in the sample calcined at 700 °C to a bimodal distribution in the sample calcined at 1000 °C. The particles typically display sizes near those calculated from XRPD measurements. However, the size distributions obtained from the SEM measurements are complementary to those obtained from XRPD since the relation between the average sizes obtained from both techniques gives us information about the crystallite formation in the ceramic. Finally, it is worth noting that for LCMO calcined at 700 °C the average particle diameter obtained from SEM technique is around 130 nm, which is almost 3 times bigger than that cal12

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culated by XRD. Such relation shows that for samples calcined at this temperature, the particles are constituted of several crystallites. When the calcination temperature increases, the relation L/D decreases

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thus revealing that the grain is basically formed by coalescent crystallites.

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Fig. 5. SEM micrographs of LCMO calcined for 16 h at 700, 800, 900 and 1000 °C.

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Fig. 6. Particle size distributions of the samples calcined at 700, 800, 900 and 1000°C for 16 h.

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Table 2. Comparison between the crystallite size (D) calculated by WH analysis (DRX) and particle size (L) obtained by SEM technique, for several calcination temperatures. * Main distribution. **Weighted Average. # Relative density (d) estimated from geometric method. D (nm)

L (nm)*

L (nm)**

L/D*

L/D**

d (%)#

700

40.2

130.0

149.0

3.23

3.71

50

800

168.9

160.7

197.8

0.95

1.17

52

900

326.1

249.2

285.8

0.76

0.87

55

1000

428.6

494.9

584.96

1.15

1.36

70

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T (oC)

.

To estimate the B-site structural order in the LCMO samples, temperature dependent magnetization of LCMO samples was investigated using an applied magnetic field of 100 Oe. The data is displayed in Fig. 7a. The plots show a clear single ferromagnetic (FM) transition around >? ~235 K for all

investigated LCMO samples. This high >? single magnetic transition is consistent with an atomically 14

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ordered system with a strong ferromagnetic (FM) superexchange interaction between high-spin cations 

Co2+ (
  ,  = 3⁄2) and Mn4+ (
  ,  = 3⁄2). Similar results were obtained by Barón-González

et al [11] for ~95% ordered LCMO systems. Fig. 7b shows the calcination temperature dependence of magnetic susceptibility data of LCMO in the paramagnetic region. The Curie-Weiss law, which is given @

= A> − >' B/C, with C being the Curie-Weiss constant and >' the Curie-Weiss temperature, is

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by

satisfied. For all samples, the positive value of >' D >E confirms a dominant FM interaction, and from

the Curie constant it is possible to obtain the effective paramagnetic moment FG6HH I for all samples (see

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Table 3).

Fig. 7. (a) Temperature dependence of magnetization (FC) for all LCMO samples, at an applied magnetic field of 100 Oe. (b) DC susceptibility and fits in paramagnetic region using Curie–Weiss law.

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Table 3. Magnetic properties of LCMO obtained under different calcination temperatures. M (10 kOe), Mr and Hc are the magnetization at 10 kOe, the remanent magnetization (both by formula unit) and the coercive field, respectively. G6HH (GJ )

M (10 K, 40 kOe) AGJ /K. L.)

Mr (10 K) AGJ /K. L.)

5.02

6.34

4.12

2.53

800

6.88

7.42

4.94

2.94

900

7.33

7.96

5.26

3.00

1000

9.97

8.93

5.89

3.18

11.88 7.92 5.52

2.90

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Hc (10K) (kOe)

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C (emu.K/ mol Oe)

T ( C) o

The M-H hysteresis loops of LCMO samples measured at 10 K are shown in Fig. 8. The curves

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reveal that the complete saturation of the magnetization was not yet achieved at M = 4 T for any sample. However, the magnetization systematically increased with calcination temperature achieving a value of 5.89 µB/f.u., which is very close from the one corresponding for ideal effective spin of 6.0 µB/f.u. in LCMO and, moreover, it falls within the highest ordered systems reported. According to Blasse [53], one can estimate the structural B’/B’’ ordering through the experimental and theoretical saturation magnetic moments ratio (called δ) and, by definition, should equal to one Aδ = 1B in a complete ordered

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sample. For our samples, we obtained 0.98, 0.88, 0.82 and 0.69 for LCMO1000, LCMO900, LCMO800 and LCMO700, respectively. The high structural ordering obtained for temperatures lower than 1000 °C highlights the appropriateness of the Pechini method to get ordered LCMO samples. On one hand, the method uses polymeric precursors that include the metals in long organic chains which facilitates the

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chemical reaction and produces more reactive small particles. On the other hand, the slow heating and cooling rates applied also favor the structural ordering. Additionally, by using temperatures below 1000

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°C oxygen deficiency is minimized thus ruling out a potential disorder promoter.

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Fig. 8. Magnetic hysteresis loops of LCMO samples, at 10 K. Inset shows the approximately linear dependence of coercitivity with the calcination temperature.

A linear decrease of coercitivity (Hc) as the calcination temperature and magnetic order increase can be observed in Fig. 8 (inset). From the magnetization values achieved, we conclude it is possible to

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tune this physical quantity just by changing the calcination temperature, as illustrated in Fig. 9.

Fig. 9. Calcination temperature dependence of the LCMO magnetization at 10 K and 10 kOe.

Although the calcination echoes in the B-site ordering in LCMO, it is important to elucidate whether the procedure did preserve the oxidation state of Co and Mn. We carried out XPS analyses of the Co 2p core levels of all samples. The data shown in Fig. 10a reveals no shift of Co 2p3/2 and Co 2p1/2 17

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peaks as the calcination temperature increases. The spectra show a main peak located at 780.2 eV for Co 2p3/2, while Co 2p1/2 peak is centered at 796.3 eV. Routinely, the Co 2p3/2 peak is used for the sake of sample comparison (it is observed at 780.5 eV for CoO [54]). The weaker satellite peak observed at 787.1 eV is also characteristic of CoO [55]. Therefore, this analysis confirms the predominance of Co2+

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species [30,55]. Fig. 10b shows the region around the Mn 2p energies. The peak related to Mn 2p3/2 is centered at around 642.4 eV, while for Mn 2p1/2 it is observed at 654.0 eV. The Mn 2p3/2 peak was more intense and symmetric, coherent with no mixed oxidation states of Mn. The main XPS peak of MnO2, which is related to Mn 2p3/2, is observed at 642.2 eV [54–56]. Therefore, the oxidation states of all mag-

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netic ions do not change with calcination temperature and, in the general, they are very similar among

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all LCMO samples and essentially comprising Co2+ and Mn4+ species.

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Fig. 10. XPS spectra of LCMO calcined at different temperatures for the (a) Co 2p and (b) Mn 2p energy regions.

Raman spectroscopy has been extensively used to probe structural ordering and spin-phonon coupling in complex perovskites [19,57–62] in rare-earth based manganites with double perovskite structure [23]. In Raman analyses, the position and bandwidth corresponding to each phonon are important to understand the structural ordering evolution for distinct synthesis conditions. Fig. 11 shows the room temperature Raman spectra obtained for LCMO calcined at different temperatures. The LCMO puff spectrum is shown for completeness. According to Wyckoff site occupation, the space group 2 /

 or #14) and the number of formulae per unit cell (Z=2), group theory predicts 24 Raman-active (CO

18

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modes, which can be decomposed in terms of the irreducible representation (i.r.) of the factor group 2/ as 12P ⨁ 12R , and 33 IR-active modes, whose decomposition in terms of the i.r. of this factor

group is 17PT ⨁ 16RT . At room temperature, despite the long acquisition times employed, only 11 bands were observed in the Raman spectra of all samples. Those observed below 300 cm-1 were too

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weak to be captured. This low Raman intensity collected is common in manganites with this type of structure even at low temperatures [19,20,63,64]. In general, the Raman spectra is dominated by two modes observed at around 648 and 499 cm-1, which are usually assigned as the symmetric (S) stretching, like a “breathing” mode, and the mixed antistretching (AS) – bending vibrations of BO6 octahedra, re-

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spectively [64]. The low wavenumber phonons are less pure and involve octahedral bending and tilts [22]. Besides the modes observed in the wavenumber range from 100 up to 900 cm-1, broad bands were

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observed around 1168 and 1278 cm-1, which are associated to stretching overtones (see the inset in Fig.

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11a).

Fig. 11. (a) Room temperature Raman spectra of LCMO samples calcined at different temperatures. (b) Detachment between symmetric (S) and antisymmetric (AS) stretching modes. (c) and (d) Calcination temperature dependence of S and AS stretching phonon positions. (e) and (f) Calcination temperature dependence of S and AS stretching phonons FWHM. (g) Calcination temperature dependence of the intensity ratio between the S and AS stretching modes.

19

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Upon calcination temperature increasing, all Raman-active modes become more intense and narrower, even for low wavenumbers. This fact comes from the increasing in the crystallite ordering, which permits the phonons to propagate longer distances inside the crystal so the phonon lifetime increases. Since the phonon lifetime is proportional to the reciprocal bandwidth, the bandwidth decreases under

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calcination temperature increasing. This effect can be observed in Figs. 11e and 11f. By the same token, the narrower the bandwidth, the higher the Raman intensity, according to Fig. 11a. This observation is in agreement with Zhao et al. [64] who observed similar effect in LNMO when the size of nanoparticles increased. As shown in Figs. 11c and 11d, as the calcination temperature increases, it shifts both the S

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and the AS Raman stretching modes. In general, a blue shift can be observed for both modes with increasing calcination temperature that seems to rise the stability closer to 1000°C. In addition, we ob-

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serve that a detachment between S and AS stretching modes occurred (Fig. 11b). In general, ordered samples tend to exhibit more detached S/AS phonons, which is in agreement with previous observations [44,65]

Despite the volume cell increasing measured by the XRD analysis, which usually echoes in phonon softening, we observed S and AS stretching phonons hardening (Fig. 11c and 11). However, this apparent anomalous behavior is explained by the particle increasing, which leads to a hardening of the

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phonons due to their stabilization. In addition, the B-site structural ordering usually reduces the phonon anharmonicity. Troung et al. [23] showed that the B-site ordering has a stronger impact on the FWHM, and the bands in disordered compounds are relative wider than in an ordered ones. We observed that the FWHM of S stretching mode decreased 10 cm-1 under calcination, while for AS phonon the decreasing

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was at about 9 cm-1. Also, the ratio between S and AS phonon intensities increased with the increasing temperature (see Fig. 11g) as well as S and AS phonons detachment (Fig. 11b). Therefore, the Raman

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analysis suggests that when the calcination temperature increases up to 1000 °C, it strongly influences the structural ordering. For temperatures higher than 1000 °C, oxygen vacancies formation is expected [18,66] and those can decrease the site ordering via antisite defects and valence mixtures. Therefore, in rare earth based manganites, the order can be proved by AS and S Raman stretching phonon parameters. Particularly, in LCMO, S and AS phonons should be observed at 648 and 500 cm-1, respectively, which yields a detachment of 148 cm-1. In ceramics, dielectric properties have intrinsic and extrinsic contributions. The first ones depend on the structural features while the second ones depend also on other chemical and physical aspects of the sample (microstructure, defects, dopants…). On one hand, regarding the intrinsic contributions we 20

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have changed only the B-site structural order of the LCMO samples and, on the other hand, extrinsically we promote changes through the calcination temperature modifying the samples’ microstructure. Since we can tune the structural disorder, it’s equally possible to impact the intrinsic dielectric properties of LCMO and the way the B-site order will affect them. IR reflectance spectroscopy is an ideal tool to per-

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form this investigation since LCMO is a semiconductor with very a low charged defect concentration and, in this case, the infrared dielectric response (1011-1014 Hz) is fully determined by the phononic and electronic polarizations, whose origins are purely intrinsic. Fig. 12 shows the infrared reflectivity spectra measured for all samples. We can observe four groups of distorted IR-active bands for all samples. This is compatible with an IR-active phonon spectrum that comes from the aristotype NaCl-type struc-

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ture of double ordered perovskite (space groupV3W, XO or #225), which exhibits four well-defined

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IR- active bands. Because of the distortion from the cubic cell due to the monoclinic structure 2 /, the four bands of the parent phase split into 33 IR-active bands, as discussed before. Since Co and Mn ions occupy centrosymmetric sites in the monoclinic structure, they do not contribute to the Raman spectra, but in the IR-spectra, which is very sensitive to the B-site structural ordering, they greatly contribute. We fitted the IR reflectivity spectra according to Gervais and Piriou’s semiquantum fourparameters model [67] for the dielectric function, which can be written as: ` \],^_ @\` a;\b],^_

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 AYB = Z ∏d

` \],c_ @\` a;\b],c_

,

(3)

where ε(ω) is the complex dielectric function in the IR radiation range, ε∞ the electronic contribution to

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the dielectric function, ω the frequency and γ the FWHM (or damping) of the transverse (TO) or longitudinal (LO) optical phonon branches. Since at quasinormal incidence the reflectivity is given by the

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Fresnel relation

g-A\B@

e AYB = f



f ,

g-A\Ba

(4)

we can fit e AYB using Eqs. (3) and (4) altogether. Fig. 12 shows the best fit (solid red lines) for all spectra. From Kramers-Kronig analysis, we obtained the imaginary part of the dielectric function, ε′′AωB, and the imaginary part of the reciprocal die-

lectric function, iA1/εB, whereby the TO and LO optical frequencies are obtained, respectively (see Fig. 13).

21

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Fig. 12. Infrared reflectivity spectra of LCMO ceramics calcined at 700 – 1000 °C, for 16 h. Open circles indicate the experimental data, while the solid red lines represent the calculated reflectivities.

Fig. 13. Imaginary parts of (a) the dielectric function and of (b) the reciprocal of dielectric function calculated from Kramers-Kronig analysis for the LCMO ceramics in the far-infrared region (80–750 cm-1). 22

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Table 4 shows the complete phonon parameters for the LCMO calcined at 900 °C obtained from the fittings. In addition, the oscillator (dielectric) strengths, Δd,kl , and dielectric losses, tanδj, are also shown for each phonon. The oscillator strength can be described in terms of the optical parameters (lon-

-

Δd,kl = \ `m × ]c_

` ` ∏po\p,^_ @\],c_ q

` ` ∏pr]o\p,c_ @\],c_ q

,

while the dielectric losses are given by ` u-] b],c_ v\],c_

-m a∑] u-]

.

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! δ = ∑d
! td = Y

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gitudinal and transverse frequencies and damping) as (5)

(6)

( γj,TO) ωj,LO -1 (cm-1) (cm )

γj,LO

∆εj

108×tan δj /ω

131.7

7.7

0.08

471

170.0

16.9

2.78

13360

190.6

12.4

0.39

3107

21.8

278.0

21.7

1.35

3936

284.5

34.4

306.0

29.0

0.36

1459

344.0

56.0

344.8

48.0

0.02

144

386.1

17.8

386.5

17.4

0.04

1673

403.0

31.6

425.0

25.8

0.92

897

ωj,TO (cm-1)

1

131.4

10.4

2

164.0

13.8

3

173.0

24.7

4

265.0

6 7

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8

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N°

5

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Table 4. Dispersion parameters from the fittings of the FTIR spectrum of LCMO sample calcined at 900 °C.

(cm-1)

433.8

36.4

449.9

27.0

0.15

287

10

470.0

50.5

483.0

37.5

0.14

299

11

558.0

50.1

596.0

45.6

0.67

1004

12

600.0

69.0

622.0

55.6

0.03

45

13

633.0

65.9

660.2

26.4

0.04

66

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9

ε∞ = 3.7; Σ∆εj = 7.01 εs =ε∞ + Σ∆εj = 10.71

Σtan δj /ω = 25868 x 10-8 Qu × f = 116 THz

Similarly to what was observed for the widths of the Raman-active modes, the higher the calcination temperature, the narrower are the IR-active modes, as it is shown in Fig. 14 for the four strongest polar phonons. Again, this observation expresses an anharmonicity reduction, which is due to the reduc-

23

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tion of defects and optimization of spatial charge distribution with the calcination temperature increas-

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ing.

Fig. 14. Calcination temperature dependence of the widths of TO phonon branches #2, #4, #8 and #11.

limit AYd,wl >> YB, namely

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From the oscillator strengths, we can estimate the static dielectric constant, εs, in the microwave

(7)

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ε= = εZ + Σ∆εd .

The dependence of the static dielectric constant and unloaded quality factor with the calcination temperature is shown in Fig. 15a. We can see that the calcination temperature induces an increasing in

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the dielectric constant, i.e., the higher is the B-site structural order, the higher is the dielectric constant. Since the electronic contribution εZ is almost independent of the calcination temperature, we observed that the modes at 163, 263, 406 and 558 cm-1 (labeled as #2, #4, #8 and #11) feature the highest oscillator strengths, and therefore give the main contribution to the static dielectric constant, εs. In particular, for the sample calcined at 1000 °C, disregarding the electronic contribution, the modes #2 and #4 contribute with more than 70% of the dielectric constant, as shown in Fig. 15b, which shows as εs increases under the calcination temperature increasing. Fig. 15b illustrates the departure of ∆ = = A>B −

= A> = 700 °CB of = from = at the calcination temperature of 700 °C (=@} B and the contribution of

the modes #2 and #4 to = A>B. This contribution, as well as the dielectric constant, increases with the

24

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calcination temperature. These modes are in the frequency ranges 100 – 180 cm-1 (mode #2) and 250 – 330 cm-1 (mode #4). Both are associated to Slater-type mode [68,69], which corresponds mainly to B

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ion motion against oxygen vibrations.

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Fig. 15. (a) Calcination temperature dependence of the static dielectric constant and unloaded quality factor in LCMO. (b) Calcination temperature dependence of the depart constant [∆ = = A>B − = A> = 700 °CB], and the temperature variation from 700 oC of the sum of the dielectric strengths of modes #2 and #4.

According to Silva et al. [69], in ordered ceramic samples obtained at 1000 °C, the colossal dielectric constant (CDC) effect in LCMO is purely extrinsic. Our results for the dielectric constant show that such extrinsic contributions are independent on the B-site structural order, since our (infrared) static dielectric constant is always small. In fact, for the disordered samples the dielectric constant is still lower than for the ordered samples. Thus, although the CDC effect in LCMO depends also on the synthesis conditions – which affect the dielectric constant through the semiconducting nature of the sample [13] [70], it is mainly due to the contribution of charged defects [71] or oxygen vacancies [18,42,44] acting 25

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as charge carriers. Finally, the crystalline structure evolution under calcination temperature and its respective B-site structural ordering enhancement strongly influenced the intrinsic dielectric losses (tan t = ∑d
! td ) in LCMO. From the losses obtained in the fit (see Table 4 for the sample calcined at €T × K = K / tan t,

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900 °C), we can estimate the unloaded quality factor as (7)

whose behavior under the calcination temperature in the microwave radiation frequency (10 GHz or structural ordering in LCMO echoes in a €T increasing. 4. Conclusions

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0.3333 cm-1) is shown in Fig. 15a. We observe that €T increased from 83 up to 124 THz. Thus, the

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In this paper, we have investigated La2CoMnO6 ceramic samples obtained by polymeric precursors method calcined at different temperatures. Structural and micro-structural analyses showed that finegrained (nanometric) materials presenting single phase monoclinic structure were obtained for calcination temperature ranging from 700 °C to 1000 °C. XPS and magnetic characterizations have been employed to confirm that Co2+ and Mn4+ were the oxidation states of the B-site cations. Raman and infrared experiments showed significant improvement of the structural order and the optical vibrational

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properties of the materials. As a whole, our results prove that the site ordering can be improved by changing the calcination temperature and, simultaneously echoing in changes of the intrinsic dielectric

Acknowledgments

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and magnetic properties of LCMO.

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The Brazilian authors acknowledge the partial financial support from CNPq, CAPES, FAPEMA, FAPEMIG and FUNCAP (Brazilian funding agencies).

Author information

Corresponding Author *

CWAP - E-mail: [email protected]

References

[1]

P.K. Davies, H. Wu, A.Y. Borisevich, I.E. Molodetsky, L. Farber, Crystal Chemistry of Complex Perovskites: New Cation-Ordered Dielectric Oxides, Annu. Rev. Mater. Res. 38 (2008) 369–401. doi:10.1146/annurev.matsci.37.052506.084356. 26

ACCEPTED MANUSCRIPT

R. Mani, P. Selvamani, J.E. Joy, J. Gopalakrishnan, T.K. Mandal, Study of Ba3M(II)M(IV)WO9 (M(II) = Ca, Zn; M(IV) = Ti, Zr) perovskite oxides: competition between 3C and 6H perovskite structures., Inorg. Chem. 46 (2007) 6661–7. doi:10.1021/ic7007655.

[3]

O. Valdez-Ramírez, F. Gómez-García, M. a. Camacho-López, E. Ruiz-Trejo, Influence of the calcium excess in the structural and spectroscopic properties of the complex perovskite Ba3CaNb2O9, J. Electroceramics. 28 (2012) 226–232. doi:10.1007/s10832-012-9716-5.

[4]

A. Dias, C.W.A. Paschoal, R.L. Moreira, Ordered Barium Magnesium Niobate Ceramics, J. Am. Ceram. S. 87 (2003) 1985–1987.

[5]

M.W. Lufaso, Crystal Structures, Modeling, and Dielectric Property Relationships of 2:1 Ordered Ba3MM’2O9 (M = Mg, Ni, Zn; M' = Nb, Ta) Perovskites, Chem. Mater. 16 (2004) 2148–2156. doi:10.1021/cm049831k.

[6]

M.W. Lufaso, E. Hopkins, S.M. Bell, A. Llobet, Crystal Chemistry and Microwave Dielectric Properties of Ba 3 MNb 2 - x Sb x O 9 (M = Mg, Ni, Zn), Chem. Mater. 17 (2005) 4250–4255. doi:10.1021/cm050631y.

[7]

M.C. Castro, C.W. de A. Paschoal, F.C. Snyder, M.W. Lufaso, Relaxations in Ba2BiSbO6 double complex perovskite ceramics, J. Appl. Phys. 104 (2008) -. doi:http://dx.doi.org/10.1063/1.3026654.

[8]

A. Dias, L.A. Khalam, M.T. Sebastian, C.W.A. Paschoal, R.L. Moreira, Chemical substitution in Ba(RE1/2Nb1/2)O-3 (RE = La, Nd, Sm, Gd, Tb, and Y) microwave ceramics and its influence on the crystal structure and phonon modes, Chem. Mater. 18 (2006) 214–220.

[9]

E.F. V Carvalho, E.M. Diniz, C.W.A. Paschoal, Behavior of the elastic and mechanical properties of Ba2BiTaO6 compound under pressure changes, Comput. Mater. Sci. 40 (2007) 417–420. doi:http://dx.doi.org/10.1016/j.commatsci.2007.01.020.

[10]

F.N. Sayed, S.N. Achary, O.D. Jayakumar, S.K. Deshpande, P.S.R. Krishna, S. Chatterjee, et al., Role of annealing conditions on the ferromagnetic and dielectric properties of La2NiMnO6, J. Mater. Res. 26 (2011) 567–577. doi:10.1557/jmr.2011.4.

[11]

A.J. Barón-González, C. Frontera, J.L. García-Muñoz, B. Rivas-Murias, J. Blasco, Effect of cation disorder on structural, magnetic and dielectric properties of La2MnCoO6 double perovskite., J. Phys. Condens. Matter. 23 (2011) 496003. doi:10.1088/0953-8984/23/49/496003.

[12]

S. Yáñez-Vilar, M. Sánchez-Andújar, J. Rivas, M. a. Señarís-Rodríguez, Influence of the cationic ordering in the dielectric properties of the La2MnCoO6 perovskite, J. Alloys Compd. 485 (2009) 82–87. doi:10.1016/j.jallcom.2009.05.103.

AC C

EP

TE D

M AN U

SC

RI PT

[2]

27

ACCEPTED MANUSCRIPT

Y.Q. Lin, X.M. Chen, Dielectric, Ferromagnetic Characteristics, and Room-Temperature Magnetodielectric Effects in Double Perovskite La2CoMnO6 Ceramics, J. Am. Ceram. Soc. 94 (2011) 782–787. doi:10.1111/j.1551-2916.2010.04139.x.

[14]

M. Wakeshima, D. Harada, Y. Hinatsu, Crystal structures and magnetic properties of ordered perovskites A2R3+Ir5+O6 (A=Sr, Ba; R=Sc, Y, La, Lu), J. Alloys Compd. 287 (1999) 130–136. doi:http://dx.doi.org/10.1016/S0925-8388(99)00057-2.

[15]

Y. Hinatsu, Y. Izumiyama, Y. Doi, A. Alemi, M. Wakeshima, A. Nakamura, et al., Studies on magnetic and calorimetric properties of double perovskites Ba2HoRuO6 and Ba2HoIrO6, J. Solid State Chem. 177 (2004) 38–44. doi:http://dx.doi.org/10.1016/S0022-4596(03)00302-5.

[16]

M. Wakeshima, D. Harada, Y. Hinatsu, Crystal structures and magnetic properties of ordered perovskites BaLnIrO (Ln = lanthanide), J. Mater. Chem. 10 (2000) 419–422. doi:10.1039/A907586K.

[17]

M. Wakeshima, D. Harada, Y. Hinatsu, N. Masaki, Magnetic Properties of Ordered Perovskites Ba2LnIrO6 (Ln=Sm, Eu, Gd, and Yb), J. Solid State Chem. 147 (1999) 618–623. doi:http://dx.doi.org/10.1006/jssc.1999.8425.

[18]

R.I. Dass, J.B. Goodenough, Multiple magnetic phases of La2CoMnO6-δ (0~δ~0.05), Phys. Rev. B. 67 (2003) 014401. doi:10.1103/PhysRevB.67.014401.

[19]

K.D. Truong, J. Laverdière, M.P. Singh, S. Jandl, P. Fournier, Impact of Co⁄Mn cation ordering on phonon anomalies in La2CoMnO6 double perovskites: Raman spectroscopy, Phys. Rev. B. 76 (2007) 132413. doi:10.1103/PhysRevB.76.132413.

[20]

R.B. Macedo Filho, A. Pedro Ayala, C. William de Araujo Paschoal, Spin-phonon coupling in Y2NiMnO6 double perovskite probed by Raman spectroscopy, Appl. Phys. Lett. 102 (2013) 192902. doi:10.1063/1.4804988.

[21]

M.C. Castro, E.F.V. Carvalho, W. Paraguassu, A.P. Ayala, F.C. Snyder, M.W. Lufaso, et al., Temperature-dependent Raman spectra of Ba2BiSbO6 ceramics, J. Raman Spectrosc. 40 (2009) 1205–1210. doi:10.1002/jrs.2263.

[22]

R.X. Silva, H. Reichlova, X. Marti, D.A.B. Barbosa, M.W. Lufaso, B.S. Araujo, et al., Spinphonon coupling in Gd(Co1/2Mn1/2)O3 perovskite, J. Appl. Phys. 114 (2013) 194102. doi:10.1063/1.4829902.

[23]

K. Truong, M.P. Singh, S. Jandl, P. Fournier, Influence of Ni/Mn cation order on the spin-phonon coupling in multifunctional La2NiMnO6 epitaxial films by polarized Raman spectroscopy, Phys. Rev. B. 80 (2009) 134424. doi:10.1103/PhysRevB.80.134424.

AC C

EP

TE D

M AN U

SC

RI PT

[13]

28

ACCEPTED MANUSCRIPT

P. Kayser, M.J. Martínez-Lope, J.A. Alonso, M. Retuerto, M. Croft, A. Ignatov, et al., Crystal Structure, Phase Transitions, and Magnetic Properties of Iridium Perovskites Sr2MIrO6 (M = Ni, Zn), Inorg. Chem. 52 (2013) 11013–11022. doi:10.1021/ic401161d.

[25]

M. Hashisaka, D. Kan, a. Masuno, T. Terashima, M. Takano, K. Mibu, Spin-filtering effect of ferromagnetic semiconductor La2NiMnO6, J. Magn. Magn. Mater. 310 (2007) 1975–1977. doi:10.1016/j.jmmm.2006.11.007.

[26]

H. Itoh, J. Ozeki, J. Inoue, Electronic structure and spin-filter effect of ferromagnetic insulators with double perovskite structure, J. Magn. Magn. Mater. 310 (2007) 1994–1996. doi:10.1016/j.jmmm.2006.10.688.

[27]

X.L. Wang, M. James, J. Horvat, S.X. Dou, Spin glass behaviour in ferromagnetic La 2 CoMnO 6 perovskite manganite, Supercond. Sci. Technol. 15 (2002) 427–430. doi:10.1088/09532048/15/3/328.

[28]

X.L. Wang, J. Horvat, H.K. Liu, A.H. Li, S.X. Dou, Spin glass state in Gd2CoMnO6 perovskite manganite, Solid State Commun. 118 (2001) 27–30.

[29]

K.D. Chandrasekhar, A.K. Das, A. Venimadhav, Spin glass behaviour and extrinsic origin of magnetodielectric effect in non-multiferroic La2NiMnO6 nanoparticles., J. Phys. Condens. Matter. 24 (2012) 376003. doi:10.1088/0953-8984/24/37/376003.

[30]

J. Krishna Murthy, A. Venimadhav, Reentrant cluster glass behavior in La2CoMnO6 nanoparticles, J. Appl. Phys. 113 (2013) 163906. doi:10.1063/1.4802658.

[31]

Y.Q. Lin, X.M. Chen, X.Q. Liu, Relaxor-like dielectric behavior in La2NiMnO6 double perovskite ceramics, Solid State Commun. 149 (2009) 784–787. doi:10.1016/j.ssc.2009.02.028.

[32]

M.G. Masud, A. Ghosh, J. Sannigrahi, B.K. Chaudhuri, Observation of relaxor ferroelectricity and multiferroic behaviour in nanoparticles of the ferromagnetic semiconductor La(2)NiMnO(6)., J. Phys. Condens. Matter. 24 (2012) 295902. doi:10.1088/0953-8984/24/29/295902.

[33]

N.S. Rogado, J. Li, A.W. Sleight, M.A. Subramanian, Magnetocapacitance and Magnetoresistance Near Room Temperature in a Ferromagnetic Semiconductor: La2NiMnO6, Adv. Mater. 17 (2005) 2225–2227. doi:10.1002/adma.200500737.

[34]

D. Choudhury, P. Mandal, R. Mathieu, A. Hazarika, S. Rajan, A. Sundaresan, et al., Near-RoomTemperature Colossal Magnetodielectricity and Multiglass Properties in Partially Disordered La2NiMnO6, Phys. Rev. Lett. 108 (2012) 127201. doi:10.1103/PhysRevLett.108.127201.

[35]

J. Krishna Murthy, a. Venimadhav, Magnetodielectric behavior in La2CoMnO6 nanoparticles, J. Appl. Phys. 111 (2012) 024102. doi:10.1063/1.3673862.

AC C

EP

TE D

M AN U

SC

RI PT

[24]

29

ACCEPTED MANUSCRIPT

R.N. Mahato, K. Sethupathi, V. Sankaranarayanan, Colossal magnetoresistance in the double perovskite oxide La[sub 2]CoMnO[sub 6], J. Appl. Phys. 107 (2010) 09D714. doi:10.1063/1.3350907.

[37]

S. Kumar, G. Giovannetti, J. van den Brink, S. Picozzi, Theoretical prediction of multiferroicity in double perovskite Y2NiMnO6, Phys. Rev. B. 82 (2010) 1–6. doi:10.1103/PhysRevB.82.134429.

[38]

M.P. Singh, K.D. Truong, S. Jandl, P. Fournier, Multiferroic double perovskites: Opportunities, issues, and challenges, J. Appl. Phys. 107 (2010) 09D917–09D917–3. doi:10.1063/1.3362922.

[39]

M. Fiebig, Revival of the magnetoelectric effect, J. Phys. D-APPLIED Phys. 38 (2005) R123– R152.

[40]

J.F. Scott, Multiferroic memories Model interfaces, Nat. Mater. 6 (2007) 256–257.

[41]

I. Žutić, J. Fabian, S. Das Sarma, Spintronics: Fundamentals and applications, Rev. Mod. Phys. 76 (2004) 323–410. http://link.aps.org/doi/10.1103/RevModPhys.76.323.

[42]

T. Kyômen, R. Yamazaki, M. Itoh, Correlation between Magnetic Properties and Mn / Co Atomic Order in LCMO: I. Second-Order nature in Mn/Co Atomic Ordering and Valence State, Chem. Mater. 15 (2003) 4798–4803.

[43]

I.O. Troyanchuk, A.P. Sazonov, H. Szymczak, Phase Separation in La 2-x Ax CoMnO6 (A = Ca and Sr) Perovskites, J. Exp. Theor. Phys. 99 (2004) 363–369.

[44]

M. Viswanathan, P.S.A. Kumar, V.S. Bhadram, C. Narayana, A.K. Bera, S.M. Yusuf, Influence of lattice distortion on the Curie temperature and spin-phonon coupling in LaMn0.5Co0.5O3., J. Phys. Condens. Matter. 22 (2010) 346006. doi:10.1088/0953-8984/22/34/346006.

[45]

P.A. Joy, Y.B. Khollam, S.K. Date, I. La, Spin states of Mn and Co in LaMn0.5Co0.5O3, Phys. Rev. B. 62 (2000) 8608–8610.

[46]

R. Dass, J.-Q. Yan, J. Goodenough, Oxygen stoichiometry, ferromagnetism, and transport properties of La2-xNiMnO6+δ, Phys. Rev. B. 68 (2003) 1–12. doi:10.1103/PhysRevB.68.064415.

[47]

F.N. Sayed, S.N. Achary, S. Deshpande, B. Rajeswari, R.M. Kadam, S. Dwebedi, et al., Role of Annealing Atmosphere on Structure, Dielectric and Magnetic Properties of La2CoMnO6 and La2MgMnO 6, Zeitschrift Für Anorg. Und Allg. Chemie. 640 (2014) 1907–1921. doi:10.1002/zaac.201400215.

[48]

M.P. Pechini, Method of Preparing Lead and Alkaline Earth Titanates and Niobates and coating method using the same to form a capacitor. Patent Number: US3330697 A, Patent US 3330697, 1967.

AC C

EP

TE D

M AN U

SC

RI PT

[36]

30

ACCEPTED MANUSCRIPT

C.L. Bull, D. Gleeson, K.S. Knight, Determination of B-site ordering and structural transformations in the mixed transition metal perocskite La2CoMnO6 and La2NiMnO6, J. Phys. Condens. Matter. 15 (2003) 4927–4936.

[50]

A.C. Larson, R.B. Von Dreele, General Structure Analysis System (GSAS), 1994.

[51]

G.K. Williamson, W.H. Hall, X-ray line broadening from filed aluminium and wolfram, Acta Met. 1 (1953) 22–33.

[52]

N.S. Gonçalves, J. a. Carvalho, Z.M. Lima, J.M. Sasaki, Size–strain study of NiO nanoparticles by X-ray powder diffraction line broadening, Mater. Lett. 72 (2012) 36–38. doi:10.1016/j.matlet.2011.12.046.

[53]

G. Blasse, Ferromagnetic interaction in non-metallic perovskites, J. Phys. Chem. Solids. 26 (1969) 1969–1971.

[54]

J.F. Moulder, J. Chastain, Handbook of X-ray Photoelectron Spectroscopy: A Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, Perkin Elmer Corp., 1992.

[55]

H. Guo, J. Burgess, S. Street, A. Gupta, T.G. Calvarese, M. a. Subramanian, Growth of epitaxial thin films of the ordered double perovskite La2NiMnO6 on different substrates, Appl. Phys. Lett. 89 (2006) 022509. doi:10.1063/1.2221894.

[56]

A.T. Fulmer, J. Dondlinger, M.A. Langell, Passivation of the La2NiMnO6 double perovskite to hydroxylation by excess nickel , and the fate of the hydroxylated surface upon heating, Appl. Surf. Sci. 305 (2014) 544–553.

[57]

R.L. Moreira, F.M. Matinaga, A. Dias, Raman-spectroscopic evaluation of the long-range order in Ba(B’1/3B"2/3)O3 ceramics, Appl. Phys. Lett. 78 (2001) 428. doi:10.1063/1.1339254.

[58]

J.E.F.S. Rodrigues, D.M. Bezerra, A.R. Paschoal, A.P. Maciel, C.W.D.A. Paschoal, Probing phase formation and structural ordering in Ba3ZnNb2O9 films using confocal Raman microscopy, Vib. Spectrosc. 72 (2014) 8–14. doi:10.1016/j.vibspec.2014.02.001.

[59]

J. Deng, J. Chen, R. Yu, G. Liu, X. Xing, Crystallographic and Raman spectroscopic studies of microwave dielectric ceramics Ba(Ca1/3Nb2/3)O3, J. Alloy. Compd. 472 (2009) 502–506. doi:10.1016/j.jallcom.2008.05.006.

[60]

J.E.F.S. Rodrigues, D. Morais Bezerra, A. Pereira Maciel, C.W. a. Paschoal, Synthesis and structural ordering of nano-sized Ba3B′Nb2O9 (B′ = Ca and Zn) powders, Ceram. Int. 40 (2014) 5921–5930. doi:10.1016/j.ceramint.2013.11.037.

[61]

J.E.F.S. Rodrigues, E. Moreira, D.M. Bezerra, A.P. Maciel, C.W. de Araujo Paschoal, Ordering and phonons in Ba3CaNb2O9 complex perovskite, Mater. Res. Bull. 48 (2013) 3298–3303. doi:10.1016/j.materresbull.2013.05.005.

AC C

EP

TE D

M AN U

SC

RI PT

[49]

31

ACCEPTED MANUSCRIPT

A.P. Ayala, I. Guedes, E.N. Silva, M.S. Augsburger, M. del C. Viola, J.C. Pedregosa, Raman investigation of A2CoBO6 (A=Sr and Ca, B=Te and W) double perovskites, J. Appl. Phys. 101 (2007) -. doi:http://dx.doi.org/10.1063/1.2745088.

[63]

M.N. Iliev, M. V Abrashev, A.P. Litvinchuk, V.G. Hadjiev, H. Guo, A. Gupta, Raman spectroscopy of ordered double perovskite La2CoMnO6 thin films, Phys. Rev. B. 75 (2007) 104118. doi:10.1103/PhysRevB.75.104118.

[64]

S. Zhao, L. Shi, S. Zhou, J. Zhao, H. Yang, Y. Guo, Size-dependent magnetic properties and Raman spectra of La2NiMnO6 nanoparticles, J. Appl. Phys. 106 (2009) 123901. doi:10.1063/1.3269707.

[65]

M. Balli, P. Fournier, S. Jandl, K.D. Truong, M.M. Gospodinov, Analysis of the phase transition and magneto-thermal properties in La2CoMnO6 single crystals, J. Appl. Phys. 116 (2014) 073907. doi:10.1063/1.4893721.

[66]

H.Z. Guo, A. Gupta, J. Zhang, M. Varela, S.J. Pennycook, Effect of oxygen concentration on the magnetic properties of La2CoMnO2 thin films, Appl. Phys. Lett. 91 (2007) 202509. doi:10.1063/1.2814919.

[67]

F. Gervais, B. Piriou, Temperature-Dependence of Transverse-Optic and Longitudinal-Optic Modes in TiO2, Phys.Rev. B Solid State. 10 (1974) 1642–1654.

[68]

J. Hlinka, J. Petzelt, S. Kamba, D. Noujni, T. Ostapchuk, Infrared dielectric response of relaxor ferroelectrics, Phase Transitions. 79 (2006) 41–78. doi:10.1080/01411590500476438.

[69]

R.X. Silva, R.L. Moreira, R.M. Almeida, R. Paniago, C.W. a. Paschoal, Intrinsic dielectric properties of magnetodielectric La2CoMnO6, J. Appl. Phys. 117 (2015) 214105. doi:10.1063/1.4921441.

[70]

M. Zhu, Y. Lin, E.W.C. Lo, Q. Wang, Z. Zhao, W. Xie, Electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with cationic ordering, Appl. Phys. Lett. 100 (2012) 062406. doi:10.1063/1.3683550.

[71]

M.C. Ferrarelli, D.C. Sinclair, A.R. West, H.A. Dabkowska, A. Dabkowski, G.M. Luke, Comment on the origin(s) of the giant permittivity effect in CaCu3Ti4O12 single crystals and ceramics, J. Mater. Chem. 19 (2009) 5916–5919. doi:10.1039/b910871h.

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Highlights For the manuscript

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Structural order, magnetic and intrinsic dielectric properties of magnetoelectric La2CoMnO6

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We investigate the impact of thermal treatment temperature on magnetic and intrinsic dielectric properties of La2CoMnO6. Raman active and polar phonons analysis were employed to probe the structural ordering evolution and intrinsic dielectric properties of La2CoMnO6. We showed the giant dielectric constant in La2CoMnO6 has an extrinsic origin.

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Rosivaldo X. Silva, Alan S. de Menezes, Rafael M. Almeida, Roberto L. Moreira, R. Paniago, Xavi Marti, Helena Reichlova, Miroslav Maryško, Marcos Vinicius S. Rezende and Carlos William A. Paschoal