Solid-state synthesis of LaSrMnO3 powders for smart coatings

Accepted Manuscript Title: Solid-state synthesis of LaSrMnO3 powders for smart coatings Author: M.M. Mikhailov V.A. Vlasov T.A. Utebekov A.N. Sokolovskiy A.A. Lovizkii A.E. Smolin PII: DOI: Reference:

S0025-5408(16)32172-9 http://dx.doi.org/doi:10.1016/j.materresbull.2017.01.038 MRB 9131

To appear in:

MRB

Received date: Revised date: Accepted date:

21-11-2016 18-1-2017 26-1-2017

Please cite this article as: M.M. Mikhailov, V.A. Vlasov, T.A. Utebekov, A.N. Sokolovskiy, A.A. Lovizkii, A.E. Smolin, Solid-state synthesis of LaSrMnO3 powders for smart coatings, Materials Research Bulletin (2017), http://dx.doi.org/10.1016/j.materresbull.2017.01.038 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.

ip t cr us an M d Ac ce pt e Highlights

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• The synthesis of La(1-х)SrхMnO3 at temperatures below the sintering temperature of La2O3+MnСO3 is implemented. • The basic compound La(1-х)SrхMnO3 is formed at temperatures as low as 800°C after a heating time of 2 hours.

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• After an increase in temperature up to 1200 °C and a heating time of 6 hours the concentration of the compound reached 92.1 %. Solid-state synthesis of LaSrMnO3 powders for smart coatings

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a

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M.M. Mikhailova, V.A. Vlasovb,1, T.A. Utebekova, A.N. Sokolovskiyc, A.A. Lovizkiia, A.E. Smolina

Tomsk State University of Control System & Radioelectronics, Tomsk 634050, Russia

b

University of Washington, Seattle, Washington 98195, USA

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Abstract

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c

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Tomsk Polytechnic University, Tomsk 634050, Russia

In this paper the dependencies of particle size distribution, phase composition, diffuse reflection spectra, absorption spectra, and emissivity of powders from the mixtures La2O3+SrCO3+MnCO3 on a synthesis temperature in the range of 800–1200 °С are investigated. Samples were characterized using X–ray diffraction (XRD), high resolution scanning electron microscopy (SEM), and a spectrophotometer. It is found that the basic compound La(1–х)SrхMnO3 is formed even at such low temperature as 800 °C with a heating time of 2 hours. An explanation of the processes occurring in the synthesized powders was suggested. The conclusion about the possibility of obtaining the powder-pigments for the absorbing smart temperature stabilizing coatings by high-temperature synthesis without the use of mechanical effects was made. 1

Corresponding author. E-mail address: [email protected] (V.A. Vlasov).

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Keywords: Powders, Solid-state synthesis, Manganites, Coatings, Granulometric composition,

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Particle size distribution, Reflection and absorption spectra.

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1. Introduction

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Ceramic compounds such as La(1-х)АхMnO3 are widely used in storage devices thanks to the presence of phase transition (PT). The position of the PT depends on the concentration (C) of atoms

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(A), which are exchangeable with La3+cations. When C = 0, PT is in the negative temperature region where (TN = 140 °K [1]). When C = 15–30 wt.% the temperature (TN) is shifted up to room

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temperature or even higher. Investigations of PT in La(1-х)АхMnO3 solid solutions have been mainly regarded in changes of the electric, magnetic, and dielectric properties of the ceramic samples [2–4].

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In recent years, the studies of emissivity (ε) temperature dependence of La(1-х)АхMnO3 and

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other compounds have been performed in Japan and China [5–9]. This research was also carried out on ceramic samples and were aimed at the formation of the absorbing coatings based on La(1х)Sr(Ca)хMnO3

compounds for ceramic tiles.

The creation of temperature stabilizing (TS) coatings on the basis of temperature-dependent ε compounds instead of the usual thermal control coatings based on constant ε compounds is an urgent problem for spacecraft (SC). Such TS coatings are able to maintain a temperature at a predetermined level in the following cases: during the approach of a spacecraft into the shadow of Earth or other planets; at the rotating of around its axis, when there is no power source; and also in case where optical properties degrade due to the space factors [10].

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TS coatings are able to change the emissivity and flows of radiated energy under a change of external conditions in order for the object temperature to remain constant. Thus, these are called intelligent or smart coatings. Such a TS coating can be widely used in terrestrial conditions to maintain the temperature of

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technological processes in chemical, food, pharmaceutical and in industrial construction. For

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example, they can be used in the regulation of heat flows in places with high temperatures during the day and cool nights. The emissivity of the external surfaces of houses and industrial buildings is

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usually 0.85–0.95. The emissivity of TS coatings will be 0.3–0.4 at a decrease of temperature of the surrounding area at night up to zero or even to negative values [6]. This can keep the temperature

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inside a building at a predetermined level without the additional energy.

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Ceramic tile coatings have a number of technological shortcomings when applied to the surface of products. This is especially true for complex surface shapes. The result being that during

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operation, such tiles can easily flake or crack.

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The enamel coatings have a number of technological advantages over the ceramic coatings. They (enamel coatings) are easily applied to the surface of complex shapes, possess sufficient mechanical strength, as do not crack during use, and are lighter when performing the same functions. Therefore, it is desirable to produce the TS coatings as enamels with the La(1-х)АхMnO3 pigments [10].

Since TS coatings are subject to the individual active rays of the solar spectrum in terrestrial conditions and together with the charged particles in the conditions of the SC, they should have a high photo- and radiation stability (PRS). Mechanical treatment has a significant negative influence on the PRS of any dielectric and semiconductor powders by creating grains and granules leading to dislocations and point defects formation [11]. Obtaining pigments for the TS coatings should not be associated with grinding or splitting that leads to the formation of defects affecting on the PRS. Therefore, the most efficient way to get pigments with high PRS is a synthesis without the use of

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pressure. Also, the synthesis temperature should be below the sintering temperature of the initial mixture of powders. The particle dimensions and their distribution functions influence reflection and absorption

important to carry out joint investigations of these properties.

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spectra. They also significantly influence stability of such powders to irradiation. Therefore it is

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This paper presents the first results of the investigations of the phase and granulometric compositions, the diffuse reflection and absorption spectra, and temperature dependence of

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emissivity of the powders synthesized from the mixtures La2O3+SrCO3+MnСO3 at 800–1200 °С.

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The synthesized powders are intended for the manufacture of TS coatings as enamels.

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2. Materials and methods

Powders La2O3, MnCO3, and SrCO3 certified with "high purity" and "chemically pure" were

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mixed in the required weight ratio with distilled water. The mixture was diffused in a magnetic

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stirrer for 2 hours. Then the mixture was evaporated in an oven at 150 °C. Subsequent heating of the mixture was carried out in the predetermined conditions. Photomicrographs of the synthesized powders were obtained via a scanning electron microscope TM–1000. The distribution function of the powder particles by size was calculated from the photos using the cross-sections method by 300 points. The decomposition of the functions was performed on elementary components of the normal law. The area of Gaussian was determined as the product of height and width at half height (H1/2): S=n·H1/2. The X–ray diffraction (XRD) was carried out using a X–ray diffractometer Shimadzu XRD 6000. The diffuse reflectance spectra were recorded with a spectrophotometer Shimadzu–3600 in the range of 220–2800 nm. The temperature dependence of emissivity ɛ = f(T) was determined by the calorimetric method in the range from -70 °C to +120 °C.

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3. Results and discussion The X–ray diffraction data (Fig. 1) show that the main phase of La0.825Sr0.175MnO3 is formed a quantity of 20% at a temperature of 800 °C. Besides the decomposition of MnСO3 occurs with the formation

of

Mn3O4

by

the

reactions:

2La2O3+4MnCO3+О2→4LaMnO3+4СО2↑

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MnCO3+О2→2Mn3O4+6СО2↑.

and

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With the temperature increasing, the formation of Mn3O4 decreases, while the concentration of

SrCO3 reagents remain at a temperature of 800–1000 °C.

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the main phase (MP) – the compound La0.825Sr0.175MnO3 increases. Initial unreacted La2O3 and

The maximum concentration of MP for 2 hours of heating time is 84.4%. The large

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concentrations of the MP can increase of the synthesis time. For example, by increasing the sintering

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time of the powders up to 6 hours at 1200 °C, the yield of the MP is 92.1% (Fig. 2). The pictures of the powders synthesized by the heating for 2 hours at 800, 900, and 1000 °C are

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shown in Fig. 3. From the distribution functions of the particles by the size n = f(r), derived from

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these pictures, it follows that the particle sizes of the powders are in the range of 0.3–3.5 µm. The decomposition of the functions into the elementary bands – the Gaussians (G) showed that the minimum variation is obtained when the quantity of components is equal to three. The highest intensity corresponds to G with a maximum at 0.8–0.9 µm. Analysis showed (Table 1) that an increase of synthesis temperature from 800 to 900, 1000, 1100, and 1200 °C leads to increasing of the 1stG area from 77.1 to 84.9 and 91.6 µm-1, and then to decreasing to 75 and 68.4 µm-1. The 2ndG has opposite changes: first the area reduces from 63.6 to 56.8 µm-1 and 54.4 µm-1, and then increases to 65 and 70.7 µm-1 with an increase in synthesis temperature. The area of the 3rdG is much smaller than the area of the first two G’s. Qualitatively, 3rdG is changed to be similar to the area of 2ndG: first it is reduced to a temperature of 1000 °C, and then it is increased at the synthesis temperature of 1100 °C and 1200 °C.

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The maxima distributions of the particles with the increasing synthesis temperature from 800 to 1200 °C are shifted toward larger sizes: for the 1stG from 0.82 to 0.91 µm, for the 2ndG from 1.67 to 1.95 µm, and for the 3rdG from 3.08 to 3.32 µm. The dimensions of the particles of the 1st, 2nd, and 3rdG increase by 0.09, 0.26, and 0.15 µm, respectively.

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At T≥1000°С coarsening of the powder particles occurs. It may be due to the "adhesion and

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sintering" portion of the particles of the 1stG with the formation of granules. A comparison of the small and medium-sized particles shows that the small particles size is about 2 times smaller than

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the average particles size. This ratio suggests the average particles are not individual grains, but are formed from fine particles. At dense packing, each average particle consists of eight small particles

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(Fig. 5a).

But for larger particles of the 3rdG such correspondence is not observed. For example, assume

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that T = 800–900 °C, particles with the size 0.82–0.85 µm (rav = 0.83 µm) are converted into the particles with the size of 3.02–3.08 µm (rav = 3.05). Then we get: 3.05–(3×0.83) = 0.55 µm. If all

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particles, including 3rdGparticles, are presented in the form of a sphere, the edge inscribed in a cube would be equal to 3.05 µm. Three particles with the size of 0.83 µm and one particle with the size of 0.55 µm are stacked on the edge of large cubical particles obtained at a temperature of 800–900 °C (Fig. 5b).

For T = 1000–1100оС the size of the coarse particles increases to 3.24–3.27 µm (rav = 3.25 µm). At the same temperature the increasing of the fine particles size to 0.9–0.91 µm (rav = 0.905 µm) occurs. Therefore, three particles with the size of 0.905 µm and a particle with the size of 0.535 µm are stacked in the length of the large particles edge. For both sections of the synthesis temperatures of 800–900 °C and 1000–1100 °C we obtained large spherical granules. Four particles are stacked on the edges of cubes inscribed in these spheres: three particles of size 0.83–0.905µm and one particle size of 0.535–0.55µm.

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The synthesis at 1200°C produces particles of the 1st and 2ndG of roughly the same size as at the temperature 1000–1100 °C. The number of particles of the 1stG decreases, while the 2ndG increases. The size and number of particles in the 3rdG increase compared to the synthesis temperature at 1000–1100 °С. When the particle size of the 1stG is 0.91 µm, the particles of the 3rdG consist of

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three particles with a size of 0.91 µm and a particle with the size of 0.57 µm.

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The maximum of the integral curve with an increase in synthesis temperature from 800 to 1200

under the curves remain approximately the same.

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°C is first shifted towards the smaller sizes, then at T˃1000 °С – towards the larger ones. The areas

Thus, it was found that the high synthesis temperatures in a range of 800–1200 °C from

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mixtures of the powders La2O3+SrCO3+MnCO3 for a 2 hours heating time yields two compounds:

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La(1-х)SrхMnO3 and Mn3O4. The concentration of La(1-х)SrхMnO3 increases with rising of the synthesis temperature. Its maximum value is 84.4%. The concentration of Mn3O4 decreases from

to 92.1%.

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х)SrхMnO3

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22.7% to 15.6%. An increase in synthesis time of up to 6 hours enlarges the concentration of La(1-

Particles of 4 dimension types are formed for all values of the synthesis temperature. The smallest particles with the size of 0.53–0.57 µm are the nuclei of the larger particles. In the process of temperature rising from 800 to 900, 1000, 1100, and 1200 °C they are also formed, but do not exist independently. Most of them increase up to 0.82–0.91 µm. These particles are grain–crystals also. These grains are combined into granules of the average size from 1.67 to 1.93 µm and larger sizes from 3.08 to 3.3 µm. The average sized granule consists of eight particles with a size from 0.82–0.91 µm. The large granules include particles with the size of 0.82–091 µm in an amount of 75%, and the remaining 25% are the smallest particles with a size of 0.53–0.57 µm. The reflection peak is recorded in the shape of a "protrusion" at 300–800 nm with a peak at 520 nm in the ρλ spectra of the powder, synthesized at T=800 °C, in the visible range (Fig. 6). This

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spectrum is defined by the mixture formed at the synthesis of the compounds La(1-х)SrхMnO3 (19.9%), Mn3O4 (22.7%), and the unreacted powders of La2O3 (50.5%), SrCO3 (7.2%) (Table 2). Qualitatively, the powder synthesized at 900 °C has the same spectrum ρλ. The registered "protrusion" is in 300–800nm with a maximum at 480 nm. The reflectance decreases with the

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increase of the wave length in the region of λ>800 nm. This spectrum is defined by the mixture

of the unreacted powders of La2O3 (48.0%), SrCO3 (3.1%).

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formed at the synthesis of the compounds of La(1-х)SrхMnO3 (35.1%), Mn3O4 (13.9%), and the part

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The spectrum ρλ of the powder synthesized at T=1000 °C is not qualitatively different from the previous two spectra. The "protrusion" in the visible range is registered. The projection is continuing

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to shift toward shorter wavelengths (from 480 to 440 nm). Its width is reduced compared with its

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parameters in the spectra of the powders synthesized at 800 and 900 °C. In the NIR of spectra ρλ powders synthesized at 800 and 900 °C the reflection coefficient

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decreases monotonically with the increasing wavelength. With the increasing of the synthesis

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temperature from 800 to 900 °C the helix angle of the reflection line decreases. And for the powder synthesized at 1000 °C it is approximately equal to zero. This spectrum is determined by the mixture formed at the synthesis of the compounds of La(1-х)SrхMnO3 (59.6%), Mn3O4 (18.9%), and the unreacted powder of La2O3 (21.4%).

The increase in the synthesis temperature to 1100 and to 1200 °C leads to qualitative changes in the types of formed compounds and the spectra ρλ in both ranges. The lanthanum oxide is absent in the mixtures of the powders. There are La(1-х)SrхMnO3 and Mn3O4 only. The reducing of the reflection coefficient is registered as a "ravine" with a minimum at 620 nm in the visible region. The transition from the "projections" to the "ravines" in the reflection spectra occurs when the concentration of lanthanum oxide is approximately equal to 50%. This concentration is less than 50% at the temperature 800 – 900 °С and more than 50% - at 1000 – 1200 °С. The synthesized

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powders at C = 50% consist of La(1-х)SrхMnO3 and Mn3O4 only. There is no white powder of lanthanum oxide. Another transition, at the same synthesis temperature, takes place in the near IR region – from

five powders in this area are approximated by a power law:

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K=αλβ,

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the reduction of the reflectance to its increase with the rising of the wavelength. Spectra ρλ for all

where α and β – coefficients.

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The absorption coefficient K was calculated by the Kubelka–Munk–Gurevich formula: К/S=(1-ρ∞)2/2ρ∞,

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where ρ∞ – the reflectance of a thick layer of the powder, and S – scattering coefficient.

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The exponent β was obtained after assessing with the numbers 1.45, 0.4, 0.1, -0.28, and -0.35 for the samples synthesized at 800, 900, 1000, 1100, and 1200 °C, respectively (Fig. 7). The β

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changes from positive to negative values depending on the composition obtained after the synthesis

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of the compounds and their concentrations. The exponent β has positive values at concentrations of La0.825Sr0.175MnO3 lower than 50% in the mixtures of the synthesized powders and at higher concentrations – values are negative.

The resulting spectra ρλ depends on the synthesis temperature and allows us to consider the whole range of 0.2–2.8 µm as two individual areas. In one area a blatant band is registered, while in the other area the reflection coefficient is monotonically changed as wavelength increases. The band in the visible region is distinguished by the composition and concentration of the synthesized powder mixtures. At the synthesis temperature 800, 900, and 1000 °С the peaks of reflection are recorded. They are determined by the absorption coefficient of the synthesized compounds of La0.825Sr0.175MnO3+Mn3O4 with high absorption coefficients and the unreacted components of the initial powder mixture La2O3 + SrCO3 having high absorption coefficients. At the synthesis temperatures 1100 and 1200 °С the synthesized powder consists of only

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La0.825Sr0.175MnO3+Mn3O4 with a high absorption coefficient. In the visible range of the spectra ρλ the absorption band in the form of a ravine-like is recorded. For the comparison of the parameters of the band at 620 nm to known results, decomposition of this band into elementary components was carried out. The absorption band was obtained by

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subtracting the reflectance of the "ravines" from reflectance values at the edges of "ravines".

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Gaussian was chosen as a form of the elemental constituents of this band. A decomposition of this band for the spectrum of the powder, synthesized at 1200 °C (Fig. 6), showed the presence of three

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components with maximums at 1.52, 1.92, 2.58 eV and a half-width of 0.36, 0.74, 1.04 eV (Fig. 8). By now, a large amount of work has been devoted to the study of the absorption band at 620

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nm. But there is no definite opinion about this one so far. The absorption band in the visible region

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of the LaSr(Са)MnO3 compounds is associated with the existence of the paramagnetic and ferromagnetic phases and two types of charge carriers, electrons and polarons [12]. It is determined by either direct electron transitions of Mn3+→Mn4+ or through the transfer of electrons to oxygen:

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Mn3+→О2→Mn4+. By increasing of the concentration of LaSr(Са)MnO3 an increase in the intensity of the absorption band in this spectral region was recorded. The intensity rises with the increase in concentration of the substituent cations as well. In

[13], the registered absorption band in the

visible region was associated with the transfer of excitation energy. The same band shape was recorded in the reflectance spectra of ceramic samples of lanthanum manganite

[14], In the absorption spectra of the films LaSrMnO3 measured by superimposing a

magnetic field, the bands were registered decomposition of whose gives several elementary components with peaks at 1.4, 1.7, 1.9, 2.1, and 2.3 eV [15]. The comparison of these results in this paper with the decomposition data in [16], shows that the band at 1.52 eV is located between bands at 1.4 and 1.7 eV. The band at 1.92 eV is very close to the band at 1.9 eV. The band at 2.58 eV is located in a higher energy region than the bands at 2.1 and 2.3 eV.

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The band at 1.52eV can be determined by the superposition of two bands at 1.4 and 1.7 eV, associated with transitions p→d and d→d in ions Mn3+. Such a situation may be explained by the redistribution of spectral weight between electronic transitions of different natures. In the presence of the metallic phase in the sample, spectra are a superposition of two components [16]. The band

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attributed to both d→d and 4A2g→4T2gtransitions in the ions Mn4+ [17].

The band at 2.58 eV is

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at 1.9 eV is associated with forbidden transitions t1gπ→eg in ions Mn3+

The closest to our data are the results of [18], specifically devoted to the determination of the

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nature of the absorption band in the lanthanum manganite films in the visible region. The absorption bands in the form of “projections”, that had low intensity, have been registered on the integral curve

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at 1.92, 2.3, and 2.6 eV. Two of them (at 1.9 and 2.6 eV) coincide with the bands obtained in the

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present study. The authors have analyzed all proposed earlier interpretations of the absorption bands in the visible region. They concluded that the combination of the orbital degeneracy and correlation

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effects can provide a reasonable explanation.

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Further intensive studies are needed in order to determine the nature of the absorption bands in the visible region of the LaSrMnO3 compound. Presumably, it can be assumed that absorption in the visible range of the powders synthesized at a temperature of 800–1000 °C is determined by the electron transitions between levels in the cations formed during the synthesis of the compounds. The unreacted initial powders contribute to absorption to some extent via their non-stoichiometrical defects.

The spectra ρλ of the powders synthesized at 1100–1200 °С qualitatively are similar with the absorption spectra of the films

[15,18], and the reflection spectra of ceramic samples

[6],

consisting of 100% of the compound LaSrMnO3. In these spectra, the absorption band is mainly detected by the ferromagnetic component at a certain contribution of the paramagnetic phase. The absorption in the near IR region of the powders synthesized at 800 and 900 °C. This is largely detected by electron transitions between the levels in the conduction band (Fig. 9a).

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Electron’s energy distribution obeys a power–law dependence of the classical set for semiconductors: к = αλβ. This distribution was confirmed repeatedly in diffuse reflectance spectra of irradiated powderized zinc oxide [19]. The exponent β of this distribution has positive values. An insignificant contribution to this distribution was made by electrons from the ferromagnetic

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component (Fig. 9b).

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In the spectra of powders synthesized at 1100 and 1200 °C the absorption was determined mainly by the free electrons of the ferromagnetic phase. The energy of these electrons is equal to the

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highest energy electron in the paramagnetic phase in the range of 0.44–1.24eV (λ=1000–2800 nm). Therefore, the total distribution is changed in the opposite method, compared to the distribution in

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classical semiconductors and in compounds synthesized at 800 and 900 °С. The exponent β of this

highest energy (Fig. 9c).

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distribution has a negative value. The highest concentration of electrons in this distribution has the

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At this interpretation there is a relationship between the nature of absorption defined by the

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spectra ρλ in the visible and near infrared regions and the composition of powders synthesized at different temperatures.

The emissivity of powder synthesized at 1200 °C was registered by the calorimetric method in “TERM” at temperature range from -70 °C up to +120 °C [20]. The investigations showed that emissivity changed from 0.4 to 0.78 in this temperature range (Fig. 10). By using these experimental data and the following equation, the emissivity’s dependence on the temperature of La0.825Sr0.175MnO3 composition (in case of 100% pure La0.825Sr0.175MnO3 powder) was calculated: ɛexp= εLaСLa + εMnСMn,

where εLa, εMn – emissivity of La0.825Sr0.175MnO3 and Mn3O4 compositions, respectively; СLa, СMn – concentration of La0.825Sr0.175MnO3 and Mn3O4 compositions, respectively (СLa+ СMn =1). In calculations the emissivity of Mn3O4 was considered constant and equaled to 0.9.

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The calculations showed the temperature dependence ε =f(T) is qualitatively similar to the experimental curve for La0.825Sr0.175MnO3 and Mn3O4 compounds. It is close to dependencies obtained for ceramic samples with 100% pure of La0.825Sr0.175MnO3 [8]. Therefore the addition of Mn3O4 in quantity of 10-15% to the main phase should not influence the shape of the temperature

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dependencies of emissivity of synthesized powders.

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The emissivity of La(1-х)SrхMnO3 compound εLa is defined by the emissivity of ferromagnetic (εf) and paramagnetic (εp) components. It can be calculated from the following relationship:

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εLa = εfСf + εpСp,

where Сf, Сp is the concentration of ferromagnetic and paramagnetic components, respectively.

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The modes of La(1-х)SrхMnO3 powder synthesis at temperatures below 1200 °C may have

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practical value. They allow powders in the ranging 0.3–3.5 µm with a maximum distribution of 0.8– 0.9 µm to be obtained without the use of mechanical effects. These sizes are similar to the sizes of

reaches 92.1%. An miniscule supplement of Mn3O4 (7.9 %) to the main phase does not

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х)SrхMnO3)

[20]. The content of the main phase (the compounds La(1-

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known pigments like TiO2 and ZnO

influence functional characteristics of powder used in thermal control coatings. This supplement will serve as the filler, as done in common household paints. For example, a chalk is added as the filler in usual paints together with addition of TiO2 powder-pigment [21].

4. Conclusions

The experiments analyzed the processes occurring during the synthesis of La(1-х)SrхMnO3 powder at temperatures below the sintering temperature of the mixture La2O3+MnСO3+SrCO3. The evolution of compounds while increasing temperatures from 800 up to 1200 °C was tracked. It is found that the basic compound La(1-х)SrхMnO3 is formed at temperatures as low as 800 °C after a heating time of 2 hours. After an increase in temperature to 1200 °C and a heating time of 6 hours the concentration of the compound reached 92.1%.

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The change in particle size distribution, phase composition, and the diffuse reflectance spectra of the synthesized powders with an increase in synthesis temperature from 800 to 900, 1000, 1100, and 1200 °C was investigated. The relationship between these properties has been shown. The explanation of the obtained dependencies is given. The conclusion about the possibility of obtaining

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synthesis without the use of mechanical effects was made.

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the powder-pigments for the absorbing smart temperature stabilizing coatings via high–temperature

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Acknowledgments

This work was financially supported by the State Task in scientific research №4.1088.214/K in

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References

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the framework of the project.

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[1]. R.I. Zainullina, N.G. Bebenin, V.V. Ustinov, Ya.M. Mukovskii, D.A.Shulyatev, Phase

Ac ce pt e

transitions in La1-xCaxMnO3 (0.2
[2].

L. Conceição, N.F.P. Ribeiro, J.G.M. Furtado, M.M.V.M. Souza, Effect of propellant on the

combustion synthesized Sr-doped LaMnO3 powders. Ceramics International 35 (2009) 16831687.

[3]. A. Bouderbala, J. Makni-Chakroun, W. Cheikhrouhou-Koubaa , M. Koubaa, A. Cheikhrouhou, S. Nowak, S. Ammar-Merah, Structural, magnetic and magnetocaloric study of La0.7xEuxSr0.3MnO3 (x=0.1, 0.2 and 0.3) manganites. Ceramics International 41 (2015) 73377344.

Page 15 of 30

[4]. S.B. Kansara, D. Dhruv, B. Kataria, C.M. Thaker, S. Rayaprol, C.L. Prajapat, M.R. Singh, P.S. Solanki, D.G. Kuberkar, N.A. Shah, Structural, transport and magnetic properties of monovalent doped La1-xNaxMnO3 manganites. Ceramics International 41 (2015) 7162-7173. Y. Shimakawa, T. Yoshiake, T. Kubo, T. Machida, K. Shinagawa, A. Okamoto et al. Appl.

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[5].

Phys. Lett. 80 (2002) 4864.

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[6]. G. Tang, Y. Yu, Y. Cao, W. Chen, The thermochromic properties of La1-xSrxMnO3

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compounds. Solar Energy Materials & Solar Cells 92 (2008) 1298-1301.

[7]. X. Shen, G. Xu, C. Shao, The effect of B site doping on infrared emissivity of lanthanum

an

manganites La0.8Sr0.2Mn1-xBxO3 (B=Ti or Cu). Journal of Alloys and Compounds 499 (2010) 212-214.

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[8]. X. Shen, G. Xu, C. Shao, C. Cheng, Temperature dependence of infrared emissivity of doped manganese oxides in different wavebands (3–5 and 8–14 µm). Journal of Alloys and

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Compounds 479 (2009) 420-422.

Ac ce pt e

[9]. Y. I. Lee, Optical Conductivity in the Manganite La1-xSrxMnO3 (x=0.175). International Journal of Innovative Research in Advanced Engineering (IJIRAE) 1 (2014) 115- 118.

[10]. X. Shen, G. Xu, C. Shao, C. Cheng, Temperature dependence of infrared emissivity of doped manganese oxides in different wavebands (3–5 and 8–14 µm). Journal of Alloys and Compounds 479 (2009) 420–422. DOI: 10.1016/j.jallcom.2008.12.090

[11]. M.M. Mikhailov, The absorbing thermally stabilizing material on the bse of manganites of the rare–earth elements, its production method and termostabilizing coating on its basis. Patent of RF №2404128 from 20.11.2010, priority 12.05.2008. [12]. E. Dagotto, Nanoscale Phase-Separation and Colossal Magnetoresistance, Springer–Verlag, Berlin, 2002.

Page 16 of 30

[13]. Y. Tokura, Fundamental features of colossal magnetoresistive manganese oxides in colossal magnetoresistive oxides. Ed Reading Gardon Breach Science Publ. 2 (2000) 1–52. [14]. K. Takenaka, K. Iida, Y. Sawaki, S. Sugai, Y. Moritomo, A. Nakamura, Optical Reflectivity Spectra Measured on Cleaved Surfaces of La1−xSrxMnO3: Evidence against Extremely Small

ip t

Drude Weight. Journal of the Physical Society of Japan 68 (1999) 1828–1831. ISSN:

cr

00319015

[15]. A.E. Grebenkova, I.S. Sokolov, N.V. Edelman, V.I. Andreev, Y.M. Chichkov, Linear and

us

quadratic magneto–optical effects in transmitted light in thin films La0.7Sr0.3MnO3. JETP Letters 98 (2013) 460–464. DOI: 10.1134/S0021364013210078

an

[16]. E. Yu. Grebenkova, I. S. Edelman, A.I. Sokolov, E.V. Eremin, M.V. Rautsky, N.V. Andreev,

M

V.I. Chichkov, Y.M. Mukovsky, Magnetic and magneto–optical properties of polycrystalline films La0.7Sr0.3MnO3. Izvestiya RAN.: Physics 77 (2013) 1383–1386.

d

[17]. A.S. Moskvin, A.A. Makhnev, L.V. Nomerovannaya, N.N. Loshkareva, A.M. Balbashov,

Ac ce pt e

Interplay of p-d and d-d charge transfer transitions in rare earth perovskite manganites. Phys. Rev. B. 82 (2010) 035106. DOI: 10.1103/PhysRevB.82.035106

[18]. E.A. Balykina, E.A. Ganshina, G.S. Krinchik, A.Yu. Trifonov, Magneto-optical properties of new manganese oxide compounds. JMMM 117 (1992) 259–269. DOI: 10.1016/03048853(92)90319-J

[19]. M.W. Kim, P. Murugavel, S. Parashar, J. S. Lee, T. W. Noh, Origin of the 2eV peak in optical absorption spectra of LaMnO3: an explanation based on the orbitally degenerate Hubbard

model. New Journal of Physics 6 (2004) 156.

[20]. M.M. Mikhailov, Nanotechnology to improve photo - and reflecting the radiation resistance powders. Scientific works, Volume 4 Publisher: University of Tomsk, Tomsk, 2014.

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[21]. M.M. Mikhailov, V.V.Neshchimenko, S.A.Yuryev, Optical properties and radiation stability of submicro-and nano powders titanium dioxide measured in situ. Radiation Physics and

us

cr

ip t

Chemistry, 121 (2016) 10-15. DOI: 10.1016/j.radphyschem.2015.12.006

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Figure Captions

Fig. 1. The X–ray diffraction patterns of the compounds obtained by the synthesis of the powders

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mixtures La2O3+SrCO3+MnСO3 at the temperature 800-1200 °С and heating time of 2 and 6 hours. Fig.2. The dependence of the concentration of the synthesized compounds La0.825Sr0.175MnO3 and

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Mn3O4 and unreacted initial powders on the synthesis temperature from the powder mixtures of

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La2O3+SrCO3+MnСO3 at the heating time of 2 hours. Fig.3. The pictures of the powders synthesized by heating of the La2O3+SrCO3+MnСO3 mixtures for 2 hours at the temperature: 800 (a), 900 (b), 1000 (c), 1100 (d), and 1200 °C (e). Fig.4. The functions of the particle size distribution of the powders synthesized by heating of the mixtures La2O3+SrCO3+MnСO3 at the temperature 800-1200 °С during 2 hours and their decomposition into components.

Fig. 5. The granule of average sizes consisting of eight small particles with the size 0.82–0.91 µm (a), and the granule of large size including sixty-four particles (b). Along the length of the edge the granule consists of: 3 particles with the size of 0.905 µm and a particle with the size of 0.535 µm. Fig.6. The diffuse reflection spectra of the powders obtained from the high temperature synthesis of mixtures La2O3+MnСO3+SrCO3 at the temperature 800-1200 °С.

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Fig.7. The logarithmic dependencies of the absorption coefficient in the NIR region of the powders synthesized by the heating of the mixtures La2О3+SrСО3+MnСO3 at the temperature 800-1200 °С. Fig.8. The absorption band and elementary components of the Gaussian shape of the powder synthesized by the heating of the mixtures La2О3+SrСО3+MnСO3 for 2 hours at 1200 °С.

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Fig.9. The diagrams of the energy levels distribution of the electrons in the conduction band: the

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classic distribution for semiconductors (a); distribution determined by the combined effect of the paramagnetic and ferromagnetic phases (b); distribution determined by the effect of the

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ferromagnetic phase (c). In the lower part of the figure – the logarithmic dependencies of the absorption coefficient in the near IR region on the wavelength the energy levels corresponding to

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these distributions.

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Fig. 10. The temperature dependences of emissivity of: 1 - powder consisting of La(1-х)SrхMnO3

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(84,4%) and Mn3O4 (15,6%); 2 - powder of La(1-х)SrхMnO3 (100%).

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Table 1

800

rav (µm)

0.82

900

0.85

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№1

Т (°С)

d

Gaussian

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Dependence of the average particle size (rav) and the area of Gaussians (S) on the synthesis temperature of compound La0,825Sr0,175MnO3 from the mixture of the powders La2O3+SrCO3+MnСO3 1000

1100

1200

0.90

0.91

0.91

S (µm -1)

77.1

84.9

91.6

75.0

68.4

rav (µm)

1.67

1.67

1.70

1.95

1.93

S (µm -1)

63.6

56.8

54.4

65.0

70.7

rav (µm)

3.08

3.02

3.27

3.24

3.3

S (µm -1)

14.7

14.0

9.3

13.4

14.0

rav (µm)

1.44

1.39

1.38

1.60

1.69

S (µm -1)

155.4

155.7

155.3

153.4

153.1

№2

№3

Table 2 The values of the concentration of compound La0,825Sr0,175MnO3, the reflectance in different regions of the spectrum of the mixtures of the powders La2O3+SrCO3+MnСO3 at different heating temperature during 2 hours

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800

900

1000

1100

1200

С (mass. %)

19.6

35.1

56.9

79.7

84.4

620 nm

6.8

6.6

5.8

4.7

5.0

1000 nm

5.4

5.6

5.2

5.0

2500 nm

4.0

4.8

5.5

7.5

6.3

cr

10.4

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d

M

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ρ (%)

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Т (°С)

Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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Figure 8

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Figure 9

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Figure 10

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