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Journal of Thermal Analysis and Calorimetry

, Volume 133, Issue 1, pp 421–428 | Cite as

Brown pigments based on perovskite structure of BiFeO3−δ

  • Žaneta Dohnalová
  • Petra Šulcová
  • Petr Bělina
  • Milan Vlček
  • Nataliia Gorodylova
Article
  • 254 Downloads

Abstract

Light brown inorganic pigments based on BiFeO3 doped by Sr2+ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi1−x Sr x FeO3−δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO3 is 1046 K, whereas the substitution of 20 mol% of Bi3+ by Sr2+ ions shifted it to 1403 K and powder with composition Bi0.65Sr0.35FeO3−δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi0.85Sr0.15FeO3−δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).

Keywords

Reddish-brown pigment Ferrite Perovskite Strontium iron bismuth oxide 

Introduction

Most inorganic pigments have been known for a very long time; however, some of them become unacceptable due to the presence of toxic elements and strict environmental laws. The industrially available reddish-brown pigments are based on either the spinel or rutile structure, where the coloring element is problematic Cr3+ or the structure of Fe2O3 whose thermal stability is not so high. The Color Pigments Manufacturers Association, Inc. recorded the following structures of industrial complex inorganic color pigments with red or reddish-brown hues [1]: red 101/102 (haematite), brown 24 (Cr–Sb–Ti rutile), brown 29 (Cr–Fe haematite), brown 33 (Zn–Fe–Cr spinel), brown 34 (Ni–Fe spinel), brown 35 (Fe–Cr spinel), brown 37 (Mn–Nb–Ti rutile), brown 39 (Cr–Mn–Zn spinel), brown 40 (Mn–Cr–Sb–Ti rutile), and brown 46 (Cr–Fe–Mn spinel). Therefore, there is current interest in the field of research in new inorganic pigments for developing more thermally stable red and reddish-brown pigments that present intense tonalities and that are in agreement with the technological and environmental requirements [2]. The study of the thermal stability of mixed oxides is very important for various applications [3, 4, 5].

The research of new environmentally friendly inorganic reddish-brown pigments in the past decade was concentrated on praseodymium-doped CeO2, which offers colors ranging from brick red to dark brown [6, 7, 8]. Various reddish-brown pigments were also prepared by next substitution in the system CeO2–Pr6O11. Formation of brown pigments by the addition of Fe2O3 to the Ce–Pr system has been investigated [9, 10, 11]. Lanthanide ions, especially Er3+, were used for the change in color hue of spinel pigments with the general formula MgFe2−x Er x O4. An increase in the content of trivalent erbium cations results in pigments of a light brown hue. The pigments displayed good resistance to sunlight, but this was reduced as the content of erbium increased [12]. Brown spinels with utilization as corrosion inhibitors Zn1−x Mg x Fe2O4 were prepared by the sol–gel method [13]. The substitution of magnesium ions by zinc ions is connected with a decrease in band gap values and, therefore, leads to the change in color from brick red to brown. The increasing content of Zn2+ ions almost does not affect the brown hue. Bao et al. [14] synthesized and characterized Fe3+-doped Co0.5Mg0.5Al2O4 pigments with high near-infrared reflectance by the sol–gel method. The gradual addition of ferric ions results in a change in the resulting color of the pigment. Without ferric ions, the pigment is blue, with higher additions gradually passing to green, brown, and, finally, to black. New non-traditional brown pigments are based on the structure of Na2V6O16·xH2O. The ultrathin and superlong Na2V6O16·xH2O nanoribbon was tested as a cool color pigment with high near-infrared reflectance and thermal performance. The nanoribbon appears in brilliant brown with red and yellow hues and with a spectral absorption edge below 575 nm. The nanoribbon has high spectral reflectance (62.4–76.2%) in the 700–1000-nm-wavelength region and near-infrared solar reflectance (59.1%) due to its unique morphology [15]. A big part of new reddish-brown inorganic pigments belongs to the group of perovskites based on the LnFeO3 structure, which are usually prepared either by a solid-state reaction or by the sol–gel method [16, 17, 18, 19, 20]. James et al. investigated the effect of lanthanide ions on the shift of band gap and optical properties of Bi1−x M x FeO3 (M = La3+, Y3+) powders in UV–Vis–NIR regions of light. The pigments were tested for their coloring application in a substrate material such as poly(methylmethacrylate) (PMMA). All results show that these powders can be classified as interesting and environmentally friendly inorganic pigments with a reddish-brown color hue [21].

The environmentally friendly composition of bismuth iron oxide offers the possibility to test this material as an inorganic pigment. Bismuth iron oxide (BiFeO3) is a well-known ferroelectric and antiferromagnetic material having a rhombohedral symmetry belonging to the R3c space group and with a melting temperature of 850 °C [19, 20]. It is a technologically and scientifically interesting material whose main applications are as photocatalytic compound, infrared detector, ultrafast optoelectronic device, flame retarder, etc. [22, 23, 24]. Studies on BiFeO3 show the difficulties in the preparation of the perovskite free of secondary phases [25, 26, 27]. In the case of preparation of BiFeO3 by a solid-state reaction from the mixture of oxides, several ternary phases can be formed: the orthorhombic Bi2Fe4O9, the rhombohedral perovskite BiFeO3, which decomposes peritectically to Bi2Fe4O9 and the liquid phase at ≈ 935 °C, and cubic Bi25FeO40 [28, 29, 30, 31]. The difficulties of the processing of single-phase BiFeO3 powder are given not just by thermodynamic instability of BiFeO3 but also by evaporation of bismuth during the preparation. During material preparation, Bi undergoes easy evaporation and generates bismuth vacancies. James et al. [21] overcome these defects by the partial substitution of Bi3+ by rare earth ions. Another possibility is to replace trivalent Bi by divalent Sr. This substitution leads to a change in the lattice symmetry from the rhombohedral distorted perovskite to the cubic perovskite and results in oxygen deficiency in the lattice [32]. Li et al. systematically investigated the crystal structure and electronic and magnetic properties of the system Bi1−x Sr x FeO3 in the range x = 0.2–0.67.

However, there is no study regarding pigmentary application properties or the thermal stability of these materials. Therefore, the main aim of our study was to synthesize Bi1−x Sr x FeO3−δ powder in the range of substitution (x = 0–0.35; with step size 0.05) and to evaluate the effect of Sr ions on the thermal stability, particle size distribution, and color parameters of powders.

Experimental

Synthesis of pigments

Compounds Bi2O3 (99.8% purity, Lachema Pliva, as, CZ), SrCO3 (96% purity, ML Chemica, CZ), and Fe2O3—TP 303 (Precheza a.s., CZ) were employed as the initial reagents for the preparation of inorganic pigments in the composition Bi1−x Sr x FeO3−δ , where x = 0–0.35. The synthesis of the pigments was based on the classical ceramic route, i.e., a solid-state reaction supported by mechanochemical activation. The initial reagents were weighted in appropriate proportions (laboratory scale) and thoroughly homogenized in a mortar grinder Pulverisette 2 (Fritsch GmbH, Germany) for 15 min. Then, the reaction mixture was subjected to mechanochemical activation in a planetary mill Pulverisette 5 (Fritsch GmbH, Germany) for 6 h, at a rotation speed of 200 rpm. The reaction mixtures were ground with agate balls (ø 10 mm) in a ball-to-powder mass ratio of 20:1. The activated reaction mixtures were formed into pellets, kept in the corundum crucibles, and heated in air at a temperature of 773–1273 K (with step size 100 K) for 1 min. The heating rate employed for heating treatment was 10 °C min−1. Then, the intermediates were cooled inside the furnace to room temperature, ground in an agate mortar, and subjected to the determination of their phase compositions by XRD analysis.

Final powders that were tested from a pigmentary application point of view were heated at 1173 and 1273 K for 2 h, with a heating rate of 10 K min−1. Particle size distribution of the final powders was improved by wet milling in a planetary mill Pulverisette 5 (Fritsch GmbH, Germany) in ethanol and zircon beads (ø 1.6–1.8 mm) for 15 min.

Characterization of powders

To study the reactions taking place during the ferrite formation at high-temperature treatment, the thermal analysis method was used. Simultaneous TG–DTA analysis of initial reagents and reaction mixture for the synthesis of Sr0.2Bi0.8FeO3 powder was performed by using an STA 449C Jupiter (Netzsch, Germany), which allows the evaluation of data with simultaneous registration of the thermoanalytical curves TG and DTA. Powder specimens (225–300 mg) in corundum crucibles were heated up to a temperature of 1700 K with a heating rate of 10 K min−1 in air. α-Al2O3 was used as a reference material.

The concentration (w/w) of impurities in the SrCO3 sample was analyzed by using an Elva X energy-dispersive X-ray fluorescence spectrometer (Elvatech Ltd., Kiev, Ukraine) that was equipped with a Pd X-ray tube and a thermoelectrically cooled Si-pin detector PF 550 (Moxtek, USA). The main impurity in SrCO3 is formed by Ca (2.5%) and Ba (1.4%); next, there are Fe, Cr, and Ti in very small amounts.

The phase composition of the pigments was studied by X-ray diffraction analysis. The diffractograms of the samples were obtained by using a MiniFlex 600 (Rigaku, Japan) diffractometer working in Bragg–Brentano (θ/2θ) geometry with 1D D/teX Ultra silicon strip detector and Kβ filter. The data were collected within 2θ angle range from 10° to 80° at a step size of 0.02° and a speed of 10 °C min−1 by using CuKα line. CuKα1 (λ = 0.15418 nm) radiation was used for the angular range of 2θ < 35°, and CuKα2 (λ = 0.15405 nm) was used for the range of 2θ > 35°. The identification of individual phases was based on the matching of the obtained diffraction patterns with the data contained in the JCPDS database [33].

The thermal stability of the final pigments was tested by using a heating microscope EM201-15 (Hesse Instruments, Germany). The samples in the form of tablets were gradually heated from room temperature to 1473 K, and a change in the sample’s areas was detected. The heating rate was 10 K min−1.

Particle size distribution of the samples was measured by using a Mastersizer 2000/MU (Malvern Instruments, UK). The equipment employs a scattering of incident light on particles. The amount of 0.1 g of pigment was ultrasonically homogenized in 40 mL of Na4P2O7 solution (c = 3 mol dm−3) for 2 min. An appropriate amount of suspension (for attenuation of 12.5% ± 0.5) was added to 800 mL of Na4P2O7 solution (c = 0.15 mol dm−3) and measured. The signal was evaluated on the basis of Mie theory.

The color of the synthesized pigments was evaluated after their application to the organic matrix (dispersive acrylic paint Luxol, AkzoNobel) in mass tone. The slurry containing 1 g of the pigment and 1.5 cm3 of the organic matrix was homogenized in an agate mortar. Colored paints were prepared by the deposition of the slurries on the white non-absorbing paper. The thickness of the wet film was 100 μm. The color properties of all films were objectively evaluated by measuring the spectral reflectance by using a spectrophotometer ColourQuerst XE (HunterLab, USA). The measurement conditions were as follows: an Illuminant D65 and measuring geometry d/8°. For description of color, the CIE L*a*b* color space (also referred as CIELAB) was used. In this color space, L* indicates the lightness and a* and b* are the chromaticity coordinates. In a*b* diagram, a* and b* indicate color directions: +a* is the red direction, −a* is the green direction, +b* is the yellow direction, and −b* is the blue direction. The center is achromatic; as a* and b* values increase, the saturation of the color also increases. The value C (chroma) represents saturation of the color and is calculated according to the formula: C = (a*2 + b*2)1/2. The color hue of pigments being expressed as a hue angle H° = arc tg(b*/a*) is also possible [34].

Results and discussion

The first task of this work was to study the reactions taking place in the mixture of bismuth oxide, iron oxide, and strontium carbonate for the preparation of powder described by the theoretical formula Sr0.2Bi0.8FeO3. The effects on the DTA curve were evaluated with help of the results of XRD analysis (Table 1) and also with the help of TG/DTA analysis of initial reagents Bi2O3 and SrCO3.
Table 1

Phase composition of calcinated mixtures 0.2SrCO3–0.4Bi2O3–0.5Fe2O3 with annealing time 1 min

T/K

Detected phases

773

Bi2O3, Fe2O3, SrCO3

873

Fe2O3, Bi2O3, Bi25FeO40, SrCO3,

973

Bi25FeO40, Fe2O3, α-BiFeO3, SrCO3, Bi2O3, Bi0.81Sr0.19O1.4

1073

α-BiFeO3, Bi0.81Sr0.19O1.4, Fe2O3, Bi25FeO40, SrCO3

1173

α-BiFeO3, Bi0.75Sr0.25O1.356, β-BiFeO3

1273

Sr0.2Bi0.8FeO3

Thermoanalytical curves of Bi2O3 are given in Fig. 1. At the DTA curve, two endothermic effects with a minimum at 1010 and 1093 K were recorded. The first peak corresponds to the phase transformation of monoclinic α-Bi2O3 to cubic modification δ-Bi2O3. The second peak represents the melting of δ-Bi2O3. The TG curve recorded the total mass loss (0.78%). This mass loss is caused by the partial oxygen loss, because bismuth oxide is known as oxide with an excess of oxygen in its crystal lattice [35]. The partial oxygen loss is connected at the DTA curve, only with two slight breaks at a temperature of about 581 and 653 K.
Fig. 1

TG and DTA curves of Bi2O3 (256.9 mg)

The TG/DTA curves of SrCO3 are shown in Fig. 2. Thermal decomposition of strontium carbonate is accompanied by the reversible transformation from a rhombic to hexagonal crystal structure. This process is recorded on the DTA curve by an endothermic effect with a minimum at 1212 K. The endothermic effects with a minimum at 1455 and 1513 K are connected with the thermal decomposition of SrCO3, which takes place in a multistage process. The decomposition was detected on the TG curve by mass loss (29.77%) [36].
Fig. 2

TG and DTA curves of SrCO3 (305.7 mg)

The thermoanalytical curves of the reaction mixture 0.2SrCO3–0.4Bi2O3–0.5Fe2O3 are shown in Fig. 3. At the DTA curve, four endothermic peaks were detected in the temperature region at 300–1273 K. In the temperature region at 300–873 K, the endothermic peak at 440 K was recorded at the DTA curve. The peak is accompanied by mass loss at the TG curve and corresponds to the removal of moisture from iron oxide. A slight break recorded at the DTA curve at a temperature about 697 K is also accompanied by mass loss at the TG curve. This effect is caused by the partial oxygen loss from the initial reagent Bi2O3. Another very slight break was detected at the DTA curve at a temperature about 873 K, which is connected with the formation of the new phase Bi25FeO40. The formation of bismuth iron oxide in the temperature region 773–873 K was proved by XRD analysis of the mixture. The mixture heated at 773 K contains only the initial reagents (Bi2O3, Fe2O3, and SrCO3), whereas the mixture heated at 873 K contains next-to-initial reagents and also Bi25FeO40 (Table 1). At the DTA curve, there is a sign of an endothermic peak at a temperature about 1013 K. This slight break corresponds to the phase transformation of Bi2O3. In Fig. 1, this effect was recorded as a sharp endothermic peak with a minimum at 1010 K. At the DTA curve in Fig. 3, this effect appears only as a break, because the region between 950 and 1090 K is also connected with the formation of new phases: BiFeO3 and Bi0.81Sr0.19O1.4 (Table 1). The formation of new phases was overcome by the phase transformation of α-BiFeO3 to β-BiFeO3, which took place at 1085 K. The last endothermic effects at 1154 and 1187 K are connected with decomposition of the rest of SrCO3, and the exothermic affect at 1209 K is connected with the formation of Sr0.2Bi0.8FeO3. Mass loss in the temperature region 873–1273 K can be caused not only by the evaluation of CO2 from SrCO3 but also by oxygen loss from final Sr0.2Bi0.8FeO3.
Fig. 3

TG and DTA curves of the reaction mixture SrCO3–Bi2O3–Fe2O3 (225 mg)

The total mass lost during the STA treatment was 3.99%, but the theoretical mass lost, which is connected only with the evaluation of CO2, is 2.98%. The difference between the values of experimental and theoretical mass loss is done by the removal of the moisture at the beginning of the reaction (from Fe2O3) and also by the formation of oxygen deficiency in the final product Sr0.2Bi0.8FeO3. Composition of the sample with the theoretical formula Sr0.2Bi0.8FeO3 was verified by EDX analysis (JOEL JSM-5500 LV, Joel Inc., USA), and the result proved the formation of oxygen deficiency. The formula Sr0.2Bi0.78FeO2.75 was obtained after the recalculation of elemental composition to perovskite formula provided that the valence of Fe is III.

On the basis of the results of the STA analysis, the temperatures 1173 and 1273 K were chosen for the synthesis of pigments Bi1−x Sr x FeO3 (x = 0–0.35). Phase composition of the pigment Sr0.2Bi0.8FeO3−δ after heating at 1173 or 1273 K (2 h) was again proved by XRD analysis. Both samples are single phased. In the case of the temperature at 1173 K, the lines of Sr0.2Bi0.8FeO3 were identified at the diffraction pattern and in the case of the temperature at 1273 KC the lines of Sr0.2Bi0.8FeO2.9 were identified.

Thermal stability of the final products Bi1−x Sr x FeO3−δ (x = 0–0.35) was tested by a heating microscope. The main goal of the measurement was to find out whether the increasing amount of Sr ions can affect the thermal stability of the products and also whether the powders can be used for coloring of ceramic glazes. From the results in Table 2, it is evident that Sr ions markedly increased the thermal stability of the samples. The temperature of deformation of BiFeO3 (calcinated at 1173 K; 2 h) tablet is only 1046 K, and a small amount of Sr ions (x = 0.05) shifted the deformation temperature to 1301 K. The thermal stability of Bi0.65Sr0.35FeO3−δ powder is the highest, which is almost 1434 K. An increasing amount of Sr ions offers the possibility to use the powders for the coloring of ceramic glazes with a recommended firing temperature between 1273 and 1423 K. Nevertheless, this is only a theoretical possibility, because from Fig. 4 it is evident that the deformation of powder proceeded in two steps. The first step, sintering (T sint), started at a temperature about 20–100 K less than the second step, melting (T def).
Table 2

Thermal stability of the powders Bi1−x Sr x FeO3−δ

Sample

T sint/K

T def/K

BiFeO3/1173 K

1024

1046

Bi0.95Sr0.05FeO3−δ

1229

1301

Bi0.9Sr0.1FeO3−δ

1282

1313

Bi0.85Sr0.15FeO3−δ

1296

1329

Bi0.8Sr0.2FeO3−δ

1309

1403

Bi0.75Sr0.25FeO3−δ

1335

1421

Bi0.7Sr0.3FeO3−δ

1337

1428

Bi0.65Sr0.35FeO3−δ

1347

1434

Fig. 4

Thermal behavior of samples BiFeO3 (1), Bi0.9Sr0.1FeO3 (2), Bi0.8Sr0.2FeO3 (3), and Bi0.65Sr0.35FeO3 (4)

The main criterion for the testing of color properties of the powders is the width of their particle size distribution. Pigments fit for application to an organic binder should have 90% of particles < 10 μm. The preparation of powders by heating at a temperature close to the sintering temperature led to the creation of powders with coarse particles (Table 3). Values of d 50 of all powders with strontium are < 3 μm, but values of d 90 are in the region 15–25 μm. The BiFeO3 powder, whose thermal stability is the lowest, was prepared by calcination at 1173 K, yet its particles are significantly larger. The measurement of the color properties of such materials is not effective, and particle size distribution has to be improved. After 15 min of wet milling in ethanol and zircon beads, fine powder was obtained. Any dependence between particle size and an increasing amount of Sr ions was not observed. Also after milling, the particle sizes of the BiFeO3 powder are significantly larger.
Table 3

Particle size distribution of the pigments (calcining temperature 1273 K)

Sample

Before milling

After milling

d 50/μm

d 10d 50/μm

d 50/μm

d 10d 50/μm

BiFeO3 1173 K

15.32

6.88–63.91

5.19

2.57–20.69

Bi0.95Sr0.05FeO3

2.82

0.88–19.03

1.85

0.47–5.21

Bi0.9Sr0.1FeO3

2.64

0.79–19.41

1.50

0.42–7.94

Bi0.85Sr0.15FeO3

2.66

0.88–21.70

1.51

0.42–5.73

Bi0.8Sr0.2FeO3

2.89

0.87–19.52

1.69

0.47–5.82

Bi0.75Sr0.25FeO3

2.99

0.71–25.55

1.72

0.45–6.29

Bi0.7Sr0.3FeO3

2.49

0.71–19.97

1.71

0.48–6.05

Bi0.65Sr0.35FeO3

2.58

0.88–21.84

1.63

0.45–6.42

The color of the synthesized pigments applied to an organic matrix in mass tone is expressed by their CIELAB color coordinate values depicted in Table 4. The BiFeO3 (1173 K) pigment application is dark brown; its color is given by the smallest amount of red component (a*) and also by the smallest amount of yellow component (b*). Lightness of the color film (L* = 38) is comparable with the lightness of the Bi0.8Sr0.2FeO3−δ sample, which was also prepared by calcination at 1173 K. These two samples are the darkest, and they have the lowest color saturation. An increase in temperature at about 100 K led to the impairment of the BiFeO3 pigment due to melting. In case of the Bi0.8Sr0.2FeO3−δ sample, the increase in temperature positively affected its resultant color. The powder Bi0.8Sr0.2FeO3−δ and its application became lighter and contained a bigger amount of the red component. Also, the amount of yellow component is higher, but the difference is no longer so significant.
Table 4

Colour properties of the pigments applied into organic matrix (calcining temperature 1273 K)

Sample

L*

a*

b*

C

BiFeO3/1173 K

38.00

14.17

16.28

21.58

48.96

Bi0.95Sr0.05FeO3

43.29

17.18

22.09

27.98

52.13

Bi0.9Sr0.1FeO3

44.45

19.14

24.55

31.13

52.06

Bi0.85Sr0.15FeO3

45.57

20.38

26.23

33.22

52.15

Bi0.8Sr0.2FeO3

45.10

20.28

24.89

32.11

50.83

Bi0.8Sr0.2FeO3/1173 K

37.73

14.59

22.79

27.06

57.37

Bi0.75Sr0.25FeO3

43.60

20.21

23.71

31.15

49.56

Bi0.7Sr0.3FeO3

44.64

20.06

24.52

31.68

50.71

Bi0.65Sr0.35FeO3

44.12

19.84

24.00

31.14

50.42

The doping of BiFeO3 by strontium ions results in a rise of the lightness to 43.29. A further increase in the strontium content up to x = 0.15 is connected with a slight growth of lightness to 45.57. The amount of red and yellow components also increased as a result of the growing range of the substitution (x = 0.05–0.15), and, therefore, the orange-brown color of the Bi0.85Sr0.15FeO3−δ sample is distinguished by the highest saturation. A further increase in strontium content in pigment composition decreased all color parameters. Change in the red hue has a slightly decreasing nature, and the L*, b*, and C parameters have also been shifted to lower values, but they have a fluctuating nature. The same trend was observed in the change in hue angle, which describes the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown.

Conclusions

This work contains results regarding the synthesis of inorganic pigments based on BiFeO3 doped by Sr2+ cations. The main role of the alkaline earth element is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The initial composition of pigments is described by the general formula Bi1−x Sr x FeO3−δ , where x = 0–0.35 with step size 0.05. Pigments were synthesized by a solid-state reaction. The results show that an increasing amount of Sr2+ ions built into the BiFeO3 significantly shifts the thermal stability of BiFeO3. The thermal stability of BiFeO3 is 1046 K, whereas the substitution of 20 mol% of Bi3+ by Sr2+ ions shifted it to 1403 K and powder with composition Bi0.65Sr0.35FeO3−δ has thermal stability that is higher than 1434 K. The color parameters of the brown pigments were evaluated in the color space CIE L*a*b* after their application to the organic bonding system. The increase in the calcining temperature caused the creation of pigments with a lighter and more orange-brown color hue. The increasing content of the strontium cation up to 15 mol% is connected with an increase in the color parameters (a*) and (b*) and lightness (L*). The Bi0.85Sr0.15FeO3−δ pigment prepared by calcination at 1273 K/2 h offers the most interesting color properties.

Notes

Acknowledgements

This work has been supported by Grant Agency of Czech Republic, Project No. 16-06697S.

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2017

Authors and Affiliations

  • Žaneta Dohnalová
    • 1
  • Petra Šulcová
    • 1
  • Petr Bělina
    • 1
  • Milan Vlček
    • 2
    • 3
  • Nataliia Gorodylova
    • 1
  1. 1.Department of Inorganic Technology, Faculty of Chemical TechnologyUniversity of PardubicePardubiceCzech Republic
  2. 2.Institute of Macromolecular ChemistryAcademy of Sciences of the Czech RepublicPragueCzech Republic
  3. 3.Joint Laboratory of Solid State Chemistry, Institute of Macromolecular Chemistry, Academy of Sciences of the Czech RepublicUniversity of PardubicePardubiceCzech Republic

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