Structural and magnetic characterization of (1-x) KNN-xBLFO ceramic powders obtained by the combustion reaction method

Journal Pre-proofs Structural and magnetic characterization of (1-x) KNN-xBLFO ceramic powders obtained by the combustion reaction method Elvira-Giraldo Sebastián, C.F.V Raigoza, Gaona J. Sonia PII: DOI: Reference:

S0304-8853(19)32400-X https://doi.org/10.1016/j.jmmm.2019.166197 MAGMA 166197

To appear in:

Journal of Magnetism and Magnetic Materials

Received Date: Revised Date: Accepted Date:

15 July 2019 15 November 2019 22 November 2019

Please cite this article as: E-G. Sebastián, C.F.V Raigoza, G.J. Sonia, Structural and magnetic characterization of (1-x) KNN-xBLFO ceramic powders obtained by the combustion reaction method, Journal of Magnetism and Magnetic Materials (2019), doi: https://doi.org/10.1016/j.jmmm.2019.166197

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Structural and magnetic characterization of (1-x) KNN-xBLFO ceramic powders obtained by the combustion reaction method Elvira-Giraldo Sebastián, Raigoza C. F. V*, Gaona J. Sonia Ceramic Materials Science and Technology Group (CYTEMAC), Universidad del Cauca. Popayán, Colombia *Calle 5 No 4-70, [email protected] Abstract The lead-free ferroelectric system (1-x)K0.5Na0.5NbO3-x(Bi0.8La0.2FeO3), KNN-xBLFO, was synthesized by a solution combustion method. Complete solubility was obtained for all x values used. The modification of the original bonds and the generation of new bonds were characterized by infrared and Raman spectroscopy. The modification of the KNN structure during BLFO addition was determined by X-ray diffraction which showed a monoclinic-orthorhombic phase transition. The lattice parameters and the percentage of each phase present were determined by Rietveld refinement. Scanning electron microscopy showed how the particle morphology changed with the incorporation of BLFO. A ferrimagnetic behavior for different x values was identified by magnetic characterization with the most significant result obtained for x=0.40.

Keywords: Ceramics materials, Solution combustion method, Phase Transition, Microstructure, Ferrimagnetism. 1.

Introduction

Technological demand requires more diverse applications which have been fulfilled to a great extent by the properties of dielectric ceramic materials. It is well known that the properties of the materials depend on their microstructure, which in turn depends on parameters such as synthesis process, temperature and doping agents. Recent studies on ceramic materials with a perovskite structure showed the effect of additives on the dielectric properties and their potential applications [1, 2, 3]. K0.5Na0.5NbO3 (KNN) is a solid solution between NaNbO3 (antiferroelectric) and KNbO3 (ferroelectric) in a 50:50 ratio. This composition has a morphotropic phase boundary (MPB) between two orthorhombic phases with a remarkable functionality increase, which is why the KNN and its derivatives are among the most promising lead-free ferroelectric materials [4]. The synthesis and sintering of this compound are difficult 1

due to the low melting temperature and sublimation presented by the alkaline elements. Meanwhile, bismuth ferrite BiFeO3 (BFO) is a multiferroic material with perovskite structure, rhombohedral symmetry and spatial group R3c. It is difficult to obtain because the bismuth evaporates easily during its preparation, which deteriorates the properties of the final product due to the presence of secondary phases, vacancies, and fluctuations in the valence of the iron ions. Recent reports in the literature suggest that the above defects can be corrected by partial replacement of Bi with alkaline earth elements or rare earths [5]. The replacement of bismuth by lanthanum can modify the structure of BFO from rhombohedral to tetragonal/orthorhombic at room

temperature.

For

example,

the

structure

of

(Bi0.8La0.2)FeO3

(BLFO)

is

tetragonal/orthorhombic; this substitution allows for a total BLFO solubility in the KNN structure. In a similar way, BLFO can limit the volatilization of alkaline ions in KNN, making possible the synthesis of the binary solid solution KNN-BLFO [6]. KNN-BLFO properties can be modulated by varying the BLFO content, resulting in materials with different applications such as multiferroic materials with multiple technological possibilities [Error! Bookmark not defined., 7]. Based on these works, we present the synthesis process and the magnetic response of ceramic powders of (1 - x) K0.5Na0.5NbO3 - xBi0.8La0.2FeO3) (x = 0.05, 0.10, 0.25, 0.40, 0.50), denominated KNN- xBLFO. 2. Materials and Methods The solution combustion synthesis (SCS) is a versatile, simple and fast process, which allows obtaining a variety of nano-sized ceramic materials. This technique involves the self-sustained reaction of a homogeneous solution of oxidants and fuels [8, 9]. KNO3 (Panreac, 99.0%), NaNO3 (Panreac, 99.0%), NH4NbO(C2O4)2(H2O)2 (Companhia Brasileira de Metalurgia e Mineração, CBMM), Bi(NO3)·5H2O (RA- Chemicals, 98%), La(CH3COO)3 (Aldrich, 97%), and Fe(NO3)3·9H2O (Aldrich, 97%) were used as precursors, while urea (Merck, 98%) and glycine (Merck, 99.5%) were used as fuels; the latter used in a 50/50 ratio. Each of the reagents was macerated and dissolved in water with constant agitation to obtain the maximum possible homogeneity; the amounts of precursors and fuel were calculated according to the value of x. After mixing the precursors with the fuels, the solution obtained was heated on a plate at 200°C with constant agitation to evaporate the solvent, followed by combustion in an oven at 600°C. After combustion, the product was kept at 700ºC for 2 hours to obtain the desired phase. Infrared 2

transmittance and Raman scattering spectroscopy, and X-ray diffraction (XRD) analyses were used for structural characterization. Infrared spectra were obtained with a Thermo Scientific Nicolet iS10 FT-IR spectrometer; Raman scattering spectra were obtained with an EZ Raman-N Raman analyzer (Enwave Optronics) coupled to a Leica DM300 microscope, using a wavelength laser excitation source of 532 nm and an integration time of 10 s for each spectrum at 32% power. Signal deconvolution was carried out with Fityk 0.9.8 software, which allowed for qualitative and semi-quantitative analysis of the bands obtained in the spectra [10]. X-ray diffraction was obtained with a PANalytical X'pertPRO diffractometer, with Cu Kα radiation in a 2θ range: 20-60ᵒ, with a step of 0.02ᵒ and a step time of 2 s. The GSAS program was used for Rietveld refinement of the diffractograms and allowed to conclude the structural effect of the BLFO addition in the KNN. The microstructural characteristics were determined with scanning electron microscopy (SEM) using a Philips model XL30-FEG. For the magnetization measurements, a QuantumDesign Versalab (VSM) vibrant sample magnetometer was used. 3. Results and Discussion Figure 1 shows the spectra obtained for the ceramic powders of the KNN-xBLFO for the different concentrations studied.

x=0.50

Transmitance ( a. u.)

x=0.40

x=0.25

x=0.10

x=0.05

x=0.00 4000 3500 3000 2500 2000 1500 1000 -1

Wavenumber (cm )

500

Figure 1. IR spectrum of the ceramic powders of (1-x) KNN-xBLFO

3

It is possible to observe a band located between 3700 cm-1 and 3000 cm-1 attributed to O-H bonds associated with the mode of flexion of the H-O-H group of the adsorbed water. Two bands are evident in all spectra: a wide and stretched band at ~1500 cm-1 and a smaller one located at 1650 cm-1, attributed to the asymmetric and symmetric vibrational mode of the nitrate groups [11], these bands suggest that nitrates were not completely eliminated. Finally, between 400 and 1000 cm-1, the bands are associated with metal-oxygen bonds that inform about the modifications that the structure undergoes [12], so that this was the range analyzed by deconvolution. Figure 2a shows the deconvolution of the KNN spectrum where three bands are clearly observed: the first at ~556 cm-1 corresponds to the vibrational mode of NaNbO3 and/or KNbO3 [13], the second to ~661 cm-1 corresponds to the vibration of the NbO6 octahedra, indicating the existence of the perovskite phase and the third at ~ 800 cm-1 correspond to vibrations of the Nb-O bond [14, 15, 16, 17]. For x=0.05 (Figure 2b), new bands are observed due to the formation of new bonds. The bands at 510 cm-1 and 854 cm-1 correspond to vibrations of the Bi-O bond [18, 19]. In addition, the first two bands of the KNN suffer displacement towards higher wave numbers, from 556 to 568 cm-1 and from 561 to 571 cm-1.

NaNbO3 KNbO3

Nb-O

NaNbO3 KNbO3

(b)

NbO6

(a)

NbO6

Nb-O Bi-O

Bi-O

400

500

600

700

-1 800

Wavenumber (cm )

900

1000

400

500

600

700

(c)

NbO6

-1 800

Wavenumber (cm )

1000

(d)

NbO6 Nb-O

O-Fe-O

Nb-O

O-Fe-O

Bi-O

Bi-O

Bi-O

Bi-O Fe-O

400

900

Fe-O

500

600

700

800

-1

Wavenumber (cm )

900

1000

400

500

600

700

-1

800

Wavenumber (cm )

900

1000

4

(f)

(e)

NbO6 Nb-O

NbO6

O-Fe-O

Nb-O

O-Fe-O

Bi-O

Bi-O

Bi-O

Bi-O

Fe-O

Fe-O

400

500

600

700

-1

Wavenumber (cm )

800

900

1000

400

500

600

700

-1

800

Wavenumber (cm )

900

1000

Figure 2. IR spectra deconvolution of the KNN-xBLFO system for x: (a) 0.00, (b) 0.05, (c) 0.10, (d) 0.25, (e) 0.40, (f) 0.50.

As x increases (Figures 2c-2f), new bands are formed, which are attributed to vibrations of the OFe-O bond of the octahedral FeO6, characteristic of the perovskite structure of BiFeO3 [20]. Because Nb and Fe occupy the same position in the lattice, an increase in Fe percentage increases the O-Fe-O band, while the bands corresponding to the NbO6 and Nb-O bonds decrease. Figure 3a shows the diffractograms corresponding to KNN-xBLFO ceramic powders treated at 700ºC/2h. Figure 3b zooms on the peaks between 44-60°. There are no secondary phases, which confirms the complete solubility between the two systems. According to the analysis made using the GSAS software, Table 1, the crystal symmetry changes when BLFO increases (Figure 3a). Initially (x = 0.0) two phases of the KNN coexist, one monoclinic (P1m126%) and one orthorhombic (Amm2- 74%) [21, 22]. For x = 0.05, the monoclinic phase increases to 31%, the orthorhombic phase Amm2 decreases to 52%, and a new orthorhombic phase appears with a Pbnm spatial group and a percentage of 17%, characteristic of BLFO. For x = 0.10, the monoclinic phase increases to 49% while the Amm2 phase decreases to 35% and the Pbnm remains almost constant (16%). For x = 0.40 the characteristic phases of the KNN decrease, the monoclinic to 15% and the Amm2 to 30%, while the Pbnm phase characteristic of the BLFO increases to 55%. For the highest percentage of BLFO used (x = 0.50) the Pbnm phase increases to 69%, the Amm2 phase decreases to 23% and the monoclinic phase decreases to 8%.

5

(214)O

(122)O

(024)O

(202)O

(111)M

x=1.00 x=0.50

(214)O (121)M

(110)M

(b)

x=0.50 (112)M

(101)M

(202)O

(020)M

(110)O

(024)O

(104)O

(002)M

(010)M

(110)O

(104)O

(012)O

(012)O (001)M

x=1.00

20

25

30

35

40

2 (degree)

45

50

x=0.40

x=0.25

x=0.10

x=0.10

x=0.05

x=0.05

x=0.00

x=0.00

55

(121)M

x=0.25

(112)M

(012)M

(102)M

(020)M

(002)M

(111)M

(110)M

(101)M

(010)M

(001)M

x=0.40

60

45

50

2 (degree)

55

60

Figure 3. (a) X-ray diffractograms of KNN-xBLFO ceramic powders, (b) zoom in the 44º-60º range

The peaks undergo a relocation characteristic of the phase transition: the diffraction planes (002), (012) and (112), located between 44-60° (Figure 3b), are displaced to higher angles (decrease in the lattice parameters) for all the values of x except for x = 0.40. Additionally, the  angle is also modified, resulting in distortion of the crystal lattice. This lattice deformation may be due to the difference between the ionic radii of the KNN (rK+=1.64 Å, rNa+=1.39 Å, both in coordination 12 and rNb5+=0.64 Å, in coordination 6 [23]) and the BLFO (rBi3+ =1.40 Å, rLa3+ =1.36 Å, both in coordination 12 [24] and rFe3+=0.645 Å, in coordination 6 [23]). Although the ionic radii of Na and Bi do not differ much, they present a great difference with the radius of potassium, which can explain the variation in the volume of the cells [25]. Generally, change in the microstructure of a sample affects the intensity and the width of the X-ray diffraction peaks. Improving the Scherrer formalism, Williamson and Hall identified that the grain size and lattice strain are two main sources of X-ray diffraction peak broadening [26]. Therefore, based on the WilliamsonHall approach, full width at half maximum of intensity (as a function of grain size, as well as strain within the lattice), the total peak broadening (βhkl) is given by the equation [27]: 6

hkl  s  D

(1)

where βD and βS are the peak widths due to the crystallite size and lattice strain, respectively. According to Williamson-Hall, D is given by Scherrer`s equation [28] and the expression for S is obtained from Stokes and Wilson [29], and equation (1) then becomes:  k  hkl    D cos 

   4 tan  

(2)

k    4 sin   hkl cos     D  Where  is the Bragg angle,

(3)

 the deformation and D the crystallite size [30]. According to

equation (3), there is a linear relationship between βhkl cos and 4sin from which the crystallite size D is obtained. This is shown in Figure 4 for each of the BLFO concentrations in the solid solution (x values). Furthermore, Table 1 shows the values of D for each of the concentrations. When the BLFO concentration increases, the crystallite size decrease from 68.81 nm (x = 0) to 41.12 nm (x = 0.50). -4

y = 2,6774 x 10 x + 0,0337 2 R = 0.9888 3,40 1,44

y = 4,2153 x 10 x + 0,0136 2 R = 0.9874

1,40

x = 0.40

2

hkl cos  (x10 )

1,42

x = 0.50 -3

1,38 4,80 4,60

-3

y = 4,3600 x 10 x + 0,0398 2 R = 0.9927

4,40 4,20 2,72 2,70

x = 0.10 -4

y = 3,1724 x 10 x + 0,0266 2 R = 0.9876

2,68 2,08 2,06

x = 0.05 -4

y = 3,6889 x 10 x + 0,0202 2 R = 0.9874

2,04

0,5

x=0 1,0

4 sen 

1,5

2,0

Figure 4. Plot of βhklcosθ vs 4sinθ of KNN-BLFO samples

7

Table 1. Lattice parameters and phases obtained from the Rietveld refinement adjustment using the GSAS program. The crystallite size was calculated from Figure 4. (1-x)K0.5Na0.5NbO3-xBi0.8La0.2FeO3 x = 0.05 x = 0.10 x = 0.40 a (Å) 7.9271 8.0208 7.8022 b (Å) 7.8928 7.8528 7.7400 Phase c (Å) 7.8630 7.5955 7.7678 P1m1 90.669 91.359 89.899  Volume P1m1 (Å3) 491 503 469 Phase % P1m1 31 49 15 a (Å) 3.9549 3.9736 4.0165 Phase b (Å) 5.6499 5.6741 5.5497 Amm2 c (Å) 5.58846 5.7165 5.7344 Volume Amm2 (Å3) 124 126 127 Phase % Amm2 52 35 30 a (Å) 5.8432 5.5923 5.6091 Phase b (Å) 5.5593 5.6710 5.5942 Pbnm c (Å) 7.7761 7.7865 7.9030 Volume Pbnm (Å3) 252 246 247 Phase % Pbnm 16 15 55 Crystallite size (nm) 68,81 52,05 34,82 102,33 0.82 2.30 2.90 2.80 2 * The calculated lattice parameters are similar to those reported by Tellier et al. [31]. Refined parameter*

x = 0.00 7.8832 7.9036 8.0077 90,214 498 26 3.9774 5.6464 5.6714 120 74

x = 0.50 8.0267 7.8667 7.9258 90.6317 500 8 3.7142 5.3684 5.5751 111 23 5.4869 5.5102 7.7549 234 69 41,12 1.22

x =1.00

5.5826 5.6311 7.9039 248.473 100 2.10

The effect of the size of the dopant ion in the crystal structure is measured using the tolerance factor t, proposed by Goldschmidt, which quantifies the degree of distortion of the perovskites in terms of ionic packing [32]. 𝑡=

(1 ― 𝑥)((0,5 ∗ 𝑟𝐾 + ) + (0,5 ∗ 𝑟𝑁𝑎 + )) + 𝑥 ((0.8 ∗ 𝑟𝐵𝑖5 + ) + (0.2 ∗ 𝑟𝐿𝑎3 + )) + 𝑟𝑂2 + ((1 ― 𝑥) ∗ 𝑟𝑁𝑏 + ) + (𝑥 ∗ 𝑟𝐹𝑒3 + )

(4)

If the tolerance factor is less than one, there is compression forces acting on the Nb-O bonds, consequently the K+-O, Na+-O bonds will be under tension. The cooperative rotation of the oxygen octahedra takes place to reduce the stress of the lattice [33], generating a monoclinicorthorhombic phase transition, with reduction in the lattice parameters, and therefore, in the volume of the unit cell. Figure 5 shows the behavior of the tolerance factor after inclusion of BLFO in the KNN lattice.

8

1,015

Tolerance Factor

1,010

1,005

1,000

0,995

0,990 0,0

0,1

0,2

x

0,3

0,4

0,5

Figure 5. Decrease in the tolerance factor with the increase in BLFO.

With Raman spectroscopy it is possible to determine the phase transition of the systems. Figure 6(a) shows the Raman spectra of the KNN-xBLFO. For pure KNN, two strong bands are observed at 625 cm−1 (1) and 265 cm−1 (5) which are respectively associated with stretching and bending modes of the O-Nb-O bond. The modes between 200-900 cm-1 are associated with vibration modes of the BO6 octahedra of the perovskite. The modes 1A1g (υ1), 1Eg (υ2), and 2F1u (υ4) correspond to stretching [34]. When adding BLFO, the mentioned bands are modified. The A1g (υ1) mode is of special interest in systems with a perovskite structure, because it corresponds to a symmetric vibration mode of the BO6 octahedra and usually appears as an intense mode at 620 cm−1, so the evolution of this band as the increases percentage of BLFO was analyzed (figure 6b). The change in bond length between Nb5+ and the oxygens to which it coordinates in the octahedra [BO6] causes a decrease in the force constant, causing the cation located in site B to move away from the center. The replacement of K+ and Na+ by Bi3+ and La3+ in position A and of Nb5+ by Fe3+ in position B, causes a local structural disorder and a great reticular distortion, to maintain the local charge balance. To observe the displacement and deformation of the bands associated with the vibration mode 1 and 2 described, Figure 7 shows the deconvolutions between 450 and 750 cm-1 of the Raman spectra of Figure 6. The displacement of the vibrational modes is evident, which may be due to the deformation of the perovskite structure when generating vacancies caused by the incorporation of the BLFO. The widening of the bands is a consequence of the characteristic vibrational modes of the BLFO and can also be due to the local disorder of the structure due to the coexistence of the two phases.

9

 

2  1

(a)

1

2



(b)

x = 0.50

x = 0.50

x = 0.40

x = 0.40

x = 0.25

x = 0.25

x = 0.10

x = 0.10

x = 0.05

x = 0.05

x = 0.00

x = 0.00

200 300 400 500 600 700 800 900 1000 -1 Wavenumber (cm )

400

500

600 -1 Wavenumber (cm )

700

Figure 6. (a) Raman spectra of the system (1-x) KNN-xBLFO, (b) zoom of the Raman spectrum in the range between 400 and 760 cm (a)

x = 0.00

-1

x = 0.05

(b)

(c)

x = 0.10

1

2

450

500

550

600

650 -1

Wavenumber (cm )

(d)

450

700

750 450

x = 0.25

500

550 600 -1 650 Wavenumber (cm )

700

500

550

600

650

-1

Wavenumber (cm )

(e)

750 450

700

750450

x = 0.40

500

550 600 -1 650 Wavenumber (cm )

700

500

550 600 -1 650 Wavenumber (cm )

(f)

750450

700

750

x = 0.50

500

550

600

-1 650

Wavenumber (cm )

700

750

Figure 7. Deconvolution of the Raman spectrum of Figure 8 (b) in the 450-750 cm-1 range.

10

Figure 8 shows the SEM micrographs of the powders obtained. According to these micrographs, each composition results in a particular morphology and particle size. For example, for x = 0 we can see particles of uniform morphology (cubic) and size between 200 nm and 1.20 m. For x = 0.05 the morphology is the same but the particle size is clearly reduced (100 nm) and there are some aggregates. For x = 0.10 aggregates are predominant, formed by cubic particles. For BLFO with x = 0.25 there are no defined particles, and only aggregates are observed. When BLFO increases to x = 0.40, the aggregate`s size decreases. Finally, for x = 0.50 particles with defined morphology (needles) reappeared with approximately 2 m in length and 20 nm wide and few aggregates. Aggregates can result from magnetic interactions between the particles 7. Since there is no presence of secondary phases, the change in morphology can be attributed to the phase transition experienced by the system, which implies a change in symmetry and a modification of the crystalline planes.

A cubic

morphology was reported for KNN [35]. Some author`s reported a needle morphology for BFO nanoparticles [36]. This morphology results from a vertical aggregation, propelled by a local stress and the decrease of the superficial free energy [37].

(a)

(b)

(c)

(d)

(e)

(f)

Figure 8. Scanning electron microscopy of the system (1-x) KNN-xBLFO for: (a) x = 0.00; (b) x =0.05; (c) x =0.10, (d) x =0.25, (e) x =0.40, (f) x =0.50.

11

The KNN system is diamagnetic, so it does not present spin ordering; in turn, the BiFeO3 system presents G-type antiferromagnetic order [38]. With the inclusion of the BLFO in the KNN, structures that must interact magnetically are combined (monoclinic-orthorhombic for the KNN, orthorhombic for the BLFO). Figure 9 shows the curves of magnetization vs. magnetic field (MH) for three temperatures (50 K, 200 K, 300 K). There is a small ferrimagnetic response at 50 K for the different percentages of BLFO, noting a greater response at 40%, a result that is consistent with the analysis of previous studies carried out for the system [17]. Table 2 shows the results of coercive field (Hc) and remanent magnetization (Mr), together with the respective structure which determines the magnetic response. Because there are no results for saturation magnetization, magnetization values are reported to the maximum field (MHmax). As observed at each temperature, both the remanent magnetization and the maximum field magnetization increase with the percentage of BLFO, with the highest value for x=0.40. The results can be explained based on the structural analysis already done: at higher percentages of BLFO the orthorhombic structure is more significant and will be strongly influenced by the monoclinic structure of the KNN, creating distortion in the chain of spins, resulting in hysteresis cycles increasingly prominent. However, for x > 0.40 the effect of the KNN on the BLFO is less significant, resulting in the predominant antiferromagnetic behavior of BLFO, which is observed in Figure 9(d). The hysteresis cycles result from distortion (inclination) of the antiferromagnetic order of the Fe/O/Fe spin chains in the BFO. The low values of the remanent magnetization and the absence of saturation can be attributed to the antiferromagnetism in the sample. 0,6

(a)

300K 200K 50K

Magnetization (emu/g)

Magnetization (emu/g)

0,4 0,2 0,0 -0,2

0,4 0,2 0,0 -0,2

-0,4

-0,4

-0,6

-0,6

-0,8

(b)

50K 200K 300K

0,6

-0,8

-30

-20

-10 0 10 Magnetic Field (kOe)

20

30

-30

-20

-10 0 10 Magnetic field (kOe)

20

30

12

(c)

50 K 200K 300K

0,6

(d)

50 K 200K 300K

0,4 Magnetization (emu/g)

0,4

Magnetization (emu/g)

0,6

0,2 0,0 -0,2 -0,4

0,2 0,0 -0,2 -0,4 -0,6

-0,6

-0,8

-0,8 -30

-20

-10 0 10 Magnetic Field (kOe)

20

30

-30

-20

-10 0 10 Magnetic Field (kOe)

20

30

Figure 9. Magnetization curves vs. applied magnetic field for the system (1-x) KNN-xBLFO, with x: (a) 0.05, (b) 0.10, (c) 0.40, (d) 0.50

Table 2 Parameters obtained from magnetization curves vs. applied field KNN-xBLFO 0.05

0.10

0.40

0.50

T (K)

Structure

MHmax (emu/g)

HC (kOe)

50 200 300 50 200 300 50 200 300 50

Monoclinic (31%) / orthorhombic (52%) – orthorhombic (16%)

0.6095 0.3134 0.1980 0.5633 0.2769 0.1700 0.5616 0.3015 0.2440 0.7760

Diamagnetic weak antiferromagnetic

200 300

Monoclinic (49%) /orthorhombic (35%) – orthorhombic (19%) Monoclinic (15%) /orthorhombic (30%) – orthorhombic (55%) Monoclinic (8%) /orthorhombic (23%) – orthorhombic (69%)

0.4378 0.3033

0.0020 0.2695 0.2027 0.1724

Mr (emu/g)

0.0002 0.0169 0.0120 0.0086

Type G antiferromagnetic

4. Conclusions KNN-xBLFO single-phase powders were obtained at 700ºC/2h with the solution combustion method, for all stoichiometries studied. The crystal phase and lattice parameters were stablished by X ray diffraction and Rietveld refinement and agree with those reported in the literature. These methods allowed to confirm complete solubility between KNN and BLFO, and the coexistence of the monoclinic phase of KNN with the orthorhombic phase from BLFO, overcoming the problems reported with obtaining KNN and BLFO. Furthermore, the magnetic response (ferrimagnetic) of the obtained KNN-xBLFO is different from the KNN response (ferroelectric) and the BLFO response (antiferromagnetic). 13

Acknowledgements The author acknowledges the financial support from Universidad del Cauca and to the Companhia Brasileira de Metalurgia e Mineração (CBMM) for the donation of the niobium ammonium oxalate used in this research.

References Credit autor statement

 Sebastián Elvira: Investigation, Methodology  Sonia Gaona Jurado: Investigation, Conceptualization, Formal analysis, Writing – original draft preparation, Writing – review & editing  Claudia Fernanda Villaquirán R.: Investigation, Conceptualization, Methodology, Formal analysis, Project administration, Writing – original draft preparation, Writing – review & editing.



Inclusion of BLFO in the KNN structure generates new bonds, which results in the appearance of new bands in the IR spectra and as modification of the Raman bands.



KNN presents a structural phase transition due to incorporation of BLFO.



KNN`s typical cubic morphology is modified by BLFO; at higher concentrations the needle morphology predominates.



The highest ferromagnetic response is obtained at x = 0.40



There is a small ferromagnetic response for the different percentages of BLFO, with a greater response at 40%.

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