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Effect of Li insertion in the crystal structure and magnetism of barbosalite prepared using solvothermal method
Materials Chemistry and Physics 240 (2020) 122133
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Effect of Li insertion in the crystal structure and magnetism of barbosalite prepared using solvothermal method N. Joseph Singh a, L. Herojit Singh a, **, S.S. Pati b, J.A.H. Coaquira c, A.C. Oliveira c, Junhu Wang d, V.K. Garg c, * a
Department of Physics, National Institute of Technology Manipur, Langol, 795004, India Department of Chemistry, National Institute of Technology Jamshedpur, Jharkhand, 831014, India Institute of physics, University of Brasília, 70919-970, Brasília, DF, Brazil d M€ ossbauer Effect Data Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, 116023, China b c
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� Barbosalite was synthesized by solvothermal. � Li occupies the interstitial near to Fe(III) site of barbosalite. � The Increase in the Li transformed to LiFePO4. � Magnetic studies shows faster response compared to Structure.
A R T I C L E I N F O
A B S T R A C T
Keywords: Structural transformation Iron hydroxyl phosphate M€ ossbauer spectroscopy Magnetic transformation SQUID And XRD
The effect of Lithium insertion in the crystal structure and magnetic properties of Barbosalite [Fe3(PO4)2(OH)2], a polymorph of iron hydroxyl phosphate synthesized from variable Fe precursor (Fe(II) and Fe(III)), have been investigated. Effect of distortion in the crystal structure of Barbosalite appeared with minimum lithium hy droxide (LiOH.H2O) concentration of 0.5 M as depicted from the XRD patterns. Further, appearance of fresh ossbauer spectroscopy and peaks from 2 M is well matched with the crystal structure of LiFePO4. Studies with M€ SQUID Magnetometer intriguingly reveals that Li intercalation in the barbosalite affects only Fe(III) sites whereas the Fe(II) sites remains unaffected till 2 M. However, further increase in the Li concentration leads to structural transformation and results in LiFePO4 phase. Comparative studies of the structural and magnetic properties, magnetic transition are also discussed.
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (L. Herojit Singh), [email protected] (V.K. Garg). https://doi.org/10.1016/j.matchemphys.2019.122133 Received 27 November 2018; Received in revised form 20 August 2019; Accepted 5 September 2019 Available online 6 September 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
N. Joseph Singh et al.
Materials Chemistry and Physics 240 (2020) 122133
1. Introduction
source and Ni-filtered with CBO monochromator operating at 45 kV and €ssbauer spectra, both at 298 K and at 80 K, were recorded 15 mA. The Mo with a constant acceleration velocity transducer coupled to 57Co in Rh matrix source with an initial activity of 25 mCi in the standard trans mission geometry. The velocity calibration per channel was done with a (1.9 mg 57Fe/cm2) iron foil. The magnetization measurements were performed using a vibrating sample magnetometer module of a physical property measurement system (PPMS, Quantum Design).
Iron hydroxyl phosphates are well known minerals and important catalysts for several chemical processes and also have important roles in passivation of metal surfaces, corrosion inhibition and reactions of iron compounds contained in various soils with phosphate fertilizers [1–4]. Among these, barbosalite and lipscombite have been identified as effi cient catalysts for the selective dehydrogenation of isobutyric acid to methacrylic acid, which can be esterified to produce methyl methacrylate, a very important intermediate in a large number of chemical processes. Iron hydroxyl phosphate has also shown to have high efficiency as an electrode for Li battery [5–7]. The natural minerals of iron hydroxyl phosphates include barbosalite (Fe3(PO4)2(OH)2), rockbridgeite (Fe5(PO4)3(OH)5), beraunite (Fe6(PO4)4(OH)5.6H2O), and whitmoreite (Fe3(PO4)2(OH)2.4H2O). Barbosalite named by Marie Louise Lindberg (Smith) and William T. Pecora in 1955 in honor of Brazilian geologist Aluízio Licínio de Miranda Barbosa from Minas Gerais, Brazil - is a basic hydroxyphosphate, with greenish blue to almost black in color and occurs as a hydrothermal product of triphylite Li(Fe(II), Mn(II))PO4 [8]. A crystallo-chemical characterization of barbosalite presents a challenging act because of its fibrous and microcrystalline character. The presence of other transition metal ions alongside iron makes the situation even more complicated to characterize the chemical properties of the crystal [16]. Apart from geoscience, an understanding of crystal chemistry and physics of the basic iron phosphates is vital for materials science too as has been found in recent years that iron hydroxyl phosphate minerals with mixed valence states of iron can be used as catalysts in methyl methacrylate synthesis [3] and as positive-electrode materials in rechargeable batteries [9]. The flexibility in the structure of FePO4 and Fe based phosphorous hydroxide enables the insertion of Li which is known for its capacity and conductivity (thermal/ionic) as a suitable cathode material [10]. Structural investigation of LiFePO4 to FePO4 on removal and insertion of Li using XRD and Mӧssbauer revealed that the removal of Li results in the transformation of Fe(II) to Fe(III) [11]. Several methods have been adopted to synthesize LiFePO4 including electrospinning, solid state reaction, ball milling, sol-gel, co-precipitation, solvothermal etc. and notably, each of the synthesis methods includes Fe(II) as the iron pre cursor [12–15]. The synthesis of LiFePO4 from Fe(III) salt precursor in the conventional method is very rarely found in the literature. In the present studies, an attempt has been made to understand the physical and chemical insights of iron hydroxyl phosphate synthesized using a modified solvothermal method and also to understand the transformation of hydroxyl phosphate to triphylite structure of LiFePO4. The intermediates formed during the transformation of the iron hy droxyl phosphate to LiFePO4 as an effect of Li concentration are dis cussed by mapping the properties of the local structure of Fe atoms using €ssbauer spectroscopy. Mo
3. Results and discussion Fig. 1 shows the XRD patterns of samples Fe(II)-0 and Fe(II)-2.5. The non-lithiated sample (Fe(II)-0) consists of FePO4 as a major constituent whereas the lithiated sample (Fe(II)-2.5) matched with the diffraction pattern of LiFePO4. On changing the oxidation state of precursor from Fe (II) to Fe (III), a large deviation in the diffraction pattern was observed. The sample Fe (III)-0 shows the nucleation of barbosalite (Fig. 2a). The lattice param eters of the Fe(III)-0 was found to be a ¼ 7.3211 Å, b ¼ 7.4373 Å, c ¼ 7.4139 Å, which is close to the parameters reported by Redhammer et al. [16]. From Fig. 2, shift in the peak position was observed as LiOH. H2O is introduced during the synthesis. To understand the effect of Li on the transformation of Fe(II) Fe2(III) (PO4)2(OH)2 to LiFePO4 and precise control over the sample properties, a series of intermediate Li content samples were also synthesized. The lowest LiOH.H2O concentration (0.5 mol/L) seems to have shifted the XRD peaks to the higher angle which is attributed to the Li insertion in the lattice of barbosalite, causing strain in the lattice structure. The shifts in the peak positions were significantly large at the initial concentration of Li which almost saturated for the higher concentrations. Introduction of 2 M of LiOH. H2O shows a trace signal of LiFePO4 possibly because of the initiation of the LiFePO4 phase (Fig. 2e) and with the higher concentration of LiOH. H2O (i.e. 3.0 M), Fe(II)Fe2(III)(PO4)2(OH)2 transformed to LiFePO4 (Fig. 2g). The lattice parameters determined using MAUD software is shown in Fig. 3. Incorporation of Li increases the lattice parameter. Abrupt changes in the lattice parameter ‘a’ and ‘b’ were observed from LiOH.H2O concentration of 2.0 M. Increase in the LiOH.H2O concen tration above 2.0 M initiates the formation of the LiFePO4 phase.
2. Experimental details FeCl3.6H2O, FeSO4.7H2O, H3PO4, LiOH.H2O, and ethylene glycol were procured from Sigma-Aldrich and used with no further purifica tion. The Fe based phosphates were synthesized through solvothermal method. The synthesis performed with two different Fe precursors. In the synthesis the 15 mL of Fe precursor (0.5 M of FeSO4.7H2O/ FeCl3.6H2O) was mixed with 15 mL of H3PO4 (0.98 M) thoroughly then transferred in to Teflon lined steel autoclave and subjected to a tem perature of 448 K for 15 h. The lithiation was performed by introducing 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 M LiOH.H2O in the synthesis. The samples are marked as Fe(II)-x and Fe(III)-x, where (II) and (III) represent the oxidation state of precursor Fe and x is the molar concentration of LiOH. H2O. Basic identification of the oxide phases of iron was done using RIGAKU Ultima IV X-Ray diffractometer, with a Cu-Kα as the radiation
Fig. 1. XRD of (a) Fe(II)-2.5 (LiFePO4) and (b) Fe(II)-0 (FePO4 as a major component). 2
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Materials Chemistry and Physics 240 (2020) 122133
Fig. 2. XRD for (a) Fe(III)-0 (Fe3(PO4)2(OH2)), (b) Fe(III)-0.5, (c) Fe(III)-1, (d) Fe(III)-1.5, (e) Fe(III)-2, (f) Fe(III)-2.5 (Fe3(PO4)2(OH2) þ LiFePO4) and (g) Fe (III)-3 (LiFePO4).
Fig. 4. Room temperature (298 K) M€ ossbauer spectra of (a) Fe(II)-0 (b) Fe(III)0 (d) Fe(III)-0.5 (d) Fe(III)-1.0 (e) Fe(III)-1.5 (f) Fe(III)-2.0 (g) Fe(III)-2.5 (h) and Fe(III)-3.0.
(IS) of 1.24 mm/s and quadrupole splitting (QS) of 2.71 mm/s is attributed to the FePO4 phase which consists of 61%. Second sub-spectrum having IS and QS of 0.70 mm/s and 2.77 mm/s respec tively (with spectral area 7%) may be because of the intermediate compound having Fe oxidation slightly higher than Fe(II). The third sub-spectrum corresponds to oxidation state of Fe(III). When the syn €ssbauer thesis was carried out using the FeCl3.6H2O precursor, the Mo analysis shows the sample consists of Fe3(PO4)2(OH)2 as shown in Fig. 4b. Deconvolution of the spectra results in 32% of Fe(II) and Fe(III) of 68% which satisfies the Fe(II)/Fe(III) ratio in accordance with the Fe3(PO4)2(OH)2 unit cell. Synthesis carried out in the presence of €ssbauer spectra. As the 0–1.0 M LiOH.H2O solution gives similar Mo LiOH.H2O concentration increases beyond 1.0 mol/L, few €ssbauer Fe3(PO4)2(OH)2 lattices transform to triphylite, LiFePO4. Mo spectrum of Fe(III)- 2.0 could be fitted into three sub spectra. Two of the sub spectra are assigned to the Fe(II) and Fe(III) of Barbosalite where as the third one with IS of 1.2 mm/s and QS of 2.95 mm/s is associated with Fe(II) of LiFePO4. Further increase in the LiOH.H2O concentration re sults in higher percentage of LiFePO4 (Fig. 4f). Fig. 4h shows the €ssbauer transformation of Fe3(PO4)2(OH)2 to LiFePO4 (Fe(III)-3). Mo spectrum is deconvoluted into two spectra. The first spectrum with IS of 1.22 mm/s, QS of 2.95 mm/s with an area of 82% is attributed to divalent Fe atoms of LiFePO4. The second spectrum having IS of 0.46 mm/s, QS of 0.77 mm/s and area of 18% is from the trivalent Fe atoms assigned ferric pyrophosphate (Fe4P6O21) by Bazzi et al. [19](See. Table 1). €ssbauer parameters are depicted in Figs. 5 and Least square fitted Mo 6. The IS corresponding to the Fe(III) and Fe(II) of the barbosalite phase and the transformed Fe compounds are found to be almost constant (Fig. 5b). This clearly indicates that the phase formed has distinct oxidation state without electron hopping during the course of structural
Fig. 3. Lattice parameter of the Barbosalite with respect to the concentration of the LiOH.H2O incorporated during the synthesis.
Samples prepared with LiOH.H2O concentration of 2.0 M (i.e. Fe (III)-2.0) found to have barbosalite of ~94% and ~6% of LiFePO4. Intriguingly, the sample Fe(III)-2.5 shows a sudden change in phase concentration to ~ 8% barbosalite and ~92% LiFePO4. Significant changes in lattice parameters ‘a’ and ‘c’ were also observed for higher concentrations of lithium hydroxide along with phase transformation. A similar shift in the peak position of iron hydroxyl phosphate was also observed in iron (III) hydroxyl phosphate reported by Y. Song et al. [6]. It is reported that the lattice shifts from a ¼ 5.1918 Å, c ¼ 12.9927 Å to a ¼ 5.2493 Å, c ¼ 12.7189 Å as the Fe (III) hydroxyl phosphate is exposed to LiOH.H2O at 90 � C for 5 days in an autoclave. The protons of the hydroxyl groups in these compounds were observed to be replaced by lithium ions with structure retention. For further understanding of the changes obtained, magnetic studies were carried out using €ssbauer and SQUID. Mo It is reported that electrochemical incorporation of lithium into the cathode materials results in disordered compounds which are good candidates for the secondary lithium batteries [17,18]. Fig. 4 shows the €ssbauer spectra of the samples as pre room temperature (298 K) Mo €ssbauer spectrum of Fe(II)-0 have been resolved into three pared. The Mo sub-spectra as shown in Fig. 4a. The first sub-spectrum with isomer shift 3
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Materials Chemistry and Physics 240 (2020) 122133
Table 1 Least square fitted M€ ossbauer parameters at 298 K of the samples synthesized with Fe(II) and Fe(III) precursor. Γ: line width, IS: Isomer shift and QS: quad rupole splitting. Sample (at 298 K)
Γ (mm/s)
IS (Fe) (mm/s)
QS (mm/s)
Area (%)
Fe(II)-0
0.46(0) 0.40(0) 0.41(0) 0.32(1) 0.27(2) 0.36(0) 0.30(0) 0.35(0) 0.30(0) 0.44(0) 0.31(1) 0.45(0) 0.28(1) 0.45(3) 0.36(5) 0.41(4) 0.34(0) 0.45(0) 0.34(0)
1.24(0) 0.70(0) 0.46(0) 0.42(0) 1.10(1) 0.42(0) 1.09(0) 0.43(0) 1.09(0) 0.42(0) 1.09(0) 0.42(0) 1.08(0) 1.20(0) 0.44(1) 0.45(1) 1.22(0) 0.46(1) 1.22(0)
2.71(0) 2.77(1) 0.43(0) 0.39(1) 3.56(2) 0.43(0) 3.56(0) 0.41(0) 3.56(0) 0.47(0) 3.59(0) 0.49(0) 3.52(0) 2.95(1) 0.56(1) 0.89(3) 2.96(0) 0.77(1) 2.95(0)
61 7 32 68 32 69 31 67 33 79 21 72 15 13 6 12 82 18 82
Fe(III)-0 Fe(III)-0.5 Fe(III)-1.0 Fe(III)-1.5 Fe(III)- 2.0 Fe(III)-2.5 Fe(III)-3.0
Fig. 6. Quadrupole splitting of the Fe(II) (hollow rectangles) and Fe(III) (hol low circles) in barbosalite. Solid triangles are for LiFePO4, and solid circles represent the ferric pyrophosphate (Fe4P6O21).
However, the formation of LiFePO4 initiates at 2.0 M of LiOH.H2O. As the Li content increases beyond this concentration (stage 3), an abrupt change is observed in the area of LiFePO4. Fig. 3 depicts the strain developed resulting from Li insertion in the crystal lattice of barbosalite. The strain destabilizes the structure of barbosalite above 1.5 M and in order to compensate the excess energy, the barbosalite transformed to the LiFePO4 structure. In stage 4, Fe(III)-2.5 consist of 82% of stoi chiometric LiFePO4. Fe(III) experiencing IS of 0.45 mm/s and QS of 0.89 consisting of 12% is assigned to ferric pyrophosphate (Fe4P6O21) [19] which was not visible in XRD. The absence of the ferric pyrophosphate peaks in XRD may be plausibly because of the amorphous nature of the compound [20]. At 3.0 M of LiOH.H2O, LiFePO4 consists of 82% and 18% of Fe(III). The QS for Fe(III) and Fe(II) of Fe3(PO4)2(OH)2 are shown in Fig. 6. It shows that the QS of Fe(II) remains constant but that of Fe (III) increase monotonically. This may be understood as resulting from the distortion of Fe(III) site, which is possible when Li gets inserted at the interstitial sites adjacent to Fe(III) sites. Fig. 7 shows the M H loop at 300 K and 5 K. The graph shows a linear and unsaturated curve with negligible coercitivity, which shows the paramagnetic and antiferromagnetic nature. The slope of the M H loop decreases as Li is introduced in the lattices. This indicates the magnetic moment of Fe3(PO4)2(OH)2 reduces as the Li got intercalated. For further understanding of the magnetic properties and the effect of Li on Fe3(PO4)2(OH)2, low temperature measurement was carried out. €ssbauer spectra at 80 K in Fig. 8 show the changes in the hyperfine Mo splitting of the Fe because of to the interaction with Li. The width of the spectrum increases and the hyperfine field decreases as the Li interca lation in the lattice of barbosalite increases. The effect of Li insertion is first observed in the Fe(III) cites experiencing Bhf of 50.8 T indicated as f1 in Table 2. In the sample Fe(III)-1.0, the Fe(III) contributing to 50.8 T decomposes into two having 50.9 and 47.9 T (f2) (Fig. 9). Increase in the Li content further introduces a component with lower Bhf (<44 T i.e. f3). The area under the spectra of Fe(III) experiencing Bhf 50.8 T de creases gradually till 1.0 M of LiOH.H2O (Fig. 10). This area was observed to decrease abruptly when the LiOH.H2O > 1.0 M. The
Fig. 5. Isomer shift (a) and area (b) of the of the Fe(III) and Fe(II) components of the barbosalite (B–Fe(II) and B–Fe(III)) and LiFePO4 (Li–Fe(II)) and Fe(III) represents the ferric pyrophosphate (Fe4P6O21).
transition. The area of the respective phase as plotted in Fig. 4a can be categorized into four stages. The first stage i.e. from Fe(III)-0 to Fe(III)1.0 shows the area ratio of Fe(II) to Fe(III) maintained at 1:2 indicating there is no structural transformation of barbosalite. As the Li content increases in stage 2, the Fe(III) area increases concomitant to the decrease in Fe(II). At 1.5 M of LiOH.H2O, the Fe(III) increases to 79% from 67%. The increase in the 13% because of the oxidation of Fe(II) to Fe(III). In the course of oxidation, the Fe1-x (II) Fe3þx(III) (PO4)2(OH)2 preserved the barbosalite structure which is well supported by XRD data. 4
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Materials Chemistry and Physics 240 (2020) 122133
Table 2 Least square fitted M€ ossbauer parameters of the samples at 80 K synthesized with Fe(II) and Fe(III) precursor. Γ: line width, IS: Isomer shift and QS: quad rupole splitting. SampleS (at 80 K)
Γ (mm/ s)
IS (Fe) (mm/ s)
QS (mm/ s)
Bhf (T)
Area (%)
Representation of the sub spectra
Fe(III)-0
0.29 (0) 0.41 (4) 0.49 (1) 0.30 (1) 0.50 (9) 0.43 (2) 0.47 (1) 0.31 (0) 0.83 (0) 0.36 (9) 0.34 (2) 0.55 (2) 0.33 (1) 0.62 (9) 2.06 (0) 0.72 (4) 0.85 (3) 0.44 (4) 0.76 (9) 1.34 (9) 0.81 (9) 0.28 (2) 0.78 (5) 0.48 (2) 0.29 (0) 0.43 (1) 0.34 (0)
0.53 (0) 0.45 (2) 1.15 (1) 0.53 (0) 0.59 (3) 0.44 (1) 1.22 (0) 0.54 (0) 0.45 (0) 0.42 (0) 0.37 (2) 1.24 (1) 0.55 (0) 0.50 (1) 0.40 (0) 0.35 (1) 1.19 (1) 0.53 (0) 0.55 (1) 0.47 (2) 0.68 (2) 1.33 (0) 1.29 (2) 0.53 (0) 1.34 (0) 0.53 (0) 1.34 (0)
0.26 (0) 0.44 (2) 1.65 (1) 0.26 (0) 0.36 (6) 0.39 (1) 1.48 (1) 0.26 (0) 1.11 (9) 0.76 (9) 0.30 (0) 1.48 (1) 0.25 (0) 0.39 (3) 1.16 (7) 0.30 (0) 1.52 (1) 0.24 (0) 0.29 (2) 0.06 (4) 0.64 (0) 3.07 (1) 1.54 (3) 0.74 (1) 3.06 (0) 0.83 (1) 3.07 (0)
50.8 (0) –
57
f1
13
f2
32.8 (3) 50.9 (1) 47.9 (2) –
30
f3
54
f1
7
f4
10
f2
32.7 (0) 50.7 (0) 45.3 (5) 44.1 (4) –
29
f3
54
f1
6
f4
3
f5
8
f2
32.5 (4) 50.8 (0) 47.9 (2) 32.9 (2) –
29
f3
23
f1
10
f4
26
f5
7
f2
32.8 (1) 49.7 (1) 46.0 (2) 38.3 (2) –
34
f3
18
f1
20
f4
30
f5
8
f6
–
5
f7
32.3 (1) –
19
f3
32
f6
–
68
f7
–
19
f6
–
81
f7
Fe(III)-0.5
Fe(III)-1.0
Fig. 7. M
H loop of the Fe(III)-0, Fe(III)-0.5, and Fe(III)- 2.0 at 300 K and 5 K.
Fe(III)-1.5
Fe(III)-2.0
Fe(III)-2.5
Fe(III)-3.0
the hyperfine field of the Fe(III) gets affected by the introduction of Li(I). The splitting of the ~50 T sextets to 50, 47 and >44 T is understood as resulting from the coupling of the magnetic moment of Fe(III) and diamagnetic Li(I). The coupling of the diamagnetic cations reduces the net magnetic moment resulting in low Bhf. ZFC (Fig. 11) of pure and 0.5 M LiOH.H2O doped Fe3(PO4)2(OH)2 shows a sharp transition around 176 K which is attributed to the tran sition from paramagnetic to antiferromagnetic. For the sample with 2.0 M of LiOH.H2O, a broad transition around 50 K was found which was present in the earlier sample too with a low intensity. This transition resembles the magnetic transition in LiFePO4 and FePO4. Referring to the XRD of the sample synthesized with 2.0 M of LiOH, although most of the peaks were matched with barbosalite, a signature of peak
Fig. 8. M€ ossbauer spectra at 80 K of (a) Fe(III)-0 (b) Fe(III)-0.5 (c) Fe(III)-1.0 (d) Fe(III)-1.5 (e) Fe(III)- 2.0 (f) Fe(III)-2.5 (f) and(g) Fe(III)-3.0.
decrease in the area is concomitant with the increase in the area of the Fe (III) experiencing Bhf of ~47.9 T and <44 T. Further observation on the sextet of Fe(II) experiencing Bhf ~ 32 T was found to have no changes with respect to Bhf, QS and IS. This indicates the interaction of the Li occurs with Fe(III). The transformation of the sextet to triphylite doublet €ssbauer spectra obtained at initiates from 2 M of LiOH.H2O. From the Mo 278 K, it was observed to have a gradual increase in the QS of Fe(III). This indicates the Fe(III) sites getting distorted by Liþ incorporated. This is further supported by the low temperature (80 K) measurements where 5
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Materials Chemistry and Physics 240 (2020) 122133
Fig. 11. FC and ZFC of Fe(III)-0, Fe(III)-0.3 and Fe(III)-1.2.
corresponding the LiFePO4 phase was also observed. This indicates that the magnetic transitions occur even before the structural transition.
Fig. 9. Hyperfine field of the Fe(III) component experiencing ~50.8 T (f1) and the Li coupled Fe(III) resulting to lower hyperfine field with ~47 T (f4) and <45.3 T (f5).
4. Conclusions Pure as well as Li doped barbosalite were synthesized using sol vothermal method. Li insertion in the lattice of barbosalite distorts the Fe(III) sites. Further introduction of Li destabilizes the barbosalite structure and transform it into triphylite (LiFePO4). Low (80 K) tem perature measurements support the residence of Li in the Fe(III) cites as the magnetic hyperfine field of the Fe(III) is altered which decomposes into three components, one around 50 T and the others at 47.9 T and <44 T. SQUID measurements predict the paramagnetic to antiferro magnetic transitions at 176 K. The intensity of the magnetic transition was drastically reduced in the sample synthesized with 2.0 M of LiOH. H2O. The magnetic transition resulting from the Li incorporation is observed to be a step ahead than the structural transition. Acknowledgement The author LHS thank DST and Science and Engineering Research Board (SERB) with project file no. EMR/2016/001524 for the financial support. The author thanks DST-INSPIRE for providing scholarship. The ~es for X-rays diffractometry measure authors thank Edi M. Guimara ments, John Mantilla for magnetic measurements, Kh. Chanchan Devi for assisting in the X-ray spectra using MAUD software, and Amit Garg for reading the manuscript. References [1] Q. Chen, C. Wei, Y. Zhang, H. Pang, Q. Lu, Feng Gao, Single-crystalline hyperbranched nanostructure of iron hydroxyl phosphate Fe5(PO4)4(OH)3⋅2H2O for highly selective capture of phosphopeptides, Sci. Rep. 4 (2014) 3753. [2] W. Meisel, H.I. Guttmann, P. Gutlich, The influence of phosphoric acid on steel and on its corrosion products: a m€ ossbauer spectroscopic approach, Corros. Sci. 23 (1983) 1373–1379, 1983. [3] D. Rouzies, J.M.M. Millet, D. Siew Hew Sam, J.C. Vedrine, Isobutyric acid oxidative dehydrogenation over iron hydroxyphosphates: I. Catalytic properties and role of water, Appl. Catal. Gen. 124 (1995) 189–203. [4] J.M.M. Millet, D. Rouzies, J.C. Vedrine, Isobutyric acid oxidative dehydrogenation over iron hydroxyphosphates.: II. Tentative description of the catalytic sites based on m€ ossbauer spectroscopic study, Appl. Catal. 124 (1995) 205–219. [5] Priscilla Reale, Scrosati Bruno, Synthesis and thermal behavior of crystalline hydrated iron(III) phosphates of interest as positive electrodes in Li batteries, Chem. Mater. 15 (2003) 5051–5058. [6] Y. Song, Peter Y. Zavalij, Natasha A. Chernova, M. Stanley Whittingham, Synthesis, crystal structure, and electrochemical and magnetic study of new iron (III) hydroxyl-phosphates, isostructural with lipscombite, Chem. Mater. 17 (2005) 1139–1147. [7] N. Marx, L. Bourgeois, D. Carlier, A. Wattiaux, E. Suard, F. Le Cras, L. Croguennec, Iron(III) phosphates obtained by thermal treatment of the tavorite-type FePO4⋅H2O
Fig. 10. Area of the Fe(III) and Fe(II) of barbosalite and Fe(II) in LiFePO4.
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[14] M. Kuzmanovi�c, D. Jugovi�c, M. Mitri�c, B. Joki�c, N. Cvjeti�canin, D. Uskokovi�c, The use of various dicarboxylic acids as a carbon source for the preparation of LiFePO4/ C composite, Ceram. Int. 41 (2015) 6753–6758. [15] Y. Zhu, S. Tang, H. Shi, H. Hu, Synthesis of FePO4⋅xH2O for fabricating submicrometer structured LiFePO4/C by a Co-precipitation method, Ceram. Int. 40 (2014) 2685–2690. [16] G.J. Redhammer, G. Tippelt, G. Roth, W. Lottermoser, G. Amthauer, Structure and Mӧssbauer spectroscopy of barbosalite Fe2þFe3þ2(PO4)2(OH)2 between 80 K and 300 K, Phys. Chem. Miner. 27 (2000) 419–429. [17] H. Hwang, H. Kim, J. Cho, MoS2 nanoplates consisting of disordered graphene-like layers for high rate lithium battery anode materials, Nano Lett. 11 (2011) 4826–4830. [18] Y. Liu, X. Li, H. Guo, Z. Wang, W. Peng, Y. Yang, R. Liang, Effect of carbon nanotube on the electrochemical performance of C-LiFePO4/Graphite battery, J. Power Sources 184 (2008) 522–526. [19] K. Bazzi, M. Nazri, V.M. Naik, V.K. Garg, A.C. Oliveira, P.P. Vaisnava, G.A. Nazri, R. Naik, Enhancement of eectrochemical behavior of nanostructured LiFePO4/ carbon cathode material with excess Li, J. Power Sources 306 (2016) 17–23. [20] L. Rossi, K.P. Velikov, A.P. Philipse, Colloidal iron(III) pyrophosphate particles, Food Chem. 151 (2014) 243–247.
7
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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Effect of Li insertion in the crystal structure and magnetism of barbosalite prepared using solvothermal method N. Joseph Singh a, L. Herojit Singh a, **, S.S. Pati b, J.A.H. Coaquira c, A.C. Oliveira c, Junhu Wang d, V.K. Garg c, * a
Department of Physics, National Institute of Technology Manipur, Langol, 795004, India Department of Chemistry, National Institute of Technology Jamshedpur, Jharkhand, 831014, India Institute of physics, University of Brasília, 70919-970, Brasília, DF, Brazil d M€ ossbauer Effect Data Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, 116023, China b c
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� Barbosalite was synthesized by solvothermal. � Li occupies the interstitial near to Fe(III) site of barbosalite. � The Increase in the Li transformed to LiFePO4. � Magnetic studies shows faster response compared to Structure.
A R T I C L E I N F O
A B S T R A C T
Keywords: Structural transformation Iron hydroxyl phosphate M€ ossbauer spectroscopy Magnetic transformation SQUID And XRD
The effect of Lithium insertion in the crystal structure and magnetic properties of Barbosalite [Fe3(PO4)2(OH)2], a polymorph of iron hydroxyl phosphate synthesized from variable Fe precursor (Fe(II) and Fe(III)), have been investigated. Effect of distortion in the crystal structure of Barbosalite appeared with minimum lithium hy droxide (LiOH.H2O) concentration of 0.5 M as depicted from the XRD patterns. Further, appearance of fresh ossbauer spectroscopy and peaks from 2 M is well matched with the crystal structure of LiFePO4. Studies with M€ SQUID Magnetometer intriguingly reveals that Li intercalation in the barbosalite affects only Fe(III) sites whereas the Fe(II) sites remains unaffected till 2 M. However, further increase in the Li concentration leads to structural transformation and results in LiFePO4 phase. Comparative studies of the structural and magnetic properties, magnetic transition are also discussed.
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (L. Herojit Singh), [email protected] (V.K. Garg). https://doi.org/10.1016/j.matchemphys.2019.122133 Received 27 November 2018; Received in revised form 20 August 2019; Accepted 5 September 2019 Available online 6 September 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
N. Joseph Singh et al.
Materials Chemistry and Physics 240 (2020) 122133
1. Introduction
source and Ni-filtered with CBO monochromator operating at 45 kV and €ssbauer spectra, both at 298 K and at 80 K, were recorded 15 mA. The Mo with a constant acceleration velocity transducer coupled to 57Co in Rh matrix source with an initial activity of 25 mCi in the standard trans mission geometry. The velocity calibration per channel was done with a (1.9 mg 57Fe/cm2) iron foil. The magnetization measurements were performed using a vibrating sample magnetometer module of a physical property measurement system (PPMS, Quantum Design).
Iron hydroxyl phosphates are well known minerals and important catalysts for several chemical processes and also have important roles in passivation of metal surfaces, corrosion inhibition and reactions of iron compounds contained in various soils with phosphate fertilizers [1–4]. Among these, barbosalite and lipscombite have been identified as effi cient catalysts for the selective dehydrogenation of isobutyric acid to methacrylic acid, which can be esterified to produce methyl methacrylate, a very important intermediate in a large number of chemical processes. Iron hydroxyl phosphate has also shown to have high efficiency as an electrode for Li battery [5–7]. The natural minerals of iron hydroxyl phosphates include barbosalite (Fe3(PO4)2(OH)2), rockbridgeite (Fe5(PO4)3(OH)5), beraunite (Fe6(PO4)4(OH)5.6H2O), and whitmoreite (Fe3(PO4)2(OH)2.4H2O). Barbosalite named by Marie Louise Lindberg (Smith) and William T. Pecora in 1955 in honor of Brazilian geologist Aluízio Licínio de Miranda Barbosa from Minas Gerais, Brazil - is a basic hydroxyphosphate, with greenish blue to almost black in color and occurs as a hydrothermal product of triphylite Li(Fe(II), Mn(II))PO4 [8]. A crystallo-chemical characterization of barbosalite presents a challenging act because of its fibrous and microcrystalline character. The presence of other transition metal ions alongside iron makes the situation even more complicated to characterize the chemical properties of the crystal [16]. Apart from geoscience, an understanding of crystal chemistry and physics of the basic iron phosphates is vital for materials science too as has been found in recent years that iron hydroxyl phosphate minerals with mixed valence states of iron can be used as catalysts in methyl methacrylate synthesis [3] and as positive-electrode materials in rechargeable batteries [9]. The flexibility in the structure of FePO4 and Fe based phosphorous hydroxide enables the insertion of Li which is known for its capacity and conductivity (thermal/ionic) as a suitable cathode material [10]. Structural investigation of LiFePO4 to FePO4 on removal and insertion of Li using XRD and Mӧssbauer revealed that the removal of Li results in the transformation of Fe(II) to Fe(III) [11]. Several methods have been adopted to synthesize LiFePO4 including electrospinning, solid state reaction, ball milling, sol-gel, co-precipitation, solvothermal etc. and notably, each of the synthesis methods includes Fe(II) as the iron pre cursor [12–15]. The synthesis of LiFePO4 from Fe(III) salt precursor in the conventional method is very rarely found in the literature. In the present studies, an attempt has been made to understand the physical and chemical insights of iron hydroxyl phosphate synthesized using a modified solvothermal method and also to understand the transformation of hydroxyl phosphate to triphylite structure of LiFePO4. The intermediates formed during the transformation of the iron hy droxyl phosphate to LiFePO4 as an effect of Li concentration are dis cussed by mapping the properties of the local structure of Fe atoms using €ssbauer spectroscopy. Mo
3. Results and discussion Fig. 1 shows the XRD patterns of samples Fe(II)-0 and Fe(II)-2.5. The non-lithiated sample (Fe(II)-0) consists of FePO4 as a major constituent whereas the lithiated sample (Fe(II)-2.5) matched with the diffraction pattern of LiFePO4. On changing the oxidation state of precursor from Fe (II) to Fe (III), a large deviation in the diffraction pattern was observed. The sample Fe (III)-0 shows the nucleation of barbosalite (Fig. 2a). The lattice param eters of the Fe(III)-0 was found to be a ¼ 7.3211 Å, b ¼ 7.4373 Å, c ¼ 7.4139 Å, which is close to the parameters reported by Redhammer et al. [16]. From Fig. 2, shift in the peak position was observed as LiOH. H2O is introduced during the synthesis. To understand the effect of Li on the transformation of Fe(II) Fe2(III) (PO4)2(OH)2 to LiFePO4 and precise control over the sample properties, a series of intermediate Li content samples were also synthesized. The lowest LiOH.H2O concentration (0.5 mol/L) seems to have shifted the XRD peaks to the higher angle which is attributed to the Li insertion in the lattice of barbosalite, causing strain in the lattice structure. The shifts in the peak positions were significantly large at the initial concentration of Li which almost saturated for the higher concentrations. Introduction of 2 M of LiOH. H2O shows a trace signal of LiFePO4 possibly because of the initiation of the LiFePO4 phase (Fig. 2e) and with the higher concentration of LiOH. H2O (i.e. 3.0 M), Fe(II)Fe2(III)(PO4)2(OH)2 transformed to LiFePO4 (Fig. 2g). The lattice parameters determined using MAUD software is shown in Fig. 3. Incorporation of Li increases the lattice parameter. Abrupt changes in the lattice parameter ‘a’ and ‘b’ were observed from LiOH.H2O concentration of 2.0 M. Increase in the LiOH.H2O concen tration above 2.0 M initiates the formation of the LiFePO4 phase.
2. Experimental details FeCl3.6H2O, FeSO4.7H2O, H3PO4, LiOH.H2O, and ethylene glycol were procured from Sigma-Aldrich and used with no further purifica tion. The Fe based phosphates were synthesized through solvothermal method. The synthesis performed with two different Fe precursors. In the synthesis the 15 mL of Fe precursor (0.5 M of FeSO4.7H2O/ FeCl3.6H2O) was mixed with 15 mL of H3PO4 (0.98 M) thoroughly then transferred in to Teflon lined steel autoclave and subjected to a tem perature of 448 K for 15 h. The lithiation was performed by introducing 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 M LiOH.H2O in the synthesis. The samples are marked as Fe(II)-x and Fe(III)-x, where (II) and (III) represent the oxidation state of precursor Fe and x is the molar concentration of LiOH. H2O. Basic identification of the oxide phases of iron was done using RIGAKU Ultima IV X-Ray diffractometer, with a Cu-Kα as the radiation
Fig. 1. XRD of (a) Fe(II)-2.5 (LiFePO4) and (b) Fe(II)-0 (FePO4 as a major component). 2
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Materials Chemistry and Physics 240 (2020) 122133
Fig. 2. XRD for (a) Fe(III)-0 (Fe3(PO4)2(OH2)), (b) Fe(III)-0.5, (c) Fe(III)-1, (d) Fe(III)-1.5, (e) Fe(III)-2, (f) Fe(III)-2.5 (Fe3(PO4)2(OH2) þ LiFePO4) and (g) Fe (III)-3 (LiFePO4).
Fig. 4. Room temperature (298 K) M€ ossbauer spectra of (a) Fe(II)-0 (b) Fe(III)0 (d) Fe(III)-0.5 (d) Fe(III)-1.0 (e) Fe(III)-1.5 (f) Fe(III)-2.0 (g) Fe(III)-2.5 (h) and Fe(III)-3.0.
(IS) of 1.24 mm/s and quadrupole splitting (QS) of 2.71 mm/s is attributed to the FePO4 phase which consists of 61%. Second sub-spectrum having IS and QS of 0.70 mm/s and 2.77 mm/s respec tively (with spectral area 7%) may be because of the intermediate compound having Fe oxidation slightly higher than Fe(II). The third sub-spectrum corresponds to oxidation state of Fe(III). When the syn €ssbauer thesis was carried out using the FeCl3.6H2O precursor, the Mo analysis shows the sample consists of Fe3(PO4)2(OH)2 as shown in Fig. 4b. Deconvolution of the spectra results in 32% of Fe(II) and Fe(III) of 68% which satisfies the Fe(II)/Fe(III) ratio in accordance with the Fe3(PO4)2(OH)2 unit cell. Synthesis carried out in the presence of €ssbauer spectra. As the 0–1.0 M LiOH.H2O solution gives similar Mo LiOH.H2O concentration increases beyond 1.0 mol/L, few €ssbauer Fe3(PO4)2(OH)2 lattices transform to triphylite, LiFePO4. Mo spectrum of Fe(III)- 2.0 could be fitted into three sub spectra. Two of the sub spectra are assigned to the Fe(II) and Fe(III) of Barbosalite where as the third one with IS of 1.2 mm/s and QS of 2.95 mm/s is associated with Fe(II) of LiFePO4. Further increase in the LiOH.H2O concentration re sults in higher percentage of LiFePO4 (Fig. 4f). Fig. 4h shows the €ssbauer transformation of Fe3(PO4)2(OH)2 to LiFePO4 (Fe(III)-3). Mo spectrum is deconvoluted into two spectra. The first spectrum with IS of 1.22 mm/s, QS of 2.95 mm/s with an area of 82% is attributed to divalent Fe atoms of LiFePO4. The second spectrum having IS of 0.46 mm/s, QS of 0.77 mm/s and area of 18% is from the trivalent Fe atoms assigned ferric pyrophosphate (Fe4P6O21) by Bazzi et al. [19](See. Table 1). €ssbauer parameters are depicted in Figs. 5 and Least square fitted Mo 6. The IS corresponding to the Fe(III) and Fe(II) of the barbosalite phase and the transformed Fe compounds are found to be almost constant (Fig. 5b). This clearly indicates that the phase formed has distinct oxidation state without electron hopping during the course of structural
Fig. 3. Lattice parameter of the Barbosalite with respect to the concentration of the LiOH.H2O incorporated during the synthesis.
Samples prepared with LiOH.H2O concentration of 2.0 M (i.e. Fe (III)-2.0) found to have barbosalite of ~94% and ~6% of LiFePO4. Intriguingly, the sample Fe(III)-2.5 shows a sudden change in phase concentration to ~ 8% barbosalite and ~92% LiFePO4. Significant changes in lattice parameters ‘a’ and ‘c’ were also observed for higher concentrations of lithium hydroxide along with phase transformation. A similar shift in the peak position of iron hydroxyl phosphate was also observed in iron (III) hydroxyl phosphate reported by Y. Song et al. [6]. It is reported that the lattice shifts from a ¼ 5.1918 Å, c ¼ 12.9927 Å to a ¼ 5.2493 Å, c ¼ 12.7189 Å as the Fe (III) hydroxyl phosphate is exposed to LiOH.H2O at 90 � C for 5 days in an autoclave. The protons of the hydroxyl groups in these compounds were observed to be replaced by lithium ions with structure retention. For further understanding of the changes obtained, magnetic studies were carried out using €ssbauer and SQUID. Mo It is reported that electrochemical incorporation of lithium into the cathode materials results in disordered compounds which are good candidates for the secondary lithium batteries [17,18]. Fig. 4 shows the €ssbauer spectra of the samples as pre room temperature (298 K) Mo €ssbauer spectrum of Fe(II)-0 have been resolved into three pared. The Mo sub-spectra as shown in Fig. 4a. The first sub-spectrum with isomer shift 3
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Materials Chemistry and Physics 240 (2020) 122133
Table 1 Least square fitted M€ ossbauer parameters at 298 K of the samples synthesized with Fe(II) and Fe(III) precursor. Γ: line width, IS: Isomer shift and QS: quad rupole splitting. Sample (at 298 K)
Γ (mm/s)
IS (Fe) (mm/s)
QS (mm/s)
Area (%)
Fe(II)-0
0.46(0) 0.40(0) 0.41(0) 0.32(1) 0.27(2) 0.36(0) 0.30(0) 0.35(0) 0.30(0) 0.44(0) 0.31(1) 0.45(0) 0.28(1) 0.45(3) 0.36(5) 0.41(4) 0.34(0) 0.45(0) 0.34(0)
1.24(0) 0.70(0) 0.46(0) 0.42(0) 1.10(1) 0.42(0) 1.09(0) 0.43(0) 1.09(0) 0.42(0) 1.09(0) 0.42(0) 1.08(0) 1.20(0) 0.44(1) 0.45(1) 1.22(0) 0.46(1) 1.22(0)
2.71(0) 2.77(1) 0.43(0) 0.39(1) 3.56(2) 0.43(0) 3.56(0) 0.41(0) 3.56(0) 0.47(0) 3.59(0) 0.49(0) 3.52(0) 2.95(1) 0.56(1) 0.89(3) 2.96(0) 0.77(1) 2.95(0)
61 7 32 68 32 69 31 67 33 79 21 72 15 13 6 12 82 18 82
Fe(III)-0 Fe(III)-0.5 Fe(III)-1.0 Fe(III)-1.5 Fe(III)- 2.0 Fe(III)-2.5 Fe(III)-3.0
Fig. 6. Quadrupole splitting of the Fe(II) (hollow rectangles) and Fe(III) (hol low circles) in barbosalite. Solid triangles are for LiFePO4, and solid circles represent the ferric pyrophosphate (Fe4P6O21).
However, the formation of LiFePO4 initiates at 2.0 M of LiOH.H2O. As the Li content increases beyond this concentration (stage 3), an abrupt change is observed in the area of LiFePO4. Fig. 3 depicts the strain developed resulting from Li insertion in the crystal lattice of barbosalite. The strain destabilizes the structure of barbosalite above 1.5 M and in order to compensate the excess energy, the barbosalite transformed to the LiFePO4 structure. In stage 4, Fe(III)-2.5 consist of 82% of stoi chiometric LiFePO4. Fe(III) experiencing IS of 0.45 mm/s and QS of 0.89 consisting of 12% is assigned to ferric pyrophosphate (Fe4P6O21) [19] which was not visible in XRD. The absence of the ferric pyrophosphate peaks in XRD may be plausibly because of the amorphous nature of the compound [20]. At 3.0 M of LiOH.H2O, LiFePO4 consists of 82% and 18% of Fe(III). The QS for Fe(III) and Fe(II) of Fe3(PO4)2(OH)2 are shown in Fig. 6. It shows that the QS of Fe(II) remains constant but that of Fe (III) increase monotonically. This may be understood as resulting from the distortion of Fe(III) site, which is possible when Li gets inserted at the interstitial sites adjacent to Fe(III) sites. Fig. 7 shows the M H loop at 300 K and 5 K. The graph shows a linear and unsaturated curve with negligible coercitivity, which shows the paramagnetic and antiferromagnetic nature. The slope of the M H loop decreases as Li is introduced in the lattices. This indicates the magnetic moment of Fe3(PO4)2(OH)2 reduces as the Li got intercalated. For further understanding of the magnetic properties and the effect of Li on Fe3(PO4)2(OH)2, low temperature measurement was carried out. €ssbauer spectra at 80 K in Fig. 8 show the changes in the hyperfine Mo splitting of the Fe because of to the interaction with Li. The width of the spectrum increases and the hyperfine field decreases as the Li interca lation in the lattice of barbosalite increases. The effect of Li insertion is first observed in the Fe(III) cites experiencing Bhf of 50.8 T indicated as f1 in Table 2. In the sample Fe(III)-1.0, the Fe(III) contributing to 50.8 T decomposes into two having 50.9 and 47.9 T (f2) (Fig. 9). Increase in the Li content further introduces a component with lower Bhf (<44 T i.e. f3). The area under the spectra of Fe(III) experiencing Bhf 50.8 T de creases gradually till 1.0 M of LiOH.H2O (Fig. 10). This area was observed to decrease abruptly when the LiOH.H2O > 1.0 M. The
Fig. 5. Isomer shift (a) and area (b) of the of the Fe(III) and Fe(II) components of the barbosalite (B–Fe(II) and B–Fe(III)) and LiFePO4 (Li–Fe(II)) and Fe(III) represents the ferric pyrophosphate (Fe4P6O21).
transition. The area of the respective phase as plotted in Fig. 4a can be categorized into four stages. The first stage i.e. from Fe(III)-0 to Fe(III)1.0 shows the area ratio of Fe(II) to Fe(III) maintained at 1:2 indicating there is no structural transformation of barbosalite. As the Li content increases in stage 2, the Fe(III) area increases concomitant to the decrease in Fe(II). At 1.5 M of LiOH.H2O, the Fe(III) increases to 79% from 67%. The increase in the 13% because of the oxidation of Fe(II) to Fe(III). In the course of oxidation, the Fe1-x (II) Fe3þx(III) (PO4)2(OH)2 preserved the barbosalite structure which is well supported by XRD data. 4
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Materials Chemistry and Physics 240 (2020) 122133
Table 2 Least square fitted M€ ossbauer parameters of the samples at 80 K synthesized with Fe(II) and Fe(III) precursor. Γ: line width, IS: Isomer shift and QS: quad rupole splitting. SampleS (at 80 K)
Γ (mm/ s)
IS (Fe) (mm/ s)
QS (mm/ s)
Bhf (T)
Area (%)
Representation of the sub spectra
Fe(III)-0
0.29 (0) 0.41 (4) 0.49 (1) 0.30 (1) 0.50 (9) 0.43 (2) 0.47 (1) 0.31 (0) 0.83 (0) 0.36 (9) 0.34 (2) 0.55 (2) 0.33 (1) 0.62 (9) 2.06 (0) 0.72 (4) 0.85 (3) 0.44 (4) 0.76 (9) 1.34 (9) 0.81 (9) 0.28 (2) 0.78 (5) 0.48 (2) 0.29 (0) 0.43 (1) 0.34 (0)
0.53 (0) 0.45 (2) 1.15 (1) 0.53 (0) 0.59 (3) 0.44 (1) 1.22 (0) 0.54 (0) 0.45 (0) 0.42 (0) 0.37 (2) 1.24 (1) 0.55 (0) 0.50 (1) 0.40 (0) 0.35 (1) 1.19 (1) 0.53 (0) 0.55 (1) 0.47 (2) 0.68 (2) 1.33 (0) 1.29 (2) 0.53 (0) 1.34 (0) 0.53 (0) 1.34 (0)
0.26 (0) 0.44 (2) 1.65 (1) 0.26 (0) 0.36 (6) 0.39 (1) 1.48 (1) 0.26 (0) 1.11 (9) 0.76 (9) 0.30 (0) 1.48 (1) 0.25 (0) 0.39 (3) 1.16 (7) 0.30 (0) 1.52 (1) 0.24 (0) 0.29 (2) 0.06 (4) 0.64 (0) 3.07 (1) 1.54 (3) 0.74 (1) 3.06 (0) 0.83 (1) 3.07 (0)
50.8 (0) –
57
f1
13
f2
32.8 (3) 50.9 (1) 47.9 (2) –
30
f3
54
f1
7
f4
10
f2
32.7 (0) 50.7 (0) 45.3 (5) 44.1 (4) –
29
f3
54
f1
6
f4
3
f5
8
f2
32.5 (4) 50.8 (0) 47.9 (2) 32.9 (2) –
29
f3
23
f1
10
f4
26
f5
7
f2
32.8 (1) 49.7 (1) 46.0 (2) 38.3 (2) –
34
f3
18
f1
20
f4
30
f5
8
f6
–
5
f7
32.3 (1) –
19
f3
32
f6
–
68
f7
–
19
f6
–
81
f7
Fe(III)-0.5
Fe(III)-1.0
Fig. 7. M
H loop of the Fe(III)-0, Fe(III)-0.5, and Fe(III)- 2.0 at 300 K and 5 K.
Fe(III)-1.5
Fe(III)-2.0
Fe(III)-2.5
Fe(III)-3.0
the hyperfine field of the Fe(III) gets affected by the introduction of Li(I). The splitting of the ~50 T sextets to 50, 47 and >44 T is understood as resulting from the coupling of the magnetic moment of Fe(III) and diamagnetic Li(I). The coupling of the diamagnetic cations reduces the net magnetic moment resulting in low Bhf. ZFC (Fig. 11) of pure and 0.5 M LiOH.H2O doped Fe3(PO4)2(OH)2 shows a sharp transition around 176 K which is attributed to the tran sition from paramagnetic to antiferromagnetic. For the sample with 2.0 M of LiOH.H2O, a broad transition around 50 K was found which was present in the earlier sample too with a low intensity. This transition resembles the magnetic transition in LiFePO4 and FePO4. Referring to the XRD of the sample synthesized with 2.0 M of LiOH, although most of the peaks were matched with barbosalite, a signature of peak
Fig. 8. M€ ossbauer spectra at 80 K of (a) Fe(III)-0 (b) Fe(III)-0.5 (c) Fe(III)-1.0 (d) Fe(III)-1.5 (e) Fe(III)- 2.0 (f) Fe(III)-2.5 (f) and(g) Fe(III)-3.0.
decrease in the area is concomitant with the increase in the area of the Fe (III) experiencing Bhf of ~47.9 T and <44 T. Further observation on the sextet of Fe(II) experiencing Bhf ~ 32 T was found to have no changes with respect to Bhf, QS and IS. This indicates the interaction of the Li occurs with Fe(III). The transformation of the sextet to triphylite doublet €ssbauer spectra obtained at initiates from 2 M of LiOH.H2O. From the Mo 278 K, it was observed to have a gradual increase in the QS of Fe(III). This indicates the Fe(III) sites getting distorted by Liþ incorporated. This is further supported by the low temperature (80 K) measurements where 5
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Materials Chemistry and Physics 240 (2020) 122133
Fig. 11. FC and ZFC of Fe(III)-0, Fe(III)-0.3 and Fe(III)-1.2.
corresponding the LiFePO4 phase was also observed. This indicates that the magnetic transitions occur even before the structural transition.
Fig. 9. Hyperfine field of the Fe(III) component experiencing ~50.8 T (f1) and the Li coupled Fe(III) resulting to lower hyperfine field with ~47 T (f4) and <45.3 T (f5).
4. Conclusions Pure as well as Li doped barbosalite were synthesized using sol vothermal method. Li insertion in the lattice of barbosalite distorts the Fe(III) sites. Further introduction of Li destabilizes the barbosalite structure and transform it into triphylite (LiFePO4). Low (80 K) tem perature measurements support the residence of Li in the Fe(III) cites as the magnetic hyperfine field of the Fe(III) is altered which decomposes into three components, one around 50 T and the others at 47.9 T and <44 T. SQUID measurements predict the paramagnetic to antiferro magnetic transitions at 176 K. The intensity of the magnetic transition was drastically reduced in the sample synthesized with 2.0 M of LiOH. H2O. The magnetic transition resulting from the Li incorporation is observed to be a step ahead than the structural transition. Acknowledgement The author LHS thank DST and Science and Engineering Research Board (SERB) with project file no. EMR/2016/001524 for the financial support. The author thanks DST-INSPIRE for providing scholarship. The ~es for X-rays diffractometry measure authors thank Edi M. Guimara ments, John Mantilla for magnetic measurements, Kh. Chanchan Devi for assisting in the X-ray spectra using MAUD software, and Amit Garg for reading the manuscript. References [1] Q. Chen, C. Wei, Y. Zhang, H. Pang, Q. Lu, Feng Gao, Single-crystalline hyperbranched nanostructure of iron hydroxyl phosphate Fe5(PO4)4(OH)3⋅2H2O for highly selective capture of phosphopeptides, Sci. Rep. 4 (2014) 3753. [2] W. Meisel, H.I. Guttmann, P. Gutlich, The influence of phosphoric acid on steel and on its corrosion products: a m€ ossbauer spectroscopic approach, Corros. Sci. 23 (1983) 1373–1379, 1983. [3] D. Rouzies, J.M.M. Millet, D. Siew Hew Sam, J.C. Vedrine, Isobutyric acid oxidative dehydrogenation over iron hydroxyphosphates: I. Catalytic properties and role of water, Appl. Catal. Gen. 124 (1995) 189–203. [4] J.M.M. Millet, D. Rouzies, J.C. Vedrine, Isobutyric acid oxidative dehydrogenation over iron hydroxyphosphates.: II. Tentative description of the catalytic sites based on m€ ossbauer spectroscopic study, Appl. Catal. 124 (1995) 205–219. [5] Priscilla Reale, Scrosati Bruno, Synthesis and thermal behavior of crystalline hydrated iron(III) phosphates of interest as positive electrodes in Li batteries, Chem. Mater. 15 (2003) 5051–5058. [6] Y. Song, Peter Y. Zavalij, Natasha A. Chernova, M. Stanley Whittingham, Synthesis, crystal structure, and electrochemical and magnetic study of new iron (III) hydroxyl-phosphates, isostructural with lipscombite, Chem. Mater. 17 (2005) 1139–1147. [7] N. Marx, L. Bourgeois, D. Carlier, A. Wattiaux, E. Suard, F. Le Cras, L. Croguennec, Iron(III) phosphates obtained by thermal treatment of the tavorite-type FePO4⋅H2O
Fig. 10. Area of the Fe(III) and Fe(II) of barbosalite and Fe(II) in LiFePO4.
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