物理化学学报(Wuli Huaxue Xuebao) Acta Phys. ⁃Chim. Sin. 2012, 28 (5), 1021-1029 May doi: 10.3866/PKU.WHXB201202271 [Article] 1021 www.whxb.pku.edu.cn 1200 °C 合成 Mn3O4-Fe2O3 体系的物相关系、 结构和阳离子分布 王 蓉2 杨承旭 1 时迎国 3 孙玉增 1 李国宝 1,* 金头男 2,* 秦高梧 3,* 廖复辉 1 林建华 1,* (1 北京大学化学与分子工程学院, 北京分子科学国家实验室, 稀土材料化学及应用国家重点实验室, 北京 100871; 2 北京工业大学材料科学与工程学院, 北京 100022; 摘要: 3 东北大学材料各向异性与织构教育部重点实验室, 沈阳 110819) 在空气气氛中 1200 °C 温度下合成了 Mn3O4-Fe2O3 体系的各类样品, 并将其快速淬火到室温. X 射线粉 末衍射(XRD)分析表明这样得到的该体系样品存在三个固溶体 Mn3-3xFe3xO4 (0.00£x£0.278), Mn3-3xFe3xO4 (0.291£x£0.667)和 Mn2-2xFe2xO3 (0.89£x£1.00). X 射线粉末衍射数据的结构精修显示它们分别具有 I41/amd 空 间群的黑锰矿结构、Fd3m 空间群的尖晶石结构和 R3c 空间群的赤铁矿结构. 各固溶体之间都存在两相共存的 区域. 57Fe 穆斯堡尔谱数据显示 Fe 在各个物相中都是 Fe3+, 在黑锰矿和尖晶石中存在两种结晶学环境不同的 Fe3+, 而在赤铁矿中只存在一种 Fe3+. 结合 X 射线光电子能谱(XPS)的数据, 可以认为黑锰矿和尖晶石中的阳离 3+ 3+ 3+ 3+ 2+ 3+ 子分布可以用分子式 Mn2+ 1-xFex [Mnx Fex Mn2-3x]O4 表示, 而赤铁矿为 Mn2-2xFe2x O3. 关键词: 相关系; 结构; 中图分类号: 57 Fe 穆斯堡尔谱; X 射线光电子能谱; 阳离子分布; Mn3O4; Fe2O3 O641 Phase Relationship, Structure and Cationic Distribution of Oxides in the Mn3O4-Fe2O3 System Synthesized at 1200 °C WANG Rong2 YANG Cheng-Xu1 SHI Ying-Guo3 SUN Yu-Zeng1 LI Guo-Bao1,* JIN Tou-Nan2,* QIN Gao-Wu3,* LIAO Fu-Hui1 LIN Jian-Hua1,* (1State Key Laboratory of Rare Earth Materials Chemistry and Applications, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China; 2College of Material Science and Engineering, Beijing University of Technology, Beijing 100022, P. R. China; 3Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819 , P. R. China) Abstract: A series of oxides in the Mn3O4-Fe2O3 system have been synthesized at 1200 °C in air, followed by quenching to room temperature. Three solid solutions, Mn3-3xFe3xO4 (0.00£x£0.278), Mn3-3xFe3xO4(0.291£ x£0.667), and Mn2-2xFe2xO3 (0.89£x£1.00), have been identified by powder X-ray diffraction (XRD). Rietveld refinement of the XRD data show that the solids belong to the hausmannite phase with the space group I41/ amd, the spinel phase with the space group Fd3m, and the hematite phase with the space group R3c, respectively. Between these are two-phase regions. 57Fe Mössbauer spectra indicate that the valence state of Fe in the three solid solutions is +3; in addition, there are two crystallographically independent Fe3 + ions in the unit cells of the hausmannite and spinel phases, and one Fe3+ in the hematite phase. Analyses of 57Fe 3+ 3+ 2+ 3+ Mössbauer spectra and X-ray photoelectron spectra (XPS) revealed that a formula of Mn2+ 1-x Fex [Mnx Fe x Mn 2-3x] O4 describes the cation distribution of both the hausmannite and spinel phases, but that for the hematite Received: December 8, 2011; Revised: February 13, 2012; Published on Web: February 27, 2012. ∗ Corresponding authors. LI Guo-Bao, Email: liguobao@pku.edu.cn. JIN Tou-Nan, Email: tnjinkim@bjut.edu.cn. QIN Gao-Wu, qingw@smm.neu.edu.cn. LIN Jian-Hua, Email: jhlin@pku.edu.cn. The project was supported by the National Key Basic Research Project of China (973) (2010CB833103) and Scientific Research Key Program of Beijing Municipal Commission of Education, China (KM201010005019). 国家重点基础研究发展规划项目(973) (2010CB833103)和北京市教委重点基金(KM201010005019)资助 Ⓒ Editorial office of Acta Physico⁃Chimica Sinica Acta Phys. ⁃Chim. Sin. 2012 1022 Vol.28 3+ phase is Mn3+ 2-2xFe2x O3. Key Words: Phase relationship; spectroscopy; 1 Structure; 57 Fe Mössbauer spectroscopy; Cation distribution; Introduction Manganese iron oxides have been extensively studied due to their applications to many electronic devices.1,2 A lot of studies have been performed on the phase relationships, magnetic and electronic properties of the FeOx-MnOy system.3-27 Several phases, such as hausmannite, spinel, hematite, and bixbyite, have been found in this system. Various magnetic and electronic properties are found for these phases. For example, Fe3O4 has a metal-insulator transition occurred at about -153 °C (noted as the Verwey temperature (TV) after the work reported by Verwey12); below TV, Fe3O4 crystallizes in the space group Cc with a=1.189310(1) nm, b=1.185418(2) nm, c=1.678310(2) nm, β =90.2367(2)° at -193 ° C;13-19 above TV, Fe3O4 is an inverse Fe spinel Fe3 + [Fe2 + Fe3 + ]O4 crystallizing in space group Fd3m with a≈0.84 nm, where eight Fe3 + ions locate in tetrahedral 8a sites (0, 0, 0) (noted as A sites), eight Fe2 + plus the remaining eight Fe3 + ions in octahedral 16d sites (5/8, 5/8, 5/8) (noted as B sites) and O2- in 32e sites (~3/8, ~3/8, ~3/8);20-22 the paramagnetic to ferrimagnetic phase transition occurs at about 585 ° C for Fe3O4. While Mn3O4 is a normal spinel with all the tetrahedral A sites are occupied by a divalent cation (Mn2 + ) and all the octahedral B sites are occupied by trivalent cations (Mn3+);23 at 1182 °C, this compound undergoes a tetragonal to cubic phase transition;24 the paramagnetic to ferrimagnetic phase transition occurs at about -231 °C for Mn3O4; below -231 ° C, a complex succession of rearrangements takes place in the magnetic structure.25-27 Cubic spinels over a continuous range of composition from Mn3O4 to Fe3O4 are reported to be stable between about 1200 and 1600 ° C in air,10,11 most of them can be quenched to room temperature. It is very interesting that how the cations (Fe2 + , Fe3 + , Mn2 + , Mn3+ ) distribute between the tetrahedral (A) and octahedral (B) sites for Mn3-xFexO4 because both Fe3+ and Mn2+ intend to occupy the tetrahedral A sites. Several different points of view were presented in the literature.28-31 For example, FeMn2O4 was suggested to be Mn2+[Fe2+Mn4+]O4 by Eschenfelder28 after the analy2+ 3+ Mn0.91 sis of the magnetic moment of this compound, to be Fe 0.09 29 3+ 3+ 2+ [Fe0.09Fe0.82Mn1.09]O4 by Tanaka et al. with the help of Mössbau3+ 2+ 3+ 2+ 3+ Mn 1-y Mn 0.5 [Fe 0.5 Mn 0.5 er technique, and to be Fe 0.5 Mn 2+y/2 Mn4+y/2]O4 30 by Kulkarni and Darshane using Mössbauer technique (here, A[B2]O4 means that the cation A occupies the tetrahedral site and B the octahedral site of the spinel). In addition, Battault et al.31 suggested that Mn3-xFexO4 (0≤x≤1.05) should be Mn12+-y Fe3y + [Fe3z + Mn 22+-y-z Mny2 + ]O4. In order to find a clear picture for this question, X-ray diffraction, 57Fe Mössbauer spectra, and X-ray photoelectron spectroscopy (XPS) have been performed on the samples in the system Fe-Mn-O synthesized at 1200 ° C and X-ray photoelectron Mn3O4; Fe2O3 quenched to room temperature in this study. 2 Experimental All the samples were synthesized by high-temperature solidstate reaction using Fe2O3 (AR) and MnCO3 (AR) as the starting materials. The oven-dried reagents were mixed and homogenized by grinding about 30 min with an agate mortar and a pestle. The mixtures were subjected to 12 h calcinations at 800 °C with intermediate grindings. They were then pressed into pellets to undertake four 12 h heat treatments at 1200 °C followed by quenching in water with intermediate grinding and then pressing into pellets. All the treatments were done in air. The mass of the samples were monitored before and after heat treatments. The maximum difference was about 4 mg for the 6 g samples. Therefore, the compositions of the samples were considered to be the same as the initial ones. The phase purity of the sample was checked by powder X-ray diffraction on a Rigaku D/Max-2000 diffractometer with graphite monochromatized Cu Ka radiation at 40 kV, 100 mA. Powder X-ray diffraction (PXRD) data for Rietveld refinement carried out with GSAS program32,33 were collected on a Bruker D8 Advance diffractometer with Cu Kα1 (λ=0.15407 nm) radiation (2θ range: 10°-120° ; step: 0.0197° ; scan speed: 20 s· step-1) at 50 kV and 40 mA. The 57Fe Mössbauer spectra were obtained using 57Co diffused into rhodium as a source of gamma rays at room temperature.34 Absolute velocity calibration was carried out with an Fe foil (25 pm thick); isomer shifts (IS) are reported with reference to Fe. The spectra were computer-fitted using a general Lorentzian routine, and a nonlinear least-square curve-fitting procedure was employed to obtain the best fit to the experimental data. We used IS and quadrupole splitting (QS) to characterize the species. The X-ray photoelectron spectroscopy (XPS) patterns were acquired with a UK Kratos Axis Ultra spectrometer with Al KR X-ray source operated at 15 kV, 15 mA. The chamber pressure was less than 6.7×10-7 Pa. Electron binding energies were calibrated against the C 1s emission at Eb=284.8 eV. 3 Results and discussion 3.1 Phase relationship 3.1.1 Hausmannite phase Although the sample is quenched from 1200 °C to room temperature by dropping the sample into water, it is found that the obtained Mn3O4 still crystallizes in tetrahedral space group I41/ amd without obtaining the cubic phase as reported by Crum et al.10 using the in situ measurement technique. This phenome- No.5 WANG Rong et al.: Phase Relationship, Structure and Cationic Distribution of Oxides in the Mn3O4-Fe2O3 System 1023 non has been mentioned by Muan and Somiya,6 and is due to a displacive transformation35 from cubic spinel to tetrahedral hausmannite. The lattice parameters for hausmannite Mn3O4 obtained by us agree well with the reported values36-40 as shown in Table 1. The powder XRD patterns of the samples with the nominal formula Mn3-3xFe3xO4 (x=0, 0.063, 0.125, 0.250, 0.278, noted as S1, S2, S3, S4, S5, respectively) are very similar and can be refined well with the help of GSAS using the similar structural model of hausmannite. Typical Rietveld plots are shown in Fig.1 for sample S3 with the corresponding details listed in Table 2. The relationship between the lattice parameters (a and c) and the amount of Fe in the phase does not agree with the Vegardʹs law41,42 as shown in Fig.2, which may be attributed to the fact that there are phase transitions for these samples during quenching. It is found that the powder XRD patterns of one sample with the nominal formula Mn3-3xFe3xO4 (x=0.286, noted as S6) conTable 1 Reported lattice parameters for Mn3O4 at room temperature in the space group I41/amd Reference a/nm c/nm (36) 0.5752 0.9470 JCPDS 24-0734 0.57621 0.94696 (37) 0.5756 0.9439 (38) 0.571 0.935 (39) 0.576 0.946 The open circle indicates the sample is single phase (hausmannite phase). The (40) 0.5765 0.9442 solid circle means that there are two phases (hausmannite and spinel phase) in the this work 0.57642 0.94798 sample, and the data shown are just the data for hausmannite phase in the sample. Fig.1 Rietveld plots of powder X-ray diffraction (XRD) patterns for the sample S3 The symbol + represents the observed value, the solid line represents the calculated value, the marks below the diffraction patterns are the calculated reflection positions, and the difference curve is shown at the bottom of the figure. Table 2 Rietveld refinement details of the sample S3a,b Atom x, y, z Occupancyc Mn/Fe1 0.0000, 0.2500, 0.8750 0.875/0.125 Mn/Fe2 0.0000, 0.5000, 0.5000 0.875/0.125 O 0.0000, 0.4746, 0.2627(1) 1.000 a b space group: I41/amd with a=0.58232(1) nm and c=0.92517(1) nm; the R factor of the refinement: Rwp=0.016, Rp=0.013; c The occupancies of Mn and Fe in each site are determined by 57Fe Mössbauer spectra and XPS. Fig.2 Lattice parameters of the hausmannite phase in different samples of Mn3-3xFe3xO4 sist of diffraction peaks coming from two phases: hausmannite and spinel, which can be fitted well with two-phases model listed in Table 3 with the help of GSAS as shown in Fig.3. 3.1.2 Spinel phase The cubic spinel phase can be quenched to room temperature when more Fe is doped into Mn3O4. The XRD patterns of the samples with the nominal formula Mn3-3xFe3xO4 (x=0.294, 0.299, 0.303, 0.313, 0.323, 0.345, 0.374, 0.400, 0.500, 0.556, 0.588, 0.625, 0.667, named as S7, S8, …, S19) are very similar to the cubic spinel Mn3O4. Rietveld refinements are performed for the XRD patterns of samples S7, S9, S11, S12, S13, S15, S17, S18, and S19 with good fitting as shown in Fig.4 using the corresponding parameters listed in Table 4. The lattice parameter a decreases linearly with the increase of Fe content in the spinel phases Mn3-3xFe3xO4, which agrees well with Vegardʹs law as shown in Fig.5. The XRD patterns of the samples with the nominal formula Mn3-3xFe3xO4 (x=0.770, noted as S20) can be fitted well by Rietveld refinement using two-phase model (spinel phase and hematite phase) as shown in Fig.6 with the corresponding details listed in Table 5. The compositions of lower and upper ends of the spinel phase Mn3-3xFe3xO4 are x= 0.291 and x=0.667, respectively. 3.1.3 Hematite phase Because the synthesis temperature is just 1200 °C, the samples obtained around FeOx are hematite phase.6,10 The XRD pat- Acta Phys. ⁃Chim. Sin. 2012 1024 Vol.28 Rietveld refinement details of the sample S6a Table 3 Item Value phase hausmannite spinel space group I41/amd Fd3m a/nm 0.59619(1) 0.85540(1) c/nm 0.87775(1) lattice parameter Mn/Fe1 x, y, z 0.0000, 0.2500, 0.8750 0.0000, 0.0000, 0.0000 occupancy 0.724/0.276b 0.709/0.291c 0.0000, 0.5000, 0.5000 0.6250, 0.6250, 0.6250 Mn/Fe2 x, y, z occupancy 0.724/0.276 b 0.709/0.291c O x, y, z occupancy 0.0000, 0.4723(1), 0.2602(1) 0.2354(1), 0.2354(1), 0.2354(1) 1.000b 1.00c R factor a Rwp 0.014 Rp 0.011 The mole ratio of spinel phase to hausmannite phase for this sample is 0.877:1, which is obtained by the Rietveld refinement. b The occupancies of Mn and Fe in each site are calculated by the lever rule with the following equation: (4´3xh+8´ 3xsF)/[4(3-3xh)+8(3-3xs)F)]=3xa/(3-3xa). Here xh, xs, xa are the value of x in hausmannite phase, spinel phase, and the average value of x in the sample Mn3-3xFe3xO4 with xs=0.291, xa= 0.286. F (=0.877) is the mole ratio of spinel phase to hausmannite phase for the sample. The value of xh is obtained to be 0.276, which agrees well with that the sample S5 (Mn3-3xFe3xO4, x=0.278) is a single phase sample. c The occupancies of Mn and Fe in each site are 57 determined by Fe Mössbauer spectra and XPS. terns of the samples with the nominal formula Mn2-2xFe2xO3 (x= 0.90, 0.93, 0.935, 0.95, 0.96, 0.97, 0.98, 1.00, noted as S21, S22, …, S28) are similar to hematite Fe2O3.43,44 The structural model of hematite Fe2O3 is used to refine the XRD patterns for samples S21, S22, S24, S26, and S28 with good fitting as shown in Fig.7 for sample S21. The details on the refinement are listed in Table 6. The change of the lattice parameters (a and c) agrees well with Vegardʹs law as shown in Fig.8, from which the composition range for hematite phase Mn2-2xFe2xO3 obtained under our condition is 0.89≤x≤1.00. 3.2 57Fe Mö ssbauer spectra The 57Fe Mössbauer spectra of the typical samples of hausmannite phase Mn3-3xFe3xO4 (0.00≤x≤0.278), spinel phase Mn3-3xFe3xO4 (0.291≤x≤0.667), and hematite phase Mn2-2xFe2xO3 (0.89≤x≤1.00) are shown in Fig.9. Because Battault et al.31 had already reported the Mössbauer spectra of Mn3-3xFe3xO4 (0.00≤ x≤0.35), only the spectrum of the sample S5 of hausmannite phase is collected as shown in Fig.9(a). Two sextets with an isomer shift of 0.33 and 0.36 mm·s-1 can be derived from this spectrum, which indicates the presence of two non-equivalent sites of the Fe3+ ion associated with the presence of Fe3+ ions in tetrahedral (A) and octahedral (B) sites.31,45 It is found that the ratio of Fe3+ in A and B sites is about 1:2. Therefore, similar as that reported by Battault et al., 31 the formula for hausmannite phase Mn3-3xFe3xO4 (0.00≤x≤0.278) may be suggested as 3+ 2+ Fex3 + [Mnx2 + Fe 3+ Mn 1-x 2x Mn 2-3x]O4. For spinel phase, the spectra of Fig.3 Rietveld plots of powder XRD patterns for the sample S6 The symbol + represents the observed value, the solid line represents the calculated value, the marks below the diffraction patterns are the calculated reflection positions, and the difference curve is shown at the bottom of the figure. The upper marks are for tetrahedral hausmannite phase and the lower marks are for cubic spinel phase. The left figure is for the whole patterns and right one is for the patterns between 26° and 36°. seven samples are collected. They all show two sextets with an isomer shift of between 0.23 and 0.40 mm·s-1 as listed in Table 7 indicating that the oxidation state of Fe in spinel phase are +3. The ratios of Fe3+ ions in both A and B sites are around 1:2. Therefore, the formula for spinel phase Mn3-3xFe3xO4 (0.291≤x≤ Fig.4 Rietveld plots of powder XRD patterns for the sample S7 The symbol + represents the observed value, the solid line represents the calculated value, the marks below the diffraction patterns are the calculated reflection positions, and the difference curve is shown at the bottom of the figure. The peak around 22° comes from the MYLAR X-ray film, which is attached by the sample when the XRD data were collected through transmission method. No.5 WANG Rong et al.: Phase Relationship, Structure and Cationic Distribution of Oxides in the Mn3O4-Fe2O3 System Rietveld refinement details of the sample S7a,b Table 4 Table 5 c Rietveld refinement details of the sample S20a Atom x, y, z Occupancy Item Mn/Fe1 0.0000, 0.0000, 0.0000 0.706/0.294 phase hematite spinel Mn/Fe2 0.6250, 0.6250, 0.6250 0.706/0.294 space group R3c Fd3m O 0.2351(1), 0.2351(1), 0.2351(1) 1.000 lattice parameter 0. 84977(1) a 1025 Value space group: Fd3m with a=0.85540(1) nm. b The R factor of the refinement: a/nm 0. 50382(1) Rwp=0.013, Rp=0.011. c The occupancies of Mn and Fe in each site are determined by 57Fe Mössbauer spectra and XPS. c/nm 1. 37445(1) Mn/Fe1 x, y, z 0.0000, 0.0000, 0.1448(1) 0.0000, 0.0000, 0.0000 occupancy 0.11/0.89b 0.33/0.67b Mn/Fe2 x, y, z 0.6250, 0.6250, 0.6250 occupancy 0.33/0.67b O x, y, z 0.6969(1), 0.0000, 0.2500 0.2351(1), 0.2351(1), 0.2351(1) occupancy 1.000b 1.00b R factor a Fig.5 Lattice parameter a of the cubic spinel phase in different samples of Mn3-xFe3xO4 Rwp 0.017 Rp 0.013 The mole ratio of hematite phase to spinel phase for sample S20 is 1.55:1, which is obtained by the Rietveld refinement. b The occupancies of Mn and Fe in each site are set as that expected for the end members of spinel and hematite. (a) Fig.7 (b) Rietveld plots of powder XRD patterns for the sample S7 The symbol + represents the observed value, the solid line represents the calculated value, the marks below the diffraction patterns are the calculated reflection positions, and the difference curve is shown at the bottom of the figure. Table 6 a Rietveld refinement details of the sample S21a,b Atom x, y, z Occupancyc Mn/Fe1 0.0000, 0.0000, 0.1448(1) 0.10/0.90 O 0.6969(1), 0.0000, 0.2500 1.000 space group: R3c with a=0.50381(1) nm, c=1.37451(1) nm. b The R factor of the refinement: Rwp=0.013, Rp=0.010. c The occupancies of Mn and Fe in each site are determined by 57Fe Mössbauer spectra and XPS. Fig.6 Rietveld plots of powder XRD patterns for the sample S20 The symbol + represents the observed value, the solid line represents the calculated value, the marks below the diffraction patterns are the calculated reflection positions, and the difference curve is shown at the bottom of the figure. The upper and lower marks are for spinel and hematite phase, respectively. The figure (a) is for the whole patterns and the figure (b) is for the patterns between 30.0° and 40.0°. 2+ 3+ Fex3 + [Mnx2 + Fe 3+ 0.667) is also suggested as Mn 1-x 2x Mn 2-3x]O4. For hematite phase, the spectrum for the sample S25 is shown in Fig.9(i). Only one sextet is observed with an isomer shift of 0.38 mm·s-1 indicating one site of the Fe3 + ion, which agrees well with the structural data as shown in Table 6. The formula 3+ for hematite phase is suggested to be Mn2-2x Fe3+ 2x O3. 3.3 XPS data XPS data of the representative samples in the three solid solutions were obtained to check the oxidation state of Fe and Mn in the samples. It is found that there is a shoulder at the Acta Phys. ⁃Chim. Sin. 2012 1026 Fig.8 Vol.28 Lattice parameters (a, c) of the hematite phase in different samples of Mn2-2xFe2xO3 Fig.9 57 Fe Mössbauer spectra of different samples (a) S5; (b) S9; (c) S14; (d) S15; (e) S16; (f) S17; (g) S18; (h) S19; (i) S25. The solid black squares are measured data, the blue line is the simulated data for the site A, the green line for site B, and the red line is the total simulated data. peak of 2p3/2 for MnFe2O4 as shown in Fig.10. Because the 57Fe Mössbauer spectra for MnFe2O4 (Fig.9(h)) has shown that the oxidation state of Fe is + 3, it is reasonable to believe that the oxidation state for Mn in this sample is +2. Therefore, the two peaks found in the XPS data of Mn 2p for MnFe2O4 around 2p3/2 should be attributed to the difference between the tetragonal and octahedral sites for Mn2 + . The obtained binding energy of Mn2+ in the tetragonal site and the octahedral site are 639.8 and 641.2 eV, respectively. These values are closed to the values of 640.6 to 641.0 eV reported for Mn2 + .46,47 This result indicates that the present XPS data can show the difference of Mn 2p peaks between the tetragonal and octahedral sites, which will be used in the analysis of the XPS data for both hausmannite and spinel phases. No.5 WANG Rong et al.: Phase Relationship, Structure and Cationic Distribution of Oxides in the Mn3O4-Fe2O3 System 1027 Table 7 Analysis of the Mössbauer spectra for Mn3-3xFe3xO4 x ISA/(mm·s ) ISB/(mm·s-1) QSB/(mm·s-1) y(FeA3+)/% y(FeB3+)/% 0.278 0.326 0.356 0.303 0.233 0.270 -0.068 0.126 34.2 65.8 0.037 0.025 31.5 0.400 0.250 68.5 0.313 0.019 0.047 35.5 0.500 64.5 0.346 0.400 0.057 0.024 30.2 69.8 0.556 0.366 0.386 0.064 -0.003 33.7 66.3 0.588 0.310 0.368 0.022 0.038 32.7 67.3 0.625 0.315 0.395 0.013 0.033 34.1 65.9 0.667 0.294 0.384 0.075 0.047 35.7 64.3 -1 QSA/(mm·s-1) IS: isomer shift; QS: quadrupole splitting; A: tetrahedral site; B: octahedral site; y: molar fraction of FeA3+ or FeB3+ in both A and B sites Fig.10 XPS data of Mn 2p of MnFe2O4 and Mn3O4 As it is known, the cation distributions in Mn3O4 have been extensively studied. Several studies suggested a Mn2 + [Mn2 + Mn4 + ]O4 structure (Model A) for Mn3O4.30,46-49 However, more studies have been in favor of a Mn2+ [Mn3+ ]2O4 structure (Model B) for Mn3O4.23-27,50-52 It is found that the XPS data for Mn 2p of Mn3O4 can be fitted well with the two models as shown in Fig.10. It should be mentioned that Model A is divided in two models: Model A1 and Model A2. In literature,46,47 the binding energy of Mn2 + in Mn2 + [Mn2 + Mn4 + ]O4 was supposed to be the Table 8 a same. Therefore, the fitting of the data was performed using two different binding energies. This is noted as Model A1. However, as mentioned above, two binding energies are obtained for Mn2 + in tetragonal and octahedral sites. In this case, tree binding energies should be used to fit the data. This is noted as Model A2. The corresponding data are listed in Table 8. This result indicates that the XPS only could not give a choice. In this article, we accept the Mn2 + [Mn3 + ]2O4 structure for Mn3O4. In addition, we also accept that there is no Mn4 + in Mn3-3xFe3xO4 as many researchers believed.31 2+ As mentioned in last section, the structure of Mn 1-x Fex3+ [Mnx2+ 3+ 3+ Fe 2x Mn 2-3x]O4 is suggested for both hausmannite and spinel phases. This suggests that Mn 2p3/2 peak can be divided into three parts with the ratio PTMn2+:POMn2+:POMn3+=(1-x):x:(2-3x) (PTMn2+ is the amount of Mn2+ in tetragonal site, P OMn2+ the amount of Mn2 + in octahedral site, POMn3 + the amount of Mn3 + in octahedral site). It is found that all the XPS data of Mn 2p for the samples belonging to both hausmannite and spinel phases can be fitted well using the above suggestion as shown in Fig.11. The lines in Fig.11 are fitted results using the model listed in Table 9. For hematite phase, the XPS data of Mn 2p are almost the same with one binding energy of 641.5 eV for Mn 2p3/2, which is comparable to the value of 641.9 eV for that of α-Mn2O3.46 Therefore, it is suggested that the oxidation state of Mn in hematite phase is +3. The XPS data of Fe 2p for the samples belonging to hausmannite, spinel, and hematite phases are shown in Fig.12. It is easy to note that there is no signal for S1 because there is no Fe in this sample (S1 is Mn3O4). The other spectra are almost the same. They all show the typical patterns for α-Fe2O3.53 Therefore, it is reasonable to suggest that Fe in all of these samples is Fe3 + , which agrees well with the 57Fe Mössbauer spectra for these samples. Suggested binding energy parameters of Mn 2p3/2 by different models E(Mn 2p3/2)/eVa FWHM/eV Model A1 642.4 2.5 Model A2 642.7 2.5 Model B 641.8 2.4 E(Mn 2p3/2)/eVb FWHM/eV 641.6 1.7 E(Mn 2p3/2)/eVc FWHM/eV Ratiod 640.8 2.5 1:0:2 640.6 1.5 1:1:1 640.7 1.8 2:0:1 the value for Mn4+ (Model A1 and Model A2) or Mn3+ (Model B) at the octahedral site; b the value for Mn2+ at the octahedral site; c the value for Mn2+ at the tetrahedral site; d It is the ratio of the amount of Mn4+, Mn3+, and Mn2+ in the case of a, b, and c; FWHM: full width at half maximum Acta Phys. ⁃Chim. Sin. 2012 1028 Fig.11 Vol.28 XPS data of Mn 2p of Mn3-3xFe3xO4 and Mn2-2xFe2xO3 The scatter is the experimental data. The lines are fitted results using the model listed in Table 9. Table 9 Suggested binding energy parameters of Mn 2p3/2 for Mn3-3xFe3xO4 x EB1/eVa FWHM1/eV EB2/eV FWHM2/eV EB3/eV FWHM3/eV Ratiob 0 641.8 2.4 640.7 1.8 2:0:1 0.188 642.1 2.4 641.2 1.6 640.7 1.6 1:0.04:0.52 0.375 642.1 2.4 641.2 1.6 640.7 1.6 1:0.08:0.54 0.75 642.1 2.4 641.1 1.6 640.5 1.7 1:0.20:0.60 0.833 642.3 2.4 641.2 1.6 640.6 1.6 1:0.24:0.62 0.909 642.1 2.2 641.2 1.6 640.5 1.8 1:0.28:0.64 0.968 642.1 2.2 641.2 1.6 640.3 1.6 1:0.31:0.66 1.034 642.2 2.2 641.2 1.8 640.5 1.6 1:0.36:0.68 1.111 642.1 2.2 641.2 1.6 640.5 1.6 1:0.42:0.71 1.765 642.4 1.8 641.2 1.6 639.8 1.6 1:2.5:1.75 641.2 1.8 639.8 1.5 0:2:1 2.000 a EB1, EB2, and EB3 are the binding energies of Mn3+ in octahedral site, Mn2+ in octahedral site, and Mn2+ in tetragonal site. FWHM1, FWHM2, and FWHM3 are the full width at the half maximum of the peaks corresponding to the binding energies of Mn3+ in octahedral site, Mn2+ in octahedral site, and Mn2+ in tetragonal site. b Fig.12 4 It is the ratio of the amount of Mn3+ or Mn2+ at the case of EB1, EB2, and EB3. XPS data of Fe 2p for the samples in hausmannite (a), spinel (b), and hematite (c) phases Conclusions Three solid solutions, hausmannite phase Mn3-3xFe3xO4 (0.00≤ x≤0.278), spinel phase Mn3-3xFe3xO4 (0.291≤x £0.667), and hematite phase Mn2-2xFe2xO3 (0.89≤x≤1.00), were synthesized at 1200 ° C followed by quenching into water. Between them there are two-phase regions. 57Fe Mössbauer spectra and XPS show that a formula of Mn 12+-x Fex3 + [Mnx2 + Fe 3+2x Mn 23+-3x]O4 can be used to describe the cations distribution of the hausmannite and spinel phases. 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