Synthesis of Highly Uniform and Compact Lithium ... - ACS Publications

Mar 27, 2017 - State Key Laboratory of Electronic Thin Film and Integrated Devices, ... cofired ceramics (LTCC) technology has become an important...
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Synthesis of Highly Uniform and Compact Lithium Zinc Ferrite Ceramics via an Efficient Low Temperature Approach Fang Xu,†,‡ Yulong Liao,*,†,‡ Dainan Zhang,‡ Tingchuan Zhou,‡ Jie Li,‡ Gongwen Gan,‡ and Huaiwu Zhang*,‡ †

Center for Applied Chemistry, University of Electronic Science and Technology of China, Chengdu 610054, China State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China

‡

S Supporting Information *

ABSTRACT: LiZn ferrite ceramics with high saturation magnetization (4πMs) and low ferromagnetic resonance line widths (ΔH) represent a very critical class of material for microwave ferrite devices. Many existing approaches emphasize promotion of the grain growth (average size is 10−50 μm) of ferrite ceramics to improve the gyromagnetic properties at relatively low sintering temperatures. This paper describes a new strategy for obtaining uniform and compact LiZn ferrite ceramics (average grains size is ∼2 μm) with enhanced magnetic performance by suppressing grain growth in great detail. The LiZn ferrites with a formula of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 were prepared by solid reaction routes with two new sintering strategies. Interestingly, results show that uniform, compact, and pure spinel ferrite ceramics were synthesized at a low temperature (∼850 °C) without obvious grain growth. We also find that a fast second sintering treatment (FSST) can further improve their gyromagnetic properties, such as higher 4πMs and lower ΔH. The two new strategies are facile and efficient for densification of LiZn ferrite ceramics via suppressing grain growth at low temperatures. The sintering strategy reported in this study also provides a referential experience for other ceramics, such as soft magnetism ferrite ceramics or dielectric ceramics.

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INTRODUCTION With the rise of solid state electronic circuit and microwave analog integrated circuit (MMIC) technology, phased array radar systems have been great changes. From the first generation passive phased arrays to the third generation phased arrays using MMIC, the functions and features of phased array radar systems have obtained vast improvement, such as multifunctions, miniaturization, and high frequency. However, the high frequency of devices often causes higher microwave loss, which leads to new challenges that some devices are no longer applicable for the phased array systems. For instance, phase shifters based on MEMS or semiconductors have higher microwave loss when the phase-shift angle exceeds 300° at high frequency.1,2 Fortunately, ferrite ceramics, a class of insulating magnetic oxides with high resistivity and appropriate permeability, are good candidates materials for high frequency (microwave) devices, such as phase shifters and circulators.3 Recently, spinel lithium−zinc ferrite ceramic has attracted a lot of attention in phased array radar applications due to their high saturation magnetization (4πMs) and low ferromagnetic resonance line widths (ΔH).4−6 To meet the miniaturization and integration requirements of devices, low temperature cofired ceramics (LTCC) technology has become an important method and has been widely applied in the microwave ceramics field. Inevitably, a low sintering temperature (below melting point of Ag, 960 °C) often leads to insufficiency of grain growth © XXXX American Chemical Society

and excessive pores between grains, which immensely increase microwave loss. To obtain LiZn ferrite ceramics with high 4πMs and low ΔH at low temperatures, adding proper additives to promote grain growth is very simple and effective. However, in this work, the results demonstrate that an inverse behavior (suppressing grain growth) could also be helpful to achieve ferrite materials with enhanced magnetic properties. Compared with the methods of preparing a fully dense ceramic by means of suppressing grain growth,7−10 we sinter the LiZn ferrites by using two new strategies, namely repeated two-step sintering (TSS) and fast second sintering treatment (FSST) in an O2 atmosphere. The methods are found facile but effective at obtaining densification of ferrite ceramics by suppressing grain growth. The results indicated that highly uniform and compact LiZn ferrite ceramics (average grain size is ∼2 μm) with superior magnetic properties were achieved by using TSS and FSST methods.

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EXPERIMENTAL SECTION

Materials and Methods. Polycrystalline LiZn ferrite ceramics (Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4) were prepared using a solid state method. First, raw materials of powders Li2CO3 (≥99%), ZnO (≥99%), TiO2 (≥99%), Fe2O3 (≥99.7%; Kelong,Chengdu, China), Received: January 13, 2017

A

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 1. (a) Two class sintering curves of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ferrite ceramics sintered at low temperatures with the same heating rate and holding time, 4 h. Upper left: two-step sintering (TSS) including a high and transient temperature at 950 °C (corresponding to point B) and a lower and hold temperature at 850 °C (corresponding to point C). Left lower: two-step sintering/fast second sintering treatment (TSS/FSST). Upper right: normal sintering (NS) for 4 h at 900 °C. Right lower: normal sintering/fast second sintering treatment (NS/FSST). (b) XRD patterns of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ceramics of LTG sintered at different curves (left) and zoom in on main peaks (311) (right).

Figure 2. Rietveld refinement of LiZnMnTi ferrite ceramics with different sintering methods [(a) NS, (b) TSS, (c) NS-FSST, (d) TSS-FSST]. The differences lines [observed value (black points) − calculated value (red lines)] are displayed in dark cyan. The positions of the Bragg scattering are expressed by a green vertical line. binder and pressed into toroidal samples (18 × 8 mm) with ∼10 MPa intensity of pressure. So far, the ferrite samples were obtained. To achieve uniform and compact ferrite ceramics, new thermal treatment strategies are designed to sinter the ferrite samples. As shown on the left side of Figure 1a, the samples were sintered by using a repeated two-step sintering method, named TSS (every isothermal sinter time is 80 min, three repetitions, the highest and lowest temperature of two-step sintering are 950 and 850 °C, respectively). For further enhancment of densification and magnetic properties of ceramics, we carry out fast second sintering treatment for samples that

and Mn3O4 (≥98.5%, Aladdin, Shanghai, China) were weighed. Deionized water was added and averagely mixed in a ball mill (Nanjing Machine Factory, Nanjing, China) at a rotation speed of 250 rpm for 4 h with steel balls as milling media. Next, these powders were calcined at 800 and 950 °C in an O2 atmosphere for 2 h. According to mass ratio 1:1, the ferrite powders presintered at 800 and 950 °C were mixed. The ceramics powders (50% 800 °C and 50% 950 °C presintered powders) and Bi2O3 (≥99%, Kelong, Chengdu, China) powders (the mass fraction 0.25 wt %) were mixed for 6 h. After drying again, the mixtures were granulated with 15.0 wt % PVA as a B

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. (a) Changes in relationship between cell parameters of the Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ceramics and sintering methods (SS represents standard samples Li0.435Zn0.195Fe2.34O4 from JCPDS database). (b) A diagrammatic model of ionic substitutions in Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ceramics.

Figure 4. SEM images of the samples (low temperature group) sintered at different sintering curves: (a) samples sintered at 900 °C based on NS, (b) zoom in of red area in a, (c) sintered at 850 °C with instantaneously highest temperature 950 °C based on TSS, (d) zoom in of red area in c. have been sintered, named FSST (heating up to 900 °C at a rate of 5 °C/min and keeping the temperature for 1 h). By contrast, we conduct common sintering experiments, named normal sintering (NS) and normal sintering−fast second sintering treatment (NS-FSST), respectively (as are shown in right part of Figure 1a). The heating rate, holding time, and sintering atmosphere are the same. All the sets of experiments, named the low temperature group (LTG), possess low sintering temperatures with an average of 900 °C. Additionally, in order to investigate the influence of sintering temperature on grain size and densification, we carry out another experiment (high temperature group (HTG) with an average of 930 °C), which only increases sintering temperature (increase by 30 °C) in the insulation stage (as were shown in BC and EF stages in Figure 1a).

Experimental Measurements. Sample volume densities were measured by the Archimedes method in distilled water. The weighing mass of samples in the air is m0. After filling the gap in the samples with distilled water, the mass was weighed again, marked m1. Next, the samples were immersed in distilled water and their mass weighed, named m2. The density of samples can be calculated by the formula:

ρ=

m0 ρ0 m1 − m2

(1)

where ρ0 is the density of distilled water. After that, the density of the Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ferrite sintered at 1050 °C (as a theoretical density) was divided by the measure densities to obtain relative densities of ferrite ceramics sintered at different temperatures C

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry with various sintering curves. Diffraction peaks were measured by using XRD (Cu Kα radiation, Rigaku, Japan). The results of XRD refinement were obtained from Rietica software. The cross profile microstructures of the ceramics were investigated using a scanning electron microscope (SEM, JSM-6490, and JEOL). The element type and content were obtained with an energy dispersive spectrometer (EDS, JSM-6490, and JEOL). The change of mass and heat of the sample were investigated using a simultaneous thermal analyzer (TGA/DSC 1, Mettler-Toledo, and Switzerland). The ferromagnetic resonance line widths (ΔH) of the samples with a diameter of about 1.0 mm were measured in the TE106 perturbation method cavity at 9.5 GHz. The magnetic hysteresis loop was measured using a vibrating sample magnetometer (VSM) with a ±5000 Oe direct current magnetic field. And all the tests were carried out under room temperature.

constant, reliability factors (Rp, Rwp, and Rexp), coordinates, and the occupied ionic ratio of metal ions of the ferrites are listed in Tables S1 and S2 (see the Supporting Information).5 Results indicate that the calculated curves are well matched with experimental data. The positions of Bragg scattering are nearly coincident with the spinel phase. It proves that the pure spinel structure LiZn ferrites were obtained. Figure 3a shows the changes of lattice constant (a) and unit cell volume (V) of standard Li0.435Zn0.195Fe2.37O4 ferrites (from JCPDS database) and the ferrite ceramics calculated from XRD refinement data. Apparently, the effect of the sintering process on the lattice constant is weak. The TSS and FSST methods can faintly increase the lattice constant (from 8.3685 to 8.3716 Å). This indicates that the main influence on crystal structure is raw material formula rather than sintering method. The phenomenon where the lattice co nstant of the Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 is larger than the lattice constant of Li0.435Zn0.195Fe2.37O4 ceramic (8.3445 Å) can be attributed to substitution of big ions (ionic radius is larger than Fe3+).12 According to the report of Shannon,13 the effective ion radii of metal ions in Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ceramics were obtained (see the Table S1). Due to substitution of Mn2+ (0.66 Å), Mn3+ (0.58 Å), and Ti4+ (0.605 Å), the equivalent radius of the Fe3+ (in tetrahedron or octahedron) increased, which could lead to an increase of lattice constant and enlargement of unit cell volume. This process was schematically shown as Figure 3b. In addition, the XRD diffraction peaks of HTG are displayed in Figure S1 (see the Supporting Information). It can be seen that the spinel structure LiZnMnTi ferrites were synthesized. Microstructure and Sintering Theory. Fault surface images of the LiZnMnTi ferrite ceramics are shown in Figure 4. Figure 4a and c indicate SEM images of samples by NS and TSS thermal treatment strategies, respectively (NS, sintering samples at O2 atmosphere based on treatment method of upper right in Figure 1a; TSS, according to method on the top left of Figure 1a, sintering ferrite ceramics in an O2 atmosphere). And the SEM images of the ferrites treated by fast second sintering are shown in Figure S2 (see the Supporting Information). It is apparent that there is partly abnormal grain growth (AGG) in Figure 4a and Figure S2a. This proves that the repeated twostep sintering strategy is very effective for controlling grain growth. To further analyze the theory of abnormal growth, the elements and content of abnormal grains and small grains are investigated in detail. Figure 5 shows the EDS results of the ferrites sintered by NS strategy (a, big grains) and TSS strategy (b, small grains). For the Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 ferrite doped with 0.25 wt % Bi2O3, there are five elements that can be clearly detected (Zn, Mn, Ti, Fe, and O) in the grains. The proportions of elements in the ferrites are displayed in Table S3 (Supporting Information). The Li content cannot be detected because Li is a light element. However, the element Bi (volume of addition is 0.25 wt %) is not shown in Figure 5. This can be explained by Bi2O3 liquid formation, and the Bi3+ does not substitute Fe3+ in B sites. The result is consistent with XRD refinement results (i.e., the pure LiZn spinel structures were obtained at a low sintering temperature, and Bi2O3 is the sintering aid). In the process of sintering, when the sintering temperature is ∼850 °C (Bi2O3 starts to soften and viscose flow of Bi2O3 is slow), the powders only move and diffuse (i.e., rearrangement). A theoretical model of grain change during the liquid phase sintering is proposed as shown in Figure 6.14 In the initial state (corresponding to point A of Figure 1a), the

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RESULTS AND DISCUSSIONS Structure Analysis by XRD. Figure 1b shows X-ray diffraction patterns of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 (LiZ-

Figure 5. Energy dispersive X-ray spectroscopy of the ferrites sintered by different sintering strategies: (a) NS sintering strategy, (b) TSS sintering strategy.

nMnTi) ceramics (low temperature group) and a stick pattern of Li0.435Zn0.195Fe2.37O4. Though the sintering temperature is low (∼900 °C), the patterns of the ceramics have similar peaks with a standard X-ray diffraction powder pattern in the JCPDS database (i.e., JCPDS −37−1471). Besides the diffraction peaks (corresponding to (111), (220), (311), (222), (400), (422), (511), (440), (620), (533), (622), and (444) of Li0.435Zn0.195Fe2.37O4), there are no other peaks that can be clearly detected. Compared with the stick pattern of Li0.435Zn0.195Fe2.37O4, the diffraction peaks of the prepared ferrites systematically shift to a low diffraction angle, which indicates that the lattice constant and unit cell volume get increased.11 To further verify the phase structure and cation distribution of the Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4, Rietveld refinement of the XRD pattern was carried out. Figure 2 shows the results of Rietveld refinement of LiZnMnTi ferrite ceramics with different sintering methods. The calculated lattice D

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 6. A theoretical model and proposed process during the liquid phase sintering: (a) blend of crystalline grains and Bi2O3 powders at low temperature, (b) rearrangement of grains when temperature exceeds melting point of Bi2O3, (c) part grain growth based on NS, (d) formation of uniform and compact structure by two-step sintering.

1a). At this stage, the activity of the reactant and changes of sintering temperature are vital for grain growth or densification. Point D represents the time that the ferrites start to naturally cool (from 600 °C to indoor temperature). Comparatively speaking, the powders presintered at 950 °C are hard for growth without sintering aids at a 900 °C sintering temperature. This can be explained by activation energy.15 When the presintering temperature exceeds 800 °C (reaches 950 °C), compound powders can further react and the activation energy can enhance (i.e., higher energy can trigger grain growth again). Figure S3 (see the Supporting Information) shows the TGA/ DSC of compounds presintered at 950 °C. It is apparent that there is no peak in heat flow curves. This indicates that no obvious solid-phase reaction happened when the temperature changed from room temperature to 1000 °C. This phenomenon can be explained by the reduction in activity of the compounds (have been presintered). And the compounds could be hard to react without sintering aids when sintered at ∼900 °C. However, the powders presintered at 800 °C work easily for second growth of grains when sintered at higher temperatures or sintering aids are added in sintering process.16 Thus, to keep the high activity of powders and prevent abnormal second grain growth, we use the mixing powders as final sintered powders. Due to the different sintering process, abnormal grain growths happened as shown in Figure 4a. By contrast, the sintering strategy (TSS) at high temperature (∼950 °C) can achieve a temporary and compact structure, and lower temperature (∼850 °C), enhancing densification, can effectively avoid abnormal growth of crystal particles.17 For the powders presintered at 950 °C, high activation energy makes grain growth hard. This can effectively control abnormal grains in the sintering process. On the contrary, the powders with a 800 °C presintering temperature can diffuse, grow, and achieve a temporary and compact structure when Bi2O3 becomes a liquid phase. This process can be described by Figure 6a,b, and d. The SEM images of grains are shown in Figure 4c and d. Figure S2 represents SEM images of fast second sintering treatment (FSST) of NS and TSS. No distinct change can be

Figure 7. (a) Variation of specific saturation magnetization (σs) of different sintering ferrite ceramics of LTG. (b) Calculated saturation magnetization (Ms) based on σs and testing density.

reactants including small grains (less than 1 μm) and solid additives Bi2O3 stay apart, and there was a relatively large space between those particles, see Figure 6a. With the temperature increasing, Bi2O3 powders start to soften and then transform into liquid (corresponding to point C of Figure 1a, ∼850 °C). In the meantime, rearrangement and dissolution happen, and pores start to be filled. This process can be briefly described as Figure 6b. When the temperature further increased, there were two different mechanisms (i.e., grain growth and densification) at the final sintering stage (corresponding to BC stage of Figure E

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 8. Ferromagnetic resonance (FMR) line width fitted spectra (Lorentzian Fit) of ferrite ceramics with different sintering methods: (a−d) samples of low temperature group (LTG), (e−h) samples of high temperature group (HTG).

Supporting Information). Apparently, sintering methods have a rare influence on grain growth when the sintering temperature reaches ∼930 °C. It indicates that the sintering kinetics are adequate for the grain growth of powders doped with 0.25 wt % Bi2O3 when the sintering temperature reaches 930 °C.

observed from the SEM images after FSST. This can be explained by insufficient sintering kinetics (short hold time and reduction of powder activity after first sintering, corresponding to the EF stage of Figure 1a). SEM images of samples sintered at higher temperature are displayed in Figure S4 (see the F

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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ceramics are displayed in Figure 8 (Figure S5 shows the fitted spectra of Gauss Fit, see the Supporting Information). The FMR line widths (ΔH) and fitting error (R-squared) can be calculated from the charts in Figure 8 and Figure S5. The ΔH value of the samples based on Lorentz fit and the R-squared of Lorentz and Gauss fitting are summarized in Figure 9. Obviously, the R-squared values of entire Lorentz fitting points are very close to 1.0 (>0.992), which is a better fitting model than Gauss (R-squared approximately is 0.990). The result is consistent with previous relevant fitting reports.19 As was described by Srivastava et al. in polycrystalline garnets,20 the FMR line widths can be expressed as ⎛ H2 ⎞ ΔH = ΔHint + 2.07⎜ a ⎟ + 1.5(4πMs)P ⎝ 4πMs ⎠ Figure 9. FMR values of samples (LTG, solid line; HTG, imaginary line) based on Lorentzian fit and R-squared of Lorentzian and Gaussian fitting (in the inset, the circle is Lorentzian fit and the star is Gaussian fit).

(2)

where ΔHint is the intrinsic line widths, the second part of the equation is anisotropic line widths, and the last part is attributed to the porosity of grains. As previously discussed above in Figure 7, the value of Ms is greater than 310. Thus, ΔH mainly depends on the last part, 1.5(4πMs)P. When the sintering temperature reaches ∼930 °C, the effect of sintering methods on grain size and porosity is very little (as is shown in Figure S4, the average grain size is nearly the same and porosity is small). Therefore, according to eq 2, the FMR has little fluctuation (see dotted portion of Figure 9, the values are ∼188 Oe). However, for samples sintered at lower temperature, ΔH has high fluctuation (from ∼205 Oe to ∼180 Oe). This can be explained by the change of 4πMs and P. On the basis of the sintering curve in Figure 1a, a few abnormal crystal grains (see Figure 4a) appeared in the samples sintered at ∼900 °C. This could lead to a large hole between nonuniform grains. However, for two-step sintering (TSS), uniform and compact grains have been obtained, which is consistent with the report by Chen et al.7,10 Meanwhile, the 4πMs of the ferrites prepared by NS is larger than that of TSS. Thus, the uniform and compact grains have lower FMR line widths. As illustrated in Figures 8 and 9, FSST can further reduce FMR line widths of the LiZn ferrites. This could be explained by rearrangement of crystal particles and reduction of porosity. Figure 7 indicates that FSST could distinctly improve the Ms value of the ferrite ceramics. According to eq 2, the FMR should be incremental when P is unchanged. The phenomenon that FSST further reduces FMR indicates that the porosity P of samples is lessened, which is consistent with SEM results. As was described by Guillaume et al., the densification of samples at the final stage of sintering governed by lattice diffusion or boundary diffusion and its mechanism can vary with pore size change.17,21 For the fine grains (in Figure 4 and Figure S4), the contribution of grain boundary diffusion to densification is dominating.17 However, when the temperature reached a certain value, the grain growth and lattice diffusion could not be ignored (see Figure S4). The grain growth along with lattice diffusion not only improves the compactness of samples but also results in performance deterioration (inner porosity increases). The densities and relative density fluctuations of ferrite ceramics are shown in Figure 10. For samples sintered at 900 °C, FSST is beneficial to the increase of density. Meanwhile, suppressing abnormal growth of crystalline grain (using TSS method) also can improve density. However, when sintering temperature increases to 930 °C, the major contribution to grain growth and densification changes from sintering methods to sintering temperature. In addition, the

Figure 10. Relationships between densities and relative densities of ferrite ceramics sintered at different temperatures and sintering curves (solid line represents samples of LTG; imaginary line represents samples of HTG; spheroidal points are densities; square points are relative densities).

Magnetic Performance. Figure 7 shows specific saturation magnetization (σs, emu/g) and calculated saturation magnetization (Ms, kA/m) of the LiZn ferrites sintered at ∼900 °C (see Figure 1, named NS, NS-FSST, TSS, and TSS-FSST, respectively). As is shown in Figure 7b, the Ms of samples exceeds 310. This indicates that appropriate ion substitution can effectively offset a decrease of Ms, when the sintering temperature is low and the grain size is small. The σs or Ms of NS is larger than that of the samples sintered by TSS. This phenomenon can be attributed to different sintering temperatures (NS, 900 °C for 4 h; TSS, 850 °C for 3 × 80 min). When the formula and additives of the ferrites are the same, a higher sintering temperature often leads to higher saturation magnetization.18 In addition, the strategy of fast second sintering treatment (FSST) can obviously further enhance saturation magnetization (maximum is ∼351.54 kA/m). This can also be attributed to the reduction of defects and grain densification. In short, the results suggest that high saturation magnetization ferrite ceramics with small grains were prepared at a low sintering temperature with appropriate sintering methods. Fitted spectra (Lorentz Fit) of ferromagnetic resonance (FMR) line widths of the Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 G

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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effect of FSST on densities is weak; which could be attributed to the insufficient sintering time (only keep high temperature for 1 h). In summary, we have discussed two new sintering strategies, namely TSS and FSST, to prepare LiZn ferrites with improved gyromagnetic properties under low sintering temperatures.

CONCLUSIONS A uniform and compact crystal structure of LiZn ferrite ceramics with a lower ΔH (∼180 Oe) and high 4πMs (>350 kA/m) can be obtained at low sintering temperatures with a repeated two-step sintering and fast second sintering treatment (TSS-FSST). The introduction of a little additive Bi2O3 can effectively reduce the sintering temperature and has no detectable effect on the spinel phase formation. SEM results show that an average grain size of uniform and compact grains is still small (∼2 μm). Compared with normal sintering (NS), the TSS can effectively suppress abnormal grain growth of highactivity grains and reduce FMR line widths, but it also results in a decrease of Ms. Meanwhile, FSST can further decreases FMR line widths and enhance 4πMs. To sum up, TSS is beneficial for controlling abnormal grain growth and improving magnetic properties. And FSST with suitable sintering temperature, sintering atmosphere, and holding time is promising to boosting grain growth (no abnormal growth) and improving magnetic performance. This study is expected to be a referential experience for other ceramics materials, such as soft magnetism ferrite ceramics or dielectric ceramics. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00111. Listings of rietveld refinement results, effective ionic radius and coordinates of metal ions, proportions of elements, XRD diffraction patterns of HTG, SEM images of the ferrite ceramics of HTG and LTG, DTA/TGA curve and ferromagnetic resonance (FMR) line widths fitted spectra (PDF)

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REFERENCES

(1) Brookner, E. Phased arrays and radars - Past, present and future. Microwave J. 2006, 49 (1), 24−46. (2) Boles, T.; Carlson, D. J.; Weigand, C. MMIC based phased array radar T/R modules. In COMCAS 2011: IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems; IEEE: New York, 2010; pp 1−4. (3) Harris, V. G. Modern Microwave Ferrites. IEEE Trans. Magn. 2012, 48 (3), 1075−1104. (4) Liao, Y.; Xu, F.; Zhang, D.; Zhou, T.; Wang, Q.; Wang, X.; Jia, L.; Li, J.; Su, H.; Zhong, Z.; Zhang, H. Low Temperature Firing of Li0.43Zn0.27Ti0.13Fe2.17O4 Ferrites with Enhanced Magnetic Properties. J. Am. Ceram. Soc. 2015, 98 (8), 2556−2560. (5) Zhou, T.; Zhang, D.; Jia, L.; Bai, F.; Jin, L.; Liao, Y.; Wen, T.; Liu, C.; Su, H.; Jia, N.; Zheng, Z.; Harris, V. G.; Zhang, H.; Zhong, Z. Effect of NiZn Ferrite Nanoparticles upon the Structure and Magnetic and Gyromagnetic Properties of Low-Temperature Processed LiZnTi Ferrites. J. Phys. Chem. C 2015, 119 (23), 13207−13214. (6) Zhou, D.; Guo, D.; Li, W. B.; Pang, L. X.; Yao, X.; Wang, D. W.; Reaney, I. M. Novel temperature stable high-epsilon(r) microwave dielectrics in the Bi2O3-TiO2-V2O5 system. J. Mater. Chem. C 2016, 4 (23), 5357−5362. (7) Chen, I. W.; Wang, X. H. Sintering dense nanocrystalline ceramics without final-stage grain growth. Nature 2000, 404 (6774), 168−171. (8) Ji, W.; Rehman, S. S.; Wang, W.; Wang, H.; Wang, Y.; Zhang, J.; Zhang, F.; Fu, Z. Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism. Sci. Rep. 2015, 5, 15827. (9) Lee, M.-G.; Chung, S.-Y.; Kang, S.-J. L. Boundary facetingdependent densification in a BaTiO3 model system. Acta Mater. 2011, 59 (2), 692−698. (10) Wang, X.-H.; Chen, P.-L.; Chen, I. W. Two-Step Sintering of Ceramics with Constant Grain-Size, I. Y2O3. J. Am. Ceram. Soc. 2006, 89 (2), 431−437. (11) Guo, J.; Randall, C. A.; Zhang, G.; Zhou, D.; Chen, Y.; Wang, H. Synthesis, structure, and characterization of new low-firing microwave dielectric ceramics: (Ca1?3xBi2x?x)MoO4. J. Mater. Chem. C 2014, 2 (35), 7364. (12) Sabine, P. A. Ferrian Chlorospinel from Carneal, Co. Antrim. Mineral. Mag. 1968, 36 (283), 948−954. (13) Shannon, R. D. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32 (5), 751−767. (14) German, R. M.; Suri, P.; Park, S. J. Review: liquid phase sintering. J. Mater. Sci. 2009, 44 (1), 1−39. (15) Zhou, T. C.; Zhang, H. W.; Jia, L. J.; Liao, Y. L.; Zhong, Z. Y.; Bai, F. M.; Su, H.; Li, J.; Jin, L. C.; Liu, C. Enhanced ferromagnetic properties of low temperature sintering LiZnTi ferrites with Li2OB2O3-SiO2-CaO-Al2O3 glass addition. J. Alloys Compd. 2015, 620, 421−426. (16) Liu, C.; Lan, Z.; Jiang, X.; Yu, Z.; Sun, K.; Li, L.; Liu, P. Effects of sintering temperature and Bi2O3 content on microstructure and magnetic properties of LiZn ferrites. J. Magn. Magn. Mater. 2008, 320 (7), 1335−1339. (17) Kang, S. J. L.; Jung, Y. I. Sintering kinetics at final stage sintering: model calculation and map construction. Acta Mater. 2004, 52 (15), 4573−4578. (18) Akhtar, M. N.; Bakar Sulong, A.; Khan, M. A.; Ahmad, M.; Murtaza, G.; Raza, M. R.; Raza, R.; Saleem, M.; Kashif, M. Structural and magnetic properties of yttrium iron garnet (YIG) and yttrium aluminum iron garnet (YAIG) nanoferrites prepared by microemulsion method. J. Magn. Magn. Mater. 2016, 401, 425−431. (19) Liao, Y.; Xu, F.; Zhang, D.; Li, J.; Zhou, T.; Wang, X.; Jia, L.; Li, Y.; Zhang, H. Magnetic properties and microstructure of low temperature sintered LiZnMnTi ferrites doped with Li2CO3-B2O3Bi2O3-SiO2 glasses. J. Alloys Compd. 2016, 680, 729−734.

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*Tel.: +86-28-83201440. Fax: +86-28-83202556. E-mail: [email protected]. *Tel.: +86-28-83207656. Fax: +86-28-83202556. E-mail: [email protected]. ORCID

Yulong Liao: 0000-0003-3761-7170 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Key Research and Development Plan (No. 2016YFA0300801); National Natural Science Foundation of China under No. 51502033, No. 61571079, No. 61131005, No. 61671118, and No. 51572042; National Basic Research Program of China under Grant No. 2012CB933104; 111 Project No. B13042; and International Cooperation Projects under Grant No. 2015DFR50870 and No. 2012DFR10730. H

DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry (20) Srivastava, A. K.; Patni, M. J. Ferromagnetic resonance of gadolinium doped calcium vanadium garnets. J. Appl. Phys. 1997, 81 (4), 1863−1867. (21) Bernard-Granger, G.; Monchalin, N.; Guizard, C. Sintering of ceramic powders: Determination of the densification and grain growth mechanisms from the “grain size/relative density” trajectory. Scr. Mater. 2007, 57 (2), 137−140.

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DOI: 10.1021/acs.inorgchem.7b00111 Inorg. Chem. XXXX, XXX, XXX−XXX