- Email: [email protected]
SiO2 Synthesized by Sol-Gel Method
JOURNAL OF RARE EARTHS Vol. 2 4 , Spec. Issue, Dec. 2006, p . 75
Structure of BaLa, Fe12- O19/Si02Synthesized by Sol-Gel Method
(*a%),
Han Zhidong %) * , Dong Limin Wu Ze (K *+), Zhang Xianyou ($EB.&) ( College of Materials Science and Engineering, Harbin University .f Science and Technology , Harbin 150040, China ) (#I&
Abstract: M-type hexaferrites BaLa,Fel2- ,OI9 powders were synthesized by sol-gel method in the presence of SiOz nanoparticles. The X-ray diffraction patterns of BaLa,Felz - 2019/Si02calcined at 1000 “c manifest that all the species have hexseems uniform at difagonal crystal structure and no diffraction peaks of SiO2 are found. The structure of BaLa,FeIZ - z019 ferent La doping dosage. Fourier transform infrared (FTIR) proves the co-existence of SiO2 and ferrites in the products. The addition of SiOz nanoparticles promotes the formation of more homogeneous and finer ferrite crystal, as proved by scanning electron microscopy (SEM) . Compared with BaLa0,SFell.SO19 powders synthesized without SiOz nanoparticles , those synthesized in the presence of SiOz nanoparticles present in smaller powder size and similar structure.
Key words : sol-gel ; hexaferrites ; nanoparticles ; SiOz; La substitution ; rare earths Article ID: 1002 - 0721(2006) - 0075 - 03 Document code: A CLC number: 0614
Hexagonal ferrites have been widely used as permanent magnets and show promising properties in microwave absorption and magneto-optic or perpendicular recording media. M-type (MFe,,O,,) (M: Ba, Sr) ferrites were studied mostly“ -31 . The intrinsic magnetic properties of M-type ferrites can be improved by partial substitution of Ba or Fe, or both‘41. For example, it has recently been shown that La-Co substituted SrFe12 019ferrites have improved magnetic proper tie^'^'. A rare earth ion may contribute to a change of new magnetic interactions, thus improve the magnetic proper tie^'^"] . Many methods, such as sol-gel method, co-precipitation method and hydrothermal method, have been developed to synthesize ferrites“’ . Among them, sol-gel method is widely used due to its simple process, impurity free and ultra fine particles. Recently, study on ferrites/Si02 nanoparticles has attracted much attention‘9”01. The paper aims at synthesizing La substituted BaM hexaferrites by sol-gel method in the presence of SiO, nanoparticles . Effects of SiOa nanoparticles on the structure and particle size of hexaferrites were investigated by XRD , l T I R and SEM .
1 Experimental 1.1 Synthesis of ferrites M-type La substituted Ba hexaferrites were syn-
*
thesized by sol-gel method. Stoichiometric amount of metal nitrates was dissolved completely in deionized water. Citric acid ( C A ) was also dissolved in deionized water. Si02 nanoparticles were put into deionized water and the solution was treated by ultrasonic for 0.5 h . All solutions as prepared were mixed together to form a homogeneous transparent aqueous solution and also treated by ultrasonic for 0. 5 h . Ammonium hydroxide (aqueous solution) was added to the mixed solution and the pH of the solution was adjusted to about 7 . After that,. the mixed solution was kept in room temperature for 2 h and then heated in water bath to evaporate water. Wet gels of high viscosity were obtained and put in an oven at 120 T to form dry gel. The dry gels were presintered at 450 T to form precursors and then annealed at 1000 “c to form the M-type Ba hexaferrites.
1.2 Characterization The M-type La substituted Ba hexaferrites as prepared were characterized by X-ray diffraction (XRD) , Fourier transform infrared (FTIR) and scanning electron microscope (SEM) . XRD patterns were recorded by X-ray diffractometer Y500 ( C h i n a ) . SEM micrograph was taken by Sirion 20 (Philip). FTIR spectra were obtained by Nicolet MAGNA-760.
2 Results and Discussion
Receiveddate: 2006-07-01; reviseddate: 2006-09-06 Foundation item: Project supported by Fund for Harbin Young Scholars (2005AFQ X J 0 31) Biography: Han Zhidong (1974 - ) , Female, Ph. D . Corresponding author (E-mail : harbinzhidonghan@yahoo. corn. cn , )
JOUrWAL OF RARE EARTHS, Vol. 24, Spec. Issue, Dec . 2006
76
2.1 XRD results Fig. 1 shows the XRD patterns of BaLa,Felz-,019 synthesized in the presence of S O z . As can be seen in Fig. 1, all samples present typical hexagonal structure. Thanks to the La substitution, the crystal constant changes"] . No diffraction peaks of SiO, can be observed, revealing the amorphous structure of S O z . The structure of BaLa,Feln-, 0 1 9 is not influenced by the addition of SiO, during synthesizing process.
2 . 2 FTIR results Fig. 2 shows the FTIR spectra of BaFelz 0 1 9 , BaL%.5Fell.5019and BaL%,, Fell., OI9 synthesized in the presence of S O z . It can be seen in Fig. 2 that BaL%.5Fell.501e and BaL%,5Fell.5 Ol9/SiOZshow similar bands at about 400 580 cm-', suggesting their similar structure. BaLq., Fell,, OI9/SiO2 also shows bands at about 1010 and 1040 cm-I , which can be interpreted as stretching of Si - 0 - Si and prove the existence of Si02 . Compared with BaFelz OI9 , the wide
-
Fig.3
SEM micrograph of B a L ~ . 5 F e l l . s 0(1a9) and BaLaos Fell .5019/Si02( b)
-
'
bands about 550 570 cm- , interpreted as the lattice vibration modes of M - 0, are found to move to lower frequency for La substituted BaM, indicating that the distribution of ions in BaFel2OI9was altered by La doping. Such results consist with those of XRD .
2.3 SEM results
P
Fig. 3 compares the morphological structure of It can be BaLq.5Fell,s019 and BaLao.5Fe,l,5019/Si02. seen in Fig.3 that the particle size of BaL~.5Fell.5019/ SiO, are finer and more homogeneous.
40 2 O/(?)
Fig. 1
XRD patterns of BaLa,Fe12_,019synthesized in the presence of SiOl
1
.
I
'
I
'
I
-
I
'
I
'
I
.
I
4o0O36oorxx)25oomlsoolmsoo
Wavenurnber/cm.'
Fig.2
FTIR spectra of BaM and La substituted BaM ferrites with and without SiOz
3 Conclusion The effects of SiO, nanoparticles on the structure and particle size of M-type La substituted BaM hexaferrites were investigated. As learned from the results of XRD, FTIR and SEM, the structure of M-type La substituted BaM hexaferrites is not influenced with the presence of SiO, nanoparticles during synthesizing process. The more important is that SiOz nanoparticles promote the formation of finer or more homogeneous particles whose size is about several hundred nanometers, much smaller than that synthesized without SiO, nanoparticles .
References : [ 1] Nie Y , He H H I Feng Z K , et a1 .
Microwave charac-
Han 2 D et al . Structure of BaLa.FeI2 - p 0 1 9 / S i 0 1
terization of ( Co ,Zn)2W barium hexagonal ferrite particles [ J ] . J . Magn. and Magn. Mater. , 2006, 33(2):
423. [2] Meshram M R , Agrawal Nawal K , Bharoti Sinha, et al . Characterization of M-type barium hexagonal ferrite-based wide band microwave absorber [ J 3. J . Magn. and Magn. Mater., 2004, 271: 207. [3] Yoshida S , Sato M , Sugawara E , et a1 Permeability and electromagnetic-interference characteristics of Fe-SiA1 alloy flakes-polymer composite [J] . J . Appl. Phys . ,
.
1999, 85(8): 4636. [4] Robinson T M . Polycrystalline hexafemtes for millimetre wave applications [ J ] . Mater. Res. Bull. , 1990, 25: 1401. [5] Mocuta H , Lechevallier L, Le Breton J M , et al. Structural and magnetic properties of hydrothermally synthesised Sr, - Nd,FelzOI9 hexagonal ferrites [ J 1 . J . Alloys and Comp . , 2004, 364: 48. [6] Ahmed M A , Ateia E, Salah L M , et al. Structural
77
and electrical studies on La3' substituted Ni-Zn ferrites [J]. Mater. Chem. and Phys., 2005, 92: 310. 71 Guo Ruiqian, Li Honggui , Sun Peimei , et a1 , Synthesis and characterization of rare earth La substituted Mtype hexagonal barium ferrite ultrafine powders [ J ] . Chinese J . Rare Metals, 2001, 25(2) : 86. 81 Peelamedu Ramesh D , Roy Rustum, Agawal Dinesh . Anisothermal reaction synthesis of garnets, femtes and spinels in microwave field [ J ] . Mater. Res. Bull. ,
2001, 36: 2723. [9] Vestal Christy R , Zhang Z John.
Synthesis and magnetic characterization of Mn and Co spinel ferrite-silica nanoparticles with tunable magnetic core [ J ] . Nano Letters, 2003, 3(12): 1739. [ 103 Anna Comas, Casula Maria F , Ennas Guido, et a1 . Xray absorption spectroscopy study of FeCo-SOz nanocomposites prepared by the sol-gel method [ J ] . J . Phys. Chem. B , 2003, 107: 30.
Structure of BaLa, Fe12- O19/Si02Synthesized by Sol-Gel Method
(*a%),
Han Zhidong %) * , Dong Limin Wu Ze (K *+), Zhang Xianyou ($EB.&) ( College of Materials Science and Engineering, Harbin University .f Science and Technology , Harbin 150040, China ) (#I&
Abstract: M-type hexaferrites BaLa,Fel2- ,OI9 powders were synthesized by sol-gel method in the presence of SiOz nanoparticles. The X-ray diffraction patterns of BaLa,Felz - 2019/Si02calcined at 1000 “c manifest that all the species have hexseems uniform at difagonal crystal structure and no diffraction peaks of SiO2 are found. The structure of BaLa,FeIZ - z019 ferent La doping dosage. Fourier transform infrared (FTIR) proves the co-existence of SiO2 and ferrites in the products. The addition of SiOz nanoparticles promotes the formation of more homogeneous and finer ferrite crystal, as proved by scanning electron microscopy (SEM) . Compared with BaLa0,SFell.SO19 powders synthesized without SiOz nanoparticles , those synthesized in the presence of SiOz nanoparticles present in smaller powder size and similar structure.
Key words : sol-gel ; hexaferrites ; nanoparticles ; SiOz; La substitution ; rare earths Article ID: 1002 - 0721(2006) - 0075 - 03 Document code: A CLC number: 0614
Hexagonal ferrites have been widely used as permanent magnets and show promising properties in microwave absorption and magneto-optic or perpendicular recording media. M-type (MFe,,O,,) (M: Ba, Sr) ferrites were studied mostly“ -31 . The intrinsic magnetic properties of M-type ferrites can be improved by partial substitution of Ba or Fe, or both‘41. For example, it has recently been shown that La-Co substituted SrFe12 019ferrites have improved magnetic proper tie^'^'. A rare earth ion may contribute to a change of new magnetic interactions, thus improve the magnetic proper tie^'^"] . Many methods, such as sol-gel method, co-precipitation method and hydrothermal method, have been developed to synthesize ferrites“’ . Among them, sol-gel method is widely used due to its simple process, impurity free and ultra fine particles. Recently, study on ferrites/Si02 nanoparticles has attracted much attention‘9”01. The paper aims at synthesizing La substituted BaM hexaferrites by sol-gel method in the presence of SiO, nanoparticles . Effects of SiOa nanoparticles on the structure and particle size of hexaferrites were investigated by XRD , l T I R and SEM .
1 Experimental 1.1 Synthesis of ferrites M-type La substituted Ba hexaferrites were syn-
*
thesized by sol-gel method. Stoichiometric amount of metal nitrates was dissolved completely in deionized water. Citric acid ( C A ) was also dissolved in deionized water. Si02 nanoparticles were put into deionized water and the solution was treated by ultrasonic for 0.5 h . All solutions as prepared were mixed together to form a homogeneous transparent aqueous solution and also treated by ultrasonic for 0. 5 h . Ammonium hydroxide (aqueous solution) was added to the mixed solution and the pH of the solution was adjusted to about 7 . After that,. the mixed solution was kept in room temperature for 2 h and then heated in water bath to evaporate water. Wet gels of high viscosity were obtained and put in an oven at 120 T to form dry gel. The dry gels were presintered at 450 T to form precursors and then annealed at 1000 “c to form the M-type Ba hexaferrites.
1.2 Characterization The M-type La substituted Ba hexaferrites as prepared were characterized by X-ray diffraction (XRD) , Fourier transform infrared (FTIR) and scanning electron microscope (SEM) . XRD patterns were recorded by X-ray diffractometer Y500 ( C h i n a ) . SEM micrograph was taken by Sirion 20 (Philip). FTIR spectra were obtained by Nicolet MAGNA-760.
2 Results and Discussion
Receiveddate: 2006-07-01; reviseddate: 2006-09-06 Foundation item: Project supported by Fund for Harbin Young Scholars (2005AFQ X J 0 31) Biography: Han Zhidong (1974 - ) , Female, Ph. D . Corresponding author (E-mail : harbinzhidonghan@yahoo. corn. cn , )
JOUrWAL OF RARE EARTHS, Vol. 24, Spec. Issue, Dec . 2006
76
2.1 XRD results Fig. 1 shows the XRD patterns of BaLa,Felz-,019 synthesized in the presence of S O z . As can be seen in Fig. 1, all samples present typical hexagonal structure. Thanks to the La substitution, the crystal constant changes"] . No diffraction peaks of SiO, can be observed, revealing the amorphous structure of S O z . The structure of BaLa,Feln-, 0 1 9 is not influenced by the addition of SiO, during synthesizing process.
2 . 2 FTIR results Fig. 2 shows the FTIR spectra of BaFelz 0 1 9 , BaL%.5Fell.5019and BaL%,, Fell., OI9 synthesized in the presence of S O z . It can be seen in Fig. 2 that BaL%.5Fell.501e and BaL%,5Fell.5 Ol9/SiOZshow similar bands at about 400 580 cm-', suggesting their similar structure. BaLq., Fell,, OI9/SiO2 also shows bands at about 1010 and 1040 cm-I , which can be interpreted as stretching of Si - 0 - Si and prove the existence of Si02 . Compared with BaFelz OI9 , the wide
-
Fig.3
SEM micrograph of B a L ~ . 5 F e l l . s 0(1a9) and BaLaos Fell .5019/Si02( b)
-
'
bands about 550 570 cm- , interpreted as the lattice vibration modes of M - 0, are found to move to lower frequency for La substituted BaM, indicating that the distribution of ions in BaFel2OI9was altered by La doping. Such results consist with those of XRD .
2.3 SEM results
P
Fig. 3 compares the morphological structure of It can be BaLq.5Fell,s019 and BaLao.5Fe,l,5019/Si02. seen in Fig.3 that the particle size of BaL~.5Fell.5019/ SiO, are finer and more homogeneous.
40 2 O/(?)
Fig. 1
XRD patterns of BaLa,Fe12_,019synthesized in the presence of SiOl
1
.
I
'
I
'
I
-
I
'
I
'
I
.
I
4o0O36oorxx)25oomlsoolmsoo
Wavenurnber/cm.'
Fig.2
FTIR spectra of BaM and La substituted BaM ferrites with and without SiOz
3 Conclusion The effects of SiO, nanoparticles on the structure and particle size of M-type La substituted BaM hexaferrites were investigated. As learned from the results of XRD, FTIR and SEM, the structure of M-type La substituted BaM hexaferrites is not influenced with the presence of SiO, nanoparticles during synthesizing process. The more important is that SiOz nanoparticles promote the formation of finer or more homogeneous particles whose size is about several hundred nanometers, much smaller than that synthesized without SiO, nanoparticles .
References : [ 1] Nie Y , He H H I Feng Z K , et a1 .
Microwave charac-
Han 2 D et al . Structure of BaLa.FeI2 - p 0 1 9 / S i 0 1
terization of ( Co ,Zn)2W barium hexagonal ferrite particles [ J ] . J . Magn. and Magn. Mater. , 2006, 33(2):
423. [2] Meshram M R , Agrawal Nawal K , Bharoti Sinha, et al . Characterization of M-type barium hexagonal ferrite-based wide band microwave absorber [ J 3. J . Magn. and Magn. Mater., 2004, 271: 207. [3] Yoshida S , Sato M , Sugawara E , et a1 Permeability and electromagnetic-interference characteristics of Fe-SiA1 alloy flakes-polymer composite [J] . J . Appl. Phys . ,
.
1999, 85(8): 4636. [4] Robinson T M . Polycrystalline hexafemtes for millimetre wave applications [ J ] . Mater. Res. Bull. , 1990, 25: 1401. [5] Mocuta H , Lechevallier L, Le Breton J M , et al. Structural and magnetic properties of hydrothermally synthesised Sr, - Nd,FelzOI9 hexagonal ferrites [ J 1 . J . Alloys and Comp . , 2004, 364: 48. [6] Ahmed M A , Ateia E, Salah L M , et al. Structural
77
and electrical studies on La3' substituted Ni-Zn ferrites [J]. Mater. Chem. and Phys., 2005, 92: 310. 71 Guo Ruiqian, Li Honggui , Sun Peimei , et a1 , Synthesis and characterization of rare earth La substituted Mtype hexagonal barium ferrite ultrafine powders [ J ] . Chinese J . Rare Metals, 2001, 25(2) : 86. 81 Peelamedu Ramesh D , Roy Rustum, Agawal Dinesh . Anisothermal reaction synthesis of garnets, femtes and spinels in microwave field [ J ] . Mater. Res. Bull. ,
2001, 36: 2723. [9] Vestal Christy R , Zhang Z John.
Synthesis and magnetic characterization of Mn and Co spinel ferrite-silica nanoparticles with tunable magnetic core [ J ] . Nano Letters, 2003, 3(12): 1739. [ 103 Anna Comas, Casula Maria F , Ennas Guido, et a1 . Xray absorption spectroscopy study of FeCo-SOz nanocomposites prepared by the sol-gel method [ J ] . J . Phys. Chem. B , 2003, 107: 30.