TINH CHAT T i r CUA HE VAT LIEU NANO LaFei^Co^Os (0 < x < 1)
LE THI THUY TIEN - NGUYEN THI PHUONG THAO H6 THI PHUONG GO ANH - NGUYEN THI THUY Trudng Dai hQC Suphgm - Dgi hgc Hue Tom tat: He vat heu nano LaFej-^tCo^Os (0 < ;c < 1) duac ch6 tao thanh cong bang phucmg phap sol-gel (gel-citrate). Phan tich nhilu xa X-ray cho thiy he mau dup'c ch8 tao don pha va co cSu tnic orthorhombic vdi kich thuac trung binh 18.8 nm. Tmh chat tii cua he vat heu hi bien ddi manh khi pha tap ion Co"", thdng so S = M/Ms giam theo ty le pha tap. He vat lieu thk hien tinh sat tu yeu, gan vai trang thai sieu thuan tir.
Tir khoa: Vat lieu perovskite, cau true nano, phuang phap sol-gel, sieu thuan tu
l . G l d l THIEU
V$t lieu perovskite LaFeOs va cac hop chat bien tinh pha tap cua chung da va dang thu hiit dirge sir chii y cua cac nha khoa hoc trong niroc va tren ihk gidi do dugc ling dung rong rai trong Isy thuat va dai s6ng nhu: che tao cac pin nhien lieu, lam chAt xiic tac trong dieu che khi, che tao cac cam bien phat hien khi doc [1]. Vat lieu perovskite LaFeOs binh thuang the hien tmh phan sat tir, tuy nhien, tinh ch4t tii ciia vat lieu se thay doi dang ke khi pha tap cac kim loai dat hiem vao vi tri A hoac kim loai chuyen ti^p vao vi tri B trong cau tnic tinh the ABO3. Coban la mot nguyen t6 kim loai ki§m th6, co tii tinh manh, co do tir tham tuang doi cao (bang hai ph4n ba do tir t h i m cua s&t), co tinh da hoa tri (+2, +3, +1), va co cac miic nang lugng dien tii trong lop 4d chua day tuc la khong bu trir momen tir nen khi pha tap vao vat lieu nen LaFeOs thi tinh chat tir ciia vat lieu bi thay doi manh do xuat hien hien tugng meo mang Jahn-Teller, trang thai h6n hgp hoa tri... Bai bao trinh bay cac ket qua nghien ciiu ve su bien doi cau tnic va tir tinh ciia vat lieu LaPeOs pha tap ion Co'''^
2. THU'C NGHIEM
He vat lieu nano LaFei.iCo;r03 (0 < J: < 1) dugc che tao bang phuang phap sol-gel (gel- citrate) [2]. Cac mu6i La(N03)3, Co(N03)3, Fe(N03)3 vai nong do O.IM dugc chuin bi theo diing hgp thiic, axit citric C6H8O7.H2O nong dp I M dong vai tro la chat tao phirc.
H6n hgp muoi nay dugc pha tron voi nhau theo ti le J ] M"^/Y.AC = 1.5 (M': tong $6 ion CO trong dung dich va ^ C : axit citric), dugc khuiy gia nhiet lien tuc d nhiet do 70°C trong vong 7 den 8 gia. Qua trinh tao phiic sii dung NH4.OH lam chat xiic tac dk d i l u chinh pH on dinh d miic 6.5-7. Sau khi hon hgp chuyen sang trang thai xerogel rdi dkn gel thi ngung khuay va gia nhiet. U gel d 200^0 trong 24 gid roi nung thieu kSt d 300^C va 500"c trong vong 10 gid de thu dugc he mau co kich thudc nanomet.
Tap chi Khoa hpc va Giao due, Trucmg Dai hpc Su pham Hue ISSN 1859-1612. S6 03(3])/2014: tr. 28-34
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LE THI T H U Y TIEN va cs.
3. KET QUA VA THAO LUAN
cau true tinh th6 cua he vat lieu duoe xac dinh thong qua ph6 nhilu x. X-ray va duoc trinh bay trong hmh 1. He m5u don pha co cau tnic true thoi, dp rong cac dinh nhieu xa tuong d5i Ion cho thiy hat cd kich thuoc be.
Cac thong sa ciu tnic mang dugc tinh toan va trinh bay trong bang 1 tu^bang 1 nha,, thiy ciu tnic tmh thJ cua he vat lieu bi thay doi manh kh. pha tap ion Co . The tich o CO so giam din, do ban kinh cua ion Co^' (0.62 A), nho hon so voi ban kmh cua ion Fe'' (0.67A). D i k nay cung din den hien tuong meo mang, lam cau tnic cua he LaFe,.
^C0x03 khong con la ciu tnic lap phucmg li hrcmg [3].
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ic 2C 20 i : :••:• 'iC "C 2-TietslDegj
Hinh 1. Gidn dd nhieu xg tia Xcua he vdt lieu nano LaFei.xCOxOj nung d 500 '^C trong 10 gid Bang 1. Cdc thdng sd mgng
X 0 0 1 0.2 0,3 0 5 I
a(A») 5.9278 5.7761 5.5921 5 5621 5.5674 5 3080
b(A°) 8.3674 8.1720 7.8903 7.8480 7.7687 7.4894
ciia h4 vdt li?u nano LaFci.^Co^O} nung a 500 "C trong 10 gid c(A»)
5.9178 5.7617 5.5782 5.5483 5.5564 5.2948
a 90"
90"
90"
90"
90"
90"
,s
90»
90"
90°
90"
90"
90"
Y 90"
90°
90"
90"
90"
90"
V[(A"y]
293.965 271.965 246.129 242.191 240.322 210.488
Cau tnic true thoi true thoi true thoi tr\re thoi true thoi tnrc thoi
TINH CHAT TU CUA HE VAT LEU NANO LaFe).,Co,03 (0 < x < 1)
Kich thudc hat tnmg binh la 18.8 mn, dugc tinh theo cong thiic Debye-Scherrer va dugc trinh bay trong bang 2. Anh SEM cho thiy dugc cau tnic cac hat cua he vat lieu k^t tinh kha ddng deu.
Bang 2. Kich thudc hgt cda he vgt lieu nano LaFei.xC0xO3 nung d 500 "C trong 10 gid
X
0 0.1 0.2 0.3 0.5 1
B (rad) 0.008 0.008 0.008 0.008 0.008 0.008
0 (degree) 15.25 16.25 16.25 15.00 15.25 14.75
D(mii) 18.8 18.8 18.8 18.7 18.7 18.7
x=0 x=0.1 Hinh 3. Dirdng cong tir tre M(H) cua he vdt lieu nano LaFei..iCo,S^i nung d 300 '^C trong 10 gid
LE THI THUY TIEN vacs.
Bang 3. Cdc thdng sd tir cua vdt lieu nano LaFei.i,Co^O3 nung d 30(fC trong 10 gid X
0 0.1
Cong thire LaFeO, LaFeoeCooiOs
M, (emu/g) 301.557x10*
5.123x10-'
Ms( emu/g) 48.275X 1 0 '
7 . 8 7 3 x 1 0 ' UM, 0.006 0.001 Thong thucmg, vat lieu perovskite LaFeOa ly tiroug the hien tinh phan sit tij. Tuy nhien tinh chat nay se bien doi thanh sat tir hay sat tir yeu khi pha tap cac nguyen t6 dit hi^m voi cac ti le khac nhau [3], [4]. Hinh 3 va hinh 4 la ket qua cua phep do ducmg cong tii he M(H) cr nhiet do phong voi tir tnrcmg ngoai dat 1.3 Tesla cua he vat lieu nung 6 300°C va SOO'C.
Ducmg cong tir tte M(H) d6i voi miu LaFeOs khi nung o 300°C va 500°C dJu cho thay miu the hien tinh sit tir yeu. Sir bijn dAi tinh chit tir phan sit tir sang sit Ms ykn cua vat li$u LaFeOs ly hrong co th6 giai thich la do qua trinh u va nung mlu trong thoi gian keo dai din din su thieu hut oxi ttong ciu tnic phan tu LaPeOs hmh thanh hSn hop hoa hi Fe*' va Fe*^ voi cae momen tir khac nhau (5 ^^ va 4 ^^) [5].
x=0.3 x=O.S
Hinh 4. Dirdng cong ti, tri M(H) cua he vdt lieu nano LaFe,..Co,03 a 500 'C trong 10 gid
TiNH CHAT Ttr CUA HE VAT LIEU NANO LaFci_Xo,03 (0
Bang 4
X
0 0.1 0.3 0.5
< x < l ) 33
Cdc thdng so tir ciia vdt lieu nana LaFe,.^COxOs nung d 500 C trong 10 gid Cong thuc
LaFeOj LaFeo.9Cooi03 LaFeo.7Coo303 LaFe(,.5Coo.503
Mr (emu/g) 242.982X 10 •
91 472X 10"' 20.515x10' 8.910X 10'
Ms (emu/g) 543.711x10' 267.049X 1 0 ' 95.111X10-' 51.666x10'
MM, 0.447 0.343 0.216 0.172 Khi pha tap ion Co , he vat lieu thi hien tinh sit tir y6u ro ret (hinh 3 va 4). Co la nguyen td da hoa tri, su thieu hut oxi trong cau tnic phan tii ciing la nguyen nhan hinh thanh nen dang hon hgp hoa tri Co^7Co^* gdp phin hinh thanh tinh sat tir yeu ciia he vat lieu. Cac thong sd tir giam din theo ndng do pha tap ion Co^' (bang 3 va 4), ti sd S = Mr/Ms nhd nhat dat dugc la 0.172 ddi vdi miu LaFeo.sCoo 5O3 (x=0.5^ gan vdi gia tri 0, chiing td tinh chat tir ciia he vat lieu nay gin vdi trang thai sieu thuan tii (S = Mr/Ms=0).
Cac thong so tir ciia he vat lieu khi nung d 500"C ldn han nhieu so vdi he vat lieu nung d 300^C. Dien tich cac dudng tii tr^ ciing ldn hon. Nhu vay cd the thay nhiet do mmg thieu ket anh hudng nhieu den tinh chat tir cua he vat lieu. Cang nung d nhiet do cao thi kich thudc hat cang ldn dan den thdng sd S = M/Ms cang ldn. Dieu nay hoan toan phu hgp vdi quy luat Hc=D^ (vdi D: kich thudc hat tinh thi) [6], [7], [8].
Nhiet dd chuyen pha sat tir-thuan tir (Tc) ciia he vat lieu tang din Tc = 478.87 ''C doi vdi LaFeOs (:c=0, 500'*C) va Tc= 495.77X ddi vdi LaFeo.7Coo,303 (x=0.3. SOOV). Nguyen nhan do Tc ctia Co ldn han so vdi Fe, vi vay, neu lugng Co dugc pha tap vao cang nhieu thi Tc ciia he se cang tang.
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x=0 x=0.3 Hinh 5. Dirdng cong tir nhiet M(T) ciia hi vat liiu nano LaFe ,.^Co,03
nung d 500 °C trong 10 gia 4. KET LUAN
He vat Heu nano perovskite LaFei.,Co,03 (x = 0, 0.1,0.2, 0.3, 0.5, 1) duoc ehi tao thanh cong bing phuong phap sol-gel (gel-cittate), the tich 6 co so giam theo ndng dp pha tap ion Co'". Kich thuoc hat trung binh 18nm duoc tinh tir cong thiic Debye-Scherrer ket hop voi ph6 nhieu xa X-ray. He vat lieu the hien tich chat sat tir yeu gan voi trang thai sieu thuan tir a nhiet dp phong. Cac thong so tir giam din theo chiiu tang cua nong dp pha tap Co.
LE THI THUY TIEN vacs.
TAI LIEU THAM KHAO
|1] Seiyama. T, Tejuca. L. G., Fierro. J. L. (1993), "In Properties and Applications of Perovskite-lype Oxides ", Mareel Dekker Inc, New York, pp 215-230.
[2] Brinker, C.J., O.W. Scherer (1990), "Sol-Gel Science: The Physics and Chemisliy of Sol-Gel Processing", Academic Press, Boston 1990.
[3J N.V.Du, D.L.Minh, N.N.Dinh, N.T.Thuy, N.D.Manh (2008), "The structure and magnetic property of nano-perovskite LaFeOs prepared by Citrate-gel, Co- precipitation and High energy milling methods", VNU Joumal of Science, Malhematic-Physics 24 No. lS,pp 109-112.
[4] P.Vavindran, R.Vidya, H.Fjellvag, A.Kjekshus (2004), "Electronic Structure and Excited-stale Properties of perovskite-like oxides LaFeOj, LaCrOi", Journal Crystal Growth 268, pp 554-559.
[5] H. Jahn and E. Teller (1937), "Stability of Polyatomic Molecules in Degenerate Electronic Slates .1 .Orbital Degeneracy", Proceedings of the Royal Society of London Scries A, Mathematical and Physical Sciences (1934-1990), 161, pp 220-235.
[6] D. J. Singh, 1.1. Mazin (2002), "Magnetism, Spin Fluctuations and Superconductivity in Perovskite Ruthenates ", Lecture Notes in Physics, 603, pp 256-270.
[7] Dang Le Minh, Phung Quoc Thanh, Hoang Van Hai, Dang Muih Hong, Bach Thanh Cong, (2006), "The magnetic property of the perovskite compound Cai.^Fe^MnOj", VNU. JOURNAL OF SCIENCE Mathematics-Physics , T.XXII, No2AP.
[8] Nguyen Thi Thuy, Dang Le Minh (2012), "Size effect on the structural and magnetic properties of Nanosizedperovskite LaFeOiprepared by different methods". Advances
in Materials Science and Engineering Volume 2012, Anicle ID 380306.
Title: MAGNETIC PROPERTIES OF NANOCRYSTALINE - PEROVSKITE TYPE LaFei.
, C o , O 3 ( 0 < x < l )
Abstract: The perovskite compound LaFei.jCo,03 {x = 0, 0.1, 0.2, 0.3, 0.5, 1) have been successfully prepared by a sol-gel method (gel-citrat). The X-ray diffraction analysis shows that the nano crystalline is single phase. The nano-LaFei.iCo^03 has orthorhombic structure and the particle size is about 18.8 nm. With the Co dopping, the magnetism of nano-LaFe,.vCo,r03 is strongly distorted, the ratio S = IAM, decreases when the concentradon Co increases. The prepared nano-LaFei.iCOi03 ejdaibits ferromagnetic behavior nearly super-paramagnedc behavior.
LE TH! THUY TIEN NGUYEN TH! PHUONG THAO HO THI PHUONG GOANH
SV Khoa Vat K, Tnrcmg Dai hpc Su pham - Dai hpc Hue ThS. NGUYEN Tffl THUY
Khoa Vat ly. Trucmg Dai hoc Su pham - D?i hgc Hue
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