T I N H SAT Tir YEU CUA N A N O PEROVSKITE LaixYxFeOj
NGUYEN THI THUY - HOANG TRONG DLTC Trudng Dgi hgc Su pham -Dgi hgc Hue
DANGLE MINH Tnrdng Dgi hgc Khoa hgc Tu nhien - DHQG Hd Ndi Tom tit: Perovskite Lai-iY^FeOj (0 < JC < 0,5) duoc chi tao bing phuong phap gel - citrat Khao sat cdu tnic bing phuong phap nhieu xa tia X va chup anh hiln vi dien tii quet (SEM) cho thiy cac mau pha tap Y hoan toan don pha va CO ciu tnic orthorhombic. Kich thudc hat trung binh dupc tinb theo cong thiic Scherrer co gia tri khoang 20 nm. Sy pha lap nguyen to dat hiem Y vao vi tti A trong cdu tnic ABO3 anh hudng den cau tnic va tinh chat tir cua he mlu. Ducmg tir trd M(H) dupc do is nhigt dp phong chi ra ring cdc mlu nano Lai-iYiFeO? thi hien tinh chdt sit tir ylu ding thdi tinh sit tir yeu cung duac khdp theo ham Langevin.
C) nhiet dp cao, LaFeOs vdi ciu tnic perovskite thd hidn tinh sit tir yen va do sy thay ddi tinh ddn ttong cdc vdt hdu LaFeOs pha tap nen loai vdt lieu nay cd nhiing ung dung quan ttpng ttong linh vyc viin thdng hidn dai vd cac thilt bi dien tii, d kich thudc nm LaFeOs va cac hpp chit pha tap ciia nd dac bidt dupc ung dung ttong ehl t^o cdc bp cdm bien khi dd ndng dp cdn, khi metan ttong cdc ham md... Cac tinh chdt thu dupc cua mlu phu thupc rit nhidu vdo phuong phdp chd tao, do dd viec cai tien qui trinh chd tao ralu la rit can thiet, ttong dd viec ha nhiet dp nung mau va tao hat cd kich thudc nhd ddc bidt dupc chii y. Bing phuong phdp gel - cittat, chiing tdi da tdng hpp dupc hot tinh thd nano LaFeOa vdi kich thudc hat ttung binh khoang 25 nm d 500°C [1], [2], [3], [4], [5].
Trong bai bdo nay, he mdu nano perovskite Lai.iYrFeOa (x = 0; 0,1; 0,15; 0,5) dupc chi tao thdnh cdng bdng phuang phdp gel - cittat. Sy pha tap nguydn td ddt hidm Y ldm cho ciu tnic tinh thd bi meo manh, kich thudc hat trung binh khoang 20 nm, h? radu the hi$n tinh sdt tir yeu gan vdi ttang thdi sieu thudn tir d nhiet dp phdng. Tinh sdt tir ydu ciia hd mau nano Lai.jYiFeOs dupc khdp theo ham Langevin cho thay tir tinh phu thupc raanh vdo cdu tnic va kich thudc tnmg binh ciia cac hat tinh thd.
THUC NGHIEM
Hd mau Laj.jYiFeOj (x=0; 0,1; 0,15; 0,5) dupc chi tao bdng phuang phdp gel - cittat, cdc mudi La(N03)3, Y(N03)3, Fe(N03)3.9H20 cd ndng dp 0,1 M vd axit citiic cd ndng dp 1 M dupc khudy, gia nhiet d SO^C tao tiidnh gel, gel duoc siy d HO^C ttong 10 gid dd khir nude sau dd nung SOCC ttong 5 gid dd loai bd cac tidn chit hiru co, cudi cimg u gel d 500'^C ttong 10 gid thu dupe he mdu bpt vdi kich thudc nm.
Phdn tich cdu tnic bang phuang phdp nhilu xa tia X vdi thilt hi nhieu xa D5005- Bruker-Germany. Dudng cong tii ttd M(H) tai nhiet do phdng ttong tii ttudng din 1,3 Tesla dupc do bdi tii kl mdu rung VSM LakeShore 7404 ( LakeShore, USA).
Tap chi Khoa hgc va Giao due, Tniong Dai hoc Su pham Hui ISSN 1859-1612, S6 01(21)/2012,lr. 12-19
TiNH SAT TU YEU CUA NANO PEROVSKITE La,JYAFCOJ
KET QUA VA THAO LUAN
Hinh 1 la gian dd nhilu xa tia X ciia he mdu nano Lai-iYjFeOs. Cdc dinh nhilu xa sac net chiing td cdc mlu don pha vdi ciu tnic orthorhombic thupc nhdm Pnma.
Sy sai lech cau tnic tinh thd dupc ddnh gia thdng qua thira sd dung ban t do Goldchrait dua ra:
I- ry^ , (1)
Vdi R^, Rg, 5g lin lupt la bdn kinh ciia cdc ion La^"*^, Fe^^ vd O^". Cdu tnic perovskite dupc coi la dn dinh khi 0,8 < ^ < 1. Didu dd keo theo cac cation phai cd kich thudc gidi han R^> 0,9 va Rg> 0,5. Khi / =1, ta cd cau tnic perovskite lap phuang. Khi t^^ 1, mang tinh the bi meo, gdc Hen kit B-O-B khdng cdn la ISO'' niia md bi be cong vd dp dai lien ket B-0 theo cdc phuong khac nhau se khac nhau, ciu tnic tinh the bj thay ddi.
Dilu nay ddn tdi sy thay ddi tinh tir ciia he vdt Hdu [6], [7].
Hinh 1. Gidn dd nhiiu xg tia Xcua h$ nano La/.^Yj^FeOj Bang 1. Hdng sd mgng (a, b, c), the lich V, thira so dung han t, bdn kinh R^
ciia hi nano La/.^YrFeOj
X 0 0,1 0,15 0,5
Mau LaFeOj LanYoiFeOj LaossYoisFeOj LaosYosFeOj
a (A'i 5.56 5.54 5.54 5.53
4 5.55 5.56 5.55 5.54
(^")
7.86 7.85 7.84 7.82
V 242.24
241.7 241.05 239.5
/
0.959 0.952 0.948 0.929
RA (A") 1.363 1.343 1.334 1.275
RB (A") 0,645 0.645 0.645 0.645 Dya vao kit qud nhidu xa tia X, hdng sd mang vd thira sd dung han cua he mlu dupc tinh todn va trinh bdy ttong bang 1. Ta thiy ring thi tich d ca sd va thira sd dung han cua cac mlu giam khi tdng ndng dp Y. Bdn kmh ion Y^'^(l,19 A°) nhd hon ban kinh ion La^"^ (1,36 A ^ nen khi thay thi Y^"^ cho La^^ dd lam cho thd tich d mang co sd vd thita
NGUYEN THI THl'Y va cs.
sd dimg ban t gidm din din sy meo mang. Chinh sy meo raang tinh thd khi pha Y la nguydn nhan chinh dnh hudng din tinh chit tir ciia cdc ralu nghien ciiu.
kX
Tir cdng thuc Scherrer D= , vdi D Id kich thudc trung binh cua cdc hat, k = 0,94 Bcose
la hdng sd, X la budc sdng tia nhidu xa, B la dp rpng cua dinh cue dai tai rapt niia chilu cao ciia dinh, 9 la gdc nhilu xa, chiing tdi tinh toan dupc kich thudc hat trung binh khodng 20 nm vd dupc ttinh bdy ttong bdng 2.
Bang 2. Kich thudc trung binh cua he mdu nanno Lai-iYxFeOi Nong do pha tap x
Kich thudc hat (nm) 0 20,31
0,1 13,60
0,15 20,87
0,5 17,70
Hinh 2 Id dnh SEM ciia radu nano Lao,g5Yo,i5Fe03, cac hat cd sy phdn bd ddng ddu vd tdch rd. Sy pha tap ion Y^" vdo hd LaFeOs dd anh hudng din sy ddng ddu vd tach bidt giira cdc hat.
Hinh 2. Anh SEM ciia mdu nano Lao,ssYo.isFe03
Hinh 3 Id dudng cong tii M(H) ciia cac mlu JC = 0; 0,1; 0,15; 0,5 dupc do ttong tir trudng cd 1,3 Tesla lai 300 K. Ta nhdn thdy cdc mlu dupc tir hda chua dat din ttang thdi bao hda.
Binh thudng, perovskite LaFe03 cd tinh phdn sdt tir va cdch dien nhung dudng cong M(H) (mdu J: = 0) Iai cho thiy he mau thi hidn tinh sdt tii ylu. Gid thilt ngudn gdc sdt tir ciia mdu LaFeOs chd tao dupc cd thi xudt phat tir hai ylu td:
(i) Mau dupc nung d nhiet dp SOO^C ttong radi ttudng khdng khi ttong radt khoang tiidi gian dai (10 gid) vd ldm n ^ p i tiieo Id se ddn tdi sy tiiilu hut oxy vd tao ra cdc Id tt^ng d vi tti cdc anion O^". Sy thilu hut nay khiln cho ttong LaFe03 khdng chi tdn t^i ion Fe^""
ma cdn cd them ion Fe'" hay ndi each khac ttong vdt Hdu tdn tai ttang tiidi hdn hpp hda tri Fe *- Fe""^. Mdmen tir cua ion Fe^* la 5 p^va ciia ion Fe^* la 4//^, nhu vdy chinh trdt ty feri tir xudt hidn tao ndn tinh sit tir ylu ciia he mlu.
(ii) Do sy meo mang tinh till ndn xuit hien ttdt ty phan sit tir nghidng (canted- antiferroraagnetic) tao ndn tinh sit tii ylu ciia mdu nano LaFeOs.
TINH SAT Tir YEU CUA NANO PEROVSKITE La, JYA^eOj
Vdi cac thdnh phin tap theo ndng dd x cdn lai thi mdu x = 0,5 cd dudng cong tir M(H) dung dung hon, bilu thi radu dl tii hda hon. Didu nay cd thd do dnh hudng cua di hudng tir tinh the. Qud trinh tii hda dupc quyet djnh bdi nhieu yen td, ttong dd quan ttpng nhdt la: Di hudng tir tinh the (K) va tii giao (X). Trong hpp chit perovskite biln tinh cd tinh chdt tu, tir giao A nhd vd it thay ddi ndn anh hudng khdng ddng kd den qud trinh tii hda, vay di hudng tir tinh thi Id nhdn td chii ylu quylt dinh den qud trinh tir hda ciia cac perovskite bidn tinh. Ndng lupng di hudng tir tinh the cd tbi vidt dudi dang bilu thiic sau.
2 4
* Mlu CO sy di hudng don true: Eua =Kuisin O+Kuisin 6 + . . . .
* Mdu tinh thd la hmh lap phuong: E^ =KJ(t^J^a5-^tI^a^+a^aJ)+K2aJ^a?a2+...
vdi Kui, Ku2 , Kl , Kl ldn luot la cac hing sd di hudng bac thdp vd bdc cao [8], [9].
Trong he ralu nano Lai-xYxFeOs (x = 0,1; 0,15; 0.5) cd La Id nguyen td phi tu cdn Y va Fe Id cac nguyen td tir tinh nen tinh chdt tir ciia he chii yen Id sy ddng gdp ciia hai nguydn td Y va Fe hay ndi cdch khac di hudng tii cua mlu la sy ddng gdp di hudng cua cd Y vd Fe (K^iu = Ky + Kpe). Dilu ndy cd the gay nen sy khdc nhau d cae dudng cong tir hda M(H) cua he mdu. Ngodi ra cdn cd sy ddng gdp ciia hdn hpp hda tti Fe *- Fe^^
vdi ttdt ty feri tii tao nen tinh sat tir yeu ddng thdi do sy thay the mpt phdn ion La^"^
bdng ion Y^"^ lam raang tinh thd bi meo manh din ddn tdn lai trdt ty phdn sit tir nghidng ttong h? mlu nano Lai-iYjFeOs (x = 0,1; 0,15; 0.5).
0.001
-0.001 -oon?
x = 0
-1.S -1.0 -0.5 0.0 0.5 1.0 1.5 H(T)
x = 0,l
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 H(T)
0.002 0.001 - f 0.000
g
S -0.001
^
U.0U2 0.001 nnno
-0.001
^inn?
1 = 0.5
-1.5 -1.0 -0.5 0.0 0.5 10 1.5 H(T)
Kinh 3. Dirdng cong M{H) cua he nano La/.jY^FeOj
1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 H(T)
NGUYEN THI THi:Y va cs.
Tinh chit sit tit cua h? mSu perovskite bi anh hirong vk Ion boi kich thitcjc hat tinh thS.
Kich thuoc hat Ion se cho gia tri luc khang tit He cao, dieu nay phu hpp vdri quy luat He
~ D ' cho cac hat tinh thi co cSu trie nm [10]. DS khao sat sir anh huong cua kich thuoc hat len tinh chit tir ciia he mlu, chting toi tmh toan theo ly thuyet ham Langevin va tir do khorp vdfi cac s6 heu thirc nghi?m.
x = 0 i ^ ^ x = 0,l
1' "i*. 1
• 1 . ; - 1 0 -0 5
x = 0,15
' U=*»J
I"
i -0 2
x = 0,5
r^-
C S 1 0 1 i
Hinh 4. Kit qua khdp giira sd lieu ihifc nghiem vd hdm Langevin Cdc vat lieu sdt tir ndu cd kich thudc hat bdng diing kich thudc ciia mpt don ddraen thi tir tinh bidn ddi manh tir sit tir sang sieu thu^n tir vdi cac gid tti lyc khang tir He = 0, dp tir du Mr = 0 vd tir dp bao hda S = (My/Ms) = 0. Dudng cong M(H) ciia he mdu nano Lai.
jtYjFeOs cho thdy cac mau cd tinh chdt tii gdn vdi trang thdi sidu thudn tir tuy nhien cd lyc khdng tir va dp tir du ciia cac mlu diu cd gid tri l^dc khdng. Dd gidi thich cho hidn tupng nay cd the budc ddu gia thiet do ddng gdp ciia cdc hat sidu thudn tir gay ra, nhung khdng phdi hodn todn do hat sidu tiiudn tu gay ra, chung tdi gid thilt Id do cdc ralu da dupc u ttong thdi gian dai (10 gid) da ddn din sy khdng ddng nhdt ve kich thudc hat va
TINH SAT Tir YEU CUA NANO PEROVSKITE La,_iY»f e03
khoang each giiia cdc hat. Va tir tnrdng tdng cdng cua ciia radu cd the dupe xem la tdng ciia hai thanh phdn:
M ( H ) = M ^ ( H > + M ' ( H ) (2)
ttong dd: M'['(H) diln ta sy ddng gdp din tii cdc hat sidu thudn tii, M ' ( H ) Id ddng gdp cua cdc hat sdt tir.
It •- H^ 2 •' vdi Mf la gia tri tir trucmg bao hoa cua pha sit tir (M,'=Mr/0.866).
„ M, ,, .. . . , S = —'- ta do vuong cua vong sat tu.
Xet qua trinh tir hoa Ichong tuong tac, cac hat sieu thuan tir c6 kich thuoc gi6ng nhau du(?c diln ta boi biSu thiic:
M ( H ) = M ( o e ) L [ i I ^ ] (4) trong do: m la moment tir va L(x) = coth(x)-l/x la phuong trinh Langevin vdi x=mH/kT. Trong he v^t lieu Laj.jYjFeOj, do sir khong d6ng nhit vk kich thuoc hat va khoang each giiia cac h^t nen bieu thirc (4) co the dugc viet lai:
M - ( H ) = M " ( » ) y f ( m ^ ) L [ ^ ] (5) vdi mj la moment tii cua moi hat vd f(mj) Id nhan td ttpng sd.
Vdi vide gid dinh cdc hat Id cdc hinh can va tii tinh ty phat ciia mdi hat cd gid tri nhd, ta cd the tinh raj dya vao hdm phdn bd kich thudc hat f(D):
vdi o va D la dp lech chudn va kich thudc hat trung binh cua he radu. Tii kich thudc hat trung binh dupc tinh d bang 2 ta cd the tinh dupc f(raj) tir dd khdp cdc sd lieu thyc nghiem vdi hara Langevin. Kdt qua cua qud trinh khdp giiia sd Hdu thyc nghiem vd ham Langevin ddi vdi he raau nano Lai.iYjFeOs (x = 0; 0,1; 0,15; 0,5) dupc trinh bdy d binh 4. Ta thay dudng M(H) thyc nghiem va dudng M(H) khdp theo ham Langevin la kha triing nhau, dieu nay chiing td tinh sit tir ylu ciia he mdu phu thupc manh vdo kich thudc hat theo qui ludt He ~ D nhu trinh bdy d tten.
NGUYEN TH[ THUY va cs.
KET LUAN
Dupc chd tao bing phuong phdp gel - cittat, he mdu Laj-^YiFeOs (x = 0; 0,1; 0,15; 0,5) hodn toan don pha vd cd kich thudc hat ttung bmh khodng 20 nra, the tich d ca sd ciia he mdu giam theo ndng dp pha tap ion Y^*, cac mau the hidn tinh sat tir ydu d nhiet dp phdng gin vdi trang thai sieu thudn tii. Tir tinh ciia h? mau php tiiupc manh vdo kich thudc hat qua vide khdp sd Heu thyc nghiem theo hdm Langevin.
TAI LifU THAM KHAO
[1] N. V. Du, D. L. Minh, N. N. Dinh, N. T. Thuy, N. D. Manh (2008). The structure and magnetic property of nano-perovskite LaFeOj prepared by Ciuate-gel, Co- precipitation and High energy milling methods. VNU Journal of Science, Mathematic - Physics 24, No. 18,109-112.
[2] P. Vavindran, R. Vidya, H. Fjellvag, A. Kjekshus (2004). Electtonic Sttucture and Excited-state Properties of perovskite-like oxides LaFeOs, LaCrOs. Joumal Crystal Growth 268, 554-559.
[3] S. Nakayama (2001). LaFeOa perovskite-type oxide prepared by oxide-mixing, co- precipitation and complex synthesis methods. Joumal gf Materials Science 36, 5643-5648.
[4] Osama Mohamed Hemeda, Mohsen Mohamed Barakat, Dalai Mohamed hemeda (2003). Structural, Electrical and Spectral Studies on Double Rare-Earth Orthoferrites Lai.^Nd^FeOs- Turk J Phys 27, 537-549.
[5] Yi-Cheng Liou, Yow (2006). Synthesis and microstmcture of (LaSr)Mn03 and (LaSrjFeOj. Ceramics International, 212-217.
[6] Kiyoshi Kobayashi, Shu Yamaguchi, Tatsuo Tsumoda (2001). Thennoelectric properties and defect stmcture of Lao.5Ndo4sSro,iFe03.^ . Solid state Ionics 144,123-132.
[7] Avner Rothschild, Scott J. Litzehnan, Harry L Fuller, Wolfgang Menesklou, Thomas Schneider, Ellen Ivers-Tiffee (2005). Temperature-independent resistive oxygen sensors based on SrTi|.„Fe,03.5 solid solutions Sensors and Actuators B 108, 223-230.
[8] Goya G. F., Berquo T. S., Fonseca M .P. Morales (2003). Static and dynamic magnetic properties of spherical magnetite nanoparticles. J. Appl Phys 94, 3520-3525.
[9] Fonseca F. C , Ferlauto A. S., Alvarez F., Goya G. F.. and Jardim (2005).
Morphological and magnetic properties of cacbon-nickel nanocoraposite thin films. J.
Appl Phys 91, 04^, ^n.
[10] Seung-Jun Lee, Jong-Ryul Jeong, Sung-Chul Shin, Jin-Chul Kim, Jong-Duk Kim (2004). Synthesis and characterization of superparamagnetic maghemite nanoparticles prepared by coprecipitation technique. J. Magn. Magn. Mater 282, 147-150.
Timi SAT TC-YEU CUA NANO PEROVSKITE U|..vYiTe03
Title: THE WEAK FERROMAGNECTIC PROPERTY OF NANO PEROVSKITES La, AY^e03
Abstract: Perovskites La|.^Y,Fe03 (0 < x < 0,5) were synthesized by the sol-gel method. The X-ray difiractiou (XRD) analysis and Scanning Electton Microscope (SEM) showed that all the Y-substimted compounds are sii^le phase with orthorhombic structure. The average crystalline particle size calculated from Scherrer's formula is about 20 nm. The doping of the second rearth element in the A position of the cotrq>ound ABO3 influenced on the crystalline structure and magnetic property of the samples. The M(H) dependence shows that the nano-sized La|.
xYiFeOs samples exhibits weak ferromagnetic behavior in the room temperature and the M(H) curves are well fitted by Langevin fimctions.
ThS. NGUYEN THI THUY
Khoa Vat ly, Tradng Dai hpc Su pham - Dai hpc Hue DT: 0985.654.598. Email: [email protected] HOANG TRONG DLTC
Khoa Su pham Ky thuat - Trucmg Dai hpc Su pham - Dai hoc Hue DANG LE MINH
Khoa Vat ly, Traong Dai hpc Khoa hpc Ty nhien - Dai hoc Quoc gia Ha N6i
